Essence in the Age of Evolution: A New Theory of Natural Kinds 9780815375067, 9781351240857

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Essence in the Age of Evolution

This exciting book defends a controversial position: biological natural kind essentialism with a neo-Aristotelian twist. It makes an interesting, novel contribution to the metaphysics of natural kinds and is a great example of what work in scientifically informed metaphysics, or the metaphysics of science, should look like. —Tuomas E. Tahko, University of Helsinki

This book offers a novel defence of a highly contested philosophical position: biological natural kind essentialism. This theory is routinely and explicitly rejected for its purported inability to be explicated in the context of contemporary biological science, and its supposed incompatibility with the process and progress of evolution by natural selection. Christopher J. Austin challenges these objections, and in conjunction with contemporary scientific advancements within the field of evolutionary developmental biology, the book utilises a contemporary neo-Aristotelian metaphysics of dispositional properties, or “causal powers”, to provide a theory of essentialism centred on the developmental architecture of organisms and its role in the evolutionary process. By defending a novel theory of Aristotelian biological natural kind essentialism, Essence in the Age of Evolution represents the fresh and exciting union of cutting-edge philosophical insight and scientific knowledge. Christopher J. Austin is Head of Philosophy at Sutton Grammar School, London, and specialises in the metaphysics of science, with a particular focus on biology. Recent publications include ‘Dispositions in Evolutionary Developmental Biology’ in Evolutionary Developmental Biology: A Reference Guide, and ‘A Biologically Informed Hylomorphism’ in Neo-Aristotelian Perspectives on Contemporary Science.

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Models, Simulations, and Representations Paul Humphreys and Cyrille Imbert Platonism, Naturalism, and Mathematical Knowledge James Robert Brown Thought Experiments in Science, Philosophy, and the Arts Edited by Mélanie Frappier, Letitia Meynell, and James Robert Brown Kuhn’s The Structure of Scientific Revolutions Revisited Edited by Vasso Kindi and Theodore Arabatzis Contemporary Philosophical Naturalism and Its Implications Edited by Bana Bashour and Hans D. Muller Science after the Practice Turn in Philosophy, History, and the Social Studies of Science Edited by Léna Soler, Sjoerd Zwart, Vincent Israel-Jost, and Michael Lynch Causation, Evidence, and Inference Julian Reiss Conceptual Change and the Philosophy of Science Alternative Interpretations of the A Priori David J. Stump Neo-Aristotelian Perspectives on Contemporary Science Edited by William M.R. Simpson, Robert C. Koons and Nicholas J. Teh Essence in the Age of Evolution A New Theory of Natural Kinds Christopher J. Austin For a full list of titles in this series, please visit www.routledge.com

Essence in the Age of Evolution A New Theory of Natural Kinds Christopher J. Austin

First published 2019 by Routledge 711 Third Avenue, New York, NY 10017 and by Routledge 2 Park Square, Milton Park, Abingdon, Oxon OX14 4RN Routledge is an imprint of the Taylor & Francis Group, an informa business © 2019 Taylor & Francis The right of Christopher J. Austin to be identified as author of this work has been asserted by him in accordance with sections 77 and 78 of the Copyright, Designs and Patents Act 1988. All rights reserved. No part of this book may be reprinted or reproduced or utilised in any form or by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying and recording, or in any information storage or retrieval system, without permission in writing from the publishers. Trademark notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe. Library of Congress Cataloguing-in-Publication Data A catalog record for this book has been requested ISBN: 978-0-8153-7506-7 (hbk) ISBN: 978-1-351-24085-7 (ebk) Typeset in Sabon by Apex CoVantage, LLC

Illustrations and figures by Sam Minton Graphic Design & Illustration: samminton.com

Contents

ContentsContents

Acknowledgements List of Figures

vii viii

Introduction

1

1 Biological Natural Kind Essentialism: Definitions and Desiderata

4

1.1  The Philosophical Theory of Natural Kinds  4 1.2  Natural Kind Essentialism  8 1.3  Aristotelian Biological Natural Kind Essentialism  12 1.4 Toward a Neo-Aristotelian Biological Natural Kind Essentialism  15 2 Essence and Explanation: Natural Kinds in the Taxonomic Tree

22

2.1  A Natural Taxonomy of Kinds  23 2.2  Natural Kinds and the Species Concept  24 2.3  Two Taxon Questions  28 2.4  Type, Telos, and Taxon  32 3 Powerfully Directed Development: A Dispositional Analysis of Ontogenesis

38

3.1  Dispositions and the Dynamics of Dependence  39 3.2  The Causal Mechanisms of Morphology  44 3.3 Development, Dispositionally 51 4 Ontogenetic Causal Primacy: The Fount and Flow of Information67 4.1 The Case Against Primacy I: Polygeny and Pragmatism 68

vi Contents 4.2 The Case Against Primacy II: Pleiotropy and Plasticity 73 4.3 Primus Inter Pares: Causal Relevance vs. Causal Responsibility 76 4.4  Parity and Pragmatism Revisited  83 4.5 A More Complex Teleology: Mapping Out Morphospace 87 5 The Essence of Natural Kinds: Unity in Diversity

97

5.1 The No Such Set Objection: Phenotypic and Genotypic Diversity  98 5.2  Essence and the Effects of Essence  102 5.3  The Form of What Matters  108 6 An Evolutionary Ontology: Priority, Modality, and the Natural State

118

6.1  The Natural State Model: Being, Backwards  119 6.2  Evolutionary Ontology: A Tale of Two Syntheses  122 6.3  The Nature of Essence  127 Conclusion Index

136 141

Acknowledgements

AcknowledgementsAcknowledgements

This book represents the culmination of a long-term philosophical research project which began during my BPhil studies at Oriel College, Oxford, and extended well beyond my PhD programme at the University of Nottingham. During my doctoral studies, which were graciously funded by the Vice Chancellor’s International Research Excellence Scholarship, I was privileged to be the student of Stephen Mumford from whose philosophical acumen, pedagogical guidance, and genuine encouragement I have immeasurably benefitted. Thanks to a generous grant from the Analysis Trust, I was able to continue my post-doctoral work on this project in the Power Structuralism in Ancient Ontologies research group at Corpus Christi College, Oxford, under the guidance of Anna Marmodoro—an astute mentor, continual colleague, and true friend without whom this book could not have been written. For various reasons, both academic and professional, I am also grateful to Timothy O’Connor, Harvey Brown, Christopher Shields, Joseph Melia, Penelope Mackie, Kim Sterelny, James Lennox, Laura Nuño de la Rosa, and William Jaworski. On a more personal note, none of my accomplishments—academic or otherwise—would have been possible without the unfailing and unquestioning support of my parents, James and Toni Austin, to whom the credit for any virtues I may possess is undoubtedly owed, or without the love of my dearest Layla, my undeniably better half.

Figures

List of FiguresList of Figures

Chapter 3 3.1 3.2 3.3 3.4 3.5

Genetic Regulatory Network Disc Development State-Space Modelling Developmental Trajectory Mapping Topological State-Space Model

48 50 54 56 57

Chapter 4 4.1 Topological Morphospace Model

90

Chapter 5 5.1 Hylomorphic Essentialism

111

Introduction

IntroductionIntroduction

For the non-random, the for-something’s-sake is present in the works of nature most of all, and the end for which they have been composed or have come to be occupies the place of the beautiful. (Aristotle, On The Parts of Animals: 645a23–25)

Only a moment’s reflection is required to see that the world which we inhabit is dizzyingly complex. To observe something as seemingly simple as the blossoming of a single flower is to gaze upon the subtle operations of a veritable cosmos unto itself unfurling with microscopic precision an utterly unique physiochemical creation. And yet, despite the swirling cacophony of creative contingency which surrounds us, we do not find ourselves lost at sea. Rather, the workings of our world are anchored in certain stability, one which grounds and guides our scientific navigation of it—namely, the presence of recognisably repeatable structural patterns: for though the fruit of every flower is a truly singular blossom, each belongs to a single sort of bouquet. Our world, in other words, is one in which the disparity among the irreplaceable individuals who occupy it is yet underwritten by the existence of a deeper unity—it is a world whose denizens’ shared structural consistencies discretely partition them into collections known as natural kinds. Though it is this fact—that our world is divided into discernibly distinct kinds of things—which serves as the scaffolding for the successes of the physical sciences, the entire evidential enterprise of the experimentally verifiable regularities of their scientia is itself seemingly supported by a more metaphysical edifice, one most notably explored and explicated by Aristotle. According to The Philosopher, the scientific comprehensibility of the world and its workings is possible precisely because the conceptual categories into which they are sorted are themselves metaphysically moored in the particularities of its naturally occurring, mind-independent causal structure. On this view, the morphological mutability of the creatures that compose the living world and the seemingly infinitely complex variability of their forms is grounded in a creative capacity which is neither unrestrictedly innovative nor contingently conscribed: with respect to organismal shape and structure,

2 Introduction not just anything goes, and this is no accident. Thus, from the Aristotelian perspective, the modality of organismal morphology represented in the natural kind structure of the world is not merely a heuristic artefact of the efforts of our scientific categorisation but rather a reflection of the metaphysical consequences of the existence of naturally congregated sets of causally efficacious capacities that form the ontological contours around which any successful such catalogue must be carved. The causal-cum-modal structure of the living world captured by its privileged division into natural kinds is, in other words, not the construction of convention, but the effluence of essence. Although this Aristotelian perspective on the nature of the biological world has been immeasurably influential in the history of both philosophy and science, its firm hold upon the metaphysical reigns of those disciplines is by now all but entirely loosed. With the advent and accession of evolutionary theory in the biological sciences, that perspective has been deemed not only unilluminating, but nigh on unintelligible. According to the tenets of evolutionary biology, because the miscellany of organismal morphology is essentially a matter of an amalgamation of vestigial inheritance, the ontological boundaries between groups of organisms must be, if not wholly illusory, merely coarse-grained abstractions from a fundamentally continuous foundation. Furthermore, because organisms are themselves essentially the products of a process whose operation they neither intrinsically constrain nor control, the denizens of a world fashioned by natural selection must be merely passive participants in the creative crafting of their own endless forms. Needless to say, the metaphysical picture of the living world that the theory of evolution presents appears to be one which cannot be painted from the palate of Aristotle’s natural kind essentialism—and indeed, the affirmation of that absolute inability is now a firm component of the contemporary catechism for philosophers of biology. The rejection of the applicability of the Aristotelian metaphysic to the living realm supported by the structure of evolutionary theory has gone hand in hand with its more general dismissal within contemporary philosophy where the conception of our world as one whose character is shaped by the causal and modal constraints placed upon it by the capacities of its constituents has decidedly fallen out of fashion. According to the now widely adopted broadly Humean metaphysic, the stable structure of our world is merely a reflection of a set of contingently realised regularities and the happenstance resultant of the intrinsically unrestrained activities of a collection of fundamentally “loose and separate” entities: in this sort of world, necessarily, anything goes. This metaphysical framework certainly provides its advocates with an ontology that is both simple and economical—two theoretical virtues contemporary philosophers are decidedly enamoured with—but these benefits can only be bought at the price of diminishing its prowess: this is an ontology whose participants are prohibited from occupying a privileged position in shaping the structure of the world. Here then

Introduction  3 the principles of the Humean metaphysic perfectly align with the picture of the living world presented by evolutionary theory—a realm wherein the fundamental passivity of its constituents underwrites its intrinsic inability to be precisely partitioned. Recent years, however, have seen this principled picture subjected to both philosophical and scientific scrutiny. On the philosophical front, contemporary metaphysics, perhaps finally fatigued from its fruitless pursuit of positivism, is currently rediscovering the viability and utility of a broadly Aristotelian philosophical programme in which the causal and modal structure of the world and its workings is metaphysically grounded in the natures of intrinsically potent properties—dispositions, the neo-Aristotelian descendant of dunamis. And as dispositions, or causal powers have increasingly become mainstays in contemporary philosophical analyses of everything from the process of perception to the operation of fundamental physics, their peripatetic corollaries—the concepts of essence and natural kind—are also now experiencing a spirited revival in both metaphysics generally and, to a lesser extent, the philosophy of biology. On the scientific front, contemporary evolutionary biology, having only recently been released from the conceptual strictures of the Modern Synthesis, is currently rediscovering a more comprehensive understanding of the process of evolution—one in which the branches of the taxonomic tree are not wholly shaped by the environmental vagaries which happen to befall an interbreeding assembly of collectively unwitting commuters of heritable molecular information. In the new field of evolutionary developmental biology, the role of organisms in that process has been radically recast: rather than being merely inertly moulded by the contingencies of their circumstances and defined by their place among the statistical variations in populational gene frequencies, the intrinsic generative capacities of their developmental systems are now being conceptualised as causally central in directing the trajectory of evolution. In light of the recent rediscovery of Aristotelian metaphysics and the rising reinvention of evolutionary theory, the time is nigh for a philosophical reexamination of biological natural kind essentialism. The aim of this book is to propose and defend a novel form of that theory, and its thesis is that this ancient doctrine, refashioned in the garments of contemporary neoAristotelian metaphysics and reinforced with the evidences of contemporary biology is, contrary to the received wisdom, both viable and attractive in the age of evolution.

1 Biological Natural Kind Essentialism

Biological Natural Kind EssentialismBiological Natural Kind Essentialism

Definitions and Desiderata

First things first—what exactly is a natural kind, and what does the claim that a natural kind has an essence amount to? As with most philosophical terms of art, ‘natural kind’ and ‘essentialism’ are often used by so many different philosophers and for a variety of distinct reasons that one must quite specifically delineate their desired meaning before undertaking a project which utilises them. The first chapter of this book does just that, focusing on what I take to be the central concepts that are associated with each term. Once I have laid out the intent and scope of ‘natural kind’, I move on to defining the basics of the theory at the centre of this book—natural kind essentialism. Importantly, however, it is a specific form of that theory— Aristotelian natural kind essentialism—which is the fundamental focus of this work, as it is its central tenets which motivate and animate the theory which this work culminates in. In this first chapter, then, after discussing the more general concept of ‘natural kind essentialism’, I detail the particulars of Aristotle’s unique brand and what I take to be its primary theoretical virtues, and offer a brief sketch of what the foundation of a contemporary, neo-Aristotelian natural kind essentialism about biological natural kinds might look like.

1.1 The Philosophical Theory of Natural Kinds The natural world that surrounds us and of which we are a part ostensibly appears to be structured in certain ways. There seem to be, for instance, rather particular ways in which the physical world is divided up into discrete entities, and among the collection of these entities which make up that world, these ways are evidentially reiterated many times over. Nature, it would seem, abhors an undifferentiated, blurry mass of existential white noise: the entities of the natural world have structure, and the whole of that world is filled up with various repetitions of those structures. Not only do we find that there are particular structures repeated throughout the natural divisions of the biological world but also that these structures appear to form distinct collections—among them are, for instance, the plants, the insects, the arthropods, and the tetrapods—which we come to know by

Biological Natural Kind Essentialism  5 our recognition of the inherent structural similarities among their members. Furthermore, the structural similarities between the members of these collections—be they anatomical, eidonomical, or physiological—appear to be no mere artifice of human convention: that the denizens of the biological world belong to these collections is a fact about the world, not about us. Such is the basic story of realism about natural kinds.1 Of course, though the simplistic story outlined earlier does capture the main intuitions at play, we need to put more flesh upon that rather bareboned outline in order to arrive at a more robust, philosophical concept of natural kinds. To begin with, let us define a kind as an ontological category defined by a set of properties p where any entity x belongs to a kind k if and only if x possesses p. While this simple definition is suitable, it is also incomplete. For not just any set of properties are capable of delineating a proper natural kind—there are two important criteria associated with that philosophical concept that those sets must meet: one ontological, the other epistemological. On the ontological front, that set’s constituents and their composition must be suitably ‘natural’. There is now a large and complex literature on the subject of metaphysical naturalness, but with respect to kinds, the ‘naturalness’ at issue is largely tantamount to mindindependence.2 A kind is a natural kind then in virtue of the existence of its properties and the coalescence of their collection both being a consequence of nature, rather than of nous—that is, rather than being a result of our theoretical interests, scientific conventions, or common conceptual practices. On the epistemological front, the set of properties which define a natural kind must be inductively rich in such a way that, in virtue of their possessing that set, we are sufficiently licenced in our ability to make a wide variety of inductive generalisations about the typical further and future property possession—as well as the limits thereon—of its members. A natural kind, in other words, must be demarcated by a set of properties which reliably licence an extensive range of possibility and probability judgements about the entities which possess it.3 The satisfaction of these two criteria in a proper concept of natural kinds, as discussed in more detail next, results in a theory according to which there exist ontologically privileged divisions among nature’s denizens founded in their possession of particular sets of properties which function as the epistemological ground for the predictive prowess of our scientific knowledge about them. Importantly, being a realist about natural kinds doesn’t commit one to denying either the existence of mind-dependent, or socially constructed kinds, or that our recognition and employment of such kinds has the ability to grant us inductive insights about the workings of the world. Even if ‘stamp collector’, for instance, is a thoroughly mind-dependent classificatory division, there are undoubtedly members of that kind, and their membership certainly licences our ability to make a variety of inductive inferences about them: that they have an affinity for organisation and cataloguing, that they likely own a magnifying glass, that they are likely

6  Biological Natural Kind Essentialism to purchase limited-edition printings published by Royal Mail, etc. Furthermore, the realist about natural kinds need not deny that the collections carved out by mind-dependent kinds, however profligate in number and permissive in membership criteria, are partly grounded in objective, mind-independent features of the world: irrespective of our classificatory practices, every stamp collector has many features in common with every other.4 For the realist about natural kinds, however, the kinds established by human convention, however anchored they may be in the objective features of their members, are mere mirages of the natural and naturally privileged divisions which constitute the fundamental architectural facets of the world, and which ontologically undergird our most successful and insightful inferences about its operation. But what precisely does this central mind-independence claim of the natural kind realist amount to? I’ve already given a rather intuitive sense of what it means for a property grouping that defines a particular kind to be suitably mind-independent, one which corresponds to the well-worn Platonic adage that such collections “carve nature at the joints”: they represent sharp divisions in the world which act as ontological boundaries around particular repeatable types of entities.5 Inherent in this colourful phrasing is the important idea that when we approach the world, our conceptual dissection of its constituents is objectively constrained in such a way that any classificatory cutting we wish to make must take place around its ossified contours. Another, perhaps more instructive way we might cash out the mind-independence claim of natural kind realism is via negativa—as the denial of the claim that the property groupings which define a natural kind are those formed, held together, and susceptible to revision by our semantic practices for the purposes of their utility in our identification and taxonomic enterprises. It might be the case, in some suitably perfected science, that some of these types of properties do in fact belong to the collection which truly defines a particular natural kind—but the important point here is that it is neither a necessary nor sufficient condition on properties belonging to that collection that they are of that type. The now classic distinction in operation here is Locke’s division between ‘real’ and ‘nominal’ sets of defining properties in his An Essay Concerning Human Understanding (1689). In Book III of the Essay, Locke makes the distinction between the property groupings that we collect together to use in our definition of entities for the purposes of identification, classification, etc., and the mind-cum-interest independent ones which nature herself has collated—the former he dubbed ‘nominal’, the latter ‘real’. The nominal definition of a kind corresponds to the grouping of properties which we typically associate with and subsequently deploy as a reliably guided criterion for picking out and cataloguing entities as belonging to that kind in virtue of their possessing this collection.6 We quite commonly identify members of the ‘tiger’ kind, for instance, by noting their being ‘striped’, ‘predatory’, ‘four-legged’, ‘ferocious’, and ‘feral’ entities—and while this collection isn’t

Biological Natural Kind Essentialism  7 wholly arbitrary, it is certainly one that human interest and societal convention has, at least partly, conceptually cobbled together. Real definitions of kinds, on the other hand, correspond to the property groupings that, although they may be “constantly found to coexist with the nominal [groupings]” are nonetheless such that they are formed “without any relation to anything without [themselves]”—that is, they are a collection of properties which have a “union in nature whether the mind joins them or not”.7 In other words, the real definition of a natural kind corresponds to a group of properties that represent a division which nature makes, not us: they are neither created by human convention nor subject to the whims of conceptual revision. To return to our example, quite independently of our recognition or acknowledgement, the naturally compresent property collection which defines the kind ‘tiger’ might plausibly include a rather specific genetic constitution, a particular lineage relation, the participation in a circumscribed breeding pool, etc. The collection of properties which define natural kinds—those that are included in their real definitions—are not then simply lists of properties that help us, to borrow a bit of phrasing from the contemporary literature, “fix the reference” of those kind terms: such lists do not necessarily (and very often, definitively do not) correspond to the property collections which represent the objective, “joint-carving” divisions inherent in the natural world. The natural kind realist’s commitment to mind-independence then amounts to upholding the claim that the world consists of more than merely nominally defined kinds and thus, as Elder (2008: 341) succinctly puts it, that quite apart from what [kind terms] we may fashion, and what condition we may lay down on the satisfaction of those [terms], certain properties just do cluster together, in instance after instance, as a function of the way the world works. In addition to providing a conceptual framework for understanding the ontological commitments of natural kind realism, utilising this Lockean distinction also aids in the explication of the aforementioned epistemological component of that theory. To see how, it is important to note that, even if their composition is in some respects subject to mind-dependent arbitration, the property collections which constitute the nominal definitions of natural kinds are not wholly arbitrary. Indeed, some such collections are better than others, and the best of them—that is, the ones which most successfully support our identification and classification of natural entities—are the ones which easily and reliably track the members of the world’s natural kinds. The success of those collections in this respect depends on a simple fact: they represent the surface level and typical features of the members of those kinds. From the standpoint of mere phenomenological accessibility, detecting the ‘striped’ features of ‘four-legged’ entities really does aid in our identification of them as members of the ‘tiger’ kind, and it does so in no

8  Biological Natural Kind Essentialism small part because these are properties which rather dependably continually crop up across a wide range of members of that kind.8 That there is, in the case of our best nominal definitions of natural kinds, a type of dependence between those collections and those that make up their real definitions, illustrates the way in which the knowledge of an entity’s natural kind membership functions as the epistemic foundation for our inductive judgements about it: in virtue of knowing the latter collection, we may become reliably informed about the constitution of former—that is, about the superficially accessible and typical features which generally characterise it as a member of that kind.9

1.2 Natural Kind Essentialism Much has been said concerning the philosophical theory of natural kinds without having mentioned the conceptual addendum of essentialism, even though it is relatively rare, in the contemporary literature at least, that any philosopher support or veto the theory without it.10 This has not been by accident, as I think it worth drawing out the commitments of the simple theory of realism about ‘natural kinds’ before examining it in the context of essentialism, however tightly these two are now bound up, as it is open for one to endorse one without endorsing the other. Even if these two are intertwined to some degree, treating them separately allows us to see more clearly what each component contributes and how they operate together. As I will construe it, there are two central conceptual components of the theory of natural kind essentialism and unsurprisingly both, though in different ways, concern modality. The first of these, and undoubtedly the one familiar to most contemporary analytic philosophers, is that the essence of a natural kind consists of those properties which it could not fail to possess—call this the necessary set component. It is important to note the scope of this component, as it doesn’t entail any modal requirements on the property possession of the members of natural kinds. It isn’t tantamount to the claim, for instance, that a particular member of a natural kind losing any of the properties which qualify it as a member of that kind—those included in the ‘real definition’ of that kind—constitutes its existential annihilation. The necessary set component of natural kind essentialism, in other words, isn’t concerned with the “persistence conditions” of entities, where their possession of kind-defining properties play an ontologically significant role in their four-dimensional delineations.11 That component applies instead to the properties of a natural kind itself, and it entails that a member of a particular natural kind could not lose this set of kind-defining properties without going out of existence qua member of that kind: members of that kind may gain or lose any number of these properties (perhaps, if some philosophers are correct, to their own destruction), but no entity is a member of that kind unless it possesses that particular set of properties. Rather than being explicated via persistence conditions, the component is perhaps

Biological Natural Kind Essentialism  9 better situated within the framework of an extensional account of de re modality with a Kripkean brand of “weak necessity”: the set of properties which constitute the essence of a natural kind is that which every member of that kind possesses in every possible world in which they are members of that kind.12 The necessary set component’s importance to the theory of natural kind essentialism is (and historically has been) widely recognised and perhaps, were we not living in an age in which some self-styled brands of that theory have unceremoniously jettisoned it, it would hardly warrant spelling out.13 For the purposes of this book, however, its explication is especially instructive: for although it is certainly a unifying thread woven throughout nearly every contemporary discussion of any essentialist theory, it is not the only, nor in some ways the most important, component of that theory. It’s true that the theory requires the essence of a natural kind be a set of properties which it necessarily possesses—and indeed, that its doing so be a mindindependent matter—but there’s more to such a set constituting the essence of a natural kind than the mere inability of its members to be bereft of it.14 The second conceptual component to the theory of natural kind essentialism, one once prominent and now slowly returning to contemporary cognisance, is that the essence of a natural kind determinatively demarcates the range of permissible and prohibited properties which its members may possess—call this the modal fount component. It is central to the theory of natural kinds that there are intrinsic constraints on the property possession of the members of natural kinds, and that it is in virtue of an entity belonging to a particular natural kind that it cannot possess just any set of properties, and of those that it may possess, that some are more likely to be than others. In virtue of their being members of their particular kind, young turtles, for instance, cannot sprout wings, and though they may grow pyramid-like shells, they do so only rarely. According to natural kind essentialism, these modalities are not merely logical: the sets of properties which a member of a kind can and cannot possess are not determined (or, at least not solely determined) by whether they can be formally entailed from their kind-defining properties—in the way that ‘having three angles’ can be from an entity’s being ‘triangular’, for instance. Instead, in the case of natural kinds, the space of de re possibility for their members’ property possession is causally constructed and constrained by the productive prowess of its defining properties. If, in other words, the collection of properties which compose the ‘real definition’ of a natural kind are to function as its essence, they must play an operatively causal role in permitting and restricting the property possession of its members in such a way that whichever properties that collection can produce (either directly or indirectly) are those they may possibly possess, and whichever it cannot, are not. The modal fount component of the theory of natural kind essentialism can be understood as providing the metaphysical ground for the epistemological

10  Biological Natural Kind Essentialism component of natural kind realism, as it is one way of cashing-out how the ‘nominal’ property set of a natural kind depends upon its ‘real’ one. According to natural kind essentialism, that dependence is causal, and the property set that constitutes the essence of a natural kind—or its ‘real’ definition—is the generative foundation of the set that our taxonomical systems (both folk and scientific) associate with its members—that is, its ‘nominal’ definition. This component is in fact at the heart of the now prominent Kripke-Putnam brand of ‘hidden structure essentialism’, where the ‘hidden structure’ that constitutes the essence of a natural kind functions as the causal ground of its members’ typical set of empirically prominent features.15 The favourite illustrative example of this dependence among those who have employed this distinction in the contemporary literature, and, indeed, one Locke himself favoured, concerns the kind ‘gold’. In these modern examples, the nominal set of properties associated with gold—the typical colour, malleability, ductility, etc., of its members—is understood as being causally grounded in its atomic number (or rather, the positively charged structure that number represents): this is the property which explains why that set, as Locke put it, “is inseparable from the real essence of gold”, it being the one “on which these qualities and their union depend”.16 In other words, it qualifies as being the ‘real essence’ of gold precisely because, as Elder (2008: 343) puts it, it is a property which is not shaped by other properties characteristic of gold. . . [for] the causal shaping goes rather in the opposite direction. . . [as] gold’s atomic number does, all by itself, determine many other properties that are characteristic of gold. According to the theory of natural kind essentialism then, the dependency of the ‘nominal’ upon the ‘real’ which grounds the possibility and success of our inductive practices about natural kinds (as discussed in the previous section) is a matter of causal uniformity: the former is, as Locke put it, “constantly found to coexist with” the latter precisely because all members of a natural kind share the same set of generatively privileged causal mechanisms.17 This is a subtle but important point because although the discovery of a set of properties commonly possessed among a particular set of entities which purportedly belong to a ‘natural kind’ is a rather commonplace occurrence, such sets are often possessed by those entities for accidental or contingent reasons. Consider, for instance, the purported natural kind ‘Oxonian’. Surely all the members of this kind will have certain things in common in virtue of which they are each understood as belonging to that kind—all have gone through the matriculation ceremony, all own at least one set of subfusc attire, etc. However, the reason why each of those members possesses this set of features is overwhelmingly likely to be different in each case—one might have those features because she was keen on studying under a particular professor and actively earned an academic scholarship,

Biological Natural Kind Essentialism  11 another because his father insisted he follow in his footsteps, allowing him no other option after sixth form. In this way, the classification of entities under the kind ‘Oxonian’ fundamentally fails to reliably licence inductive inferences about their members: they may share certain properties in common, but as they do so only accidentally, the predictive utility of that classification is substantially diminished— i.e. what may be assumed about one of those members may not be reliably assumed about the others. In the case of genuine natural kinds, however, the causal connection between the real and the nominal provides a principled ground upon which our inductive prowess about them rests: when that epistemic enterprise is successful, and reliably so, the nominal property set with which we associate any particular kind occurs among its members for a common reason—that is, on account of its being, in each instance, the product of the same causal mechanisms.18 That the connection between the properties of a natural kind which are commonly possessed among its members and those that constitute its essence is not (or not merely) logical, but causal, has important implications. On the one hand, the causal productivity of essential properties with respect to those further properties, as we have seen, is by no means a weak relation: it establishes the modal boundaries of the latter’s possession by the members of a natural kind and functions as the ontological ground of those members’ repeated possession of a characteristic such set—i.e. the nominal properties. On the other hand, however, the causal nature of that connection also entails there being, as Wilkerson (1988: 35) puts it, “a certain looseness of fit” between the ‘real’ and ‘nominal’ properties of a natural kind. For it simply isn’t the case that every member of a particular natural kind, in virtue of possessing the property set which defines that kind, will thereby also possess the set which corresponds to its nominal definition. To acknowledge that there is an important causal connection—indeed, an ontologically unidirectional dependency—between the real and nominal property sets which define a natural kind then does not amount to the claim that every member of a particular natural kind must possess the properties which constitute that latter set; indeed, as I have carefully pointed out, the former set’s causally productive role with respect to the latter establishes at most the possibility and likelihood of such possession. This is because, in general, the relation of causal production is not equivalent to that of logical entailment: a property/state of affairs/event/etc. can be causally dependent upon another without the latter’s mere existence necessitating the former’s. The proper functioning of the human circulatory system, for instance, no doubt causally depends upon the electrical impulses of the heart, but the latter’s presence doesn’t immutably and in every instance guarantee the former’s. Furthermore, the phenomena of positive and negative interference suggests that, in general, causes do not necessitate their effects: even when a property/state of affairs/event/etc. is actively causally productive of another in such a way that the latter can be conceptualised

12  Biological Natural Kind Essentialism as the effect of the former, this is yet a non-monotonic relation, in principle susceptible to obstructive intrusions.19 Even while the heart is actively performing its biomechanical function, the presence of additional impeding causal factors may at any time significantly inhibit or functionally eliminate circulatory integrity. There are good philosophical reasons then to expect that a theory of natural kind essentialism, in virtue of its positing the existence of a causal connection between the real and nominal property sets of a natural kind, must thereby accommodate there being a certain “looseness of fit” between those sets.20 For all that has been said about the modal fount component of natural kind essentialism thus far, I have yet to provide an answer to two important questions. Firstly, which types of properties are the essence of a natural kind causally responsible for establishing both the possibility and likelihood of their possession? Surely, the essence of a particular natural kind does not perform this modal duty at every “level” of property possession of its members, being exhaustively responsible in this way for every property its members might possess. But then, which types of properties are within the causal-cum-modal remit of the essence of a natural kind? Secondly, and intimately related to the first question (as we have seen), which types of inductive generalisations does the essence of a natural kind furnish about its members? Given that the claim that an entity’s membership to a particular natural kind serves to ground every possible inductive inference one might wish to make about it is surely unreasonably strong, the onus is on a theory of natural kind essentialism to provide a principled restriction on that scope. Because they in some way serve to demarcate the proper domain of essential properties, the answers to these questions are of central importance to a defence of that theory: if it is to have any hope of locating the essences of natural kinds, it had better be able to specify to some degree of precision which sort of properties it’s looking for and where to go about looking for them. With respect to the theory of biological natural kind essentialism at issue in this book, the answers which I favour are fundamentally informed by the ones given by its progenitor—Aristotle. With that in mind, it will be instructive to turn now to a brief survey of what I take to be the distinctive features of the Aristotelian theory of biological natural kind essentialism.

1.3 Aristotelian Biological Natural Kind Essentialism For Aristotle perhaps, natural kind essentialism needed no argument. That the world was objectively divided into distinct types of entities and that the inner-workings of nature were explicable in terms of these divisions was a well-entrenched philosophical position from at least the time of Socrates, and it found a prominent expression in the writings of his own teacher, Plato. But in the ancient world, it was certainly Aristotle who put the most emphasis upon the doctrine, it being one he considered utterly foundational to any sufficiently sophisticated philosophical and scientific understanding

Biological Natural Kind Essentialism  13 of the natural realm. In the metaphysics of Aristotle, the existence of these objective, unchanging, kind-defining divisions which formed the repeatable essences of natural entities epitomised the cosmic balancing act between an unchanging, undifferentiated Parmendian Monism and an unstable, everundulating Heraclitian mosaic. Aristotle’s commitment to natural kind essentialism is expressed most prominently within the metaphysical framework with which he most generally conceptualised the living world—hylomorphism.21 According to that framework, the entities which populate that world are best understood as being metaphysically bipartite, each existing as the inseparable union of two distinct, though intimately interrelated intrinsic ontological facets— matter and form. Very roughly, that distinction is often characterised as follows: the ‘form’ of an entity is comprised of the properties which define the kind of thing it is, while its ‘matter’ is comprised of the properties which define the character of its constitution. Put another way, the form of an entity refers to the set of properties which are responsible for the fundamental organisation, or structural configuration of its body, while its matter refers to the set of properties responsible for the mereological make up of its body—the “stuff” which is thus configured.22 Importantly, according to the hylomorphic framework, the forms of natural entities are ontologically repeatable in the sense that multiple entities can share the same form even if they differ quite widely in their matter, or the way in which they respectively “realise” that form.23 Furthermore, according to that framework, the collection of properties which comprise an entity’s form is neither idle nor inert, but rather plays a central role in shaping the character of the collection which constitutes its matter. As we will see, because in this framework the ontologically robust kind structure of the natural world is constructed from and shaped by its denizens being suitably intrinsically en-formed, the theory of natural kind essentialism lies at the heart of Aristotle’s hylomorphism. Consider first the necessary set component of that theory. In the Metaphysics, for instance, Aristotle continually links the form of an entity with its definition, one which is the “formula of the essence”—itself “indivisible”, and without generation or corruption.24 That the forms which define natural kinds are repeatedly instantiated throughout the ages in virtue of the act of sexual reproduction quite literally involving the passing on and preservation of one and the same form (from parent to offspring) suggests that, for Aristotle, the membership requirements for belonging to a particular natural kind are unalterably strict;25 indeed, the continual repopulation of the natural world with these kinds is, according to Aristotle, the way in which its denizens in some way “participate in the divine”, or the eternal.26 This inflexibility is in fact central to his metaphysical picture as it serves to ground the very possibility of our scientific knowledge of the world: Aristotle believed, in short, that there can be no genuine knowledge of what is accidental, or subject to change. The importance of this epistemological thesis is evinced in its entailing a metaphysical one—namely, that

14  Biological Natural Kind Essentialism the collections of properties which comprise kind-definitions are themselves incapable of variation. For Aristotle, the truth of this metaphysical thesis effectively safeguarded our world against the washings of the Hericlitian flux, an ontology wherein being is always becoming and the changeable instability of the natures of things would ensure that our epistemological grasp upon them could only ever be illusory.27 As briefly alluded to earlier, the modal fount component of natural kind essentialism also occupies a prominent place in Aristotle’s hylomorphism in that, according to that theory, the significant uniformity which exists among the matter of the members of any particular natural kind is grounded in the causal capacities of their commonly possessed form. This is because in the hylomorphic framework, the form of an entity plays a causally active role in shaping its matter in virtue of its being comprised of a set of properties which function to orient the particularities of that entity’s property possession toward some specified end.28 The compositional make up of an entity, in other words, is configured by and conformed according to the dynamical directives of its form: what the former becomes (or may become) causally depends upon what the latter is.29 Because according to hylomorphism, it is constitutive of what the form is that it be operative in this specific fashion; the theory is, as Lennox (1987: 340) puts it, a “teleological essentialism”.30 The properties which comprise an entity’s form being ‘teleological’, or ‘goal-directed’, amounts to their being responsible for initiating and actively directing a causal process, or series of processes in order to bring about the production of a particular end-state. These properties then play more than a simple localised, or short-range role within the causal architecture of an entity: in virtue of their grounding a series of processes aimed at the production of a particular end-state, they exhibit an overarching and farreaching control over the specificities of its arrangement. In the hylomorphic framework, this control is manifested in an entity’s matter being structurally shaped by the organisational processes initiated by its form: the features which the former characteristically acquires are not the resultants of extrinsic or contingent influences, but rather reflect the intrinsic dynamical directives of the latter.31 In this way, because the form of an entity is comprised of a set of kind-defining properties, Aristotle’s hylomorphism entails that the essences of natural kinds play an intrinsic and active role in directing and delimiting the production of their members’ characteristic features. But what precisely are these features? That is, what are the end-states “toward which” the form of an entity causally directs its matter? Most generally, according to hylomorphism, the form of an entity is causally responsible for the production of the organisational structures which constitute that entity’s bodily configuration: its parts, their size and shape, and their spatial and functional relations to one another. More specifically, with respect to biological entities, the form of an organism is causally responsible for initiating a generative developmental programme for the production of its particular morphological profile—that is, the patterned arrangement of

Biological Natural Kind Essentialism  15 its anatomical and eidonomical architecture. It is important to note two things about this characterisation of the teleological character of organismal form. Firstly, note that, although the form of an organism is in this way intimately related to its particular morphological profile, it is not identical with it: contrary to the commonly held notion among a great number of contemporary metaphysicians, the form of a hylomorphic entity is not comprised of the properties which constitute its physique, it is (as I have already emphasised) the cause of those properties.32 Secondly, note that, according to this characterisation, the form of organism being causally responsible for the generation of the parts which comprise its morphological profile involves its being responsible for the programmatic development of those parts: for according to Aristotle it’s true both that “a man has such and such parts because the essence of man is such and such” and that “because man is such and such the process of his development is necessarily such as it is, and therefore this part is formed first, that next”.33 On Aristotle’s teleological essentialism in other words, as Cooper (1987: 246) summarises it, it is due to a thing’s form (its being, say, an apple tree) that it develops from the seed in certain particular ways and stages, and once full grown behaves in certain other particular ways (maintains a certain shape and size, grows certain kinds of leaves and fruit at certain seasons, etc.). Because in the hylomorphic framework forms consist of kind-defining properties, it follows then that, in virtue of their universally possessing that set of properties, the ontogenetic development of the members of a particular natural kind is intrinsically causally conformed toward the uniform production of the morphological architecture which is characteristic of that kind: they are thus the features which the essence of a natural kind is causally responsible for establishing both the possibility and likelihood of their possession. And it is in virtue of this teleological role which the essence of a natural kind plays that an organism’s membership to a particular kind serves to licence a restricted class of inductive inferences about it—namely, those which concern its morphological profile and the particularities of its production.34

1.4 Toward a Neo-Aristotelian Biological Natural Kind Essentialism I have discussed in some depth the details of Aristotle’s hylomorphic essentialism because, as I earlier indicated, its general themes form the foundation of the theory of biological natural kind essentialism that is explicated throughout the course of this book. Thus the neo-Aristotelian theory developed in the following chapters will posit the existence of natural sets of intrinsic properties that function as generative capacities for particularised morphological development which are shared among groups of organisms, ontologically delineating them as members of the same kind.

16  Biological Natural Kind Essentialism More specifically, the theory I present in this book incorporates what I take to be the two most central thematic aspects of its progenitor: the intrinsically dynamic nature of essence and the corresponding teleological modality of organismal morphology. In the hylomorphic framework, both of these aspects flow from the same source—namely, the uniquely powerful character of essential properties. The neo-Aristotelian theory I offer will do no differently: its essentialism avails itself of these features by appealing to the ancient concept of dunamis’ contemporary correlate—dispositionality. Dispositional properties are properties which, unlike their ‘categorical’ counterparts whose efficacy is bestowed upon them from the nomic structure of laws above, are intrinsically imbued with causal potency. As the ontological loci of the specified production of particular states of affairs, the end-directed dynamics of these properties not only underwrite the world’s fundamental patterns of causal regularities, but shape the very contours of its modal structure. Dispositional properties (as I argue in more detail later) are thus well suited to play the neo-Aristotelian role required of essence.35 The theory that this book will explicate and defend is then one in which the essences of biological natural kinds are comprised of dispositional properties. According to that theory, it is an organism’s possession of a privileged set of intrinsically powerful, teleologically directed properties that is responsible for its production of a particular ‘morphological profile’, and it is a group of organisms’ possession of this same set that ontologically demarcates them as members of the same ‘natural kind’. It is then, on that theory, their possession of a shared set of dynamically end-directed properties which metaphysically licences the epistemological warrant of our inductive generalisations about the possible and typical ontogenetic specificities of a natural kind’s members. As I will illustrate throughout the following chapters, a sufficiently sophisticated dispositional account of “what it is to be” a natural kind is not only able to satisfy the conceptual desiderata for ‘natural kind essentialism’ laid out earlier, but is also able to provide a metaphysical framework which is more than capable of deftly mitigating the most prominent objections that have plagued biological natural kind essentialism since the advent of evolutionary theory. Of course, whatever theoretical advantages a contemporary neo-Aristotelian theory of biological natural kind essentialism might gain by the utilisation of this philosophical framework will be of little use if its conceptual scaffolding has no firm empirical footing. In order to arrive at a consistent and compelling form of such a theory then, the following chapters will examine in detail this conceptual framework’s applicability to the biological realm. Establishing this framework’s ability to accommodate and account for the data of contemporary biological science will ensure that when the theory built from it is fully formulated and defended (in Chapters 5 and 6), it is done so standing on solid ground. This chapter has diagrammed the theory’s architectural schema, but before any bricks can be laid, that ground—itself

Biological Natural Kind Essentialism  17 already cluttered with competing classificatory structures—must first be cleared: this is the task of the next chapter.

Notes 1 As Bird (2009: 503) points out, the appellation of natural kind realism is in some ways a misnomer. Philosophers generally proclaim themselves as realists about a certain class of entities when it is thought that the existence, or some characteristic feature of a particular phenomenon is best explained by the activities, and hence the existence of those types of things—genuinely accounting for the reality of that phenomenon, they claim, requires that one accept the reality of the class of entities which are its purported cause. But this is not the sense of ‘realism’ at issue here: being committed to realism about natural kinds is not to hold that in addition to the various entities which we take to populate the natural world we must also countenance the existence of some further things—kinds—as independent, fully fledged members of our ontological inventories. It isn’t, in other words, as it was in the mediaeval debates concerning the nature of ‘universals’, a realism that functions as the contrary of ‘nominalism’. 2 See Khalidi (2013) for a comprehensive discussion of this sort of ‘naturalness’. For more on the general topic of metaphysical ‘naturalness’, especially in its application to properties, see Dorr and Hawthorne (2013). 3 Although this aspect of natural kinds was present in Aristotle and his immediate progenitors, its modern explication is typically traced back to Whewell (1847), Mill (1843), and more recently Quine (1969) and Kornblith (1993). 4 It is this sentiment which underlies more “permissive” conceptions of natural kinds one finds in the contemporary literature—e.g. Wiggins’ (2001) ‘sober conceptualism’ and Dupre’s (1981) ‘promiscuous realism’. 5 See the Phaedrus (265d–266a). 6 Or, as Locke (1689: III.3.18) puts it, the nominal definition of a kind is composed of a collection of properties which we use to qualify entities as having a “right to [the] name” of that kind. 7 Locke (1689: III.6.6). 8 Chakravartty (2007: 170) charmingly refers to this phenomenon as the “systematic sociability” of these properties. 9 Of course knowledge of these sorts of ‘nominal’ features of a kind can in some cases licence further, more “extended” nominal knowledge about those kinds— e.g. about their members’ behavioural habits, typical lifestyles, etc. 10 Interestingly, Hacking (2007) has recently argued that early defenders of the philosophical position of natural kind realism were at the same time decidedly anti-essentialists. This dovetails with Amundson’s (2005) important historical work in which he shows that, contrary to what has been long assumed, those scientists who prominently defended the existence of ‘natural joints’ in the biological world did not operate within an explicitly “essentialist” framework; this is a rejection of what he, following Winsor (2003), refers to as ‘The Essentialism Story’ about the history of the concept of natural kinds in biology. 11 As interesting as this individualistic form of essentialism may be, it is not the focus of this book. For recent discussions on this sort of essentialism, see Oderberg (2011), Wiggins (2001), Elder (2004), and Lowe (2006). 12 See Kripke (1980). 13 A much discussed and fairly widely adopted exemplar of the sort of “essentialism” in question is Boyd’s (1999) ‘homeostatic property cluster’ theory. 14 Contra the explication of ‘essential properties’ that has been popular since the late 20th century in modal metaphysics—one especially prominent in the

18  Biological Natural Kind Essentialism influential work of Plantinga (1974) and Lewis (1973)—“necessary possession”, or “possession in all possible worlds” isn’t a sufficient condition for a property being ‘essential’ in the neo-Aristotelian framework. Most will perhaps be familiar with Fine’s (1994) general critique of the sufficiency of that condition, though while he favourably cites Aristotle, his argument doesn’t rest on Aristotelian grounds (of the sort surveyed in this and the following sections). 15 See Kripke (1980) and Putnam (1975), and more recently Ellis (2001); the ‘hiddenness’ of essential properties in these accounts refers, as it did for Locke, to their relative level of empirical inaccessibility in comparison to more “surface level” features. 16 Locke (1689: III.10.17; 6.6). 17 Locke (1689: III.6). 18 If one takes on board the plausible family of ideas centred around truthmaker theory and the corresponding “no miracles”-type arguments, this aspect of the connection between ‘real’ and ‘nominal’ may provide a compelling foundation for the mind-independence component of natural kind realism; on truthmaker theory, see Rodriguez-Pereyra (2005) and Merricks (2007); on the “no miracles” argument, see Putnam (1975). Khalidi (2018) has recently suggested something along these lines, arguing that it is the exhibition of this causal dependence of the ‘nominal’ upon the ‘real’ which distinguishes genuine, natural kinds from merely conventional ones. 19 See Mumford and Anjum (2011), Schrenk (2010), and Chakravartty (2007) for recent detailed discussions. 20 There are good empirical reasons to expect that any adequate theory of biological natural kind essentialism must make such accommodations as well. I address this more specifically in Chapters 5 and 6. 21 It’s worth noting that Aristotle’s hylomorphism does have a wider application in, for instance, the Categories and the Posterior Analytics, where ‘form’ is to ‘matter’ as ‘species’ is to ‘genus’. This logical form of the theory, however, is not the concern of this book and so won’t be discussed in any detail in what follows. I mention it now only to distinguish it from the ontological form of the theory at issue here, and because the failure to make this distinction has been the cause of much interpretative confusion—see Lennox (2001) for an excellent in-depth discussion of these exegetical issues. 22 This is admittedly a rather crude and fundamentally incomplete characterisation of Aristotle’s hylomorphism. Although it isn’t necessary here, and would at any rate take the dialectic of this chapter too far afield, a proper characterisation of that doctrine must include the metaphysical relation between potentiality and actuality, or more accurately, capacity and activity; the interested reader is strongly encouraged to consult Aryeh Kosman’s (2013) excellent and comprehensive work on the subject. Although this relation isn’t emphasised in many contemporary forms of that doctrine, it is absolutely indispensable to a full and rich understanding of Aristotle’s hylomorphism, especially in its formulation in the biological works; see Shields (2017) for a recent application of this hylomorphic relation in a biological context. For more on the relation between contemporary forms of hylomorphism and Aristotle’s doctrine, see Austin (unpublished). 23 Some philosophers have defended the idea that Aristotle’s hylomorphism posited ‘particularised’ forms and thus strictly excluded the possibility that any single form could be shared among numerically distinct entities. Though this is a subtly complex and multifaceted interpretive issue, I will not discuss it here, as this reading is rather contentious and not widely held. See Loux (2008) and Woods (1991) for detailed discussions.

Biological Natural Kind Essentialism  19 24 Metaphysics Ζ, esp. §8–15. 25 On the Generation of Animals I, esp. §4. 26 On the Soul II.4. 27 Metaphysics ϴ and Ε, and Posterior Analytics I. 28 I won’t here be discussing or evaluating the arguments Aristotle put forward for the existence of goal-directed processes in the natural world. For primary sources, see Physics II, Metaphysics Ζ and ϴ, On the Parts of Animals I. For a thorough contemporary examination of this topic, see Johnson (2005). 29 On the Generation of Animals V.1. 30 The importance of the form of an entity being actively dynamic within Aristotle’s hylomorphic framework cannot be overstated. Although this aspect of the theory is perhaps most prominent in the biological works, it is also central to a proper understanding of the Metaphysics. For a comprehensive discussion of this issue, see Kosman (2013). 31 Aristotle most forcefully makes this point in his arguments against Empedocles, in Physics II, On the Parts of Animals I. 32 This confusion, one which typically stems from an insular reading of the middle books of the Metaphysics, commits what Koons (2014: 153) calls ‘the statue fallacy’—namely, reading Aristotle’s artefact-based illustrations of the hylomorphic framework as exemplars, rather than analogies. As Kosman (2013: 92–93) rightly points out, these illustrations serve a dialectical, rather than a depictive, purpose. 33 On the Parts of Animals I (640a33–640b4). See also Physics II.8, where the importance of the constitutive process by which an end-state is achieved in teleological causation is highlighted. 34 In Aristotle’s metaphysics, these inferences are secured in virtue of these constitutive developmental stages being hypothetically necessitated by an organism’s form: these stages must occur in order to produce the morphological endstate which typifies that form. See On the Parts of Animals I.1 and P ­ hysics II, esp. §8. 35 As there is much more to be said about the nature of dispositional properties, I have kept the description of them here brief. See Chapter 3 for a more detailed discussion.

Bibliography Amundson, R. (2005). The Changing Role of the Embryo in Evolutionary Thought: Roots of Evo-Devo. Cambridge: Cambridge University Press. Aristotle. (1984). The Complete Works of Aristotle (Vol. I & II, J. Barnes, Trans.). Princeton: Princeton University Press. Austin, C. J. (unpublished). Contemporary Hylomorphisms: On the Matter of Form. Bird, A. (2009). Essences and Natural Kinds. In R. Le Poidevin, P. Simons, A. McGonigal, & R. Cameron (Eds.), Routledge Companion to Metaphysics (pp. 497–506). Abingdon: Routledge. Boyd, R. (1999). Homeostasis, Species, and Higher Taxa. In R. Wilson (Ed.), Species: New Interdisciplinary Essays (pp. 141–186). Cambridge, MA: The MIT Press. Chakravartty, A. (2007). A Metaphysics for Scientific Realism: Knowing the Unobservable. Cambridge: Cambridge University Press. Cooper, J. (1987). Hypothetical Necessity and Natural Teleology. In A. Gotthelf & J. Lennox (Eds.), Philosophical Issues in Aristotle’s Biology (pp. 243–274). Cambridge: Cambridge University Press.

20  Biological Natural Kind Essentialism Dorr, C., & Hawthorne, J. (2013). Naturalness. In K. Bennett & D. Zimmerman (Eds.), Oxford Studies in Metaphysics (Vol. 8, pp. 3–77). Oxford: Oxford University Press. Dupre, J. (1981). Natural Kinds and Biological Taxa. The Philosophical Review, 90(1), 66–90. Elder, C. (2004). Real Natures and Familiar Objects. Cambridge, MA: The MIT Press. Elder, C. (2008). Biological Species Are Natural Kinds. Southern Journal of Philosophy, 46(3), 339–362. Ellis, B. (2001). Scientific Essentialism. Cambridge: Cambridge University Press. Fine, K. (1994). Essence and Modality: The Second Philosophical Perspectives Lecture. Philosophical Perspectives, 8, 1–16. Hacking, I. (2007). Natural Kinds: Rosy Dawn, Scholastic Twilight. Royal Institute of Philosophy Supplement, 61, 203–239. Johnson, M. (2005). Aristotle on Teleology. Oxford: Clarendon Press. Khalidi, M. (2013). Natural Categories and Human Kinds. Cambridge: Cambridge University Press. Khalidi, M. (2018). Natural Kinds as Nodes in Causal Networks. Synthese, 195(4), 1379–1396. Koons, R. (2014). Staunch vs. Faint-Hearted Hylomorphism: Toward an Aristotelian Account of Composition. Res Philosophica, 91(2), 151–177. Kornblith, H. (1993). Inductive Inference and Its Natural Ground. Cambridge, MA: The MIT Press. Kosman, A. (2013). The Activity of Being: An Essay on Aristotle’s Ontology. Cambridge, MA: Harvard University Press. Kripke, S. (1980). Naming and Necessity. Cambridge, MA: Harvard University Press. Lennox, J. G. (1987). Kinds, Forms of Kinds, and the More and the Less in Aristotle’s Biology. In A. Gotthelf & J. G. Lennox (Eds.), Philosophical Issues in Aristotle’s Biology (pp. 339–359). Cambridge: Cambridge University Press. Lennox, J. G. (2001). Aristotle’s Philosophy of Biology: Studies in the Origins of Life Science. Cambridge: Cambridge University Press. Lewis, D. (1973). Counterfactuals. Oxford: Blackwell Publishers. Locke, J. (1689). An Essay Concerning Human Understanding (R. Woolhouse, Ed.). London: Penguin Classics, 1998. Loux, M. (2008). Primary Ousia: An Essay on Aristotle’s Metaphysics Z and H. Ithaca: Cornell University Press. Lowe, E. (2006). The Four-Category Ontology: A Metaphysical Foundation for Natural Science. Oxford: Clarendon Press. Merricks, T. (2007). Truth and Ontology. Oxford: Oxford University Press. Mill, J. S. (1843). A System of Logic, Collected Works of John Stuart Mill (Vol. 7, J. Robson, Ed.). Toronto: University of Toronto Press, 1973. Mumford, S., & Anjum, R. (2011). Getting Causes From Powers. Oxford: Oxford University Press. Oderberg, D. (2011). Essence and Properties. Erkenntnis, 75(1), 85–111. Plantinga, A. (1974). The Nature of Necessity. Oxford: Oxford University Press. Plato. (1997). Plato: Complete Works (J. Cooper & D. S. Hutchinson, Eds.). Indianapolis: Hackett.

Biological Natural Kind Essentialism  21 Putnam, H. (1975). The Meaning of “Meaning”. Minnesota Studies in the Philosophy of Science, 7, 131–193. Quine, W. (1969). Ontological Relativity and Other Essays. New York: Columbia University Press. Rodriguez-Pereyra, G. (2005). Why Truthmakers. In H. Beebee & J. Dodd (Eds.), Truthmakers: The Contemporary Debate (pp. 17–32). Oxford: Clarendon Press. Schrenk, M. (2010). The Powerlessness of Necessity. Nous, 44(4), 725–739. Shields, C. (2017). What Organisms Once Were and Might Yet Be. Philosophy, Theory, and Practice in Biology, 9(7), 1–15. Whewell, W. (1847). The Philosophy of the Inductive Sciences: Founded Upon Their History (10th ed., Vol. 1 & 2). London: JW Parker. Wiggins, D. (2001). Sameness and Substance Renewed. Cambridge: Cambridge University Press. Wilkerson, T. (1988). Natural Kinds. Philosophy, 63(243), 29–42. Winsor, M. (2003). Non-Essentialist Methods in Pre-Darwinian Taxonomy. Biology and Philosophy, 18(3), 387–400. Woods, M. (1991). Universals and Particular Forms in Aristotle’s Metaphysics. In H. Blumenthal & H. Robinson (Eds.), Aristotle and the Later Tradition, Oxford Studies in Ancient Philosophy (pp. 41–56). Oxford: Oxford University Press.

2 Essence and Explanation

Essence and ExplanationEssence and Explanation

Natural Kinds in the Taxonomic Tree

Before a novel theory of biological natural kind essentialism can be built, the ground upon which it is to be constructed must first be surveyed. This is important because, as anyone familiar with the biological sciences is all too aware, the land of the relevant conceptual playing field is at present littered with theories which purport to correctly capture the categories into which the denizens of the natural world are ontologically classified. The onus is on any novel such theory then to explicate both its place among and relation to these theories. This obligation is made more pertinent by the fact that the theory of biological natural kind essentialism has historically been associated with the hierarchical stratification of taxonomical systems and, further, that it is this very affiliation which functions as the foundation of the majority of its contemporary critiques. To affirm biological natural kind essentialism, it is believed, is to be committed to the claim (to adapt a similarly maligned sentiment) that taxonomy recapitulates ontology— that is, that the branching of the taxonomic tree is shaped by, and thus fundamentally reflects, the ontological architecture of the natural world.1 This is, however, a commitment which is widely understood as being one the defenders of that theory cannot consistently make, and for a simple reason: in the context of contemporary evolutionary biology, taking that claim seriously seems to rather straightforwardly require the rejection of essentialism. Showing how a neo-Aristotelian theory of biological natural kind essentialism can consistently and compellingly confront these challenges is the task of this chapter. To that end, a central claim this chapter makes is that the conceptual connection between the ontology of natural kind essentialism and the hierarchical architecture of biological taxonomies is not merely much more tenuous than is commonly supposed, but is in fact founded on a fundamental mistake—namely, the conflation of telos and taxon. Because this confusion, as I will show, is at the centre of the contemporary rejection of the theory of biological natural kind essentialism, once it is cleared, so too will be the conceptual ground upon which a viable form of that theory might be built.

Essence and Explanation  23

2.1 A Natural Taxonomy of Kinds In explicating the fundamental framework of the philosophical concept of natural kinds, the previous chapter (in §1.1) claimed that it is constitutive of that concept that such kinds “carve nature at the joints” in a mindindependent fashion—that is, that they represent ontological divisions in the world which are neither created nor subject to revision by human convention. If there indeed exist natural kinds whose definitions delineate genuine divisions within the natural world, we might reasonably expect that, by carefully comparing and contrasting their features, the groups they demarcate will be amenable to categorisation and classification. Of course, while this general sort of endeavour has been undertaken to varying degrees of both specificity and scope throughout the natural sciences, the classificatory systems of interest for the purposes of this book are those which have been carefully constructed to capture the world’s biological kinds. Today, these systems are generally situated within the schematic framework most notably associated with the celebrated 18th century botanist Carl Linnaeus. In this by now familiar schema, organisms are broadly categorised by a hierarchical series of taxonomical ranks which reflect distinct degrees of classificatory precision (from the ‘Domain’ to the ‘Species’). On this framework, groups of organisms are catalogued according to their unique taxonomical rank values: human beings, for instance, are a collection of organisms which are distinguished by their belonging to the Kingdom of animalia, the Class of mammalian, the Genus of homo, and the Species of homo sapiens. Given that this classificatory framework ultimately derives from the writings of Aristotle—the rightly regarded “father of biological taxonomy”—a natural question for the defender of a neo-Aristotelian form of biological natural kind essentialism is whether any of these ranks (Kingdom, Family, Genus, Species, etc.) demarcate genuine ontological divisions whereat nature is “carved at the joints”.2 Prima facie, the advocates of that theory will want not want to be overly permissive here—a theory according to which every taxonomic rank equally satisfies the criteria for being ‘natural’ in this sense, for instance, seems rather unattractive; even Linnaeus, after all, considered the majority of those ranks to be merely heuristically advantageous conceptual artefacts and countenanced only the Genus and Species ranks as truly “God-given”.3 Importantly, however, the precepts of that theory (as described in Chapter 1) provide its advocates with a restrictive principle in this respect: any taxonomic rank which genuinely corresponds to a way in which the denizens of the biological world are mind-independently divvied up must contain natural kinds whose members’ common possession of a set of causal mechanisms ground the shared generative specificities of their morphological profiles. For most (historical and contemporary) forms of that theory, this has meant that the location of natural kinds is likely limited to within the confines of a single rank—the species taxon.

24  Essence and Explanation In the contemporary literature, and in a post-Darwinian context, this rather specific restriction is guided by the supposition that the degree to which any taxon contains members which represent mind-independent divisions in the natural world is directly correlated with the degree to which its members are evolutionary significant.4 According to this metric, while the higher taxonomic ranks merely reflect certain stabilities in the ebb and flow of the evolutionary process, the species taxon “carves at the joints” of nature in virtue of it demarcating the active agents of that process. The thought here is that, because the operation of that process proceeds by way of “gene flow”—that is, by means of the exchange of genetic information among interbreeding populations—any evolutionarily significant structural division among nature’s denizens must be one which picks out the primary causal participants of that exchange.5 Families, Classes, and even Genera seem incapable of satisfying that criterion: it is qua members of the same species that the hereditary mechanisms of adaptive mutations operate among interbreeding populations.6 Thus however heuristically advantageous the dissection of the biological world by means of the higher taxa may be, those divisions have typically been regarded as lacking the ontological depth to reveal its joints: if any taxon is to contain natural kinds, it is the one in which the dynamical forces of the evolutionary process are most directly operative. In this way, the perceived viability of the theory of biological natural kind essentialism is at present intimately correlated with the degree of objectivity which we may justifiably assign the classificatory divisions of organisms at the Species level. And while this correlation was perhaps at one time of great benefit to that theory—namely, during the long period in which species were understood as being both divinely instituted and ontologically immutable—in the age of evolution, it has proven instead to be its primary pitfall. For even if, as was suggested earlier, the species taxon is the most suitable strata at which we might attempt to locate natural kinds, the consensus among contemporary philosophers is clear: embarking on any such endeavour is ultimately an exercise in futility. If then the tenability of the theory of biological natural kind essentialism is tied up with the success of that enterprise, evaluating the arguments which undergird this contemporary consensus is of prime importance to the project at hand.

2.2 Natural Kinds and the Species Concept Typically, for the aforementioned reasons (among others), the debate concerning the existence of natural kinds in the biological world is centred on the question of whether species possess the requisite conceptual qualifications to be considered as such. As I made clear in the previous chapter, the philosophical concept of ‘natural kind’ is often intimately bound up with the doctrine of natural kind essentialism and the claim that the biological world is “carved up” in a mind-independently objective fashion in virtue of

Essence and Explanation  25 organisms’ possession of particularly stable sets of intrinsic (and intrinsically powerful) properties. Thus the question as to whether biological natural kinds exist is today often phrased as follows: do organisms belong to a particular species in virtue of their possession of a mind-independent collection of intrinsic properties? For the majority of contemporary philosophers of biology, this question must be answered in the negative: the division of the natural world “specieswise” is no mind-independent matter, and even if it were, it would nevertheless make no appeal to organisms’ possession of intrinsic properties. The first part of this two-pronged claim is often supported by a simple argument: the prevailing state of conceptual pluralism about the species concept provides us with a powerful pro tanto reason to prefer an anti-realist stance about the status of the members of the species taxon. There are today, after all, a vast multitude of mutually exclusive ways to conceptually carve up the world “species-wise”, and although each certainly has value according to the extent to which it is explanatorily useful within a particular theoretical context, the belief that any one of them is capable of more correctly or completely capturing some objective, context-independent structure of the natural world seems if not untenable, then at least rather unlikely to be true. The prevalence of conceptual pluralism with respect to the ‘species concept’ can in no way be denied. Indeed, it has a long history: Darwin himself considered the multiplicity of species concepts on offer in his day to be a “laughable” affair, one ultimately rooted in biologists’ repeatedly vain attempts to “define the indefinable”.7 It’s safe to say that the situation since Darwin’s day has only become increasingly complex and that what was perhaps once comical is now plausibly catastrophic. In a widely cited survey paper, Mayden (1997) catalogues no less than 22 distinct species concepts proposed and/or operative in the contemporary biological literature—and though the great majority of them are but subtle variations on certain core themes, it nonetheless remains a fairly astonishing number.8 Those themes are represented in a few prominent categories to which the most viable contemporary species concepts belong—each of which, in their own way, claims the purchase of objectivity by capitalising on an evolutionarily significant feature of the natural world (as discussed earlier). According to interbreeding species concepts, a species is defined, as in Ernst Mayr’s (1942: 120) influential ‘biological species concept’ formulation, as a group of “actually or potentially interbreeding natural populations that are reproductively isolated from other such groups”. Because what separates one species from another is whether it is possible for the former to sexually procreate with the latter and subsequently produce viable and fertile offspring, this type of concept thus views the divisions which the species taxon delineates as revealing the reproductive joints of the natural world.9 While procreation is of course central to the evolutionary process, equally so is selection: the successive shaping of inheritably stable morphologies within a group of organisms by broadly environmental pressures is, in the end, the

26  Essence and Explanation very thing that facilitates their eventual reproductive isolation. This emphasis on the importance of selection is evident in ecological species concepts, where species are defined as groups of organisms which, as Okasha (2002: 200) puts it, “exploit the same set of environmental resources and habitats”. As what separates one species from another is whether the former occupies the same ecological niche as the latter, this type of concept views the species taxon as effectively carving up the natural world “resource-wise”. On the other hand, although the driving forces which causally undergird the process of evolution are important, one might plausibly insist that our species concept reflect the fact that members of the species taxon are first and foremost the products of that process. On phylogenetic species concepts, species are identified with genealogically distinct lineage lines, and two species are distinct just in case they constitute discrete “branches” of the phylogenetic tree: here the members of the species taxon are understood as reflections of the evolutionarily significant historical-cum-relational joints of the natural world. It isn’t especially difficult to see that these types of species concepts are by and large incompatible with one another.10 Taking on board a phylogenetic concept, for instance, requires assigning no ultimate significance to whether two groups of organisms are able to interbreed with one another when determining whether these groups represent distinct species: unless those groups actually have interbred with one another, or belong to a lineage in which their ancestors have done so, they are separate species.11 If one takes the position that the species taxon is a theoretical construct employed as a heuristic device to aid our scientific investigation and categorisation of the natural world, the exclusivity of these various types of species concepts is of little consequence. Perhaps, as many philosophers have suggested, we could simply do away with ‘species monism’—i.e. the idea that there is a single species concept that is sufficient to do the job.12 We might then classify groups of organisms according to multiple species concepts in such a way that each group will belong to several distinct species—phylogenetically, this group belongs to one species, but ecologically it belongs to another—with the consequence that any group’s conspecificity with some other will never be an unqualified affair, but must always be concept and interest relative. But what are we to make of the prevalent conceptual pluralism about the species concept if we are committed to the position that the members of that taxon reflect the mind-independently objective “joints” at which the natural world is carved? Many, if not most, philosophers think that the plausibility of this pluralism strongly suggests that this commitment simply cannot be upheld and that we ought instead adopt an anti-realist, instrumentalist stance about the members of the species taxon.13 Indeed, the general consensus appears to be, as Dupre (1999: 57) concisely put it, that [t]here is no God-given, unique way to classify the innumerable and diverse products of the evolutionary process. There are many plausible

Essence and Explanation  27 and defensible ways of doing so, and the best way of doing so will depend on both the purposes of the classification and the peculiarities of the organism in question. Even if this move from conceptual pluralism to anti-realism is a bit too quick, I suspect that for most empirically minded, data-driven philosophers it is nevertheless a compelling one. It is no surprise then that, given its historically significant association with the species taxon, the plausibility of this move has subsequently signalled the increasing perceived implausibility of biological natural kind essentialism. We could, however, choose not to make that move and instead hold firm when faced with pluralism: perhaps adopting an anti-realist position isn’t well warranted, and we should instead dig our heels in to declare that one of the competing species concepts truly does capture the objective natural kind structure of the world. Even if we’re at this moment unsure as to which one is up to the task, we may have reasons for thinking that one will in the end be better suited to do so than the others: it’s safe to say, for instance, that most philosophers view phylogenetic concepts as being generally more adept at mapping onto the objective structure of the natural world than ecological ones. If—for these sorts of reasons, or others—we reject the inference from conceptual pluralism to anti-realism, does the theory of biological natural kind essentialism thereby regain its plausibility? Unfortunately, things are not so simple—for no matter which species concept we might choose to adopt, it seems that we must do so at the cost of effectively abandoning that theory. In short, this is because even if we accept that according to these concepts organisms belong to particular species in virtue of their possession of mind-independent collections of properties, none of those candidate collections—be they phylogenetic, ecological, etc.—consist of intrinsic properties. Instead, according to each of the most popular types of contemporary species concepts surveyed earlier, an organism’s membership to a particular species is grounded in its possession of a specific set of extrinsic properties— properties which it possesses not solely in virtue of its own constitution, but in virtue of its relation to some other entity, or environment. On the interbreeding species concept, an organism is a member of a particular species in virtue of it being able to sexually reproduce with some given population of organisms—in other words, a quite particular relation must hold between it and that group. On the ecological species concept, an organism is a member of a particular species in virtue of it occupying and utilising the ecological resources of a particular environment—in other words, a quite particular relation must hold between it and those ecological resources. On the phylogenetic species concept, an organism is a member of a particular species in virtue of it “occupying” a particular evolutionary “branch” of some lineage-line—in other words, a quite particular ancestry relation must hold between it and a series of now extinct organisms (or populations of organisms) along that line.

28  Essence and Explanation In each of these cases, these extrinsic relations are not merely incidental for, as Ereshefsky (2010: 682) puts it, according to each of these species concepts, in a fundamental sense “the occurrence of certain relations is the species” as “[i]t is the occurrence of those relations that makes the organisms engaged in them members of one species versus another species”. But if an organism’s membership to a particular species is fundamentally grounded in its entering into certain relations (be they procreative, environmental, generational, etc.), then the species taxon cannot contain the essences of natural kinds. For according to the theory of natural kind essentialism (as explicated in Chapter 1), an organism’s belonging to a natural kind is a fundamentally intrinsic affair, one grounded in its possession of a particular set of causally generative mechanisms which direct its morphological development. Thus, even if the aforementioned inference from conceptual pluralism to antirealism were to be resisted and the theory of biological natural kind essentialism to subsequently declare one of the competing species concepts as being a perfectly natural carving of the joints of the biological world, it could adopt it only on pain of violating its own principles: however objectively context and interest independent it might be, a relational essence is no essence at all.14 If then, as I have suggested, the viability of the theory of biological natural kind essentialism is today intimately bound up with the plausibility of the claim that the members of the species taxon represent the essences of natural kinds, it’s no wonder that in the age of evolution, most philosophers consider it to be effectively dead on arrival—for if taxonomy is to truly recapitulate ontology, essentialism must quite clearly be off the table.15

2.3 Two Taxon Questions There’s no disputing the fact that the contemporary discussion concerning biological natural kinds wherein species are taken to be its exemplars most certainly favours an anti-essentialist position. As we have seen, that position is suggested by a rather straightforward and compelling line of thought: either natural kinds do not exist in an objective, mind-independent fashion—and so fail to “carve nature at the joints”—or else they do so in virtue of organisms’ possession of a set of non-intrinsic, relational properties. For the defender of biological natural kind essentialism this is, to say the very least, an uncomfortable disjunction. However, I find this seemingly overwhelming case against that theory on these grounds to be vastly overstated: its conclusions are rendered plausible only by it trading on a fundamental confusion concerning the type of theory that biological natural kind essentialism is. Indeed, as I argue next, those conclusions, properly understood, are at best radically orthogonal, and at worst wholly irrelevant to that theory. In what follows, I show that once an important distinction has been made concerning the theoretical function of ‘species concepts’, this case against biological natural kind essentialism may be safely dismissed.

Essence and Explanation  29 Let us take a step back and ask: what, precisely, is the theoretical role that the various types of ‘species concepts’ outlined earlier play within a classificatory schema? Following Devitt’s (2008) insightful extrapolation of Mayr’s (1961) discussion on this topic, I take it that there are two prominent (and importantly distinct) candidate functions that they might perform. A species concept might be employed to sort organisms into species and thus to provide answers to questions of the form “in virtue of what is x a member of S?”—call this the taxon-membership role. On the other hand, a species concept might be employed to specify what that species-sorting amounts to and thus to provide answers to questions of the form “in virtue of what is S a species?”—call this the taxon-category role. Operating in the taxonmembership role, species concepts are utilised to determine why it is that an organism belongs to a particular member of the species taxon (to the Hawksbill, rather than the Loggerhead species of turtle, for instance). Alternatively, in the taxon-category role, species concepts are utilised to determine why it is that a group of organisms constitute a member of the species taxon (rather than a genus, or sub-species, for instance). Pertinent to the current discussion, we might then ask: which of these roles are the various types of species concepts on offer meant to be playing? Answering this question is more difficult than might be expected because, although they quite clearly designate distinct functions, their equivocation is rather widespread in the contemporary literature. Are these species concepts meant to “provide the essential property of the species category—a property found in all and only species taxa”, or are they instead meant to provide “the property in virtue of which a particular organism belongs to one species rather than another”?16 I contend that these concepts all ostensibly operate in the taxon-category role, rather than the taxon-membership role—that is, that they are all concerned with defining “what a species is qua taxonomic rank”: either a species (qua rank) is a group of reproductively isolated, interbreeding organisms, or a group of organisms which exploit a common set of ecological resources, or a group of organisms that form a distinct phylogenetic lineage, etc. If this is the case, this is no mere auxiliary observation—for note that if the problems that plague the theory of biological natural kind essentialism on account of its close association with the species taxon are to represent genuine threats to its viability, it must be the case that a species concept’s playing the taxon-category role is somehow tantamount to, or otherwise functionally translatable in to its playing the taxon-membership role. This is because the theory of biological natural kind essentialism (as outlined in Chapter 1), if it is concerned with species at all, is interested in explicating “what it is to be” a species qua a particular member of the species taxon—that is, it is interested in providing the ontological ground for answers to species-membership questions. As the essences which are the namesake of that theory are understood as collections of causally potent

30  Essence and Explanation properties responsible for the generative specificities of an organism’s morphology, it’s clear that if any species concept is to adequately map onto a natural kind concept, it must be one whose function is to demarcate groups of organisms as distinct species in virtue of their possession of distinct such collections. Thus if the most common types of contemporary species concepts do not perform the taxon-membership role, it’s difficult to see why their conceptual baggage ought to be a burden on a theory of biological natural kind essentialism: the fact that there are many distinct, but equally viable interest-based ways to define “what it is to be” a species qua taxonomic category, each of which relies on the obtaining of certain relational facts between an organism and something else, doesn’t appear to be especially relevant to whether that theory is true. The pertinent question then is: is a species concept’s playing the taxoncategory role somehow tantamount to, or otherwise functionally translatable to its playing the role that natural kinds do within a theory of natural kind essentialism? Following Devitt (2008), I take it that this is generally not the case and for a quite particular reason: answers to taxon-category questions are not causally informative in the way required of answers to the type of taxon-membership questions that are the focus of that theory. As mentioned earlier, species concepts which function in the taxon-membership role provide answers to questions of the form “in virtue of what is x a member of S?” and within the framework of natural kind essentialism; they do so by appealing to x’s possession of a set of properties which are causally responsible for its possession of (or the possibility of its possession of) the morphological features which typify members of S.17 As we will see, this is a role which the contemporary types of species concepts thus far surveyed are not well suited to play. For the sake of brevity, I will illustrate this fact with two types of species concepts. Consider first interbreeding species concepts. As I earlier stated, this type of concept is clearly capable of functioning in the taxon-category role where a species qua taxonomic rank picks out groups of reproductively isolated, interbreeding organisms. The question is: can this concept also operate in the taxon-membership role? In the context of biological natural kind essentialism, in other words, can it provide meaningfully informative answers to questions of the form “in virtue of what is x a member of S?” that delineate a collection of properties which are causally explanatory with respect to the morphological particularities of S? I think it is rather clear that it cannot. Suppose we are interested in the famous species of Dracaena tree dracaena cinnibari, or the ‘Dragon Blood Tree’, native to the Socotra archipelago in the Arabian Sea. If we were to ask “in virtue of what is this organism a Dragon Blood Tree?”, an answer that appeals to its ability to be successfully pollinated by this organism, that organism, etc., ought to strike us as either disingenuous or hopelessly confused. That this organism belongs to a particular allogamic group doesn’t appear to offer any causally explanatory insight into why it has (or has the potential to have) a dichotomous

Essence and Explanation  31 branching structure, elongated terminal leaves, and rich “blood red” sap. Of course, it’s certainly true that in order to be a member of such a group, this organism must possess a specific set of genetic resources which are causally relevant to the generation of (at least) its reproductive morphology. However, the fact that it belongs to this group doesn’t in and of itself licence any explanatory power with respect to that morphology—that role is performed by those resources themselves, irrespective of whether any other organism or group of organisms also possesses them; it is, after all, an organism’s possession of those resources which grounds its being a member of such a group, and not the other way around.18 Although it is perhaps a more subtle affair, the situation is no different in the case of phylogenetic species concepts: their operative success in the taxon-category role doesn’t look to transfer in any straightforward way to a similar competence in the taxon-membership role. If we were again to ask “in virtue of what is this organism a Dragon Blood Tree?”, an answer that appeals to its having these parents, and their having these parents, etc., seems incapable of offering any causally rich explanation as to why it has (or has the potential to have) a dichotomous branching structure, elongated terminal leaves, and rich “blood red” sap. While it seems rather clear that in the context of the framework of natural kind essentialism these facts fail to be informative in the correct fashion, it is not uncommon to encounter resistance on this point from essentialists and non-essentialists alike: given that morphological traits are passed down through the mechanism of genetic inheritance within an ancestry line, isn’t an organism’s possession (or its potential for possession) of a particular morphological profile in an important sense causally dependent upon its standing in specific lineage relations? Appeals to this sort of dependency are indeed ubiquitous in contemporary evolutionary biology, and there’s no sense in denying that they are causally informative with respect to organismal morphology in the aforementioned fashion—they very clearly are. However, we must now ask: are the answers to the question “in virtue of what is x a member of S?” provided by phylogenetic species concepts causally informative in the way prescribed by the tenets of natural kind essentialism? I think not. To see why, note that there are two conceptually distinct sorts of causal explanations that are prominent in the philosophy of biology literature—‘ultimate’ explanations, and ‘proximate’ explanations.19 Importantly, explaining why it is that a particular organism came to have the morphological features it does by citing its (selection-shaped) generational inheritance of those features—an ‘ultimate’ explanation—is not to explain how that organism’s ontogenetic development produces those features—a ‘proximate’ explanation. Or, to put it another way, explaining why it is that a particular group of organisms came to have a specific set of morphological features is one thing, and explaining how those features repeatedly “crop up” in the members of that group is another. Because the essence of a natural kind consists of properties which are causally responsible for

32  Essence and Explanation its members’ morphological profile, it should go without saying that it is the latter sort of explanation which is the purview of natural kind essentialism’s utilisation of taxon-membership criteria. ‘Ultimate’ explanations, causally informative though they may be, are simply not fit to serve. There is undoubtedly a sense in which such explanations are elucidatory with respect to the presence of morphological features among organism groups, but as it is one altogether incapable of illuminating the operation of the morphological mechanisms which causally undergird those features, it is not the sense in which the essence of a natural kind is explanatory with respect to organismal morphology (as outlined in Chapter 1, §1.2). What’s the upshot of this distinction? I have argued that while the various species concepts at play within the contemporary literature adequately function in the taxon-category role, their utility in the taxon-membership role, from the perspective of natural kind essentialism, is rather limited: they fail to delineate any collection of properties which might plausibly play the explanatory role required of essence. I suggest then that this failure entails that the two central problems for biological natural kind essentialism which stem from its association with these concepts—the implausibility of ‘naturalness’ in light of pluralism and the necessity of extrinsic membership criteria—pose no serious threat to the neo-Aristotelian form of that theory that is the focus of this book. For if these species concepts function merely in the taxon-category role, the fact that there are many distinct, but equally viable, interest-based ways to define “what it is to be” a species qua taxonomic category, each of which relies on the obtaining of certain relational facts between an organism and something else, will have no bearing whatsoever on whether that theory’s kinds are capable of being defined by their members’ possession of natural collections of intrinsic properties. And as it is precisely this latter concern which is at issue in the question of the viability of biological natural kind essentialism, the case against it on these grounds must be judged as quite plainly missing its mark.

2.4 Type, Telos, and Taxon At the beginning of this chapter, I explained why it is that the theory of biological natural kind essentialism is today intimately bound up with the species taxon: if any taxonomic category is to properly “carve at the joints” of nature, it is surely the one at which the dynamics of the evolutionary process are most directly operative. Thus, as I earlier pointed out, the perceived viability of that theory within the contemporary literature is closely correlated with the question of whether the classificatory divisions of organisms at the species level are capable of correctly capturing the essences of natural kinds. In the preceding section, I argued that one of the most prominent reasons for answering that question in the negative—namely, the purported non-naturalness and non-intrinsic nature of the species concept—ought to be dismissed.

Essence and Explanation  33 On the other hand, however, although I find those objections unconvincing, I do not wish to defend the claim that any taxonomic rank—species or otherwise—represents an objective, mind-independent way in which the natural world is “carved at the joints”. This is because I believe, in line with the sentiments of the opponents of biological natural kind essentialism, that it is a mistake to think that the branching of the taxonomic tree is shaped by, and thus fundamentally reflects, the ontological architecture of the natural world. However, I part ways with those opponents in that I believe the thought that biological natural kind essentialism entails that ‘taxonomy recapitulates ontology’ is equally mistaken. After all, an Aristotelian form of that theory of the sort I wish to defend (as explicated in Chapter 1) is first and foremost a claim about the source and nature of ontogenetic development, and not a methodological prescription for classificatory definitions.20 According to that theory, while the essence of a natural kind is certainly typological—in that it consists of a collection of teleologically oriented properties which dynamically direct the ontogenetic development of its members toward a particular morphological profile—it is not by dint of this thereby taxonomical. Indeed, to think otherwise is to conflate telos with taxon: for while the essence of a natural kind must be directed toward a particular morphological end-state, it need not be one which corresponds to any specific member of any taxonomic rank—species or otherwise.21 In general, although it is a consequence of any particular theory of biological natural kind essentialism that some classificatory divisions which carve up the natural world will be better than others, this should not be taken as necessarily having any significant ontological import. From the perspective of a neo-Aristotelian form of that theory, the extent to which a specific conceptual categorisation of the denizens of the natural world can be shown to most accurately and successfully warrant the reliable generation of predictive prowess about their morphology will be correlated with the extent to which its classificatory contours “wrap around the edges of” the typological joints of the world’s natural kind structure. Importantly, however, this correlation does not collapse into identity: acknowledging the heuristic utility of a taxonomical framework does not require an ontological commitment to its structural features, even if that utility is understood as being fundamentally grounded in the structural features of one’s ontology. Addressing the most prominent contemporary objections to the claim that species are exemplars of natural kinds has, however, not been an unnecessary or unfruitful detour. On the one hand, dispelling those worries has cleared the conceptual playing field of one of the most obstructive barriers to a legitimate defence of the theory of natural kind essentialism in the context of contemporary evolutionary biology. On the other, it has overtly illustrated an important facet of the neo-Aristotelian form of that theory which is central to this book—namely, its focus on the causal mechanisms of morphology. For note that the replies I’ve offered to those aforementioned

34  Essence and Explanation objections conform to a common theme—the inability of those objections to properly address the causal role of essence. As I see it, this is a consequence of conceptions of natural kinds which attempt to correlate the telos of essence with the divisions of a taxon: in failing to capture the generative capacities of morphological development, the various species concepts which carve the latter must likewise fail to designate the dynamic prowess which undergirds the former.22 And it is to that prowess which we must now turn—for a positive theory of natural kinds which focuses on the causal role of essence must be capable of both providing an appropriate theoretical framework with which to conceptualise that role and locating the type of properties that are suitable to play it. Doing so in the context of a defence of a neo-Aristotelian theory of biological natural kind essentialism requires an in-depth examination of both the developmental architecture of organisms and the metaphysical schematics of a dispositional ontology—this is the project of the next chapter.

Notes 1 This phrase is adapted from the slogan with which the famed zoologist Ernst Haeckel summarised his now universally rejected ‘recapitulation theory’ of evolutionary embryology: “ontogeny recapitulates phylogeny”. The reception of Haeckel’s theory in the advent of contemporary evolutionary biology is briefly discussed in Chapter 6, §6.2. 2 For Aristotle’s classificatory schema and its applications, see the Categories and the History of Animals. 3 See Mayr (1982) for a discussion of this point. 4 For excellent historical overviews of the reshaping of Linnaean taxonomy in light of the theory of evolution, see Ereshefsky (2001) and Wilkins (2009). 5 Eldredge and Cracraft (1980); Ghiselin (1987); Dupre (1999). 6 It could be argued that an analysis which locates these mechanisms at the Species level is still too coarse-grained, as it effectively deemphasises the causal contribution of more localised, intra-species “founding populations” to the evolutionary process. For an in-depth discussion of this matter, see Mayr (1970). 7 Darwin (1887: 88). 8 Wilkins (2009) has more recently distinguished at least 26 distinct species concepts currently at play in the contemporary literature to some degree or another. 9 Of course, one might wonder whether lines drawn from the mere possibility of organismal interbreeding can really do any work in objectively “carving up the world”—see Mishler and Brandon (1987). 10 This is not to say that all of these types are entirely mutually exclusive in that adopting one necessitates the wholesale rejection of the theoretical applicability of some other: consistently applying a phylogenetic concept of species, for instance, plausibly requires employing some criterion for the detection of lineage-splitting events—e.g. a failure of intra-species interbreeding—even if that criterion isn’t strictly being utilised to demarcate distinct species. 11 I here leave aside the interesting (and widespread) case of asexually reproducing organism groups. These groups represent a rather clear instance where phylogenetic and interbreeding concepts have a clear capacity to conflict in their classificatory assignments.

Essence and Explanation  35 2 See Wilson (1999) for quite a few advocates of this perspective. 1 13 See for instance Dupre (1999), Ereshefsky (1998), and Kitcher (1984). 14 It should be noted that there is a small group of contemporary philosophers who defend a form of natural kind essentialism which features essences composed of relational properties—see, for instance, Elder (2008), Griffiths (1999), Okasha (2002), and La Porte (2004). From the perspective of a neo-Aristotelian form of that theory, however, as already explained in the previous chapter and for reasons that will be made more clear in what follows, such “essences” are fundamentally ill-equipped to perform their proper function. 15 Cf. Sober’s (1980: 353) oft-quoted remark that “essentialism about species is today a dead issue”. 16 Ereshefsky (1992: xiv); Okasha (2002: 201). 17 Cf. Chapter 1, §1.2–1.3. 18 Another way of putting the point is to say that although the counterfactual < x is a member of this interbreeding group □→ x possesses these morphologically generative genetic resources > is true, it isn’t a causal conditional. In general, this is why (contra Lewens 2012) conceptions of species qua ‘individuals’ comprised of relationally bound collections of organisms (as in Ghiselin 1974, and Hull 1978) fail to demarcate essences which are informative in the requisite fashion. 19 This distinction, as mentioned earlier, was introduced by Ernst Mayr (1961). Although it has proven extremely influential and is today a well-established dialectical doctrine, it is not without its detractors: theoretical issues in evolutionary biology—particularly the role of so-called ‘reciprocal causation’ in the ‘extended evolutionary synthesis’ (Laland et al. 2013), and the role of the ‘evolvability’ of developmental systems in evo-devo (Brown 2014)—have led some to question its validity (or at least, its utility). As the merit of these critiques has no impact on the point I make next, I do not discuss them here; these issues are examined in more detail in Chapter 6. 20 The common misconception that Aristotle advanced a ‘taxonomical essentialism’ likely stems from the widespread conflation of his metaphysical concept of eidos with a classificatory concept of species. For a detailed discussion of this error, see Lennox (2001), Pellegrin (1987), and Balme (1987). 21 An appeal to non-taxonomical, morphological ‘types’ of this sort is widely viewed as an essentially anti-evolutionary manoeuvre, as it conflicts with the “population thinking” which purportedly characterises evolutionary theory (Mayr 1959; Sober 1980). However, with its novel reconceptualisation of the explanatory framework of that theory, the rise of evo-devo has re-legitimised the utilisation of typological concepts in the biological sciences—see, for instance, Amundson (1998, 2005), Lewens (2009a, 2009b), Wagner (2014), and Brigandt (2007, 2017). The conceptual distinctives of evo-devo and their ideological implications for evolutionary theory are discussed in Chapter 6. 22 The metaphysical basis for the separation of telos and taxon in the context of my theory’s ‘typology’ is given in Chapter 5, esp. §5.3.

Bibliography Amundson, R. (1998). Typology Reconsidered: Two Doctrines on the History of Evolutionary Biology. Biology and Philosophy, 13(2), 153–177. Amundson, R. (2005). The Changing Role of the Embryo in Evolutionary Thought: Roots of Evo-Devo. Cambridge: Cambridge University Press. Aristotle. (1984). The Complete Works of Aristotle (Vol. I & II, J. Barnes, Trans.). Princeton: Princeton University Press.

36  Essence and Explanation Balme, D. (1987). Teleology and Necessity. In A. Gotthelf & J. Lennox (Eds.), Philosophical Issues in Aristotle’s Biology (pp. 275–285). Cambridge: Cambridge University Press. Brigandt, I. (2007). Typology Now: Homology and Developmental Constraints Explain Evolvability. Biology & Philosophy, 22(5), 709–725. Brigandt, I. (2017). Typology and Natural Kinds in Evo-Devo. In L. Nuno de la Rosa & G. Muller (Eds.), Evolutionary Developmental Biology: A Reference Guide. Cham: Springer. Brown, R. (2014). What Evolvability Really Is. The British Journal for the Philosophy of Science, 65(3), 549–572. Darwin, C. (1887). The Life and Letters of Charles Darwin (F. Darwin, Ed.). London: John Murray. Devitt, M. (2008). Resurrecting Biological Essentialism. Philosophy of Science, 75(3), 344–382. Dupre, J. (1999). On the Impossibility of a Monistic Account of Species. In R. Wilson (Ed.), Species: New Interdisciplinary Essays (pp. 3–22). Cambridge, MA: The MIT Press. Elder, C. (2008). Biological Species Are Natural Kinds. Southern Journal of Philosophy, 46(3), 339–362. Eldredge, N., & Cracraft, J. (1980). Phylogenetic Patterns and the Evolutionary Process. New York: Columbia University Press. Ereshefsky, M. (1992). The Units of Evolution: Essays on the Nature of Species. Cambridge, MA: The MIT Press. Ereshefsky, M. (1998). Eliminative Pluralism. In D. Hull & M. Ruse (Eds.), The Philosophy of Biology (pp. 348–368). Oxford: Oxford University Press. Ereshefsky, M. (2001). The Poverty of the Linnaean Hierarchy: A Philosophical Study of Biological Taxonomy. Cambridge: Cambridge University Press. Ereshefsky, M. (2010). What’s Wrong With the New Biological Essentialism. Philosophy of Science, 77(5), 674–685. Ghiselin, M. (1974). A Radical Solution to the Species Problem. Systematic Zoology, 23(4), 536–544. Ghiselin, M. (1987). Species Concepts, Individuality, and Objectivity. Biology and Philosophy, 2(2), 127–143. Griffiths, P. (1999). Squaring the Circle: Natural Kinds With Historical Essences. In R. Wilson (Ed.), Species: New Interdisciplinary Essays (pp. 209–228). Cambridge, MA: The MIT Press. Hull, D. (1978). A Matter of Individuality. Philosophy of Science, 45(3), 335–360. Kitcher, P. (1984). Speices. Philosophy of Science, 51(2), 308–333. Laland, K., Odling-Smee, J., Hoppitt, W., & Uller, T. (2013). More on How and Why: Cause and Effect in Biology Revisited. Biology and Philosophy, 28(5), 719–745. LaPorte, J. (2004). Natural Kinds and Conceptual Change. Cambridge: Cambridge University Press. Lennox, J. (2001). Aristotle’s Philosophy of Biology: Studies in the Origins of Life Science. Cambridge: Cambridge University Press. Lewens, T. (2009a). Evo-Devo and “Typological Thinking”: An Exculpation. Journal of Experimental Zoology (Mol. Dev. Evol.), 312(8), 789–796. Lewens, T. (2009b). What Is Wrong With Typological Thinking? Philosophy of Science, 76(3), 355–3a71.

Essence and Explanation  37 Lewens, T. (2012). Species, Essence and Explanation. Studies in History and Philosophy of Science Part C: Studies in History and Philosophy of Biological and Biomedical Sciences, 43(4), 751–757. Mayden, R. L. (1997). A Hierarchy of Species Concepts: The Denoument in the Saga of the Species Problem. In M. F. Claridge, H. A. Dawah, & M. R. Wilson (Eds.), Species: The Units of Diversity (pp. 381–423). London: Chapman and Hall. Mayr, E. (1942). Systematics and the Origin of Species. New York: Columbia University Press. Mayr, E. (1959). Typological Versus Population Thinking. In E. Sober (Ed.), Evolution and Anthropology: A Centennial Appraisal (pp. 409–412). Washington, DC: The Anthropological Society. Mayr, E. (1961). Cause and Effect in Biology. Science, 134(3489), 1501–1506. Mayr, E. (1970). Populations, Species, and Evolution. Cambridge, MA: Harvard University Press. Mayr, E. (1982). The Growth of Biological Thought: Diversity, Evolution, and Inheritance. Cambridge, MA: Harvard University Press. Mishler, B., & Brandon, R. (1987). Individuality, Pluralism, and the Phylogentic Species Concept. Biology and Philosophy, 2(4), 397–414. Okasha, S. (2002). Darwinian Metaphysics: Species and the Question of Essentialism. Sythese, 131(2), 191–213. Pellegrin, P. (1987). Logical Difference and Biological Difference: The Unity of Aristotle’s Thought. In A. Gotthelf & J. Lennox (Eds.), Philosophical Issues in Aristotle’s Biology (pp. 313–338). Cambridge: Cambridge University Press. Sober, E. (1980). Evolution, Population Thinking, and Essentialism. Philosophy of Science, 47(3), 350–383. Wagner, G. (2014). Homology, Genes, and Evolutionary Innovation. Princeton: Princeton University Press. Wilkins, J. (2009). Species: A History of the Idea. Los Angeles: University of California Press. Wilson, R. (1999). Realism, Essence, and Kind: Resucitating Species Essentialism? In R. Wilson (Ed.), Species: New Interdisciplinary Essays (pp. 187–208). Cambridge, MA: The MIT Press.

3 Powerfully Directed Development

Powerfully Directed DevelopmentPowerfully Directed Development

A Dispositional Analysis of Ontogenesis

In order to lay the groundwork for a novel theory of biological natural kind essentialism I have thus far detailed its core metaphysical commitments and demonstrated how they can be leveraged to dismiss as misconceptions some potentially detrimental objections which contemporary theories of its ilk often face. With that work having been done, it is now time to explicate the ontology of the theory I wish to propose. This chapter takes up that task by answering two principal questions: what sort of properties are fit to function as the essence of natural kinds and which properties do so? As I see it, adequately answering these questions requires adopting a two-fold approach—one which is on the one hand theoretical and on the other empirical. Attempting to answer the second, primarily empirical question without an answer to the first, primarily theoretical question is rather plausibly an exercise in futility: to paraphrase a familiar Platonic paradox, if we don’t know what we’re looking for, we have little hope of finding it.1 That said, providing an answer to the first question without an answer to the second is, while not unimportant, ultimately uninformative: the extent to which an answer to the first sort of question is a meaningful one depends in no small way upon its utility in answering questions of the latter sort. With these things in mind, the answers to these questions will form the foundation of the theory to be proposed throughout the remaining chapters of this book. In this chapter, I detail the primary metaphysical framework in which a neo-Aristotelian theory of biological natural kind essentialism ought to operate—an ontology of dispositional properties. The central conceptual features of the nature of dispositional properties, I argue, uniquely qualifies them to perform the role required of essence. After illustrating their suitability in this respect, I identify the most plausible place at which that role might be realised—the causal sub-systems whose capacities constitute the core developmental architecture in control of organismal morphology. The claim this chapter makes is that these dynamically directed generative mechanisms of ontogenesis are prime candidates to collectively constitute the neo-Aristotelian essences of biological natural kinds.

Powerfully Directed Development  39

3.1 Dispositions and the Dynamics of Dependence If a collection of properties is to properly qualify as having the potential to play the role of essence, it must meet a certain set of criteria. From the perspective of a neo-Aristotelian metaphysic, these are dynamical criteria— they are met by any such qualified candidate collection in virtue of its performing a specific functional role. As detailed in Chapter 1 (§1.2), this is a causal-cum-modal role with respect to property possession, and in the case of a neo-Aristotelian form of biological essentialism, with respect to the possession of morphological properties in particular. According to that theory, an organism’s morphological properties are fundamentally dependent upon its collection of kind-defining essential properties: it is the causal prowess of the latter collection which constructs and constrains both the character and compresence of the former. To my mind, if the essence of a natural kind is to play this causal-cum-modal role with respect to the morphology of its members, it is best conceptualised as being composed of intrinsically powerful and purposively poised properties—dispositional properties. To see why this is so, we must first consider the metaphysical distinctives of these properties in some detail.2 There is an extensive and rich tradition in the history of metaphysics, stemming back at least from Democritus’ atomism and stretching forward most notably to the isolated ontological pointillism of Hume and Lewis, which views the nature of the denizens of our universe as being fundamentally passive: like so many billiard balls, the activity of each ultimately amounts to the degree to which they are “pushed and pulled” by some other.3 This “dead world of mechanism”, as Brian Ellis (2001: 107) colourfully puts it, is in some ways enshrined in our contemporary scientific paradigms, wherein what an entity can or must do is conceived as being merely functionally derivative either of the contingencies of its extrinsic causal context, or else as a necessary consequence of the “laws of nature” which govern it. But there is another equally rich tradition, attributed principally to Aristotle, which views those modalities as being intrinsically grounded in those entities. According to this perspective, the entities which populate our world themselves play an active role in erecting the causal structure which shapes its course of events in virtue of their possession of properties which specify their particularised potential for change—these are dispositional properties. In the contemporary literature, the former tradition is upheld by those who believe that natural properties are merely ‘categorical’—that is, properties which place no causal or modal constraints upon the world. If the world is fundamentally a collection of categorical properties, those constraints are both contingent and extrinsic: either they are imbued upon it from a set of higher-order natural laws (which may have been different), or else are reducible to abstracted reflections of brute facts about its causal regularities (which may not have occurred).4 A world constructed from dispositional

40  Powerfully Directed Development properties is radically different: these are intrinsically dynamical properties, essentially defined or individuated by what they do.5 The dynamical nature of dispositional properties consists in their being causally responsible for reliably and repeatedly bringing about a particular type of state of affairs (a ‘manifestation’) upon the obtaining of a particular set of conditions (a ‘stimulus’). By functioning as metaphysical “switches” of sorts, in that they causally mediate the influence of the latter states to bring about the former ones, dispositional properties constitute the ontological infrastructure of state-transition. In the philosophy of physics, for instance, the property ‘negative charge’ is often understood as a dispositional property—when its bearers meet a like-charged particle (a stimulus condition), they repel with a certain momentum (a manifestation state). Thus the appellation of these properties: an entity’s possession of them disposes it to exemplify certain states and exhibit certain behaviours, should the appropriate circumstances arise. It is important to note, however, that the existential persistence of dispositional properties is not dependent upon such circumstances actually doing so—an ill-fated “lonely electron” which never encounters its ionic ilk yet remains negatively charged: it has the potential to bring about a particular change in its momentum irrespective of whether it ever has the opportunity to do so. Dispositional properties, in other words, are the ontological ground of the intrinsic causal capacities of entities. Of course, dispositional properties are not restricted to the realm of mereological simples—they are also, and more commonly perhaps, possessed by complex systems consisting of an entire network of causally interacting elements.6 Thus in many, if not most cases, the processual pathway from ‘stimulus’ to ‘manifestation’ spans an extensive and complex causally linked channel. This is evident even in the seemingly simple philosopher’s paragon of dispositionality—the property of ‘fragility’: more often than not, this property is embedded in a complex physical microstructure wherein its manifestation—‘breaking’—is the result of a complex, multi-stage causal process comprised of the alignment of various micro-events which over time collectively bring about decreasing degrees of structural integrity. Irrespective of the length and breadth of this sort of “causal gap”, the existence of any particular causal capacity is exhibited in such networks reliably and repeatedly executing a series of step-wise internodal causal operations to produce a particular end-state upon the occurrence of a specific set of conditions. Importantly, then, although the constitution of that channel with respect to its precise elements and their connective relations may differ among distinct systems and/or be traversed in a novel fashion in each instance it is crossed within a single system, any system which produces a particular end-state in response to a particular set of conditions possesses the causal capacity specified by that stimulus-manifestation pair. In this way, dispositional properties are functionally individuated properties—their identity consists in their capacity to perform a certain

Powerfully Directed Development  41 function: namely, the causal production of a particular end-state, or manifestation. Because, as I have just pointed out, that function can be performed by means of a variety of distinct causal channels, dispositional properties are multiply realisable properties: irrespective of any discrepancies among their constitutive causal architecture, any two systems which have the capacity to perform the same causal function ‘realise’ one and the same dispositional property.7 Thus although in any specific instance a particular dispositional property is ontologically “nothing over and above” the causal network which realises it, it must be in an important sense disassociated from that network—qua a multiply realisable property, the strict identification of it with any specific channel configuration is ultimately unattainable.8 What remains the same throughout every instance of a particular dispositional property, however, and is thus that in which its very identity consists, is its functioning as the locus of its bearer’s causal capacity to produce a specific end-state. For this reason, dispositions are understood as teleological, or goal-directed properties—ones which are dynamically oriented toward those ends. Although once commonplace, the designation of a property as ‘teleological’ is today widely regarded as tantamount to an endorsement of an inappropriate and unviable form of ‘physical intentionality’ whose efficacy essentially consists in an as yet non-existent states of affairs somehow exerting a shadowy, spatio-temporally backwards causal influence upon its bearer.9 In the case of dispositional properties, however, nothing so mysterious or nefarious is happening here: a dispositional property’s having a particular “goal” of bringing about a specific end-state is simply synonymous with its dynamically privileging its bearer toward the causal production of that state (in the event that certain circumstances obtain).10 There are generally acknowledged to be two central processual phenomena that a complex system might exhibit which affords evidence of its being goal-directed in this fashion: pleonastic pathing and persistence.11 A system exhibits pleonastic pathing with respect to a particular end-state if it is able to bring about that state via a number of alternative trajectories. If a system realises a dispositional property, then, even if the processual pathway between the obtaining of its stimulus condition and its specified end-state is a well-defined route, it is nonetheless a “wide” channel—one which consists of a variety of quantitatively and qualitatively distinct causal chains by which it may be traversed. In this way, such a system is dynamically privileged toward producing that state: the likelihood that the system does so increases in proportion to the number of available ways in which it might do so. Correspondingly, the extent to which a system’s processual pathway from stimulus to manifestation is pleonastic is positively correlated with its capacity for persistence—its ability to remain effectively undeterred in the production of its end-state in the face of a wide range of perturbative influences. If a system realises a goal-directed dispositional property, the process by which its stimulus condition is causally connected to its manifestation state is a relatively robust one. In persistent systems, the dynamical

42  Powerfully Directed Development privileging of the production of a particular end-state is exhibited in the imperviousness of its impetus to do so. In short, then, dispositional properties are teleological, goal-directed properties in virtue of the fact that they dynamically orient their bearers “toward” the production of particular states by establishing a causal directive to do so—one which is both easy to execute and not easily diverted. It is qua goal-directed properties that dispositions serve to ground inductive inferences about their bearers’ possible and likely future states. As the intrinsically causal ontological infrastructure of pleonastic and persistent state-transitions, an entity’s possession of these properties robustly disposes it toward the production of certain states, given certain circumstances. That dispositional properties are responsible for such processes is the basis for their being conceptualised as the metaphysical ground of the truth of subjunctive conditionals concerning those states—i.e. we can reliably infer that if that entity were to be in particular circumstances, it would bring about those states; in the contemporary literature, this is often framed as dispositional properties functioning as the ‘truthmakers’ of those conditionals.12 Of course, though an entity’s possession of dispositional properties certainly makes such judgements reliable, it does not render them infallible. The reason for this is simple: in any particular instance, the connection between stimulus and manifestation is bridged causally, rather than logically, and as such cannot have the force of necessity.13 That this is so is evident from the fact that the truth-values of the conditionals closely associated with any particular dispositional property are context-sensitive—and necessity is no respecter of context.14 The now familiar paragon of context sensitivity in these cases are so-called masking phenomena, wherein, although an entity possesses a particular dispositional property and its appropriate stimulus conditions are met, due to the influence of another factor within the immediate causal context—the “masker”—the manifestation state does not occur: though its grave potency may remain, following the swallowing of a cyanide pill with an appropriate antidote is unlikely to result in death.15 However, it’s important to note that our discovery of the masking conditions of a particular dispositional property does not entail the essential unreliability of the inductive inferences which that property licences with respect to its bearer’s likely states. Indeed, quite the opposite is the case, as what we learn is rather that there is a reliable correlation between those conditions and the failure of the production of those states—the utility of medicinal antidotes, for instance, depends upon the reliability of these sorts of correlations. The detection of masking conditions may make our inferential practices concerning the manifestations of dispositional properties more complex, but it does not thereby mitigate their legitimacy. Having explicated the most prominent distinguishing features of dispositional properties, we are now in a position to see why they are well suited to satisfy the criteria required of any collection of properties which might qualify as capable of performing the role of essence. As mentioned

Powerfully Directed Development  43 earlier, these are dynamical criteria, and, in the case of natural kinds, any collection which satisfies them does so in virtue of its playing a particular causal-cum-modal role with respect to morphology. For according to a neoAristotelian theory of biological natural kind essentialism, an organism’s morphological properties are fundamentally dependent upon its collection of kind-defining essential properties in that it is the causal prowess of the latter collection which constructs and constrains both the character and the compresence of the former. Because this rich form of dependence is fundamental to the doctrine of essentialism, it is not sufficient for a collection of properties to function as the essence of a natural kind that it merely “enter into the causal equation” with respect to the generation of the morphology of its members. To properly qualify as the essence of a natural kind, such a collection must function as the fundamental causal locus of that generative prowess. As the intrinsically causal ontological infrastructure of state-transitions, collections of dispositional properties are especially well suited to perform that function: unlike their categorical counterparts, dispositional properties do not contingently inherit their efficacy from any ontologically extrinsic edifice— they are, of their very own nature, empowered. These properties are thus uniquely qualified to operate as the metaphysical foundation of the de re dependency at the heart of the essentialist framework. Indeed, dispositional properties are able to perform this operation par excellence as, qua teleologically oriented capacities, their intrinsic causal role is at the same time a modal one: the end-states to which they dynamically orient their bearers define and delimit the space of possibility of those entities’ property possession. Dispositional properties, in other words, are able to serve as the intrinsic metaphysical ground of de re modality: for any state S and any entity e, it is possible for e to possess S if and only if e possesses a dispositional property “aimed at” S.16 This may seem a bold and overly restrictive claim, but its basis is both intuitive and simple: it is possible for e to possess S if and only if there are some circumstances or another whose occurrence is causally correlated with e’s coming to possess S. As the existence of such correlations is the metaphysical purview of dispositions, these properties play the fundamental causal-cum-modal role with respect to an entity’s property possession required of essential properties, in that they both construct and constrain the set of properties their bearers might possess. Furthermore, these causal correlations engender the characteristic features of the de re dependence which typifies essential properties with respect to so-called nominal, or typical property collections, as expressed in the modal fount component of essentialism (Chapter 1, §1.2). As we have seen, properties which play the role of essence must be causally responsible for the continual “cropping up” of certain sets of properties among the bearers of those essences. As previously discussed, this responsibility must be rather robust as it functions as the metaphysical ground of the reliability of our inductive inferences about the property possession of sets of entities which

44  Powerfully Directed Development possess the same essence. It should by now be clear that an essence comprised of dispositional properties is more than capable of performing this function as not only do these properties uniformly dynamically orient their bearers toward the possession of particular properties, they do so robustly via a process both pleonastic and persistent. If the essences of natural kinds are comprised of dispositional properties, our ability to make reliable inductive inferences about the typical property possession of their members is thus on firm ontological footing. Yet although the dependence of the ‘nominal’ upon the ‘real’ is by no means a weak relation, it must also be to a certain extent elastic: for although possessing a particular essence secures both the possibility and likelihood of the possession of a specific typical set of properties, it makes no metaphysical guarantee; however common and widespread, such a set is not universally possessed by every member of a natural kind. If, however, the essences of natural kinds are comprised of dispositional properties, this elasticity is both accounted for and expected. Because these properties can be possessed without manifesting and can be activated and yet fail to causally produce their specific end-states, all of the members of a particular natural kind possessing the same dispositional essence can each equally be disposed toward the possession of a specific set of properties without it being the case that every member actually does so. In this way, an essence comprised of dispositional properties is capable of establishing a relation of de re dependence between ‘real’ and ‘nominal’ that exemplifies the requisite flexibility.17 Dispositional properties then are well-qualified candidates to play the causal-cum-modal role required of properties which function as the neoAristotelian essences of natural kinds. And while their general suitability in this respect will of course be substantially expanded upon throughout the course of this book, the pertinent question at this point is whether there actually are any such properties which are operative in the specific role required of the essence of biological natural kinds. In other words, are there any intrinsically dynamic, goal-directed properties which are causally responsible for the specified production of an organism’s ‘morphological profile’? As mentioned at the beginning of this chapter, this is a question which can only be adequately answered by consulting the empirical data of the biological sciences.

3.2 The Causal Mechanisms of Morphology If a neo-Aristotelian theory of biological natural kind essentialism is to be both plausible and defensible, it must be able to designate a certain set of properties as forming the “causal ground” of the morphological profile of a certain set of organisms. To be able to make this sort of designation in an informed and non-ad hoc fashion, such a theory must adequately take into account the precise causal structure of the developmental pathways that begin in the undifferentiated embryo and end in structurally complex

Powerfully Directed Development  45 morphological features. If this theory is to be viable, those pathways—from the amorphous to the organised—which constitute the ontogenesis of organisms must be grounded in the dynamically directive prowess of dispositional properties. To see whether this is so, a detailed examination of the generative mechanisms of morphology is in order.18 Even under close scientific scrutiny, the origin of the morphological traits of an organism during its development is a phenomenon which appears to be nothing short of miraculous, and it is no coincidence that countless theologians throughout the ages have constructed the scaffolding of ‘natural theology’ upon its intricacies. Even to this day, modern proponents of the so-called theory of Intelligent Design, following in the footsteps of their philosophical progenitor William Paley, appeal to the generation of the organisational structure of organisms as a source of wonderment that is perennially awe-inspiring and, if one is even passingly acquainted with the biological sciences, it’s easy to see why.19 However, the phenomenon of the development of morphological traits is an even richer wellspring of amazement than these modern-day creationists make it out to be. For while the fact that highly complex and intricately structured systems exist independently of the tinkering manipulations of intelligent beings (namely, human beings) certainly is astonishing, how these systems come about is even more so. The real marvel is not that “Paley’s watch”, with all its organisational complexity, is lying on the beach, but rather, that it miraculously sprung from a single grain of sand: this is the picture that the phenomenon of the morphological development of organisms presents us with. But how does this happen? Clearly not all at once, but, importantly, not all together either—for development is, as we now know, a modularised process of compartmentalised collaboration. Indeed, it is a foundational fact upon which the edifice of contemporary systems biology is built that an organism’s morphological development is a rather piecemeal affair: it is controlled discretely, by individualised sub-systems which initiate and direct the formation of its various body parts—eyes, wings, fins, and the like. The developmental “discreteness” of these sub-systems stems from their relative causal autonomy in producing those features during the process of development, as they are characterised equally by an extremely high degree of causal connectivity among their constituents and an extremely low degree of causal connectivity with other parts of the organism.20 They are, in other words, discernible bundles of tightly knit causal loops whose activities are responsible for an organism’s specified development of particular traits. These highly internally integrated sub-systems whose operations causally control the generation of discrete morphological traits are known as developmental modules.21 The developmental pathway from a small collection of cells to a particular morphological trait is a causally complex one involving many distinct, though interconnected processes, but the big picture is this: in the developing embryo of an organism, a small homogenous group of undifferentiated, “pluripotent” cells known as an ‘imaginal disc’ transforms itself

46  Powerfully Directed Development into a multifaceted heterogeneous collection of specific cell types arranged in a highly complex organisational structure—those cells in that structure just is a morphological trait.22 In general, then, the process of “building” a morphological trait is thus two-fold: it requires the production of a certain set of cell types particular to the trait in question, and the arrangement of this set in a particular three-dimensional structure. More specifically, the operation of that process involves the genomes of a set of cells taking on particular ‘expression profiles’ which determine their individual developmental fates and these specifically expressed cells being spatially coordinated within a particular configuration. Thus, we can conceptualise morphological traits as having a two-fold organisational structure. The first important structural element is intra-cellular—that is, the specific genomic structure within each cell that causally determine which type of cell it is to be. According to the codon sequence of its genome—the ordered assembly of the triplicate sets of nucleotides which constitute its ‘primary structure’—each cell is capable of producing a specified range of proteins, and which particular set of proteins each cell produces determines its “fate”, finalising it into a particular functional cell type. If a cell were to produce, for instance, a wide range of structural proteins—say, collagen and elastin—that cell will perhaps function as a muscle tissue cell. If, on the other hand, it were to produce a wide range of contractile proteins—say, actin and myosin—it may function as a muscle filament cell. Both of these types of cell are required to build a properly functioning muscular system, and both are generated by the causal mechanisms of the genome; more on these in a moment. Of course, to build a functioning muscular system, not only are the proper cell types required, but they are also required to be in the proper place—this is the second important structural element of a morphological trait, the inter-cellular structure. To build an eye, for instance, requires the production of a wide variety of distinct cell types—but these various cells do not froth up from the imaginal disc of the eye in a random fashion: the elastic and collagen cells neatly form the curvature of the lens, the rod and cone cells carefully form concentric patterning in the retina, etc. Thus the process of development of a particular morphological trait involves not only differentiation and organisation within each cell (i.e. intracellularly) but also among those cells (i.e. inter-cellularly)—both “levels” of organisational structure must be in place in order to build a trait. This generative process which reaches from a miniscule, undifferentiated group of cells to a fully structured, complex cellular architecture exhibits an astonishing amount of controlled finesse in the face of a thousand-fold increase in size—but how precisely does it do so? As I detail next, this is a feat accomplished by a series of subtle genomic mechanisms operated and ordered in an intricately interwoven complex causal network. To get a grip on these details, let’s begin by examining the intra-cellular character of a morphological trait—namely, the organisational structures within each cell that

Powerfully Directed Development  47 determine its cell type. Although it’s true that the specific genome within each cell is causally responsible for determining which proteins that cell will produce, it is also true that every cell within an organism has precisely the same genome—how then do some cells become differentiated into one type and others into another? The short answer is that although each cell contains the same genome— the same sequence of deoxyribonucleic acid (DNA) bases—not all cells “make use of” that genome in the same fashion. With respect to the determination of cell type, what’s more important than which the genes a cell possesses is which genes it expresses—that is, which of its codon sequences are transcribed and translated into proteins. The specific ‘pattern of expression’ of a cell’s genome determines, from the span of potentially exploitable cell types made possible by the constitution of that genome, which type of cell it will become. Of course, no ‘pattern’ can be formed from a single unit, and the situation in an individual cell’s genome is no different—each typedefining pattern of expression consists in a sizeable number of individual genes being in specific states. Importantly, however, this pattern is no merely static collection of states: it consists in an active and dynamic coordination among these genes which reflects their place within a highly structured causal network. This is because a cell’s particular pattern of expression—its ‘expression profile’—is the result of the specific rate, amount, and timing of the “flow of transcription”—that is, its production of complementary messenger RNA (mRNA) strands to be subsequently translated into proteins—of its genome. This transcriptional “flow” of a genome is controlled and regulated by a class of proteins fittingly called ‘transcription factors’ which causally determine when, whether, and to what extent its codons are expressed. In this way, the fate-defining expression profile of a particular cell is the product of its genetic regulatory network (GRN), a dynamical architecture consisting of a series of complex causal interconnections between its individual genes via the regulatory activity of various transcription factors. The GRNs responsible for cell fate are composed of an enormous number of genes tied together in a tangled and multifaceted causal web, but although they are vastly complex, they are typically modelled in an abstract fashion as Boolean networks: here the ‘nodes’ and ‘states’ represent genes and their expression rates, and the ‘edges’ between nodes represent the regulatory dependencies and influences (via transcription factor channels) upon their respective states.23 Regulating the transcriptional flow of a GRN involves its nodes playing a number of rather complex ‘Boolean functions’, though the primary ones essentially amount to enhancing, or increasing and repressing, or decreasing the rate of transcription of other “downstream” genes within the network.24 In such complex networks, however, tracing the dynamical direction of regulatory influence is not a simple affair as the causal relations in which those nodes are bound up do not typically (if ever) stratify their relata in a strictly hierarchical, or linear fashion: due to

48  Powerfully Directed Development the ubiquity of complex motifs like recursive feedback loops, the nodes in GRNs are situated in a tightly knit web of interconnectedness—i.e. expressional interdependence;25 see Figure 3.1. The functional specificities of the edges that connect the entirety of a GRN define the ‘regulatory logic’ upon which its temporal dynamics depend, as the expression state of the entire network changes over time according to its set of regulatory ‘rules’—e.g. if the system’s nodes are in this state, then, given their being joined by these connective edges, the system will transition to this state. We can sum up the intra-cellular facet of the development of a morphological trait then as follows: the “fate” of any particular cell within an imaginal disc is a direct result of its production of a certain specified set of proteins which is determined by its genome’s particular expression profile, itself established via the dynamical directives which constitute the regulatory logic of its causally interconnected network of genes. As we have seen, however, the development of a morphological trait requires not only that an imaginal disc be composed of a collection of particular cell types but also that these various cells are arranged in a particular fashion. Now that we have a grip on how cell types are formed via intra-cellular networks of regulatory control, we are in a position to understand how specific spatial configurations of those cells are generated within an imaginal disc in the production of a morphological feature—for the inter-cellular process responsible for the patterning of cell types within that disc is just the process responsible for those cells’ intra-cellular “pattern of expression” writ large.

Figure 3.1 Genetic Regulatory Network: Simplified schematic representation of a genetic regulatory network. Each node (G) represents a gene or complex of genes, and the various arrows represent the source, target, and direction of causal influence via chemical signalling channels which effect node expression regulation; here bar-ended arrows signify negative, downregulative influence.

Powerfully Directed Development  49 The process by which a group of undifferentiated cells that compose an imaginal disc become spatially patterned into distinct cell types in specific three-dimensional structures is guided by the regulatory dynamics of a “higher-order” genetic network, one that spans from cell to cell (rather than gene to gene).26 This higher-order network establishes causal “communication” among the cells of an imaginal disc in the same way in which such networks function within those cells—namely, by way of transcription factor channels. This is because the transcription factors encoded in the genome of a cell are not limited in their range to merely intra-cellular activity, but rather can cross the boundaries of the cellular membrane to enter into other, neighbouring cells in a process known as ‘signal transduction’. There they act just as before, as causal factors which influence the “flow of transcription” of a target genome by their specified manipulation of its regulatory activity.27 Thus, by means of this inter-cellular “communication” via transcription factor based genomic regulation, individual cells within an imaginal disc can causally influence one another: just as in the intra-cellular case, these communication channels form a complex dynamical regulatory network among their nodes which direct the system’s state transitions.28 It is, in other words, the regulatory logic of the higher-order GRN of a developmental module which governs the spatial coordination, and thus the structural configuration of the cells which constitute its imaginal disc. Let’s now take a step back and take a summary look at the big picture. An organism’s production of a particular morphological feature is a process which begins with a collection of cells whose genomes are not in any fixed expression state (i.e. pluripotent cells), known as an imaginal disc, which over time take on specific expression profiles in a coordinated fashion. This process requires the activity of an entire network of genes, a certain set of which act intra-cellularly to produce the proteins that determine the particular cell types which “build” the feature in question and a set whose protein products (known as transcription factors) act inter-cellularly to regulate the intra-cellular expression profiles of other cell’s genomes, thereby controlling which genes are expressed in which cells throughout the disc, as well as when and where that expression takes place during the development of that feature. Thus we can model that process by mapping out a higherorder GRN which includes the set of genes whose expression determines particular cell types, the set of genes which control their expression, and the particularities of the causal-cum-regulatory relationships connecting them. We can then picture (as in Figure 3.2) the development of a particular morphological feature as the temporal succession of a series of expression profiles of the GRN elements in the cells which compose the imaginal disc of a developmental module which, over time, and due to the regulatory logic of its GRN, take on a controlled and continuous patterning sequence which ultimately results in the formation of stable collection of specific cell types arranged in a specific spatial configuration—that is, in a fully developed morphological feature.

Figure 3.2 Disc Development: Schematic two-dimensional representation of the early developmental stages of a multi-cellular imaginal disc constituting a module: ‘A/P’ denotes the anterior and posterior regions of the imaginal disc, distinct bubble shades represent distinct cell types, and arrows represent the causal-cum-regulatory influence of one cell type upon neighbouring cell types. Over time, and according to the specifications of its GRNs, the cellular constitution of a module becomes increasingly compartmentalised and spatially discrete.

Powerfully Directed Development  51

3.3 Development, Dispositionally Having taken a fairly in-depth (though necessarily abbreviated) look at the generative genetic mechanisms at work within the developmental modules which are causally responsible for the specified production of individual morphological features, we can now return to a refashioned form of our earlier question: does this responsibility consist in the activation of intrinsically dynamic, goal-directed capacities? In this section, I argue that it does and that, accordingly, we ought to conceptualise developmental modules as realising dispositional properties. It’s not difficult to see the dynamics which define dispositional properties at play in the causal architecture of the intra- and inter-cellular GRNs operative within developmental modules. As described earlier, the regulatory wiring of these networks consists of their nodes being causally connected in a web of expressional interdependence such that each brings about a particular state as a result of another’s (via the medium of transcription factors). Each of these nodes serves to causally mediate a series of “upstream” signals “downstream” in a specified fashion, the details of which define its place within the network and are captured by its ‘Boolean function’—a formalised representation of its potential to produce a particular state upon the occurrence of particular conditions. In this way, the internodal infrastructure which governs these networks’ systematic series of state-transitions is grounded in the dynamics designated by the intrinsic causal capacities of its constituents. However, it is not only the compositional elements of the intra- and inter-cellular networks of developmental modules which operate dispositionally, but the entire GRN itself functions as a capacitive causal fulcrum in the process of the ontogenesis of particular morphological features. Taken holistically, the GRNs of these modules form the bottleneck of the ‘developmental hourglass’ wherein the sands of a wide variety of “upstream” developmentally primitive input signals are sifted through their narrow gates in a specialised fall among a diverse set of target genes to control the “downstream” expression of a multitude of proteins that determine cellular differentiation within the ‘morphogenetic field’ of a developing imaginal disc.29 As active mediators of the flow of regulatory information, these GRNs effectively translate the dilatant ‘positional information’ of early development (e.g. the embryonically embedded maternal gradients which establish an organism’s axial orientation and segmentation) into modular morphological features by controlling character-specific gene expression throughout discrete imaginal discs.30 The morphological ontogenesis of an organism is, in other words, a process which is grounded in the dynamics designated by the intrinsic causal capacities of its developmental modules. Importantly, then, the causal role these modules play within the ontogenesis of an organism consists in their dynamically orienting that process toward the production of a privileged set of particularised morphological

52  Powerfully Directed Development traits. The developmental directives of these modules, as we have seen, are grounded in the causal specificities of their constitutive GRNs: the configurative particularities of their respective regulatory logics constrain and control their intra-disc dynamics toward the production of precise morphologies. Of course, as these GRNs are highly complex, composed of multiple sub-networks which are themselves comprised of a great number of causally connected constituents, this is a generative process which necessarily takes place at a high ‘causality horizon’ that reaches over a wide, multi-stage “causal gap” and is thus, although relatively resilient, not inerrable.31 The intricate “wiring” of these networks, in other words, abundantly furnish them with opportunities for faults. What’s notable about these networks’ generative capacities, however, is that, although they do not infallibly produce their particular morphological structures, they do so with a measure of reliability that befits a properly goal-directed system. This is especially evident in the robustness (or the imperviousness to impediment) of the generative process by which they produce those structures, for these highly causally integrated GRNs are such that variation among their component elements and regulatory “wiring” typically have little to no effect on their generative competence with respect to their capability to produce their resultant morphological structure. Module GRNs exhibit this generative robustness in two ways—one mundane, the other remarkable. The first way in which these GRNs exhibit this phenomenon is known as ‘redundancy’: here, missing/mutated/disabled elements can be effectively replaced by a number of redundant, or duplicate elements which are able to take up the causal slack of their functional role within the network. The second, more complex and interesting way in which GRNs exhibit generative robustness is known as ‘degeneracy’, which occurs in systems which have the capacity to “re-wire” the regulatory architecture of their networks in order to produce novel causal connectives in novel configurations which effectively maintain the generative function of those networks in the event of significant intra-network perturbation: here, rather than there being a collection of “back up” elements which stand ready to replace their malfunctioning duplicates, the network adaptively reassigns the functional roles of existing network elements within the system, enlisting them in new tasks which serve to preserve the generative integrity of the network.32 The generative robustness of these modules’ production of their morphological features in both of these cases clearly exhibit the characteristic markers of teleological, goal-directed activity—this is a process which is both pleonastic and persistent. However, the goal-directedness of this process is most evocatively illustrated when these modules are abstractly modelled within the representational framework of dynamical systems theory (DST), a schema which represents the conceptual union of the aforementioned Boolean modelling of GRNs and the ‘epigenetic landscapes’ of Conrad Waddington, the famed 20th century British geneticist and embryologist.33 As a novel modelling

Powerfully Directed Development  53 technique, DST has afforded contemporary theoretical biology a set of unique conceptual resources with which to understand the causal structure of biological processes, resources now rather widely utilised in analyses of everything from sub-organismal cell fate to the “evolvability” of organism populations.34 In order to see how DST models aid in illustrating the goal-directedness of developmental modules, let us take stock. We have seen that the developmental process of a module’s production of a morphological trait can be modelled as the temporal succession of the states of the overall expression profile of its imaginal disc (itself comprised of a number of individual cells’ expression profiles), the transitions of which are governed by its GRN’s regulatory logic (as in Figure 3.2). These models are unquestionably informative, but they are also rather restrictive in a significant respect: for while they are more than capable of adequately capturing the actual development of an imaginal disc, they do not offer any substantial contrastive information about that process—that is, they fail to provide any insight as to how this temporal succession of its states compares to other possible such successions. This is important because without this kind of contextual information, we arguably lack a comprehensive understanding of this process: we may understand that it privileges the production of a particular developmental end-state, but we lack the scope to understand what that privilege consists in. This is where the abstract, higher-order models of DST come into play, as they are informative in just this sense. To construct these models, we first define an abstract, multi-dimensional state-space whose individual points represent specific disc-wide expression profiles (where each specifies the expression state of each GRN element within each cell in the disc) of the sort mentioned earlier, arranged continuously (according to cellular expression values) on axes which represent a particular cell type in a particular spatial region of the disc. Having represented all of the possible states of the system—that is, all of its possible disc-wide expression profiles—we can model a module’s development of a particular morphological trait as a trajectory through this state-space, one which begins in the region of that space which represents the “initial conditions” of that disc’s expression profile and ends in the region which represents the expression profile which corresponds to its “completed” trait; Figure 3.3 schematically illustrates this type of model with respect to a simplified GRN, represented on a twodimensional state-space.35 This abstract, higher-order model puts the developmental trajectory of a module in perspective, in that it situates it within the wider context of a space of disc-wide expression possibilities as mentioned earlier, but it does not yet illustrate what this process’ privileging of its end-state consists in as it does not compare its pathing through state-space with other possible ones. With the representative machinery of our multi-dimensional statespace in hand, however, we can make such comparisons, as mapping out

Figure 3.3 State-Space Modelling: Schematic representation of a single developmental trajectory of a module through a (truncated) abstract state-space, in reference to Figure 3.2. On either side, the ‘module at t’ and ‘module at t + 2’ depict the spatial arrangement of two cell types (β and ε) within the imaginal disc with respect its anterior (A) and posterior (P) regions. Each cell type is represented as consisting of the module’s GRN elements (depicted as elliptical bases), their regulatory connections (depicted by arrows), and their particular expression levels (depicted as stacked elliptical elements). In the middle of the figure, the temporal transition of the spatial arrangement of β and ε with respect to P is modelled as a trajectory through a two-dimensional plane whose edges represent unique discwide cellular GRN-expression states, arranged such that the distance between any two edges reflects quantitative similarity with respect to spatially specific cellular expression. The ‘module at t + 2’ here represents the expression levels of the module’s GRN which constitute its developmental end-state.

Powerfully Directed Development  55 any trajectory on this space only requires our picking a state (a disc-wide cellular GRN-expression profile) and iteratively applying the module’s associated GRN regulatory logic to derive its temporally successive states. In other words, “determining the next move” of a developmental trajectory within state-space from any state requires a simple conditionalising process: for any particular regulatory network, by plugging in a specific set of expression values for the members of that network and applying the activities of the causal connectives which constitute its regulatory logic, we can derive its members subsequent expression values. Thus, because the regulatory logic of a GRN effectively acts to assign a Boolean function to each state within this state-space, we can vectorise any single state and trace the directionality of temporally successive states within that space.36 We can, in other words, plot any possible developmental trajectory for a particular imaginal disc.37 If we do so, after a number of iterations, we find that the collection of these trajectories exhibit interesting properties (see Figure 3.4). Firstly, we find that localised collections of trajectories follow similar curvatures through state-space: they appear to “stick together”, bending around similar regions of that space. Secondly, we find that multiple trajectories which begin from distinct areas in that space end in the same general area: this latter region appears to “attract” trajectories from various originating points within that space. As one may have guessed, this region corresponds to the disc-wide expression state that defines the morphological feature associated with that module. Notice that by mapping multiple possible developmental trajectories on this state-space, we are afforded a clear view of the dynamical characteristics we are interested in: here we see the system’s privileging of the production of a particular morphological end-state qua an ‘attractor region’ in statespace (e.g. φ in Figure 3.4) reflected in the common curvatures of that space around which multiple trajectories are directed toward that region. However, although here the dynamical orientation of the system can certainly be inferred from the pathing of these various developmental trajectories, it is nonetheless not made explicit, as this representation does not fully illustrate the shaping of this state-space. Perhaps, unsurprisingly, attaining this more complete picture of the causal directedness of a system requires making our model more complex. To see what this complexity consists in, we must revisit the finer details of the system’s state transitions within this space. We’ve seen that the developmental transition from any particular point in state-space to the next is determined by a kind of Boolean function which utilises the GRN’s regulatory logic operating on the particular expression profile of the GRN elements which define that state. However, the transitions between states in this space do not merely reflect the iterated applications of simple analytical operations—for the transition-function in question is a regulatory one, and so each step within a single trajectory is a step toward disc-wide regulatory stability. In other words, although the state-to-state transitions within that space take place according to the

56  Powerfully Directed Development

Figure 3.4 Developmental Trajectory Mapping: Schematic representation of a simplified, two-dimensional state-space depicting a limited selection of a module’s developmental trajectories. This truncated state-space represents the disc-wide cellular expression levels of the module with respect to two cell types (β and ε) in a particular spatial region (posterior, P). Multiple individual trajectories (depicted as arrows) from distinct initial conditions converge on a general region (φ) of developmental end-states with quantitatively similar spatially specific disc-wide cellular expression values (with respect to ε and P).

aforementioned Boolean model, each step throughout developmental time is in fact a transition from a less stable disc-wide expression profile to a more stable one, given the relevant regulatory structure. So, from any origination point within that space, the subsequent state-transitions which comprise its trajectory follow the multi-cellular expression profile of the disc’s “search” for regulatory stability, where the relevant GRN elements’ expressions “even-out” in such a way that their collected values no longer cause further significant inter-network expression alterations. With this in mind, we can now add another aspect to our state-space: each state can be given a stability measure which specifies the GRN elements’ expression values tendency to substantially shift (given the relevant regulatory logic) to a subsequent state; in effect, in this process, we are properly vectorising the state-space, in that the arrows we earlier assigned

Powerfully Directed Development  57 to each state now have a direction and a kind of magnitude.38 In DST modelling, this aspect is represented by assigning each state a particular elevation value (along an additional dimension), where the higher the elevation value, the relatively higher level of expression instability of the state—i.e. the more likely the disc-wide expression values of its GRN elements will shift to another state within that space (again, given the relevant regulatory relations in operation).39 Once we have done so, our abstract state-space is now a structured topology complete with high hills and low-lying basins with various gradient measures connecting them (see Figure 3.5). With this stability-based topological mapping of our state-space in hand, we can now understand the process of the development of a particular module in a novel fashion: if we depict the state of the module as a kind of frictionless orb, we can model the temporal succession of various distinct states of the module throughout the process of development as the dynamic trajectory of that orb through a pathway geometrically constrained by the topological ridges and valleys of the system’s Boolean regulatory configuration (as illustrated in Figure 3.5). This novel modelling puts us in the position to understand more clearly why the morphological trait which a particular module produces is generatively privileged and what that privilege consists in: that trait represents a disc-wide pattern of regulatory stability with respect to intra-module cellular expression states which “carves out” a wide, low-lying basin in the topology of state-space, and its privilege

Figure 3.5 Topological State-Space Model: Schematic topological representation of the state-space from Figure 3.4. The third dimension (U) reflects the elevation level of any particular disc-wide spatially specific expression profile for any specific coordinate, itself a measure of the relative regulatory stability; here, a higher U-value and darker colouration are inversely correlated with regulatory stability. φ, denoting a set of qualitatively similar developmental end-states with respect to ε-type expression profiles within the posterior compartment of a module (P), is shown as a low-lying basin within state-space. NB, although representing a complete such topology for a particular module, would require an immensely complex, multi-dimensional state-space, the same principles at play in this schematic would apply.

58  Powerfully Directed Development consists in the fact that the dynamics of its developmental process is shaped and constrained by the geometric curvature of that topology. Importantly, then, the framework of DST affords us a more complete picture of the generative capacity of a developmental module—for it allows us to understand not only a module’s ability to produce its associated morphological feature, but crucially also the causal-cum-structural “shape” of that capacity with respect to its developmental privileging of the production of that feature. By providing this more comprehensive picture—one builtup from the accumulation of relevant “contrastive information” about the process of development—these models of modules are also illustrative of the two aforementioned characteristics of dynamically oriented, goal-directed systems (§3.1). As we have already seen, DST models of modules are constructed from, and subsequently represent, the ‘pleonastic pathing’ of their morphological development: the result of mapping of multiple, distinct trajectories (as in Figure 3.4) illustrates the system’s generative tendency toward a particular morphological end-state, a tendency embodied in the width of the topographical channels which “flow” into the attractor basin associated with that state (as in Figure 3.5). Furthermore, the width and depth of those channels in these models effectively illustrate the robustness of that tendency. Its ‘persistence’ in the production of its morphological end-state in the face of perturbation is reflected both in those channels’ breadth and the steepness of the topological gradients from which they are carved: developmental trajectories within those channels have a lot of “wiggle room” and would have to wiggle especially hard to “escape” from them (as the intimate connection between a state’s elevation value and the probability of its being diachronically occupied suggests).40 With all of the aforementioned in mind, it is time to return to the question with which this section started: are the generative mechanisms responsible for the specified production of particular morphological features—the ones which are to occupy centre stage in an Aristotelian account of essence (as per the discussion in Chapter 2)—intrinsically dynamic, goal-directed capacities? In light of the evidences of this section, I think the answer must be an affirmative one: a close examination of the nature of developmental modules, one which encompasses the fine-grained details of the structural-cum-causal compositional particularities of their GRN architecture and the coarse-grained topological characteristics of their developmental dynamics, strongly suggests that they ought to be conceptualised as realising dispositional properties. Developmental modules, as active mediators of the flow of regulatory information, effectively translate the ‘stimuli’ of early developmental signals over a complex “causal gap” which spans an entire imaginal disc into the ‘manifestations’ of particularised morphologies. As we have seen, this is an activity which causally orients their development toward those morphologies in a robustly unwavering fashion, one capable of deftly persevering through a wide range of deviant compositional, structural, and state modifications. The generative prowess of these modules is,

Powerfully Directed Development  59 in other words, a multiply realisable, goal-directed capacity whose activation dynamically disposes its bearers to produce a particular morphological feature—that is, a dispositional property (as described in §3.1). Let us call the properties which characterise this specialised generative prowess morphomodulatory dispositions—hereafter, simply μ-dispositions. Thus the dispositional properties realised by the developmental modules of an organism—μ-dispositions—are well suited to collectively function as its neo-Aristotelian essence as they perform the requisite causal-cum-modal role with respect to its development of a particular morphological profile: their generative competency is principally responsible not only for causally constructing that profile but, in virtue of their “directedness” toward doing so, constraining its character. These dispositions are therefore responsible for the sort of de re dependence which typifies essential properties with respect to so-called nominal property collections (as described in Chapter 1, §1.2): their dynamic privileging of particular end-states is able to function as the causal foundation of the continual “cropping up” of the morphological profiles which typify organisms’ natural kinds upon which the reliability of our inductive practices about the likelihood (and unlikelihood) of their developmental trajectories is grounded. Furthermore, while the teleological character of the activity of these dispositions certainly dynamically orients the ontogenetic process, due to the complexities of the systems which realise them, they do not do so in all cases or at all costs: rather, to borrow a philosophical phrase, they “incline without necessitating”.41 In all of these ways, μ-dispositions are evidently eminently qualified candidates to collectively constitute the neo-Aristotelian essences of biological natural kinds. Properly putting these properties to work by placing them within the context of a more comprehensive and cohesive account—that is, in a fully formed neo-Aristotelian theory of biological natural kind essentialism—is yet to come. But before that can be done, an important obstacle must first be overcome. I’ve thus far argued that a neo-Aristotelian account of biological natural kind essentialism requires, and that μ-dispositions deliver, the existence of an intrinsic and causally primary generative ground of the particularised morphological profiles of the organisms which belong to natural kinds.42 However, both aspects of this requirement have recently and rather explicitly been challenged by a significant contingent of philosophers in the contemporary literature. Because satisfying this requirement is of central importance to any neo-Aristotelian theory of biological natural kind essentialism, this is a challenge which this book must now meet.

Notes 1 See the Meno (80d–e). 2 Of course, given the size of the contemporary literature on dispositions, there is the possibility for quite a lot of variation in the particulars here—but rather than comparing and contrasting the merits of various specific accounts, what I offer next is what I consider to be the most important and defining features of these

60  Powerfully Directed Development properties, ones which I think, for all practical purposes, function as the ‘lowest common denominator’ features of a wide variety of more specialised accounts. That said, this discussion of the nature of dispositional properties is while sufficiently detailed for present purposes, necessarily abridged—for more on the topic, see Cartwright (1994), Mumford (1998), Ellis (2001), Molnar (2003), and Damschen et al. (2009) and Marmodoro (2010). 3 See Hume (1748) and Lewis (1973). 4 For the classic defence of a ‘laws’ based conception of these constraints, see Dretske (1977), Tooley (1977), and Armstrong (1983), and for the canonical defence of a Humean ‘regularity’ based conception, see Lewis (1973). 5 For some good representations of this ideological contrast, see Ellis (2001), Bird (2007), Chakravartty (2007), and Mumford and Anjum (2011). 6 Here, and in what follows, I intend ‘system’ to be taken rather generally as a spatio-temporally bounded, causally interconnected collection of elements. 7 The concept of ‘multiple realisability’ was first employed in the context of debates concerning the viability of reductive materialism in the philosophy of mind, primarily by Putnam (1967) and Fodor (1974). As this concept is fairly commonplace and ubiquitous in the contemporary literature, I do not here delve into an in-depth discussion of it—see Baysan (2015) for a recent comprehensive overview of the topic. 8 The ‘irreducibility’ of dispositional properties in this respect is a complex and subtle issue, the in-depth discussion of which would take this chapter too far afield. Here the important point is only that a single, causally specific capacity may be present in multiple systems whose compositional configurations are nonidentical. A discussion of the implications of the concept of irreducibility can be found in Chapter 5, where it is put to important work. 9 There is in fact a philosophical tradition of conceptualising the teleological character of dispositional properties as amounting to kind of ‘physical intentionality’. George Molnar (2003), following in the footsteps of Ullin Place (1996), claimed that, contrary to the “Bretano Thesis” (that intentionality is the mark of the mental), dispositions are instances of properties that exhibit physical intentionality. Preferring the opposite explanatory direction, Mumford and Anjum (2011) have argued that ‘dispositionality’ is the ground of intentionality, or that intentional concepts are derived from the nature of dispositional concepts. See Oderberg (2017) for a recent entry in this tradition. 10 If ‘teleological’ strikes the reader as an inherently intentional and purposive term, it may be substituted, as Mayr (1992) influentially did, with the perhaps more sanitised and naturalised ‘teleonomic’ here, and throughout. 11 These teleological “markers” were proposed by Sommerhof (1950), who referred to them as ‘plasticity’ and ‘persistence’, respectively; I have substituted the former term, however, as I will later discuss ‘plasticity’ in a biological context (in Chapter 4). For recent prominent appeals to these features of goal-directed systems, see Nagel (1977) and Walsh (2012). 12 For more on contemporary truthmaking theory, see Beebee and Dodd (2005), and Lowe and Rami (2009). It’s worth noting that precisely explicating what the ‘truthmaking’ role amounts to and subsequently showing that dispositional properties play it with respect to the subjunctive conditionals which characterise de re modality may turn out to be an exceptionally tricky task. I won’t be addressing this issue here, as this chapter’s discussion in no way depends upon it—see Austin (2015) for a focused examination of the topic. 13 Thus the now popular class of arguments which constitute the contemporary neo-Humean rejection of dispositional properties that essentially amount to attempts to show that the causal structure of the natural world is bereft of

Powerfully Directed Development  61 “necessary connections” is simply mistaken ab initio: it may be true that we don’t find such connections, but if we’re looking for evidence of the existence of dispositional properties, we shouldn’t be expecting to find them either. 14 More formally, these are ‘variably strict’ conditionals (Stalnaker 1968; Lewis 1973) which fail the test for monotonicity—that is, their truth-values are not always preserved under strengthenings of their antecedents: see Schrenk (2010) and Mumford and Anjum (2011). 15 This antidote example is adapted from Bird’s (1998) influential treatment of the topic. 16 For present purposes, I am here only assuming that a theory which grounds de re modality in the nature of dispositional properties is possible and viable— especially as an alternative to a law-based theory. For a more in-depth explication and examination of this sort of theory, see Borghini and Williams (2008), Mumford (2004), Jacobs (2010), and Vetter (2015). 17 That the connection between the ‘real’ and the ‘nominal’ is a dispositional one is a crucial component of the theory I will propose throughout this book. I return to the themes highlighted here and discuss their significance in detail in Chapter 5 when addressing an important class of objections to biological natural kind essentialism. 18 The discussion next is not an exhaustive explication of the composition and dynamics of the relevant developmental mechanisms: it assumes some basic familiarity with the denizens of molecular biology and glosses over some of the more minute causal complexities of their interactions. For a comprehensive and fairly accessible primer on the subjects discussed next, see Davidson and Peter (2015). 19 Paley’s infamous “watchmaker” argument in his Natural Theology or Evidences of the Existence and Attributes of the Deity (1802) has since its publication served as the perennial inspiration for both defences and critiques of the ‘Intelligent Design’ hypothesis. 20 Raff and Sly (2000); Erwin and Davidson (2009). 21 Of course, many organismal sub-systems are ‘modular’, and not every such sub-system is responsible for generating morphological traits (even if they are responsible in some form or another for causally contributing to organismal development)—I employ the term ‘developmental module’ here only as a convenient way of picking out those that do. See Callebaut and Rasskin-Gutman (2005) for an excellent collection on the multifaceted subject of biological modularity. 22 Technically, the appellation ‘imaginal disc’ is in the literature reserved for the cellular collections of this sort which are found in insect larvae. Given the term’s etymology—referring to the generative capacity of such collections as containing the image of a complex morphological structure—I employ it here and throughout this book for the sake of simplicity and ease of illustration. The discerning reader is welcome to substitute its instances with the more generalised concept of ‘morphogenetic field’. 23 This modelling technique of GRNs was pioneered by Stuart Kauffman (1969). For a more detailed look at the structure of these models, see Huang and Kauffman (2012). 24 Not all regulatory relationships between GRN nodes are simple ‘enhancing’ and ‘repressing’ ones, and not all of these nodal relations are one-to-one—some nodes, for instance, act as co-enhancers or co-repressors which function to coordinate, together with a complex of other nodes, the influence of transcription at a particular network locus. For simplicity’s sake, however, and as they are unimportant for the dialectic of this chapter, I have here omitted the details of

62  Powerfully Directed Development the more subtle and complex forms of regulatory functions these nodes might perform. See Davidson (2001) for a comprehensive treatment of the subject. 25 For a closer look at the complexities of common ‘network motifs’ found in GRNs, see Yeger-Lotem et al. (2004) and Alon (2007). 26 This discussion will abstract away from certain processes which affect the spatial configuration of the cellular constituents of an imaginal disc by means other than intra- or inter-cellular regulatory signalling—e.g. mitosis (cellular division), apoptosis (cell death), etc. Although these mechanisms are extremely important, their inclusion isn’t required for present purposes—they are, after all, ultimately grounded in cell state alterations. See Salazar-Ciudad et al. (2003) for a recent in-depth look at these ‘morphogenetic mechanisms’. 27 Technically, the transcription factors from neighbouring cells activate ‘receptor proteins’ on the target cell’s membrane, which in turn activate a cascade of further intra-cellular proteins which then act upon that cell’s genome to regulate its transcription. However, as what’s important for present purposes is simply the fact that there is a causal link between cells mediated by transcription factor activity, I here pass over these more precise details. 28 Of course, in the end, or “at bottom”, the regulatory activity (e.g. activation, inhibition) among multiple cells linked in this higher-order genetic network is comprised of the “goings on” of the GRNs within the cells which compose the imaginal disc. 29 For more on the ‘developmental hourglass’ concept, see Galis and Metz (2001), and Kalinka et al. (2010). 30 The origin of the concept of ‘positional information’ is in the pioneering work of Lewis Wolpert (1971). For more on the general concept of ‘morphogens’—the class of inter-cellular signalling molecules which alter genomic expression in the process of morphogenesis—see Tabata (2001). 31 The concept of a ‘causality horizon’ is here used to indicate that these networks’ production of particular morphological features is a “higher level” operation— one which incorporates, but fundamentally functions “above” its molecular and chemical constituents’ activities. See Salazar-Ciudad and Jernvall (2013) for the introduction and more in-depth discussion of this concept. 32 A good general review of GRN robustness can be found in Greenspan (2001). For more on the ‘degenerate’ abilities of these networks to reassign two nonisomorphic elements to become isofunctional and its importance in development and evolution, see Edelman and Gally (2001), and Mason (2010). 33 For a comprehensive look the history of Waddington’s influential ‘epigenetic landscape’ concept, see Baedke (2013). See Wang et al. (2011) and Huang (2012) for primers on its contemporary application to GRNs in DST. 34 On cell fate, see Bhattacharya et al. (2011) and Verd et al. (2014). On evolvability, see Striedter (1998) and Jaeger and Monk (2014). 35 For a (relatively) accessible introduction to how this mapping is done, both theoretically and with the aid of empirical data, see Huang (2009) and Wang et al. (2011). 36 For some examples of this vectorisation process, see Wang et al. (2011) and Davila-Velderrain et al. (2015). 37 This is of course a rather complex task, given that performing it requires taking into account multiple cells, their spatial arrangement, and both intra- and intercellular regulatory interactions. 38 For the formal details of how stability-based elevation measures are assigned to these state-spaces, see Kim and Wang (2007) and Bhattacharya et al. (2011). 39 Technically, assigning an elevation value involves the stochastic simulation of groups of cells—but I pass over this complication here. See Bhattacharya et al. (2011) for the finer details.

Powerfully Directed Development  63 40 I have here rather carefully only described these models as being illustrative of, rather than as explanatory of the presence of certain system features. The question of whether these sorts of abstract, higher-order models can be genuinely explanatory with respect to those features is the focus of a lively debate in the philosophy of science—see Brigandt (2015) and Kaplan (2015) for opposing views. 41 Leibniz often utilised this phrase in defending his metaphysics from the charge of determinism and regularly applied it to both the nature of ‘reasons’ and instances of physical causation. See his correspondence with Samuel Clarke (1717) for interesting examples of both uses. 42 Cf. Chapters 1 and 2.

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64  Powerfully Directed Development Davidson, E. (2001). Genomic Regulatory Systems: In Development and Evolution. London: Academic Press. Davidson, E., & Peter, I. (2015). Genomic Control Process: Development and Evolution. Oxford: Academic Press. Davila-Velderrain, J., Martinez-Garcia, J. C., & Alvarez-Buyila, E. R. (2015). Modelling the Epigenetic Attractors Landscape: Toward a Post-Genomic Mechanistic Understanding of Development. Frontiers in Genetics, 6(160). doi:10.3389/ fgene.2015.00160. Dretske, F. (1977). Laws of Nature. Philosophy of Science, 44(2), 248–268. Edelman, G., & Gally, J. (2001). Degeneracy and Complexity in Biological Systems. Proceedings of the National Academy of the Sciences, 98(24), 13763–13768. Ellis, B. (2001). Scientific Essentialism. Cambridge: Cambridge University Press. Erwin, D., & Davidson, E. (2009). The Evolution of Hierarchical Gene Regulatory Networks. Nature Reviews Genetics, 10, 141–148. Fodor, J. (1974). Special Sciences: Or the Disunity of Science as a Working Hypothesis. Synthese, 28(2), 97–115. Galis, F., & Metz, J. (2001). Testing the Vulnerability of the Phylotypic Stage: On Modularity and Evolutionary Conservation. Journal of Experimental Zoology, 291(2), 195–204. Greenspan, R. (2001). The Flexible Genome. Nature, 2(5), 383–387. Huang, S. (2009). Reprogramming Cell Fates: Reconciling Rarity With Robustness. Bioessays, 31(5), 546–560. Huang, S. (2012). The Molecular and Mathematical Basis of Waddington’s Epigenetic Landscape: A Framework for Post-Darwinian Biology? Bioessays, 34(2), 149–157. Huang, S., & Kauffman, S. (2012). Complex Gene Regulatory Networks—From Structure to Biological Observables: Cell Fate Determination. In R. Meyers (Ed.), Computational Complexity: Theory, Techniques, and Applications (pp. 527– 560). New York: Springer. Hume, D. (1748). An Enquiry Concerning Human Understanding (P. Millican, Ed.). Oxford: Oxford University Press, 2007. Jacobs, J. (2010). A Powers Theory of Modality; or, How I Learned to Stop Worrying and Reject Possible Worlds. Philosophical Studies, 151(2), 227–248. Jaeger, J., & Monk, N. (2014). Bioattractors: Dynamical Systems Theory and the Evolution of Regulatory Processes. Journal of Physiology, 592(11), 2267–2281. Kalinka, A., Varga, K., Gerrard, D., Preibisch, S., Corcoran, D., Jarrells, J., et al. (2010). Gene Expression Divergence Recapituates the Developmental Hourglass Model. Nature, 468, 811–814. Kaplan, D. (2015). Moving Parts: The Natural Alliance Between Dynamical and Mechanistic Modelling Approaches. Biology & Philosophy, 30(6), 757–786. Kauffman, S. A. (1969). Metabolic Stability and Epigenesis in Randomly Constructed Nets. Journal of Theoretical Biology, 22(3), 437–467. Kim, K., & Wang, J. (2007). Potential Energy Landscape and Robustness of a Gene Regulatory Network: Toggle Switch. PLoS Computational Biology, 3(3), 565–577. Leibniz, G. W., & Clarke, S. (1717). The Leibniz-Clarke Correspondence (H. G. Alexander, Ed.). Manchester: Manchester University Press, 1956. Lewis, D. (1973). Counterfactuals. Oxford: Blackwell Publishers. Lowe, E., & Rami, A. (Eds.). (2009). Truth and Truth-Making. Stocksfield: Acumen.

Powerfully Directed Development  65 Marmodoro, A. (Ed.). (2010). The Metaphysics of Powers: Their Grounding and Their Manifestations. New York: Routledge. Mason, P. (2010). Degeneracy at Multiple Levels of Complexity. Biological Theory, 5(3), 277–288. Mayr, E. (1992). The Idea of Teleology. Journal of the History of Ideas, 53(1), 117–135. Molnar, G. (2003). Powers: A Study in Metaphysics. Oxford: Oxford University Press. Mumford, S. (1998). Dispositions. Oxford: Oxford University Press. Mumford, S. (2004). Laws in Nature. London: Routledge. Mumford, S., & Anjum, R. (2011). Getting Causes From Powers. Oxford: Oxford University Press. Nagel, E. (1977). Goal-Directed Processes in Biology. The Journal of Philosophy, 74(5), 261–279. Oderberg, D. (2017). Finality Revived: Powers and Intentionality. Synthese, 194(7), 2387–2425. Paley, W. (1802). Natural Theology, or Evidences of the Existence and Attribtues of the Deity, Collected From the Appearances of Nature (6th ed.). Cambridge: Cambridge University Press, 2009. Place, U. (1996). Intentionality as the Mark of the Dispositional. Dialectica, 50(2), 91–120. Plato. (1997). Plato: Complete Works (J. Cooper & D. S. Hutchinson, Eds.). Indianapolis: Hackett. Putnam, H. (1967). Pyschological Predicates. In W. Capitan & D. Merrill (Eds.), Art, Mind, and Religion (pp. 37–48). Pittsburgh: University of Pittsburgh Press. Raff, R., & Sly, B. (2000). Modularity and Dissociation in the Evolution of Gene Expression Territories in Development. Evolution and Development, 2(2), 102–113. Salazar-Ciudad, I., & Jernvall, J. (2013). The Causality Horizon and the Developmental Bases of Morphological Evolution. Biological Theory, 8(3), 286–292. Salazar-Ciudad, I., Jernvall, J., & Newman, S. (2003). Mechanisms of Pattern Formation in Development and Evolution. Development, 130, 2027–2037. Schrenk, M. (2010). The Powerlessness of Necessity. Nous, 44(4), 725–739. Sommerhof, G. (1950). Analytical Biology. Oxford: Oxford University Press. Stalnaker, R. (1968). A Theory of Conditionals. In Studies in Logical Theory, American Philosophical Quarterly Monograph Series (pp. 98–112). Oxford: Blackwell. Striedter, G. (1998). Stepping Into the Same River Twice: Homologues as Recurring Attractors in Epigenetic Landscapes. Brain, Behavior and Evolution, 52(4–5), 218–231. Tabata, T. (2001). Genetics of Morphogen Gradients. Nature, 2(8), 620–630. Tooley, M. (1977). The Nature of Laws. Canadian Journal of Philosophy, 7(4), 667–698. Verd, B., Crombach, A., & Jaeger, J. (2014). Classification of Transient Behaviours in a Time-Dependent Toggle Switch Model. BMC Systems Biology, 8(43), 1–19. Vetter, B. (2015). Potentiality: From Dispositions to Modality. Oxford: Oxford University Press. Walsh, D. (2012). Mechanism and Purpose: A Case of Natural Teleology. Studies in History and Philosophy of Biological Biomedical Sciences, 43(1), 173–181. Wang, J., Zhang, K., Xu, L., & Wang, E. (2011). Quantifying the Waddington Landscape and Biological Paths for Development and Differentiation. Proceedings

66  Powerfully Directed Development of the National Academy of Sciences of the United States of America, 108(20), 8257–8262. Wolpert, L. (1971). Positional Information and Pattern Formation. In A. A. Moscona & A. Monroy (Eds.), Current Topics in Developmental Biology (Vol. 6, pp. 183–224). London and New York: Academic Press. Yeger-Lotem, E., Sattath, S., Kashtan, N., Itzkovitz, S., Milo, R., Pinter, R., et al. (2004). Network Motifs in Integrated Cellular Networks of TranscriptionRegulation and Protein-Protein Interaction. Proceedings of the National Academy of Sciences, 101(16), 5934–5939.

4 Ontogenetic Causal Primacy

Ontogenetic Causal PrimacyOntogenetic Causal Primacy

The Fount and Flow of Information

One of the most central conceptual components of any broadly Aristotelian account of biological natural kind essentialism also constitutes one of its most contentious claims—namely, that organisms possess a privileged set of intrinsic properties which are causally primary with respect to their morphological development. Historically, this sort of claim has not been considered controversial and, at one time in relatively recent history, was in point of fact rather commonplace: in the early days of the discovery of DNA, the research programme of Mendelian genetics appeared to experimentally vindicate the adoption of a broad ‘genetic determinism’ of the sort which still colloquially lingers in popular culture today.1 However, contemporary experimental and theoretical advances in the field of developmental biology have now called that claim into serious question, and it’s no exaggeration to say that it is at present overwhelmingly viewed with scientific scepticism: the process of ontogenesis is, in short, no longer widely understood as a principally intra-organismal affair. That being the case, it’s clear that if the arguments of this book in favour of a novel neo-Aristotelian theory of biological natural kind essentialism are to be both plausible and persuasive, the validity of this now contestable claim must be vindicated. In order to do so, this chapter examines two of the most primary objections to that claim prevalent in the contemporary literature in the context of the now popular theoretical framework of ‘developmental systems theory’ and its flagship tenet—the ‘causal parity thesis’. In my view, the defensibility of this thesis has yet to be sufficiently challenged, as the standard ways in which responses to its most important instance—‘informational parity’— have been formulated all suffer from what I consider to be a fundamental mistake: they are looking for primacy in all the wrong places. In drawing a novel conceptual distinction between causal relevancy and causal responsibility, this chapter not only defends the causal primacy of developmental modules in the process of ontogenesis by utilising the dispositional framework offered in the previous chapter but also expands and enriches that framework in important ways.

68  Ontogenetic Causal Primacy

4.1 The Case Against Primacy I: Polygeny and Pragmatism As discussed in the previous chapters, central to an Aristotelian theory of essence is a particular claim about the source and nature of ontogenetic development—namely, that there are certain collections of natural and intrinsic properties that groups of organisms possess which dynamically direct their development toward the production of particular morphological profiles, or specific sets of anatomical and eidonomical structural features. That discussion has also highlighted the fact that, according to this theory, the privilege of these properties in this respect is a no mind-dependent, heuristic artefact—rather, these properties’ functioning as the fundamental causal locus of that particularised generative prowess is an ontological affair. It is vital to such a theory then that it be able to show that this privileged causal-cum-modal role that the essence of a natural kind plays in that process is an intrinsic and mind-independent one. In the context of this book, and in the parlance of its particular neo-Aristotelian theory, this is a task which requires sufficiently demonstrating that this role is the purview of μ-dispositions. What is it then about the causal structure of developmental modules which might single them out, over and above all of the other causal factors present within organismal architecture, as first among equals? According to the proponents of the now popular developmental systems theory, the simple answer is: nothing.2 Although the sort of GRNs which constitute these modules (as discussed in Chapter 3, §3.2) once occupied a privileged theoretical role in any scientific ontology, according to the ‘developmentalist’ perspective, “the empirical differences between the role of DNA and that of [the surrounding organismal architecture] do not justify the metaphysical distinctions currently built upon them”.3 The denial of these “metaphysical distinctions”, on the part of the developmentalist perspective, is based on the affirmation of the principle of causal parity, which could be stated as follows: there is no genuine or principled ontological distinction between the causal contribution of the GRNs of developmental modules and those of extra-module factors which establishes one of them as causally primary with respect to the specified production of organismal morphology.4 For the purposes of this discussion, I will examine two distinct (though interrelated) arguments in favour of causal parity. The first of these, and by far the most popular, is what I will call the argument from polygeny. This argument, raised rather notably by J. S. Mill (in his A System of Logic), centres on denying the age-old ontological distinction between ‘causes’ and ‘conditions’.5 This distinction is pre-theoretically quite plausible: presumably most of us wouldn’t cite the atmospheric medium through which solar radiation passes as the cause of a warm sunny day—rather, it’s a kind of condition which must be in place in order for the cause—the Sun’s radiation—to produce that warmth. Upon philosophical reflection, however, given that for any effect there is a multiplicity of causal

Ontogenetic Causal Primacy  69 factors whose combined contribution is required in order to bring that effect about (effects are, in other words, ‘polygenic’—having multiple causes), singling out one of those factors as the cause and all the remaining ones as merely enabling ‘conditions’ is a decision which is difficult to justify. Causes are causes after all, and, prima facie, the causal contribution of any one factor in producing some effect doesn’t look to be any more important than the contribution of every other factor in doing so. According to the argument from polygeny, for any effect phenomena we care to examine, denoting any one of its contributing causal factors as the cause of that effect can only ever be a pragmatic decision—a mind-dependent designation that “cuts no ontological ice”. Why ought we think that this is the case? Typically, this is motivated by a kind of via negativa argument which goes something like this: there simply are no ontologically significant criteria that apply to one of those causal factors which do not also apply to all of the other ones, so either no single factor is causally privileged in the production of a particular effect or else, what amounts to the same thing, every factor is “privileged”. The plausibility of this argument is illustrated when we attempt to answer the question as to what sort of criteria could possibly do that job. Upon inspection, it’s fairly easy to see that the contents of the familiar philosopher’s tool kit of logical analysis aren’t up to the task. With respect to some effect, causal primacy can’t be assigned to the single factor that is necessary for that effect to come about—a single causal factor might be necessary in that respect, but then so is every other factor in that same respect. Likewise, causal primacy can’t be assigned to the single causal factor that is sufficient for that effect coming about—if anything meets that criterion, it’s the whole complex of causal factors at play, not any single factor. These same observations apply, mutatis mutandis, for assigning causal primacy to the factor that is both necessary and sufficient for that effect coming about. The failure of these standard logical distinctions in this respect clearly buttresses the argument from polygeny and makes the case for causal primacy look significantly less promising. One plausible way in which one might counter that argument is by offering a theory of causality—that is, a general framework for understanding ‘causation’ tout court—which is able to make more fine-grained distinctions with respect to the “causal contribution” of various factors involved in producing an effect. A recent such theory, one which has been widely featured in contemporary research in the general field of the philosophy of science (and more specifically, in the philosophy of biology), might be of particular interest here. James Woodward’s (2003) ‘manipulation theory’ of causation, which is a kind of refinement of David Lewis’ (2000) ‘causal influence theory’, seemingly provides a conceptual framework which is able to effectively discriminate among causal influences with the required subtlety and subsequently deliver a suitable criterion for causal primacy. According to the manipulation theory of causation, a particular causal factor is the cause of some effect just in case “manipulations” on that factor are reliably and

70  Ontogenetic Causal Primacy repeatedly correlated with changes in that effect. In other words, among a set of relevant causal factors, a single such factor C is the cause of an effect E if changes in the “value” of C in various ways is correlated with corresponding changes in the “value” of E. On this theory, C is the cause of E—and not a mere “background condition” of E’s coming about—if E changes its states just in case C does. Assuming that counterfactual dependence generally follows causation, Lewis’ (2000: 190) relation of ‘causal influence’ can be seen as an explication of this: when a variable C is the cause of E, there will be a pattern of counterfactual dependence of the effect upon alterations of the cause. . . [such that] there is a substantial range C1, C2 . . . of different not-too-distant alterations of C . . . and there is a range E1, E2 . . . of alterations of E . . . such that if C1 had occurred, E1 would have occurred, and if C2 had occurred, E2 would have occurred, and so on. Let’s consider an example case where this criterion for causal primacy is in play. What’s the cause of a match being lit? Surely, if anything, it’s the striking of the match against the matchbox. Utilising the manipulation theory of causation, we can affirm that if we had struck the match differently— say, with less force, or at a different angle, etc.—then the effect of ‘ignition’ would have occurred differently and in a way that corresponds with that striking event. That is, we can affirm that the changes in the “value” of the ‘striking’ variable correspond to changes in the “value” of the ‘ignition’ effect, and thus, on the manipulation theory, that it is the striking which is the primary causal factor with respect to the match’s ignition. Every other causal factor relevant to the match’s ignition—the dryness of the match, the ruggedness of the matchbox, the surrounding oxygen—must certainly be present in order for the striking to cause the ignition, but while they are kept constant, it is changes in the ‘striking’ factor that are appropriately correlated with changes in the ‘ignition’: those factors function as mere background conditions against which ‘striking’ has a unique relationship to ‘ignition’. Regrettably, although this criterion for causal primacy is intuitively rather promising, it ultimately isn’t going to work. In the earlier case, while it is certainly true that if we keep the other causal factors constant, they will function as mere background conditions against which the value of ‘striking’ will co-vary with the value of ‘ignition’, their “static” and supporting role in bringing about that effect is not a consequence of ontology, but rather of convention. To see why this is so, consider what I will call the “late addition of oxygen case”.6 Suppose that we are in a sealed, deoxygenated room and that we are continually striking a dry match against a suitably ruggedly surfaced matchbox. In this situation, ignition does not occur— there’s no oxygen in the room—and no matter how much we vary the value of ‘striking’, it will in no way actively correspond to any values of ‘ignition’. However, if we start to slowly leak oxygen into the room, the match

Ontogenetic Causal Primacy  71 will eventually become enflamed—indeed, the more oxygen we let enter the room, the larger the flame will be, and the less oxygen we allow into the room, the smaller the flame will be. Or, to put it another way, changes in the value of the oxygen level will correspond to changes in the value of the ignition effect. In this scenario, then, the continual ‘striking’ of the match is, in effect, functioning as a “static”, supporting background condition, while oxygen is functioning, according to the manipulation theory’s criterion, as the cause of ignition. Plausibly, what the late addition of oxygen case illustrates is that the criterion for causal primacy derived from the manipulation theory is in the end, like all of the other criteria on offer, insufficient: its designation of one causal factor as the cause of some effect—and not a mere background condition—appears to be a rather fluid affair, one unfixed by ontology and grounded instead in pragmatism. To the reader even only slightly acquainted with discussions of causality in the contemporary developmental biology literature, the preceding discussion will have no doubt seemed fairly familiar, and for good reason: these conceptual worries are mirrored in the debates concerning the nature of biological information—in particular, the dispute over whether it represents a unique biochemical relation applicable only to some privileged developmental resource. In these debates, the typical dialectic is: among all of the intra-organismal architecture, it is the genome which is developmentally privileged with respect to the generation of morphology because it is the unique carrier of ‘information’ about that morphology. What does it mean to “contain information” in this way? Here an appeal is often made to the most viable (and widely accepted) theory of information—‘Shannon information’ (sometimes called ‘causal information’).7 It was its progenitor Claude Shannon’s (1948) purpose in the formulation of information theory to provide a framework for quantifying facts about contingency and correlation between states/entities/systems. Putting the mathematical structure aside, according to Shannon, something x is a source of information if it can occupy a number of alternative states, and something else y “carries information” about x if its state is correlated with the state of x. Here one can think of something simple, like the link between a tree’s rings and its age: there are various quantitatively distinct states which the first variable (its rings) can occupy which are reliably correlated with various quantitatively distinct states of the second variable (its age). So, a variable x “contains information” about another variable y iff the state of y causally co-varies with the state of x in such a way that changes in the value of x are reliably associated with changes in the value of y (and vice versa). Thus, one can “gain information” about the state of y by attending to the state of x (and vice versa).8 It isn’t difficult to see that the conceptual schematics of the manipulation theory of causation closely parallel those of information theory: they share a common theoretical focus on the relation of causal co-variance between state values. If we match the two up, we might say that, according to the

72  Ontogenetic Causal Primacy criterion of causal primacy distilled from the manipulation theory of causation, if x “contains information” about y, then x is the cause of y (rather than a mere background condition).9 As already mentioned, the causal privileging of the genome in morphological development is often justified on just these grounds: the genome is conceptualised as the ‘source’ of information, morphological features as the ‘receivers’ of that information, and the various cellular and extra-cellular machinery as the ‘channel’ through which that information is passed—in this way, the genome “contains information” about organismal morphology (read: the states of its codons causally co-varies with the states of an organism’s morphology) and hence is the principal cause of morphology. We can easily extend this reasoning to the GRNs which constitute developmental modules: because, as we have seen, it is the dynamics of their regulatory architecture upon which the generation of morphology depends, alterations to their structure will be reliably correlated with alterations in organismal morphology.10 If we utilise the manipulation theory to extract the aforementioned conception of causal primacy, one might think that developmental modules containing information about organismal morphology effectively establishes them as the cause of that morphology—it is these modules, after all, which uniquely bear the specialised relation of correlative state co-variance to that morphology. Unfortunately, this sort of claim looks to be fundamentally flawed for, just as in the case noted earlier, it is ultimately nous, not nature, which establishes the uniqueness of this relation. The designation of one causal factor as ‘source’ and another as ‘channel’ is, in other words, a purely pragmatic distinction: as it turns out, any reassignment of these appellations will yield informational correlations among the relevant causal factors. If we choose to treat the GRN of a developmental module as a ‘channel’—as paralleled in the late addition of oxygen case, by keeping its state “fixed”—we find that the upstream, extra-module embryonic proteins which act as the ‘stimuli’ of μ-dispositions also contain information about (i.e. have a reliable, counterfactually rich pattern of state-value correlation with) that organismal morphology. Indeed, upon closer examination, this information relation is procured rather cheaply and is for that reason relatively ubiquitous: any of the causal factors necessary for the generation of organismal morphology can be treated as ‘channels’ against which variation in the state of some other such factor can be shown to causally co-vary with the state of that morphology. To put it simply: having states that causally co-vary with the state of morphology is not the unique purview of the GRNs of developmental modules. Consequently, as Maynard Smith (2000: 189) points out, while we can accurately claim that a particular developmental module contains information about, for example, the generation of a child’s morphological features, “we can equally well say that a baby’s environment carries information about its growth; if it is malnourished, it will be underweight”.11 Here then we have an exhibition of the phenomenon of ‘informational parity’, according to which “[g]enes and non-genetic factor[s] are on a par

Ontogenetic Causal Primacy  73 insofar as non-genetic factors will carry information on any viable account of information according to which genes carry information”.12 Accordingly, just as in the late addition of the oxygen case, it seems that we must here conclude that the designation of any particular causal factor as the cause (qua the source of information) cannot be based on any ontological distinction—if it were, then either every such factor would causally primary with respect to the generative specificity of organismal morphology or else, what amounts to the same thing, no factor would be. It is on account of these sorts of considerations that the advocates of developmental systems theory would claim that module GRNs are “just one interactant in a field of context-dependent difference makers”13 and that therefore “practical, not theoretical, considerations” direct the designation of them as causally primary with respect to morphology.14

4.2 The Case Against Primacy II: Pleiotropy and Plasticity Although the next argument for ‘causal parity’ has not received much attention in the literature, it is nevertheless an important one. While the argument from polygeny makes the case that there are no criteria for distinguishing one causal factor out of many as being ontologically privileged with respect to its causal role in bringing about some effect, the argument from pleiotropy suggests that even if such a criterion were at hand, it would be one that our preferred candidate would fail to satisfy. More specifically, while the former argument’s aim is to show that no single causal factor is primarily responsible for producing some effect, the latter’s aim is to show that there is more to primacy than merely being privileged with respect to the production of that effect: primacy entails a rich sense of determination. The thought here is as follows: even if we allow that a single causal factor is primarily responsible for “bringing about” some effect, it cannot be considered causally primary with respect to that effect if it fails to be responsible for determining the particular character of that effect. Let us look again at our example case of the striking of a match, this time focusing on the type of causal factor we’re interested in—dispositional properties. Suppose we grant, ignoring for the moment the conceptual worries presented in the previous section, that it is the dispositional property of the match—its ‘flammability’—which is the privileged causal factor with respect to the ‘ignition’ effect (rather than the host of requisite stimuli factors which must also occur). As we have seen in our example, and as is typically the case, effects are not unidimensional—they are ‘pleiotropic’, having more than one way of being. In other words, very few effect-events only come in one shape and size, but are instead typified by a variety of distinct, though interrelated, particularised instances: in our example case, the variability of ‘ignition’ can be represented by a fine-grained gradient of quantitatively and qualitatively distinct values that reaches from a minute flickering of flame to a venerable bonfire atop the match-tip. Not only then do most effects have

74  Ontogenetic Causal Primacy a variety of causal factors involved in bringing them about (being polygenic), but they are also capable of being exhibited in a variety of distinct ways (being pleiotropic). Now although I have dismissed the manipulation theory of causation as being unable to provide an adequate causal primacy criterion, the basic thought behind it is, I think, correct: if a particular causal factor is to be causally primary with respect to some effect, it had better not only be responsible for bringing that effect about but also for that effect being brought about with some particular value; that is, it had better also play a privileged role in its state co-varying with the state of that effect. In our case, the thought is: if the dispositional property of ‘flammability’ is to be causally primary with respect to ‘ignition’, it had better be responsible not only for “bringing about” the ignition of the match-tip but also for the precise level of ignition that occurs in any instance. Even granting that dispositional properties play an important causal role in bringing about their associated effects (read: manifestations), upon closer examination, they appear to fail this prerequisite for causal primacy. The dispositional property of the match in our example, for instance, doesn’t look to have any sort of “causal control” over the value determination of the ignition event: rather, what does seem to have that control is all of the non-dispositional factors—the amount of oxygen, the angle and speed of the ‘striking’, the roughness of the matchbox, etc. All of these, as we saw in the previous section, are the types of causal factors whose values appear to determine the value of the relevant effect: tweak the values of these factors, and you tweak the value of the effect. In other words, it is those factors— not the dispositional property of ‘flammability’—that are responsible for the match-tip igniting in the fashion it does in any particular instance. And if it is the case that which qualitatively or quantitatively distinct effect-value is brought about in any instance depends upon a variety of other, nondispositional factors, the dispositional property in question doesn’t look to be the determiner, and thus, the cause of that effect. The conceptual worries raised for dispositional properties with respect to a criterion of causal primacy qua determinative value-control in this example case are not merely theoretical: they have an important empirical instance in the case currently under consideration—namely, the μ-dispositions of developmental modules. Although the GRN-based generative prowess of developmental modules has thus far been explicated (in Chapter 3) in terms of their dynamical privileging of the production of a single, unidimensional end-state, this is in fact a simplification.15 Indeed, as one might expect of the biological world, the real picture of that prowess possesses significantly more subtle complexities. For we now know that the morphological feature produced by a single developmental module is capable of exhibiting a wide variety of environmentally induced qualitative and quantitative variation—this is known as the phenomenon of ‘phenotypic plasticity’.16 Such morphological variability ranges from being relatively minor as when, for instance, butterflies develop distinct wing patterning in response to

Ontogenetic Causal Primacy  75 seasonal weather signals,17 to rather extreme, as displayed in water fleas’ development of large helmet-like spikes in response to receiving chemical signals from nearby predators,18 or in the caste system of ants, where hormonal signals distributed among a population produce radical changes in the morphology of its members, creating everything from winged and wispy drones to the thickly carpaced, reproductively charged queens.19 Although to the untrained eye the phenomenon of phenotypic plasticity no doubt appears to be a bit of sympathetic magic, its causes and conditions are both extensively documented and fairly well understood. To get a grip on what’s going on in cases of phenotypic plasticity, it’s important to note that developmental modules are not causally closed systems: for while their constituents—namely, the networked cells which comprise its imaginal disc—enjoy a relative measure of causal autonomy, they are yet embedded within the larger architecture of an organism and are thus fundamentally intertwined with the operative dynamics of other such sub-systems. Thus, the intra-organismal “environment” of a particular developmental module can play a crucial role in determining its intra-module “environment”—in particular, in determining the presence (and absence) of transcription factors which might interact with its constitutive GRN. This is important because, as we have already seen (in Chapter 3), the generation of a morphological feature is not accomplished simply by specific sets of proteins being present within that GRN, but by their being present in a specific fashion—at particular times and in particular places (as well as during certain periods of development generally). In this way, changes in the timing (heterochrony) and location (heterotopy) of the expression of the elements of that network—that is, changes in the “pattern of expression”, or “expression profile” of that GRN— constitute alterations in the regulatory dynamics which undergird its generative prowess.20 In other words, if the presence or absence of the transcription factors associated with a particular module’s GRN is altered, the pattern of expression of that GRN is altered and, consequently, the morphological feature whose formation depends upon the activities of that GRN is altered. Accordingly, as a result of changes in an organism’s extrinsic environment, corresponding “upstream” alterations in the heterochronical and heterotopical inter-cellular signalling of a module’s GRN are translated into the “downstream” production of further transcription factors which enact (spatial and temporal) regulatory control of its constitutive target genes which directly specify intra-module cell fate. Or, to put it more simply, environmental-based alterations in the “input” values of the GRNs of developmental modules are causally correlated with corresponding alterations in their “output” values—that is, with alterations in the quantitative and qualitative character of their associated morphological feature with respect to its precise shape, size, pigmentation, etc. It is the phenomenon of phenotypic plasticity that sets the stage for the application of the argument from pleiotropy to the case of developmental

76  Ontogenetic Causal Primacy modules. For note that a consequence of this phenomenon seems to be that “genes and gene activities can never be separated from direct environmental influence”,21 and thus that the generative specificity of a particular morphological feature must be understood as fundamentally being “the unique consequence of a particular genotype developing in a particular environment”.22 Given that it entails that the pleiotropic nature of the production of a morphological trait by a developmental module is such that which particular expression of that trait that process engenders is a matter largely determined by environmental factors, the phenomenon of phenotypic plasticity plausibly calls into question the causal primacy of that module with respect to that process. For, as illustrated earlier, according to a plausible criteria of causal primacy, if developmental modules are to be considered causally primary with respect to the production of morphological traits, they must be responsible for determining the quantitative and qualitative particularities of those traits. However, the phenomenon of phenotypic plasticity seems to rather strongly indicate that just the opposite is the case: these particularities appear instead to be primarily a result of the causal contribution of specific configurations of environmentally induced transcription factors. Indeed, the picture that this phenomenon paints is one wherein developmental modules do not appear in any significant fashion to be in “causal control” of which quantitatively and qualitatively specific variant of their associated morphological trait is produced in any particular instance. Thus even if we were to grant, as considered in the previous section, that those modules “contain information” about organismal morphology in some privileged sense, the phenomenon of phenotypic plasticity seems to suggest that they are yet uninformative in this important respect, and, consequently, that while crucial morphology-determining developmental information certainly “flows through” these modules, they are far and away from being its fount. From the perspective of the criterion of causal primacy currently under consideration then, the privileged role of the generative capacities of those modules with respect to the production of organismal morphology must be seen as rather suspect. For if it is the case that, to return to our earlier phrasing, which “effect-value” a particular μ-disposition produces in any particular instance primarily depends upon the presence and activity of a variety of non-dispositional, extra-module factors, those dispositions appear eminently unqualified to be the determiners, and thus, the causes of those effects.

4.3 Primus Inter Pares: Causal Relevance vs. Causal Responsibility Due to the problems of polygeny and pleiotropy, the defender of the causal primacy of developmental modules with respect to organismal morphology looks to be stuck in a rather tight spot. The argument from pleiotropy

Ontogenetic Causal Primacy  77 suggests that the causal factor which she would wish to label the cause— namely, μ-dispositions—aren’t up to the task as they aren’t in “causal control” of their effects in a suitably robust sense, and the argument from polygeny suggests that even if they were up to that task, so is every other relevant causal factor, and in precisely the same respect. Or, to put the point in the “information-theoretic” vernacular of the biological sciences: either μ-dispositions lack crucial information about organismal morphology—as it’s their stimulus factors whose causal co-variance “controls” morphological development—or else the information they possess isn’t unique—as they causally co-vary with morphological development in just the same way all the other contributing factors do. When the conclusions of these arguments are taken together, they pose a special problem for the neo-Aristotelian form of biological essentialism I have thus far proposed: they suggest that the μ-dispositions of developmental modules being singled-out as the primary causes of organismal morphology is nothing more than a heuristic by-product of some contingent explanatory schema, rather than the necessary consequence of a proper ontological analysis, and, further, that even if this were not the case, that their causal role in that generative process is nonetheless not a fundamentally immanent one. In other words, these arguments seem to show that the purported essence of a natural kind cannot perform the causal-cum-modal role it is meant to play in any privileged way, as it can do so in neither a plausibly mind-independent nor suitably intrinsic fashion. Is then the search for a criterion of ‘causal primacy’ of the requisite sort a hopeless endeavour? I think not. To my mind, there’s certainly a reason why, given the earlier arguments, the defender of causal primacy looks to be in such a tight spot, but it’s not because she hasn’t the conceptual resources to bolster her position. Rather, it’s because, in accepting some crucial presuppositions in the dialectic of those arguments, she’s given up the game before she can play it. Accepting those presuppositions, I will argue, is tantamount to looking for causal primacy in all the wrong places.23 As illustrated earlier, both of the arguments against causal primacy essentially operate on a common conception of ‘cause’, one that closely aligns with the notion of ‘information’—namely, Woodward’s (2003) ‘manipulation theory’, in which causal co-variance is the mark of causality. According to this conception, either μ-dispositions are “just as causal” as every other relevant factor in producing organismal morphology (given the polygeny of effects) or else they aren’t intrinsically in “causal control” of that production (given the pleiotropic nature of effects). In the contemporary literature, the arguments put forward by those who have wished to defend some form of causal primacy in this context have, as Weber (forthcoming) points out, generally fallen into one of two broad categories: information-theoretic defences and causal selection defences.24 An information-theoretic defence of causal primacy is one which provides an addendum to the concept of ‘information’ which effectively singles-out

78  Ontogenetic Causal Primacy the GRNs of developmental modules as the only developmental resource which “contains information” about organismal morphology: causal covariance of state-values is still a requirement for the information relation to obtain, but some other requirement must be met as well—and this is one only those GRNs meet. Some forms of this defence have been ‘representational’ theories, wherein “containing information” about y entails containing semantic content about y, content that is typically taken to be imbued by the selective contingencies of the evolutionary process; these are the so-called teleosemantic accounts of information according to which x’s containing information about y requires it having been the case that the states of x causally co-varying with the states of y was, at some point in evolutionary history, specifically selected for.25 There have also been a variety of non-representational forms of that defence, wherein the informational ‘content’ GRNs is typically taken to be either “instructional”,26 or “semiotic” (in some fashion).27 A causal selection defence of causal primacy, on the other hand, is one which, rather than offering a novel form of ‘content’ with which to buffer the concept of ‘information’, focuses solely on reforming the informational link of causal co-variance of state-values in such a way that effectively singles-out the GRNs of developmental modules as the only developmental resource which co-varies with organismal morphology in the right way: either that co-variance must be of a very particular type28 or else it must achieve some high degree of fine-grained specificity.29 As one might expect, philosophers have in various ways objected to the sufficiency of both of these types of defences to provide an adequate account of causal primacy which might genuinely privilege one developmental resource over all the others. Although there’s been quite a lot of ink spilled on fleshing out these arguments, and they remain the focus of a lively debate in the contemporary literature, I’ll not here be delving into the intricacies of their to-and-fro, and for a principled reason: at the heart of these two types of defences lies what I take to be a fundamental mistake in the search for a criterion of causal primacy. Notice that both of these defences’ attempts to restore causal primacy have focused on enriching the relation of causal co-variance which forms the foundation of information theory—either by adding something to that relation or else by modifying the relation itself. This general approach, centred as it is on that relation, is to my mind mistaken: for I want to suggest that while the fact that a causal factor “contains information” about an effect—that is, that its state-values correlatively covary with the values of that effect—is important, it’s not what’s most important, and therefore focusing on that relation isn’t going to lead one to an adequate criterion of causal primacy. Within any causal set-up, being a causally contributing factor that is capable of taking on multiple values, ones which correlatively co-vary with the values of the relevant effect, is undoubtedly an important role. It is, as far as I’m concerned, a clear indicator of the existence of a causal relationship, and it is by utilising these co-variance relations that we are able to exploit those

Ontogenetic Causal Primacy  79 factors in experimental and practical circumstances—a prowess clearly of central importance to the advancement of scientific research. However, although this role is important, and thus so are the set of causal factors who play this role within any particular causal set-up, there is another type of causal role that I believe is more important—namely, the one played by the causal factor that is responsible for the fact that those other factors’ values co-vary with the values of the effect. Accordingly, it is my claim that if we want to elect a candidate for ‘causal primacy’, we need to draw a distinction between (a) the contribution of factors whose values are causally correlated with the values of some effect and (b) the contribution of factors which are responsible for the existence of that correlative value-correlation. I will refer to this as the distinction between (a) causal relevance and (b) causal responsibility, and my claim is that whatever is causally responsible in this sense ought also to be considered causally primary. In what follows, I show that properly distinguishing the division of causal labour between ‘relevant’ and ‘responsible’ factors with respect to some effect brings out an important point: the fact that a particular causal factor’s values correlatively co-vary with the values of that effect is not enough to merit it the crown of causal primacy. For, as we will see, any pro tanto claim to that title that causally relevant factors might possess is one inherited from the existence and nature of causally responsible ones; this is because, in short, relevant factors depend upon responsible ones for their own relevancy. To get clearer on what ‘responsibility’ in this sense amounts to, and why we ought to consider its amounting to causal primacy, I will offer an explication by display via an examination of the special role that a particular class of properties plays. As the reader will no doubt have already guessed, given that I have claimed (in Chapter 3) that it is dispositional properties which operate as the fundamental ontological infrastructure that underlies entities’ state-transitions, it is my contention that the realm of the dispositional is the realm of the responsible. In order to see why this is so, I want to put forward two main tests which are able to indicate whether a causal factor is causally responsible for some effect—the test of counterfactual dependency, and the test of specificity determination. Passing both of these tests is at least a minimally sufficient requirement for responsibility in the aforementioned sense. Dispositional properties, as I show next, satisfy this requirement: for while it is true that the existence of a set of causal factors is required for a particular dispositional property to bring about some effect, and that their specific values are relevant to precisely how that effect is brought about, that set of factors, in and of themselves, are not responsible for the fact that they are required and relevant in those senses. That they are, I argue, is a fact established by the existence and nature of that dispositional property—and this is the mark of ‘responsibility’. Consider first then the counterfactual dependency test for causal responsibility. For a causal factor to pass this test, the existence of the valuecorrelation between some collection of causal factors and some effect must

80  Ontogenetic Causal Primacy counterfactually depend upon its existence: were it to be absent, in other words, so too would that correlative link be. Recall again our (admittedly simplistic) example causal event involving the manifestation of a dispositional property—the ignition of the struck match. As we have already seen (in §4.2), the stimulus of the match’s disposition of ‘flammability’ is comprised of a collection of causal factors—‘striking’, ‘oxygen levels’, ‘matchbox surface ruggedness’, etc.—which must all be in place in order for the disposition to manifest ‘ignition’, and whose variations in value are correlated in a fine-grained fashion with changes in how that manifestation comes about.30 But now, according to our test, we must ask: is it the case that, were the match to lack the dispositional property of ‘flammability’, fine-grained changes in the values of these causal factors—‘striking’, ‘oxygen levels’, etc.—would be correlated with corresponding fine-grained alterations in the value of the effect, ‘ignition’? Clearly not. If the match were not ‘flammable’, altering the oxygen levels, the exact stroke of the matchtip upon the box, etc., would have absolutely no effect on whether and to what degree the match becomes enflamed. This suggests that the establishment of the relationship of causal co-variance between the various values of those factors and the various possible values of the effect is dependent upon the existence of the dispositional property—and this is precisely what is required for that property to be considered causally responsible for that effect. A further indication that a particular causal factor is causally responsible for some effect is that it establishes not only that there is a functional valuecorrelation between the states of a set of other causal factors and the states of that effect but also the precise character of that correlation—that is, if it is the case that those other causal factors somehow rely upon that particular causal factor to be causally connected to that effect in the specific fashion that they are. Consider, for instance, the effect that salt (NaCl) has on two different organisms—slugs and humans. While salt has significant effects on the functioning of both of these organisms, they differ in their precise responses to it: the exact same measurement of salt which might provide nourishment and replenishment to a human’s body may have the devastating effect of dehydrating and debilitating the body of a slug. In general, the relation of the values of that causal factor—salt—with its effect have an entirely distinct character when in the context of a slug than when in a human: too much salt for a slug is not too much salt for a human, and the “safe” value-range of salt differs in each. The fact that one and the same causal factor is related in distinct ways to its effect in the context of two distinct organisms suggests, I think, that this factor can neither establish the existence of nor the specific character of its value co-variance with that effect. The specificity of that relationship, plausibly, is rather a consequence of the particular character of the dispositional property for which it serves as a stimulus condition. In other words, the difference between slugs and humans in this instance is a dispositional one, the fine-grained effects of

Ontogenetic Causal Primacy  81 the presence of salt differing in either case due to a difference in the dispositional properties which humans and slugs possess for which salt is a common stimulus. What both of these tests illustrate is that while a whole host of causal factors may be causally relevant with respect to some effect, in that their presence and precise values are important in determining whether and in what respect that effect will occur, it is dispositional properties which are causally responsible for that effect, as they establish that there is a functional relationship of causal co-variance between the various values of those other factors and the values of that effect. Without dispositional properties, not only would those relationships not exist, but they wouldn’t exist in just the particular fashion that they do. And it is for this very reason that these properties ought to be considered causally primary with respect to their associated effects—for the correlative value co-variance of causal factors with respect to some effect enshrined in most analyses as being constitutive of causal primacy is, as we have just seen, itself dependent upon and subject to those properties. In this way dispositional properties, qua causally responsible for their effects, are worthy of the crown of causal primacy. If dispositional properties play a unique and privileged role within causal set-ups, one that sets them apart as “first among equals” with respect to the production of effects, a rather straightforward resolution to the parity problem in the generation of organismal morphology presents itself. Consider again one of the serious stumbling blocks for a defence of the causal primacy of developmental modules with respect to that process—the phenomenon of phenotypic plasticity, wherein morphological traits are capable of taking on a wide variety of quantitatively and qualitatively distinct variants in correlation with their exposure to a varying range of environmental conditions. As we saw earlier, this phenomenon engenders a problem for the advocate of the causal primacy of developmental modules: in treating the GRNs of those modules as constant “background conditions”, or channels, we find that the values of environmental factors causally co-vary with the values of those modules’ associated morphological traits and thus “contain information” about those traits—so either those modules play no privileged role in the generation of organismal morphology or else the role they play is a rather deficient one. However, with the earlier discussion in mind, we can note that this problem itself rests upon a problematic premise—namely, that “containing information” is the foundation of causal primacy: for although the contribution of causal factors whose values are functionally correlated with the value of some effect is important, the contribution of the causal factor which is responsible for the existence and specification of that functional value correlation is more so. According to that distinction, “containing information” about organismal morphology is realm of causal relevance, rather than responsibility. If then, as I have argued, responsibility is the remit of dispositional properties, can it be shown that the μ-dispositions of developmental modules are responsible for organismal morphology?

82  Ontogenetic Causal Primacy Consider again the counterfactual dependency test for causal responsibility: is it the case that, were the dynamical architecture of a module’s GRN absent, fine-grained changes in an organism’s environmental conditions— and thus fine-grained changes in the amount/type/etc. of disc-interacting transcription factors—would be correlated with fine-grained qualitative and quantitative changes in its associated morphological trait? Clearly not. Without that architecture, no gathering of, or active co-operation of environmentally induced causal factors would have any effect on—let alone bear any fine-grained relation of correlative value co-variance to—the ontogenetic specificities of that trait. Of course, this should come as no surprise as, if they are to have any effect on that trait whatsoever, those factors must of necessity “pass through” that architecture: their effectiveness in that respect fundamentally depends upon their ability to alter the expression, and thus the regulatory dynamics of that architecture. This suggests that the functional relationship between the various values of intra- and extra-organismal, broadly “environmental” causal factors and the various possible quantitatively and qualitatively distinct variants of a particular morphological trait is existentially dependent upon the μ-disposition of its developmental module—and, as we have seen, this is precisely what is required for that property to be considered causally responsible for that trait.31 Consider next the specificity determination test for causal responsibility: is it the case that the nature of extra-module causal factors determine the specific quantitative and qualitative character of co-variance relation between themselves and a particular morphological trait? Here we must be careful and heed the distinction between ‘relevance’ and ‘responsibility’. As we have seen, it’s certainly true that the presence and absence of these factors is causally correlated with the expression profile of the GRN of a developmental module and are thus in “causal control” of its ontogenetic specificities in any particular instance. Importantly, however, while this control consists in causally determining which qualitatively/quantitatively specific variant of a particular morphological trait is produced in those instances, it doesn’t extend to determining the particularities of the relationship of value co-variance between those factors and those variants. In other words, the values these extra-module factors take determine which morphological variant is produced in a particular instance, but not which values produce which variants—and that latter role is precisely what is at issue in this test for causal responsibility. Indeed, just as in our example case of the effects of salt on slugs and humans, it’s clear that no complex of transcription factors, in and of themselves, are responsible for the way in which they are related to a particular morphological trait—for one and the same such factor which functions as an ‘enhancer’ (increasing the rate of transcription) in the context of one GRN can function as a ‘repressor’ (decreasing the rate of transcription) in the context of another.32 Instead, it is the dynamical architecture of developmental modules and not any collection

Ontogenetic Causal Primacy  83 of broadly “environmental” factors, which establishes the specificities of the functional relation of value co-variance between those complexes and morphological traits—and in doing so, passes the second test for causal responsibility. It is my contention then that while all of the aforementioned broadly “environmental”, extra-module factors are causally relevant to the production of organismal morphology, it is the μ-dispositions of developmental modules which are causally responsible for that process. Accordingly, because those factors could not be relevant to that process, or be relevant in the precise fashion they are, apart from those dispositions, it is the latter, rather than the former, which ought to be considered causally primary with respect to that process. Furthermore, with the earlier discussion in mind, we are now in a position to offer a principled reply to one of the central parity-based problems for the metaphysical framework of neo-Aristotelian essentialism—namely, that the role that μ-dispositions play in the generation of organismal morphology, dependent as it is upon the activities of extrinsic causal factors, is an inherently incomplete and thus fundamentally deficient one. For we can now note that this problem is grounded in the assumption that the role that μ-dispositions play in this respect is one of causal relevance: on that supposition, as previously discussed, μ-dispositions certainly “lack information” about organismal morphology. However, on the basis of the earlier arguments, that assumption ought to be rejected: μ-dispositions are not merely relevant, but responsible. This is important because while its performance requires the presence and activity of extrinsic factors, the role of ‘responsibility’ that μ-dispositions play with respect to organismal morphology is, as we have seen, not one bestowed by, or otherwise tailored to the vagaries of extra-module influences, but is instead one immanently grounded in the dynamical architecture of developmental modules. Given the nature of responsibility, then, and in line with the metaphysical framework of neo-Aristotelian essentialism, I maintain that the causal-cum-modal role that the μ-dispositions of developmental modules play in the ontogenesis of organismal morphology is a fundamentally intrinsic affair.

4.4 Parity and Pragmatism Revisited If, as I have argued, the μ-dispositions of developmental modules are to be crowned as causally primary with respect to organismal morphology, they must be shown to perform that role in not only an intrinsic fashion but also a mind-independent one—that is, it must be demonstrated that the privilege of these properties in that respect is a consequence of ontology, rather than an artefact of conventional fiat, lest the charge of parity and pragmatism remain. In the parlance of this chapter, if the μ-dispositions of developmental modules truly deserve the honorific of causal primacy, it must be shown that “environmental” causal factors cannot just as equally play the role of ‘causal responsibility’ with respect to organismal morphology.

84  Ontogenetic Causal Primacy I have claimed that the causal factor that is responsible for some effect is the one which establishes the functional relationship of correlative value co-variance between that effect and a set of other causal factors. But now we must ask: is the role of ‘causal responsibility’ one that any of the factors in some causal set-up could play? Could we not simply choose to “hold constant” any causal factor and by varying the rest of them still obtain the same functional relationship among those factors and the effect? Consider again the paradigm case of “containing information”: when the GRN of a developmental module is placed in the ‘signal’ position—the position according to which it “contains information” about a morphological trait—the environment functions as the static, “background” channel, and manipulations of the values of that GRN (for instance, via alterations to its regulatory dynamics, or in extreme cases perhaps, via alterations to its constituent codons) correlatively co-vary with changes in the value of that trait (that is, in which quantitatively and qualitatively specific variant is produced). In this rather commonplace case, the pragmatist may ask, isn’t the environment playing the role of ‘causal responsibility’ in that it is the causal factor (or complex of factors) which is effectively establishing the existence of a functional value-correlation between the states of the developmental module and those of the morphological trait in question? Indeed, given the phenomenon of ‘informational parity’ (as discussed in §4.1), should we not conclude that ‘responsibility’ is just as ubiquitous as ‘information’ and hence that the designation of any particular causal factor as primary with respect to some effect is more a reflection of convention rather than a consequence of ontology? In order for the pragmatist to be able to show that, in light of ‘informational parity’, there also exists a parity of responsibility among the developmental resources involved in the generation of organismal morphology, she must be able to show that all of the relevant causal factors can equally perform the role of responsibility in a robust fashion. Showing that isn’t trivial, as there are two subtle, yet important, points one must keep in mind in any attempt to do so. Firstly, on a more general note, the mere conceptual shuffling of positions within a relational equation does not necessarily represent an ontologically unique state of affairs: if the causal relationships among the variables is unchanged in the novel expression of the relation, so too are the roles played by those variables. Secondly, and more specifically, there is more to the role of being causally responsible for an effect than simply being the causal factor that is able to be “held constant”, while the others’ values correlatively co-vary with the value of that effect: the role of responsibility is a dynamic one and so isn’t played by a causal factor in virtue of its being in the conceptual position of background condition/channel with respect to some effect. With these two important caveats in mind, what has to be said is that it’s certainly true that, given ‘informational parity’, it’s the case both that the states of the dynamical architecture of developmental modules and of the

Ontogenetic Causal Primacy  85 extra-module environment are capable of causally co-varying with organismal morphology. For the purposes of making a judgement regarding the “parity of responsibility”, however, the pertinent question is, with respect to each case, why changes in the former are correlated with changes in the latter. In other words, in the sort of case just discussed where it appears that environmental factors are playing the role of causal responsibility with respect to the production of a particular morphological trait, we must ask: why—causally—do we obtain differing variants of that trait when we alter the GRN of a developmental module? I contend that we do so because altering the GRN of that developmental module amounts to altering the functional value-correlative relationship between the “stable” set of environmental factors and that morphological trait. If this analysis is correct, it shows that, in spite of the protestations of the pragmatist, the role of responsibility yet belongs to μ-dispositions. When we have a stable set of environmental conditions E, and we observe that varying the state of the dynamical architecture of a developmental module D results in the production of a number of variants of a particular morphological trait M, what we are observing, I claim, is a change in the relation of E-M brought about by the change in the value of D. For although there is a correlation between the various values of D (D1, D2, D3, . . .) with various values of M (M1, M2, M3, . . .), what is happening, causally, when we obtain a novel value of M in these cases is that when the value of D changes, so too does the functional relationship between the “stable” value of E and the value of M. So although it’s true that, for instance, with respect to a “stable” background condition E1, a change from D1 to D3 is correlated with a change from M2 to M4, the reason why a change in the value of M occurs upon a change in the value of D is that the existence of D1 brings it about that E1 is causally correlated with M2, and the existence of D3 brings it about that E1 is causally correlated with M4. In other words, changes in the value of D are causally correlated with changes in the value of M because changing D amounts to changing the way in which the value of E relates to the value of M. If the aforementioned understanding is correct, then an important point follows. Although by treating it as the ‘channel’ of an informational link it may first appear that the “environment” can also play the responsibility role with respect to the production of a particular morphological trait, when we examine the causal relations at play, we find that, even in this case, it is the μ-disposition of a developmental module which performs that role. It does so, as we have seen, by establishing the existence and the particular character of the functional relationship between the values of a set of environmental factors and that trait—for changes in the dynamical architecture of a developmental module amount to changes in that functional valuecorrelation (even if that change in value-correlation amounts to changing the way in which a single, “stable” value of the former relates to the values of the latter).

86  Ontogenetic Causal Primacy The natural response from the proponent of developmental systems theory and the defender of causal parity will no doubt be that the very same thing can be said, mutatis mutandis, for the “environment”—she will claim that if we simply switch E for D in the earlier example, via parity of reasoning, the same argument can be ran with the conclusion being that it is the “environment” that is causally responsible for organismal morphology in the required sense. But is that really the case? Consider the final assertion of the earlier example, with the appropriate amendments now being suggested: “changes in the value of E are causally correlated with changes in the value of M because changing E amounts to changing the way the value of D relates to the value of M”. In order for this to be true—that is, if the ‘because’ here is appropriately causal, as it must be—it would have to be the case that environmental factors are capable of establishing a functional relation of value-correlation between the dynamical architecture of a developmental module and a corresponding morphological trait. Note, however, that if this claim is true, then so must this one be: “changes in the value of D are correlated with changes in the value of M because of the existence of a functional value-correlative relationship between D and M, established by E”. This claim strikes me, as I suspect it will many, as simply implausible: it isn’t the causal purview of the “environment” to act as the architect and facilitator of the functional value-correlations which hold between extra-environmental factors (e.g. the GRNs of developmental modules) and morphological traits. Indeed, I find it exceedingly difficult to imagine any way in which the collection of causal factors which comprise an organism’s environment could plausibly be conceptualised as exhibiting this sort of active control over which states of its ontogenetic sub-systems are correlated with which states of its morphological features. And, importantly, this is precisely what ‘responsibility’ requires: the fact that when E is a background condition/channel, there exists a correlative relation between D-values and M-values is, although true, not enough to merit E the title of causal responsibility. Rather, as per the previously discussed criteria (§4.3), it must somehow be shown that the existence of E establishes, and that the nature of E specifies, that relation. That said, the onus is decidedly upon the defender of the causal parity thesis to show just that and in a fashion that mirrors the plausibility and theoretical fit of the account given in the previous section. This is a burden I think the defenders of that thesis will find both cumbersome and difficult to discharge. In the absence of any such account, and given the earlier arguments, I conclude that though it is true that developmental modules “contain information” about organismal morphology in just the same respect that environmental factors do, and accordingly that either causal factor can be “held constant” and treated as a background condition/channel, it isn’t true that, when treated thusly, these two factors operate in the same fashion, or that they play the same causal roles with respect to the specified production of morphological traits. To put it succinctly: their symmetry with

Ontogenetic Causal Primacy  87 respect to functioning as ‘information channels’ isn’t reflected in the ontology of the causal structures which constitute their respective relationships to those traits. Contrary to the pragmatist’s rebuttal, then, I claim that there is no parity of responsibility among the developmental resources involved in the generation of organismal morphology and, furthermore, that the lack thereof is not a matter of mere heuristic convention, but is instead a consequence of ontology. Thus, in line with the metaphysical framework of neo-Aristotelian essentialism, I maintain that the μ-dispositions of developmental modules perform their causal-cum-modal role in the ontogenesis of organismal morphology in a mind-independent fashion.

4.5 A More Complex Teleology: Mapping Out Morphospace If the arguments of the preceding sections have gone through, an important impediment for the tenability of a neo-Aristotelian theory of biological natural kind essentialism has been removed: one of its central and most contentious claims—that organisms possess an ontologically privileged set of intrinsic properties which are causally primary with respect to their morphological development—has been defended. In doing so, by drawing a novel distinction between ‘causal relevance’ and ‘causal responsibility’, the nature of the properties at the centre of that theory—μ-dispositions—has been thrown into sharper relief. If, however, the μ-dispositions of developmental modules are, as I have claimed, causally responsible for the generation of organismal morphology, a refinement of the initial characterisation of their generative prowess must now be made. In the previous chapter, one of the defining features—if not the defining feature—of dispositional properties was discussed in great detail: their teleological “directedness”. Dispositions are understood as goal-directed properties because, in serving as the ontological infrastructure of statetransition, they dynamically orient their bearers toward the production of a particular end-state (their ‘manifestation’). In the case of the properties presently of interest—μ-dispositions—that orientation is expressed in their role as the active mediators of the flow of regulatory information which effectively translate the ‘stimuli’ of developmental signals over a complex “causal gap” which spans an entire imaginal disc into the ‘manifestations’ of particularised morphologies.33 However, as illustrated throughout the previous sections of this chapter, in light of the phenomenon of phenotypic plasticity, the generative prowess of developmental modules cannot be fully captured by conceptualising it as consisting in the dynamical privileging of the production of a single, unidimensional end-state. This is because, as we have seen, in their role as causally responsible for organismal morphology, the μ-dispositions of developmental modules are capable of producing— and are in fact the primary producers of—a variety of quantitative and qualitative variations on their associated traits. Properly acknowledging and

88  Ontogenetic Causal Primacy accounting for their ‘responsibility’ in this respect requires the expansion of our conception of the characteristic feature of their generative capacities— their teleological “directedness”. The phenomenon of phenotypic plasticity reflects the fact that a single regulatory network of a developmental module is capable of producing a variety of distinct morphological end-states according to a variety of distinct initial developmental conditions, as altering the initial network-state of that module has regulatory consequences (specified by the “generative rules” of that network) on the expression states of its cells which ripple “downwards” and “outwards” throughout an imaginal disc during the process of development. Accordingly, because the causal pathway between upstream intra- and inter-cellular signals and downstream “trait-building” genes is one which can be traversed in many distinct ways (according to the variability in those upstream signals), the generative prowess of a single developmental module must be conceptualised as being responsible for the production of an entire range of environmentally correlated quantitative and qualitative variations on its associated morphological trait. In this way, as we have seen illustrated in the role of responsibility, the μ-dispositions of developmental modules are what philosophers refer to as ‘multi-track’ dispositions, the manifestations of which in particular instances are specific tokens of a more generalised manifestation type.34 Thus, given the phenomenon of phenotypic plasticity and the nature of ‘causal responsibility’, the morphological trait which is generatively specified by the μ-disposition of a developmental module—its end-state toward which it is dynamically oriented—cannot be fully or sufficiently characterised by a single, particularised, token instance with respect to those quantitative and qualitative dimensions, but must instead be understood as a generalised type consisting of a collection of various quantitative and qualitative variations on its associated trait: in contemporary developmental biology, this set of possible morphological permutations is known as the trait’s morphospace.35 Clearly, if by taking into account the full richness of the generative prowess of the μ-dispositions of developmental modules we must conceptualise them as being dynamically oriented toward the production of a particular morphospace M, rather than toward any environmentally correlated quantitatively or qualitatively specific variant within that space (m1, m2, m3, etc.), our earlier picture of what that teleological “directedness” consists in must now be augmented. In order to do so in a comprehensive fashion, let us first return to the types of models which were previously utilised (in Chapter 3) to illustrate the dynamical privileging of developmental modules—the topological landscapes of DST. Recall that our earlier representations of the dynamical structure of developmental modules were utilised to model ‘contrastive’ information about their generative prowess by mapping out multiple trajectories in a single state-space comprised of all of the possible expression states of its imaginal disc: once that statespace is vectorised by being assigned a stability measure, its topological

Ontogenetic Causal Primacy  89 features reveal in more detail what the teleological privileging of that prowess consists in.36 Within this model of the dynamical structure of a developmental module, the morphological trait it is “directed toward” represents a disc-wide pattern of regulatory stability with respect to its intra-module cellular expression states which “carves out” a wide, low-lying basin in that landscape, and the privileging of that end-state is illustrated by the dynamics of its developmental process being shaped and constrained by the geometric curvature of that topology. Adequately capturing the dynamical structure of the morphospace of a developmental module, given that it is comparatively more complex and comprehensive, will involve modelling many more possible developmental trajectories through that same state-space (utilising the same methodology described in Chapter 3, §3.3) to deliver a more “finegrained” picture of its topology (see Figure 4.1). Once we have done so, the resultant topological landscape, unlike our earlier representations, depicts the generative prowess of a developmental module in a suitably multifaceted fashion by featuring multiple basins of regulatory stability, each corresponding to a quantitatively and qualitatively specific variant of that module’s associated morphological trait (see Figure 4.1). This comprehensive topological mapping more adequately models the richness of the role of ‘causal responsibility’ that the μ-dispositions of developmental modules play with respect to the production of organismal morphology, but it also illuminates the teleological structure of that role in more detail. That said, upon being presented with the complex topological landscape of an entire morphospace, one might prima facie conclude that it fails to exhibit the requisite sort of ‘causal specificity’ that characterises teleologically directed systems: after all, these landscapes essentially express the plasticity and thus flexibility of the generative capacities of developmental modules to produce a wide array of morphological end-states, rather than their privileging of any specific end-state. However, a more nuanced look at these topologies reveals that this first impression is a mistaken one. For while the morphospace of a developmental module is quite clearly a reflection of its developmental plasticity, it is at the same time illustrative of its developmental constraints: the system it depicts is not one which is wholly flexible, being substantially subject to the causal whims of every incoming environmental influence during the process of development, but rather one which reliably and repeatedly ends that process within a well-demarcated range of particular states. The state-space upon which the morphospace of a developmental module is modelled may represent every possible cellular configuration its imaginal disc is able to instantiate, but the topological features of that space make it clear that only a select set of these configurations are probabilistically privileged (as represented by the landscape’s basins) and that its members are produced within a relatively narrow range of causal contexts (as represented by the valleys which feed into those basins). In this way, the morphospaces associated with developmental modules show that

90  Ontogenetic Causal Primacy nature delights in variety without indulging in it—morphological flexibility is allowed, but only within certain and specific limits.37 Furthermore, not only do the morphospaces of developmental modules exhibit generative specificity in the aforementioned sense, but they also display both of the characteristic features of teleologically directed systems. In the initial introduction of DST-based models of the causal structure of developmental modules, given their relative topological simplicity, these were evinced as holistic features of those systems.38 However, the increased complexity of the DST-based models of the morphospaces of developmental modules (as in Figure 4.1) does nothing to diminish these features—rather than “global”, these can now be seen as “local” features of those topologies. For note that each of the channels which “flow” into a particular basin in these complex topologies have both their own width and depth—two features which, given that the geometrical contours of these landscapes are representational reflections of their dynamical structure, exhibit the goaldirectedness of those systems. The ‘pleonastic pathing’ of those systems is, as we have already seen, a feature captured by the widths of those topographical channels, as they are representative of the multiplicity of distinct causal pathways along which these systems may travel in order to reach those quantitatively and qualitatively specific variants of the module’s

Figure 4.1 Topological Morphospace Model: Schematic partial representation of the complex topological features of a module morphospace. Here the orb at the top of the figure represents the system’s initial, undifferentiated expression state, and the arrows represent distinct developmental trajectories through state-space. Here, as in Figure 3.5, the elevation of state-space (along the U-axis) represents disc-wide regulatory stability, and the contoured areas at the end of each arrow represent highly stable ‘attractor basins’ which correspond to distinct disc-wide cellular expression profiles.

Ontogenetic Causal Primacy  91 morphological trait: the greater number and variety of that module’s possible developmental trajectories which result in the production of that variant, the greater the breadth of the channel which flows into its associated basin. The ‘persistence’ of those module’s production of a particular morphological end-state is again a feature captured by the depths of those channels: the height and slope of the boundary walls of a particular channel are a measure of the statistical improbability that the system’s traversal along any of its constitutive trajectories will be subject to any substantive deviation (of the sort which would alter the morphological variant it produced).39 It’s clear then that a more robust understanding of the dynamical structure of developmental modules’ role in the generation of organismal morphology requires an expansion and enrichment of our conception of the teleological character of μ-dispositions. As illustrated earlier, a fine-grained analysis of the dynamical privileging which typifies μ-dispositions reveals their being casually responsible for a complex, teleologically textured morphospace— one which reflects their polygenic capacity for specified pleiotropy. In this way, the morphospace associated with a particular μ-disposition represents the generalised type of the morphological trait toward which its development is dynamically oriented, the specific tokening of which it produces on particular occasions in correlation with the contingencies of its causal context. Thus, as illustrated in the DST-based models of those morphospaces, the teleological character of the μ-dispositions of developmental modules is significantly multi-dimensional: both a specific set of particular regions within that space and the particular pathways which are traversed to reach those regions exemplify the generative privileging and thus the goaldirectedness of the causal role those capacities play in the development of organismal morphology. That the μ-dispositions of developmental modules function in this teleologically complex fashion with respect to the dynamics of morphological development, and do so as an ontological consequence of their intrinsic nature, has important implications for the neo-Aristotelian theory of biological natural kind essentialism which will be forged throughout the following chapters. Indeed, with the distinctions in this chapter having been drawn and detailed, we now have all we need to begin doing just that: the blueprint has been drawn (in Chapter 1), the ground has been cleared (in Chapter 2), the foundation has been laid (in Chapter 3), and the tools have been sharpened (in Chapter 4)—it’s time to build.

Notes 1 The contemporary locus classicus on the nature/nurture debate as it relates to the genome is Oyama (1985), but see also Moss’ (2003) accessible more general treatment of the subject. 2 For some prominent recent defences of the ‘developmentalist’ perspective, see Oyama et al. (2001) and Griffiths and Gray (2004). 3 Griffiths and Knight (1998: 254).

92  Ontogenetic Causal Primacy 4 This is a generalised, “lowest common denominator” statement of the principle. As Stegmann (2012) points out, advocates of developmental systems theory endorse (often implicitly) a wide variety of different (and occasionally overlapping) fine-grained senses of ‘causal parity’, some with more conceptual adornments than others. 5 Mill (1843). 6 I borrow the general set-up of this case from Mumford and Anjum’s (2011: 32–34) discussion of the distinction between ‘causes’ and ‘conditions’. 7 Cf. Sterelny and Griffiths (1999: 101). 8 Typically this “correlation” between the two states/entities/systems is cashed out in terms of reduction of uncertainty, or the decrease of epistemic entropy, in the sense that knowing the value of the second variable reliably allows one to know the value of the first (and vice versa). It is important to note, however, that the informational correlation between two variables cannot be analysed (in the philosophical sense) by epistemic concepts: if there are epistemic facts to be had about those variables, they are available because there is a physical, mindindependent correlation between them. In this chapter, I construe that correlation as essentially one of counterfactual dependence; for a more explicit and detailed discussion of the relation between ‘information’ and counterfactual dependence, see Cohen and Meskin (2006). 9 The suggestion here is only that the information relation might track causal primacy and not that causation might somehow be analysable by this relation. The latter is a stronger and much more contentious suggestion, one that the essential bi-directionality of Shannon information renders rather implausible; in the biological sciences, its denial is enshrined in the so-called “Central Dogma” of protein synthesis (Crick 1958). For a recent formal account of informational systems which intimately integrates causality, see Calcott et al. (2017). 10 Cf. Chapter 3. 11 Cf. Oyama (1985) and Griffiths and Gray (1994). 12 Stegmann (2012: 913). 13 Gray (1992: 179). 14 Gannett (1999: 356). 15 I discuss the metaphysical implications of this teleological complexity with respect to the nature of μ-dispositions in §4.5. 16 Continuing empirical research suggests that the developmental specification of morphological features via environmental stimuli is not only a functionally ubiquitous phenomenon, but one that may play a vitally important part in the evolutionary process—see Fusco and Minelli (2010), West-Eberhard (2003), and Pigliucci (2001). I discuss the intersection between plasticity and evolution in the context of essentialism in Chapter 6. 17 Gibbs et al. (2011). 18 Laforsch and Tollrian (2004). 19 Miura (2005). 20 Schlichting and Smith (2002) and Whitman and Agrawal (2009). 21 Whitman and Agrawal (2009: 25). 22 Lewontin (1982: 21–22). 23 This section’s discussion closely tracks the argumentative structure in Austin (2015). 24 It should be noted that these arguments are typically defences of the causal primacy of the genome with respect to the production of either the proteome or the general organismal phenotype, rather than of the more complex and particularised GRNs of developmental modules with respect to the production of

Ontogenetic Causal Primacy  93 morphological traits. However, as far as the fundamental conceptual structure of these defences are concerned, the differences between the former and the latter are for present purposes insignificant. 25 Millikan (1984) is perhaps the locus classicus on the subject of teleosemantic accounts of information, though see Longy (2015) for an excellent comprehensive overview of the subject. 26 Cf. Stegmann (2005). 27 Cf. Sarkar (2003) and Godfrey-Smith (2000). 28 Cf. Stegmann’s (2014) ‘external ordering’ relation. 29 Cf. Woodward (2010). Waters (2007) adds the additional requirement that a causally primary factor must be an ‘actual difference maker’ that is also causally specific in Woodward’s sense. 30 Although most philosophers would undoubtedly classify some of these stimulus factors as “background conditions”, I ignore that distinction here, given the preceding discussion of causal parity which showed that any causal factor can be “held constant” while manipulations on the others are correlated with changes in the effect. For other arguments against the distinction between ‘causes’ and ‘conditions’ with respect to dispositional properties, see Mumford and Anjum (2011) and Hauska (2009). 31 Of course, it’s true that these modules’ passing the test of counterfactual dependency for causal responsibility is a fact which itself counterfactually depends on their being operative within the context of a larger, extra-module signalling system. But this isn’t any special cause for concern: no causal factor within a system is likely to function in the same way (if at all) outside of the context of that system—but this doesn’t entail that there aren’t distinct and discernible causal roles played by the factors within that system, or that those roles don’t properly belong to those factors. The role that the dynamical architecture of a developmental module plays in the production of organismal morphology can only be performed in a certain context, but in that context, it is the causal factor that does play that role, and that role is precisely the one we’re interested in with respect to ‘causal responsibility’. I thank Kim Sterelny for bringing this issue to my attention. 32 Hollenhorst et al. (2009). 33 Cf. Chapter 3, §3.2. 34 For more on the metaphysics of multi-track dispositions, see Vetter (2013) and Williams (2011). 35 On the general concept of ‘morphospace’ and its theoretical applications, see Mitteroecker and Huttegger (2009) and Rasskin-Gutman (2005). Typically, morphospaces are represented on a unidimensional plane—that is, on a nontopological space. In what follows, I use the term to refer to a more complex concept, one which combines the “static” maps of possible morphologies with the dynamical structures which reflect the causal architecture of the developmental modules which produce those mappings. 36 Cf. Chapter 3, §3.3. 37 I discuss this theme in the context of the intersection of my theory with the process of adaptive evolution in Chapter 6, §6.3. 38 See Chapter 3, §3.3. 39 Utilising experimental manipulation techniques to “unnaturally” force such systems to deviate in their developmental trajectories is the focus of interesting new research being done to illuminate in more detail the topological structure of their associated morphospaces—a study now vital to cellular research, especially in its application in the production of ‘induced pluripotent stem cells’; see Graf and Enver (2009) and Huang (2009).

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Ontogenetic Causal Primacy  95 Maynard Smith, J. (2000). The Concept of Information in Biology. Philosophy of Science, 67(2), 177–194. Mill, J. S. (1843). A System of Logic, Collected Works of John Stuart Mill (Vol. 7, J. Robson, Ed.). Toronto: University of Toronto Press, 1973. Millikan, R. (1984). Language, Thought and Other Biological Categories. Cambridge, MA: The MIT Press. Mitteroecker, P., & Huttegger, S. (2009). The Concept of Morphospaces in Evolutionary and Developmental Biology: Mathematics and Metaphors. Biological Theory, 4(1), 54–67. Miura, T. (2005). Developmental Regulation of Caste-Specific Characters in SocialInsect Polyphenism. Evolution & Development, 7(2), 122–129. Moss, L. (2003). What Genes Can’t Do. Cambridge, MA: MIT Press. Mumford, S., & Anjum, R. (2011). Getting Causes From Powers. Oxford: Oxford University Press. Oyama, S. (1985). The Ontogeny of Information. Cambridge: Cambridge University Press. Oyama, S., Griffiths, P., & Gray, R. (Eds.). (2001). Cycles of Contingency: Developmental Systems and Evolution. Cambridge, MA: The MIT Press. Pigliucci, M. (2001). Phenotypic Plasticity: Beyond Nature and Nurture. Baltimore: Johns Hopkins University Press. Rasskin-Gutman, D. (2005). Modularity: Jumping Forms Within Morphospace. In W. Callebaut & D. Rasskin-Gutman (Eds.), Modularity: Understanding the Development and Evolution of Natural Complex Systems (pp. 207–219). Cambridge, MA: The MIT Press. Sarkar, S. (2003). Genes Encode Information for Phenotypic Traits. In C. Hitchcock (Ed.), Contemporary Debates in Philosophy of Science (pp. 259–272). London: Blackwell Publishers. Schlichting, C., & Smith, H. (2002). Phenotypic Plasticity: Linking Molecular Mechanisms With Evolutionary Outcomes. Evolutionary Ecology, 16(3), 189–211. Shannon, C. (1948). A Mathematical Theory of Communication. Bell Systems Technical Journal, 27(3), 379–423. Stegmann, U. E. (2005). Genetic Information as Intstructional Content. Philosophy of Science, 72(3), 425–443. Stegmann, U. E. (2012). Varieties of Parity. Biology & Philosophy, 27(6), 903–918. Stegmann, U. E. (2014). Causal Control and Genetic Causation. Nous, 48(3), 450–465. Sterelny, K., & Griffiths, P. (1999). Sex and Death: An Introduction to Philosophy of Biology. Chicago: University of Chicago Press. Vetter, B. (2013). Multi-Track Dispositions. The Philosophical Quarterly, 63, 330–352. Waters, C. K. (2007). Causes That Make a Difference. Journal of Philosophy, 104(11), 551–579. Weber, M. (forthcoming). Causal Selection vs Causal Parity in Biology: Relevant Counterfactuals and Biologically Normal Interventions. In C. Waters & J. Woodward (Eds.), Philosophical Perspectives on Causal Reasoning in Biology (Minnesota Studies in Philosophy of Science (Vol. XXI). Minneapolis: University of Minnesota Press. West-Eberhard, M. (2003). Developmental Plasticity and Evolution. New York: Oxford University Press.

96  Ontogenetic Causal Primacy Whitman, D. W., & Agrawal, A. A. (2009). What Is Phenotypic Plasiticty and Why Is It Important? In T. N. Ananthakrishna & D. W. Whitman (Eds.), Phenotypic Plasticity of Insects: Mechanisms and Consequences (pp. 1–63). Enfield: Science Publishers. Williams, N. E. (2011). Putting Powers Back on Multi-Track. Philosophia, 39(3), 581–595. Woodward, J. (2003). Making Things Happen: A Theory of Causal Explanation. Oxford: Oxford University Press. Woodward, J. (2010). Causation in Biology: Stability, Specificity, and the Choice of Levels of Explanation. Biology and Philosophy, 25(3), 287–318.

5 The Essence of Natural Kinds

The Essence of Natural KindsThe Essence of Natural Kinds

Unity in Diversity

The singular aim of the previous chapters of this book has been to provide a conceptual framework for a neo-Aristotelian theory of biological natural kind essentialism—and, importantly, not just any framework, but one whose metaphysical structure is undergirded by empirical data. In the first two chapters, I laid out the foundations of such a theory, carefully distinguishing it as one primarily concerned with the causal-cum-modal ground of organismal morphology. In the third and fourth chapters, I argued that the central components of that theory—‘causal powers’, or goal-directed dispositional properties—are not only present within the developmental architecture which causally controls the specified production of that morphology, but are in fact responsible for the operative dynamics which define that process. In the account I present in what follows, these ‘morphomodulatory dispositions’ form the essences of natural kinds—for they function, as the aforementioned Aristotelian tenets require that they must, as the causal-cum-modal ground of the salient morphological features of the collections of organisms which possess them. On this account, it is sets of these causally privileged properties which define natural kinds—the ontological joints of the biological world are, as it were, carved around their edges. However, in order to fully explicate and defend this theory, more must be said for, as of yet, only half of its picture has been painted. In the first chapter (in §1.4), I stated that, according to a neo-Aristotelian theory of biological natural kind essentialism, the essence of a natural kind is “comprised of a natural set of intrinsic properties which constitute generative capacities for particularised morphological development”, but also that such a set must be “shared among groups of organisms, delineating them as members of the same kind”. Providing a proper vindication of the plausibility of the first half of this definition of ‘essence’—a task which the previous two chapters took up—is of course vitally important, but doing the same for the latter half is equally so. And as it is this second half which has perhaps historically been the subject of the theory’s most intense criticism, especially in light of the theoretical commitments of contemporary evolutionary biology, this is a particularly pertinent task. In this chapter, I argue that the aforementioned neo-Aristotelian framework for a theory of biological natural kind

98  The Essence of Natural Kinds essentialism has the conceptual resources to adequately respond to these critiques. Answering these important objections in detail will allow the final conceptual pillar of the theory I wish to propose to be put in place and so permit at last its edifice to be built in its entirety.

5.1 The No Such Set Objection: Phenotypic and Genotypic Diversity As discussed in the first chapter, the claim that groups of organisms share, or commonly possess, a particular group of properties is a central component of any theory of natural kind essentialism. While that claim may not be constitutive of the concept of ‘essentialism’ per se—given that one might hold that every individual organism possesses its own, unique set of properties which play the previously delineated role of essence—it is a necessary component of the concept of a ‘natural kind’. The existence of natural kinds entails that there are ontologically privileged divisions among nature’s denizens which are founded in their possession of particular sets of properties and that these properties function as the epistemological ground for the predictive prowess of our scientific knowledge about them. In other words, two organisms belong to the same ‘kind’ just in case they possess the same set of kind-defining properties, and it is in virtue of their common possession of this set (and the natures of the properties which comprise it) that we can make reliable inductive inferences about their possible and likely developmental trajectories (as discussed in Chapter 1, §1.2). In this way, the plausibility of the theory of biological natural kinds is intimately correlated with the extent to which it can be shown that such shared sets exist. It is not uncommon, however, to find the opinion expressed that this is a task which has not merely thus far been entirely fruitless, but is in fact a necessarily hopeless endeavour. Indeed, it is surely safe to say, as Samir Okasha (2002: 196) does, that virtually all philosophers of biology agree that . . . it is simply not true that the groups of organisms that working biologists treat as conspecific share a set of common morphological, physiological or genetic traits which set them off from other species. Of course, for reasons I have already indicated (Chapter 2, §2.4), although historically the debate over the existence of natural kinds has centred on the conception of those kinds as being identified with the members of the species taxon, the neo-Aristotelian theory of biological natural kinds I wish to defend is decidedly unconcerned with and should thus be definitively disassociated from such an identification. That being said however, it’s clear that the dialectical force of the point remains: the existence of biological natural kinds entails the existence of shared sets of properties among discrete groups of organisms, and philosophers have long agreed that the

The Essence of Natural Kinds  99 empirical evidence suggests that no such sets exist. This widespread agreement is often not simply characterised negatively, as being based on the mere lack of aforementioned evidence, but positively, as a necessary corollary of evolutionary theory: the process of evolution via natural selection requires the constant changing of, and thus the inherent instability of, the collective properties possessed by groups of organisms.1 For this reason, essentialism about biological natural kinds is often understood as being “precisely the ‘typological’ perspective on species that Darwin had to displace”.2 Let us refer then to the general claim that there exists neither sets of morphological nor sets of genotypic properties that are capable of sufficiently characterising, or defining the ‘essences’ of natural kinds as the ‘no such set objection’ to biological natural kind essentialism. Consider the first aspect of that claim—that there are no sets of morphological properties universally possessed by groups of organisms which could qualify as constituting their shared, kind-defining ‘essences’. As should by now be abundantly clear, if its target is the neo-Aristotelian theory of biological natural kind essentialism thus far developed throughout this book, this half of the no such set objection simply misses its mark. For according to fundamental tenets of that theory (as outlined in Chapter 1), no set of such properties is capable of functioning as the essence of a natural kind and for a principled reason: those properties are the causal consequences of—and are thus not themselves constitutive of—the essences of natural kinds. Whether morphological homogeneity exists among discrete groups of organisms is then an issue which is entirely orthogonal to determining the validity of a neo-Aristotelian theory of biological natural kind essentialism. There is, however, a way in which this half of the no such set objection might yet be applicable to a neo-Aristotelian form of that theory. For note that a core conceptual component of a neo-Aristotelian form of natural kind essentialism is the posit that the ‘real’ and ‘nominal’ property collections characteristic of a kind are bound up together in a particularly intimate relationship: the nominal causally depends upon the generative mechanisms which constitute the real. In principle, then, the nominal should reliably track the real—the former being present whenever and wherever the latter is; the reliability of this connection is, after all, the ontological foundation of the fact that ‘natural kinds’ are an inductively rich classification.3 With this in mind, we might reformulate this half of the no such set objection as follows: there is no set of morphological properties commonly possessed by the members of a supposed natural kind to sufficiently justify the claim that they each possess a shared essence (given the purported “strength” of the real-nominal connection). There are two ways in which this claim might be fleshed out, both of which are meant to illustrate the implausibility of the purported members of a natural kind, possessing a shared essence which is causally responsible for the production of their morphologies. On the one hand, it seems to be the case that some morphological properties which we would expect to be possessed by every member of a purported

100  The Essence of Natural Kinds natural kind are not possessed by all members. Here one might point to the rather ubiquitous phenomena of teratology—literally, the study of “monsters”: some sea turtles, for instance, fail to develop their characteristic flippers, but they are not for this reason cast from their kinds. Or one might consider the case of “blind” cave fish which, unlike their purported fellow kind members, don’t simply fail to develop a functioning set of eyes, but simply lack eyes full stop. In both of these cases, we must ask: why should we suppose, in light of the neo-Aristotelian posit of the de re dependence of the nominal upon the real, that these organisms belong to their respective kinds if they lack these seemingly rather basic and kind-standard features? On the other hand, it seems to be the case that even if some morphological features are possessed by every member of a purported natural kind, they are anatomically and eidonomically diverse to the point of not being plausibly causally underwritten by the same essence: all scarab beetles may have horns, but the staggering variety among their respective shapes and sizes would seem to suggest that the generative mechanisms responsible for horn production among these organisms are, even if not radically distinct, at least distinguishable to a degree which would qualify them as being nonidentical. In these sorts of cases we must ask: why should we suppose, in light of the neo-Aristotelian posit of the dependence of the nominal upon the real, that these organisms belong to a single kind? Indeed, when we take a closer look at the generative mechanisms which might plausibly serve as the common foundation of the nominal property collection of a group of organisms which belong to a purported natural kind, it seems that the neo-Aristotelian will find little solace from the suspicion cast by the questions raised earlier. For the obvious candidate for that foundation—the genotype, and in particular, the GRNs of developmental modules—doesn’t look to be an especially promising one. Historically, identifying the essence of a natural kind with a particular genome (or some privileged section thereof) has been a tempting thought—and not just among philosophers. The famed biophysicist Max Delbrück (1971: 54–55), for instance, once suggested that the Nobel committee should posthumously “consider Aristotle for the discovery of the principle implied in DNA”, and even the celebrated and influential evolutionary biologist Ernst Mayr (1997: 154) claimed, “Aristotle’s eidos [form, or essence], the seemingly metaphysical agent, is nothing else but what we now refer to as the genetic programme”. The doctrine of ‘genetic essentialism’ has of course been rather prominent among philosophers as well, being perhaps most notably defended in the microstructuralist theories of Kripke (1980) and Putnam (1975). However, while organisms might in practice be fairly reliably delineated into discrete groups according to the shared sequence-based specificities of their genomes, the extent to which those constitute a universally possessed set of properties which could serve to define the essence of a natural kind appears to be rather questionable.4 On the one hand, their potential

The Essence of Natural Kinds  101 taxonomical virtues notwithstanding, it seems that the inter-organismal uniformity of such sets is to a large extent a product of idealisation: alterations via mutation, absences via meiotic cell division, and additions via horizontal gene transfer, among many other commonplace genetic phenomena, strongly suggest that sequence-identity is a property shared by very few organisms, let alone by the large groups of organisms which purportedly belong to a single natural kind.5 On the other hand, even if the genomes of such groups of organisms were sequentially identical, this would be a state of affairs seemingly insufficient for the confirmation of a neo-Aristotelian form of essentialism. For while the causal-cum-modal role with respect to organismal morphology which that form of essentialism declares that the essence of a natural kind must play is carried out by complexes of genotypic properties, it isn’t one performed primarily in virtue of their sequential structure. As I have earlier stressed, that crucial function is instead a dynamical consequence of the causal structure of GRNs: the sequential ordering of the genomes which comprise those GRNs is of course important, but what’s “doing the work”, metaphysically, with respect to that essential role are the systematic informational interconnections among those sequences which are causally responsible for their instantiation of a specific ‘expression profile’.6 Importantly, however, as we have already seen, both the particular members and the specific causal connectives among them which comprise such networks are themselves subject to change in a variety of ways. Intra-organismally, GRN elements suffering mutational alteration or becoming otherwise functionally disabled often results in compensatory changes in the causal structure of those networks.7 Inter-organismally, this can lead to two members of the same kind possessing distinct sets of causal structures which are nevertheless productive of the same morphological properties. Indeed, over time, and in successive generations, those properties can become effectively unshackled from their molecular moorings and “autonomised” over evolutionary timescales, gaining a kind of intra-kind independence from any specific underlying genetic architecture in a phenomenon known as ‘developmental systems drift’—a state of affairs which plausibly entails the heterogeneity of the various respective real-nominal links of the supposed members of a single kind.8 The no such set objection clearly poses a significant set of potential problems for the theory of biological natural kind essentialism. As we have seen, for the neo-Aristotelian form of that theory, these problems are made especially conspicuous in the context of its theoretical posit of the intimate relation between the ‘real’ and ‘nominal’ sets of properties which typify a natural kind. With respect to the morphological properties which constitute a kind’s nominal set, it seems to be the case that (a) a kind’s real set does not uniformly perform its characteristic function of the production of a particular morphological profile in its members and that (b) the morphological variability prodigious among kind-members cannot be the causal consequence of a single real set which they all share. With respect

102  The Essence of Natural Kinds to the genetic properties which might constitute a kind’s real set, it seems to be the case not only that (a) specific collections of such properties are not universally possessed by the members of a kind, but that (b) the causal architecture principally responsible for the production of the morphology of those members also exhibits significant intra- and inter-organismal variation. If a neo-Aristotelian theory of biological natural kind essentialism is to be plausible, it must possess the conceptual resources to properly ameliorate these problems.

5.2 Essence and the Effects of Essence As I have construed it, the focus of a neo-Aristotelian theory of biological natural kind essentialism is necessarily two-fold—for at its conceptual centre is the relation between two aspects: the ‘real’ and the ‘nominal’. Thus, true to its peripatetic heritage, this theory advocates a fundamentally hylomorphic conception of natural kinds according to which the set of properties which constitutes the essence, or ‘form’, of a kind are inextricably bound up with a secondary set of properties which constitutes its ‘matter’.9 On this conception, therefore, given that the essence of a natural kind consists of a collection of causally foundational and intrinsically potent properties, properly accounting for the ‘form’ of a kind necessarily involves giving an account of the way in which those properties are causally responsible for the production of its ‘matter’. Or, to put it another, more immediately familiar way: having a proper account of the ‘real’ must be, in some fashion, to have an account of the ‘nominal’.10 It is, of course, the primary task of any theory of natural kind essentialism to pick-out ontologically privileged sets of ‘essential properties’ which define natural kinds. But, importantly, carrying out that task requires the explication of what that privilege consists in and this, as we have seen, involves having a grip on the causal consequences, or characteristic effects of those properties: to designate a class of properties as qualified candidates for the essences of natural kinds is, in the Aristotelian framework, to show how and in what respect those properties play that causal role. According to my theory, this causal-cum-modal role is grounded, just as it is in Aristotle’s hylomorphic framework, in the uniquely powerful character of essential properties. And as the dialectic of the preceding chapters has identified this potency with the contemporary correlate of the Aristotelian conception of dunamis—‘dispositionality’—the key claim of my neoAristotelian theory of biological natural kind essentialism can now be stated rather simply: the essence, or form of a natural kind is a set of causally fundamental, intrinsically dynamic, goal-directed properties responsible for the specified production of a particular set of properties which constitute that kind’s matter. More specifically, given the arguments of the preceding chapters: the essence of a natural kind is a set of μ-dispositions whose manifestations constitute a particular ‘morphological profile’. That this vitally

The Essence of Natural Kinds  103 important role which the essence of a natural kind plays is a dispositional one is, in more ways than have been previously discussed, central to my theory—for it is in virtue of this fact that the theory possesses the conceptual resources to properly respond to the no such set objection. The first worry associated with the no such set objection was that it seems to be the case that some morphological properties which we would expect to be possessed by every member of a purported natural kind are not possessed by all members. The disquiet here clearly stems from the fact that the neo-Aristotelian form of biological natural kind essentialism currently under consideration posits the existence of an intimate relationship between the essence, or form of a kind and those properties. On my theory, this relationship can certainly not be denied. As discussed in Chapter 3 (§3.1), dispositional properties are, by their very nature, “directed toward” the production of particular end-states (their manifestations) and as such dynamically orient their bearers toward the possession of those states via a robust process both pleonastic and persistent. Indeed, it is the strength of this connection between dispositions and their manifestations upon which our ability to make reliable inductive inferences about the entities which possess those properties depends as, according to the neo-Aristotelian framework, it ontologically undergirds the continual “cropping up” of a particular set of properties among them. However, if that connection is a dispositional one, although it is by no means weak, it is also to a certain extent elastic—for while an entity’s possession of a particular disposition secures both the possibility and likelihood of its possessing that property’s corresponding end-state/manifestation, it makes no metaphysical guarantee.11 This is because, in short, dispositional properties’ bringing about their end-states is a context-sensitive affair, and in two ways. Firstly, because dispositions are fundamentally causal capacities which manifest upon the occasion of receiving certain requisite ‘stimuli’, the mere possession of a disposition is insufficient for the possession of its manifestation property: outside of the appropriate circumstances obtaining, dispositional properties are, in a certain sense, dormant. Secondly, because the manifestation of a dispositional property is a diachronic (and typically multi-staged) causal process, it is susceptible to interruption: even when sufficiently stimulated, dispositional properties may be subsequently “masked” and thus be prevented from bringing about their end-states. With this unique feature of dispositional properties in mind, we can now make an important feature of my theory more perspicuous: if the essence, or form of a natural kind is a set of μ-dispositions, the morphological properties which constitute that kind’s matter need not—and, given the causal complexity of the biological realm, most assuredly will not—be uniformly and universally possessed by the members of that kind. This potential lack of uniformity, however, poses no special problem for my account: a group of organisms belonging to the same natural kind is a state of affairs which is ontologically grounded in those organisms’ shared possession of a particular

104  The Essence of Natural Kinds set of μ-dispositions, irrespective of whether that set fails in any particular organism to properly produce the entire complement of its associated set of morphological properties. Kind-membership, on my account, is grounded in form, rather than matter, and the dispositional connection I have posited between the two allows and accounts for the “flexibility” of the latter, as all of the members of a natural kind which possess the same form can each equally be disposed toward the possession of a specific set of morphological properties without it being the case that every member actually does so. Their activation of that capacity is a contingent affair and, importantly, the existence of that capacity (as in the case of the “lonely electron” discussed in Chapter 3, §3.1) in no way depends upon that activation taking place.12 Even if it’s the case that the essence of a natural kind may be universally possessed by a group of organisms without being universally manifested therein, there yet remains the worry that those organisms’ shared possession of the same, single set of kind-defining, goal-directed dispositional properties appears to be inconsistent with the wide-ranging morphological heterogeneity which exists among them. I’ve claimed that the relation between the form and matter of a natural kind is flexible in a certain sense: it is not one of causal necessitation, the common possession of that form by a kind’s members only grounding the possibility and likelihood of their possession of a particular morphological profile. However, if the relation between form and matter is one of ‘teleological directedness’, as I have also claimed, the character of the latter must be importantly constrained by that of the former: whether a set of μ-dispositions actually produces a particular morphological profile may be a contingent matter, but which morphological properties that set can and cannot produce is not.13 This being the case, it seems that morphological divergence among a group of organisms which possess the same set of μ-dispositions would be, as it were, metaphysically discouraged and therefore that the amount of morphological diversity which exists among any particular group of organisms must be inversely correlated with the likelihood that its members share such a set. As it is central to my neo-Aristotelian theory of biological natural kind essentialism that the causal-cum-modal role that the essences of kinds play with respect to the production of organismal morphology is a teleological one, this worry looks to be especially pressing. However, with the conceptual distinctions of the previous chapter having been drawn, this apparent difficulty may be rather readily dissolved. For recall that, in light of their role as causally responsible for organismal morphology, the goal-directedness of μ-dispositions cannot be adequately captured by conceptualising it as consisting in the dynamical privileging of the production of a single, unidimensional end-state. Instead, because the μ-dispositions of developmental modules are capable of producing—and are the primary producers of—a variety of quantitative and qualitative permutations on their respective morphological traits, their teleological directedness is a more complex affair:

The Essence of Natural Kinds  105 these are ‘multi-track’ dispositions whose generative competency extends to entire morphospaces.14 The theoretical upshot of this complex, responsibility-based conception of the teleological directedness of μ-dispositions is simple: the context sensitivity of the manifestations of the properties which form the essences of natural kinds allows it to be the case that a single essence may causally underwrite a multitude of morphological variation. If a single μ-disposition is, as a matter of its intrinsic generative potential, causally responsible for the production of a variety of environmentally correlated ‘token’ variations on its associated morphological ‘type’, not only is the morphological heterogeneity indicted against it in the aforementioned worry accounted for, it is also expected—it is, after all, “of the nature” of the properties which constitute the essence of a natural kind that such heterogeneity will be prevalent among members of the same kind.15 If the teleological directedness of the essence of a natural kind amounted to its dynamically orienting its bearers toward the singular production of a qualitatively and quantitatively precise morphology, two organisms belonging to the same kind would admittedly be a highly improbable, if not entirely impossible, state of affairs—a fact made evident by the sheer ubiquity of the phenomenon of phenotypic plasticity.16 For my account, however, because in their role as causally responsible for organismal morphology the properties which constitute the essences of natural kinds are by their very nature ‘plastic’, the presence of intra-kind morphological heterogeneity is not a flaw, but a feature—for this “flexibility” is an ontological consequence of the teleologically rich and causally complex connection which links the form and matter of a kind. If the fundamental mechanisms of organismal morphology which constitute the essences of natural kinds are context-sensitive in the aforementioned fashion, the prevalence of morphological variability among groups of organisms does not directly tell against their being members of a single kind: the variegated presence of a multitude of extra- or intra-cellular environmental factors may causally underwrite significant developmental disparities among organisms which nevertheless share a common set of kind-defining generative capacities. Be that as it may, properly delineating such sets has arguably been a thus far fruitless endeavour as the most empirically plausible candidates—sequentially and/or structurally specific genomes—don’t appear to be shared among discrete groups of organisms in any meaningful respect (for the reasons outlined earlier, in §5.1). As the preceding chapters have rather explicitly identified the causal-cum-modal role that the GRNs of developmental modules play in the production of organismal morphology as being constitutive of the principal function of the essence of a natural kind, this sort of diversity looks to be particularly problematic for my theory. Upon closer inspection, however, this difficulty can be shown to be engendered by a fundamentally flawed understanding of its core ontological commitments.

106  The Essence of Natural Kinds There is of course no use denying the existence of significant compositional and structural variation among the GRNs of the developmental modules within groups of organisms—both intra-organismally, over developmental time-scales, and, inter-organismally, over evolutionary time-scales—but the question is: what are the implications of this fact for my theory? If according to that theory the essences of natural kinds are intimately bound up with the GRNs of developmental modules, a number of puzzling implications would seem to follow. Given that a group of organisms would belong to the same natural kind in virtue of their shared possession of a compositionally and structurally precise set of module-specific GRNs, the population of any kind at any time would necessarily be exceedingly sparse. What’s more, given that these GRNs are continually subject to a range of modificatory contingencies over various time-scales, any organism’s membership to a particular kind would necessarily be a temporally transient and ontologically ephemeral affair. In other words, natural kinds wouldn’t have many members, and what members they would have, they likely wouldn’t have for long. This is, to put it mildly, an undesirable result: metaphysical messiness aside, such a view renders natural kinds effectively bereft of their explanatory, and hence epistemic virtues.17 Fortunately, these unwelcome implications follow from a premise which my theory rather straightforwardly rejects—namely, that the essences of natural kinds are to be identified with compositionally and structurally specific sets of genetic mechanisms. For although according to my theory the essences of natural kinds are intimately associated with the GRNs of developmental modules, that affiliation does not dissolve their distinctness into strict identity. Indeed, such a dissolution is in fact metaphysically disallowed by that theory’s “ontology of essence”. It’s certainly true that, according to my theory, the essence of a natural kind is comprised of a set of properties present in the genomes of its members, but these are no ordinary properties— these are dispositional properties. Importantly, the identity of these properties consists in their capacity to perform a specific function—namely, the causal production of a particular end-state. As we have seen (in Chapter 3, §3.1), dispositions are thus ‘multiply realisable’ properties: irrespective of any discrepancies among their constitutive causal architecture, any two systems which are dynamically oriented to perform the same causal function realise one and the same dispositional property. In this way, although in any specific instance a particular dispositional property is ontologically “nothing over and above” the causal network of the system which realises it, it must be in a significant sense disassociated from that network—qua a multiply realisable property, the strict identification of that property with any system’s specific network configuration must be ultimately unattainable. Thus, the aforementioned intra- and inter-organismal compositional or structural variation in the genetic architecture of a developmental module has no bearing whatsoever on whether it persistently realises a particular μ-disposition—for that is a matter of its continuing to dynamically orient

The Essence of Natural Kinds  107 morphological development in a specific fashion, irrespective of the operative mechanisms by which it does so. In particular, as discussed in detail in the previous chapter, it is a matter of its generative capacity continuing to causally undergird the same teleologically textured morphospace. According to my theory then, the “hierarchical disconnect” between generative function and genetic structure exhibited in the aforementioned “autonomisation” of a particular morphological trait among a group of organisms is merely a consequence of the metaphysical relation between disposition and realiser.18 On this view, the fact that many compositionally and structurally distinct underlying genetic mechanisms reliably and repeatedly play the same causal-cum-modal role with respect to the production of a particular morphological trait type is no cause for concern, but rather suggests that these varied and distinct mechanisms all instantiate a common teleologically directed, functionally defined property—that is, a single, multiply realised dispositional property.19 Importantly, then, according to my theory of biological natural kind essentialism the essences of kinds are centres of generative, rather than genetic specificity: because the μ-dispositions which comprise them are teleologically directed properties which causally orient their bearers toward the production of particular end-states, two organisms belong to the same natural kind just in case their morphological development is causally oriented to proceed along the generatively privileged curvatures of the same dynamical topology. Those capacities being underpinned in those organisms by distinct genetic mechanisms thus poses no special difficulty for my theory, for although in any particular instance a set of compositionally and structurally specific intra-module GRNs are indeed the loci of the characteristic causal-cum-modal role that μ-dispositions play with respect to organismal morphology, those properties are nevertheless not identical to that set. Indeed, given the nature of those properties, as discussed earlier, it is entirely possible that this role be played by some other class of material elements altogether: if the “RNA-world hypothesis” is correct, for instance, the GRNs of developmental modules did not always play this crucial role in organismal ontogenesis.20 This possibility, however, is of no consequence, and, furthermore, is thoroughly accounted for by an essentialism founded on dispositional properties.21 A careful focus on the “ontology of essence” that is constitutive of my theory thus reveals its general insusceptibility to the multitude of conceptual worries which are raised in the typical forms of the no such set objection against biological natural kind essentialism. Responding to these worries has I hope not only cast the details of my theory in sharper relief but also aided in distinguishing it from and illustrating the conceptual advantages it enjoys in comparison to the more common, non-Aristotelian theories of its ilk. In particular, the earlier replies to the no such set objection demonstrate the tenability of my theory in a post-evolutionary context wherein sufficiently accounting for the nature of the denizens of the biological world via

108  The Essence of Natural Kinds the process of natural selection seemingly requires the constant changing of, and hence the inherent instability of, the collective properties possessed by groups of organisms. According to my theory, the fact that there exists a great deal of morphological heterogeneity within such groups—indeed, of sufficient diversity to serve as a fertile resource upon which selection might act—does not tell against their members belonging to the same natural kind: morphological uniformity among the members of such groups is not entailed by, and would in fact be an explicitly unexpected effect of, their shared possession of a set of kind-defining μ-dispositions. This conception of essence is compatible not only with the existence of the environmentally correlated morphological variation which lies at the heart of evolutionary theory but also with the mutational alterations in the composition of the machinery which undergird that variation as the members of a group of organisms which possess a shared set of kind-defining μ-dispositions are in no way metaphysically required to mereologically mirror one another. In this way, the “ontology of essence” emblematic of my neo-Aristotelian theory of biological natural kinds secures a form of metaphysical stability which is not at odds with, and is altogether entirely consistent with, the volatility constitutive of, and the disequilibrium derived from, the process of evolution.22

5.3 The Form of What Matters According to the theory I propose, the essence of a natural kind consists of a set of intrinsic properties which function as generative capacities for particularised morphological development which are shared among groups of organisms, ontologically delineating them as members of the same kind. In fleshing out and defending both parts of this definition throughout these last chapters, I have appealed to the type and nature of the properties which qualify as ‘essential’—namely, dispositional properties and, more specifically, μ-dispositions. Their suitability in this respect, I have argued, is due to their playing a privileged causal-cum-modal role with respect to organismal morphology and thus functioning as form to matter in the requisite fashion. Having explicated the metaphysical requirements which essential properties must meet and offered a compelling candidate property type, we can now take stock and say something more specific regarding which properties in particular are of this type—that is, which properties form the ‘form’. True to its peripatetic heritage, on my neo-Aristotelian theory of biological natural kind essentialism, the ‘form’ of an organism is causally responsible for the initiation of a generative developmental programme for the production of a particular ‘morphological profile’ characteristic of its kind.23 Because any candidate essential properties must therefore lie at the causal “ground floor” of organismal morphology, I have argued that the discrete developmental modules which serve as the fundamental “building blocks” of those profiles ought to be identified as the seat of the generative prowess

The Essence of Natural Kinds  109 of those properties. Thus the essence of a natural kind, according to my theory, must be comprised of a quite specific set of μ-dispositions—namely, those which function as the dynamical baüplan (body plan) for the formation of an organism’s anatomical and eidonomical architecture which specifies the shape, size, proportion, axial orientation, and spatial patterning of these “building block” features.24 This is, the reader will recall, in accord with the rather fundamental morphogenetic function those properties have been posited to perform: as the active mediators of the flow of regulatory information, μ-dispositions effectively translate the ‘stimuli’ of early developmental signals over a complex “causal gap” which spans an entire imaginal disc into the ‘manifestations’ of particularised morphologies.25 It is in their functioning within the morphogenesis of an organism as the generatively entrenched causal foundation from which subsequent developmental processes stem that the μ-dispositions which form the essences of natural kinds perform their characteristic causal-cum-modal role in shaping and constraining the possible and typical morphological development of their members (as detailed in Chapters 3 and 4).26 As we have seen, this is a role captured by the generative prowess of μ-dispositions establishing teleologically textured morphospaces whose topological peaks and troughs carve out the various developmental pathways toward the possible particularised end-states of the morphological structures for which those properties are causally responsible. Each essential property of a natural kind is thus defined by a multifaceted, determinable developmental landscape whose various ‘attractor basins’ represent the variety of determinate forms which those properties’ morphological structures may assume (in correlation with distinct sets of stimuli).27 It is in this way that the essence of a natural kind—qua a collection of μ-dispositions—functions as the dynamical baüplan which causally undergirds the set of morphological features typically associated with its members: it establishes an organismwide morphospace, shaping and constraining the various possible (and typical) courses of its structural development, and, in any specific instance, is the “prime mover” in the environmentally determined, particularised exploration of that space.28 With this conception of ‘essence’ in mind, we can now also say something more specific about the nature of that space—that, is about the matter, or ‘morphological profiles’ which belong to natural kinds. As it is the nature of μ-dispositions to be “directed toward” a particular manifestation type, and thus be capable of producing, according to distinct sets of stimuli, an entire interrelated set of quantitatively and qualitatively precise manifestations within the limits circumscribed by that type, it’s clear that the morphological profile which an essence formed of such properties is causally responsible for must necessarily be a multifaceted one. For just as the generative prowess of each of those properties extends beyond, and thus cannot be sufficiently captured by, any single token exemplification of its manifestation type, so the matter of a natural kind—qua the collective

110  The Essence of Natural Kinds state toward which those properties are directed—cannot consist in a set of rigidly specific instances of the morphological traits those properties are responsible for. Instead, the matter of a natural kind must be conceptualised as a set of discrete morphological potentialities, each of which encompasses a unified gradient of quantitatively and qualitatively precise permutations on a general architectural theme. It must, in other words, consist of the set of trait-specific morphospaces toward which its kind-defining μ-dispositions are teleologically directed, as illustrated in Figure 5.1. According to my theory, then, given its unique conception of ‘essence’, the members of a natural kind possessing the same ‘matter’ amounts to their sharing the same set of possible morphologies—that is, the same set of generatively privileged permutations on the same set of morphological “building blocks”. Two organisms possessing the same matter then is, for lack of a better phrase, a matter of their shared morphological potentiality— itself a reflection of the aforementioned ‘plasticity’ of their shared set of μ-dispositions. In this way, the matter of any particular natural kind—qua a collection of module morphospaces—is in some sense equivalent to a probabilistically weighted, disjunctive set of organism-wide morphologies, each disjunct representing a quantitatively and qualitatively distinct collection of environmentally and/or developmentally occasioned particularised expressions of those morphospaces. It is due to this fact that, in line with the sentiment expressed in Chapter 2 (§2.4) regarding the conflation of telos with taxon, my theory does not identify natural kinds with ‘species’.29 For according to my theory, ‘natural kind’ is necessarily a more inclusive category than ‘species’, as the exploration of “morphological space” afforded by the nature of μ-dispositions outstrips the narrow confines of the more particularised, well-entrenched developmental pathways which typify the members of a species. Because the essence of a natural kind is defined by a set of determinable developmental morphospaces, particular collections of determinate end-states within those topologies cannot possibly capture the richer, more expansive conceptual space which the ontological division of ‘natural kind’ carves out—for, as illustrated in Chapter 3 (§3.3), no limited set of developmental trajectories can hope to reconstruct the geometry of an entire topology. To put it another way: because the μ-dispositions which constitute the essence of a natural kind are teleologically directed toward a generalised type of morphological structure and manifest themselves in various distinct fashions according to the varied developmental and/or environmental inputs they receive in their role of ‘responsibility’ (as discussed in Chapter 4, §4.5), no one particular token manifestation could capture the generative prowess of those properties, and hence no collection of such particularised instances of those structures of the sort which typify ‘species’ can sufficiently epitomise the essence of a natural kind.30 That said, it’s clear that my theory must be accompanied by a certain amount of epistemic humility with respect to the ‘matter’, or morphological profiles of natural kinds. For the expectation that we may be able to

Figure 5.1 Hylomorphic Essentialism: Schematic simplified representation of the relationship between form (f), matter (m), and organismal morphology— here, of a horned beetle. The form’s constitutive collection of μ-dispositions (μD1—μD3) depict their realisations in the regulatory architecture of distinct module GRNs (as in Figure 3.1). The dotted line projection from each μ-disposition in f represents its topological morphospace (as in Figure 4.1), the collection of which comprise the matter (m). As before, the low-lying attractor basins within those spaces represent distinct disc-wide expression profiles which correspond to quantitatively and qualitatively distinct developmentally privileged permutations of its associated morphological feature (here, of the cephalic and thoracic horns, and the abdomen/elytra). The upward-reaching arrows illustrate those permutations: the solid arrows point toward possible, though unrealised permutations (encircled in dotted lines), while the dotted arrows point toward the actually developed permutations which collectively constitute an organism’s exhibited morphology.

112  The Essence of Natural Kinds fully “map out” the generative prowess of any particular μ-disposition by exhaustively cataloguing every contour of its associated morphospace is rather unrealistic. According to my theory, while there is a proscribed limit on the possible variation of the token manifestations of a μ-disposition allowed by and encompassed within its manifestation type, elucidating the “ontological boundaries” of that type and subsequently being able to reliably determine which morphological variations properly “belong” to it (and thereby also which are generatively “out of bounds”) would no doubt require a not insubstantial amount of painstakingly precise empirical research.31 Importantly, however, being humble in this respect does not consign us to philosophical ignorance: as has been illustrated throughout this chapter, the metaphysical framework of my theory allows quite a lot to be said about the matter, or morphological profiles of natural kinds—not only what they are, but what they are not, and why this is the case. Throughout the course of this chapter, much has been said about both the ‘matter’ and the ‘form’ of a natural kind. My hope is that, in answering the no such set objection by utilising the ontological framework established in the previous chapters, the definition of and relation between these two aspects of natural kinds in my theory has been made significantly more perspicuous. In the context of this chapter, this clarificatory work has served a simple, though vitally important purpose—namely, the illustration of the way in which my theory of biological natural kind essentialism is firmly anchored on the shore of evolutionary ideology, unmoved by the waves of contingency and instability which might be thought to wash it away. In the next and final chapter, however, those crests will crash into that theory anew, and its metaphysical compatibility with the ontology of evolution will again be put to an important test.

Notes 1 Cf. Wilson (1999) and Okasha (2002). I address the apparent conflict between a neo-Aristotelian theory of biological natural kind essentialism and the theory of evolution with respect to the “fundamentality” of property variation in more detail in Chapter 6. 2 Griffiths (2002: 77). 3 See Chapter 1, §1.2. 4 For more on the heuristic utilisation of genome sequence specificity in systematic taxonomies and the possibility and potential pitfalls of the general project of “DNA barcoding”, see Blaxter (2004) and Will and Rubinoff (2004). 5 The natural kind essentialist could avoid these complications by “biting the bullet” here, as Wilkerson (1993) does, maintaining that genomic properties constitute the essences of natural kinds and that, as a consequence, such kinds are much more prodigious than previously assumed—e.g. for every distinct set of genetic properties, there exists a distinct natural kind. I find this move unattractive for a variety of reasons, most notably because it effectively spoils the status of natural kinds as ‘information stores’ by disrupting the character of the real-nominal link which grounds inductive inferences about their members—see Chapter 1, §1.2.

The Essence of Natural Kinds  113 6 Cf. Chapter 3, §3.2. 7 As discussed in Chapter 3, §3.3. 8 For more on the concept of morphological ‘autonomisation’, see Müller and Newman (1999), and Müller (2003). See True and Haag (2001) for a discussion of the associated phenomenon of ‘developmental systems drift’. 9 The appellation of the neo-Aristotelian essence of a natural kind as its ‘form’ is rather likely to result in a not a few furrowed brows, as it is certainly no exaggeration to say that the prevailing condition within contemporary philosophy of biology is, as Marjorie Grene (1972: 409) puts it, one of eidophobia—or, a fear of form. However, there are forms and then there are forms, and before one passes judgement on a theory of essence which makes use of that category, one must be clear on precisely what ‘form’ amounts to within that theory. As briefly eluded to in Chapter 1 (§1.4), and as implicitly illustrated throughout this and the following chapter, the neo-Aristotelian concept of ‘form’ I employ is directly inspired by, though not wholly identical to its progenitor. 10 Generally, referring to the set of properties which are casually correlated with the essence of a natural kind as its ‘matter’, rather than its ‘nominal set’ is probably to be preferred: as briefly discussed earlier (in Chapter 1, §1.1), the latter designation may give the undesirable impression that the membership criteria of such a set is principally decided by nous, rather than by nature. 11 Cf. Chapter 3, §3.1. 12 One might be tempted to compare a set of μ-dispositions to a ‘homeostatic mechanism’ of the sort employed in the now popular homeostatic property cluster theory of natural kinds, given that they both allow that every member of a kind need not be entirely morphologically identical. However, a closer reading reveals that the two are only superficially similar: the mechanism, as it were, by which this allowed in my theory is necessarily a fundamentally intrinsic one, “of the nature” of a stable, or commonly possessed set of natural properties. For more on the homeostatic property cluster theory of natural kinds, see Boyd (1999), and Wilson et al. (2007). 13 This in line with the modal fount component of natural kind essentialism, as discussed in Chapter 1, §1.2. 14 As described in detail in Chapter 4, §4.5. 15 I note in passing that Aristotle too rather explicitly declared this sort of regular and repeatable variation to be “of the nature” of a natural kind. In On the Generation of Animals IV.4 (770b13–24), he gives the example of the existence of so-called ‘smoky vines’: “Even in the case of monstrosities, whenever things contrary to the established order but still always in a certain way and not at random, the result seems to be less of a monstrosity because even that which is contrary to nature is in a certain sense according to nature . . . for instance, there is a vine which some call ‘smoky’; if it bears black grapes, they do not judge it a monstrosity because it is in the habit of doing this very often. The reason is that it is in its nature intermediate between white and black; thus the change is not a large one nor, so to say, contrary to nature; at least, it is not a change into another nature”. 16 There will of course be cases where plasticity isn’t the primary cause of such variation, or where it’s no longer the cause of that variation—e.g. where a particular variant in a population has become ‘canalised’ (cf. Flatt 2005). Some cases of intra-kind morphological variation, for instance, may occur in populations that commonly possess the same set of μ-dispositions as a result of some members possessing “extra” generative mechanisms (gained perhaps through various genetic duplication and/or mutation events) which have significant “downstream” developmental consequences. These sorts of cases however pose no explicit difficulties for my theory. Indeed if, as that theory suggests, natural

114  The Essence of Natural Kinds kinds both participate in and persist through evolutionary processes, the prevalence of this sort of variation is to be expected. 17 Cf. Chapter 1, §1.1. 18 I borrow the term ‘hierarchical disconnect’ from Ereshefsky (2012). 19 It’s worth noting, however, that interesting work has been done to experimentally demarcate ‘meta-networks’ of such mechanisms which are associated with the dynamical topologies of μ-dispositions (Jaeger and Monk 2014), research which may perhaps reveal the existence of a privileged sub-set of mechanistic components which all members of that network share—so-called ‘core’, ‘kernel’, or ‘character identity’ elements (Davidson and Erwin 2006; Wagner 2007, 2014). 20 For a good overview of the RNA-world hypothesis, see Gesteland et al. (2006). 21 As that characteristic role is a highly specific one, it may be the case that every class of mechanisms which could realise those properties must have a certain amount in common, given that any such realiser will have a rather precise “job to do”. While this is of course far and away from bolstering a reductionist position, it does suggest that the relation between realised and realiser is not entirely contingent, in that the conditions for the former’s existence are in some way significantly tied to the compositional and structural character of the latter. The nuances of this close though “non-collapsible” connection were in fact first noted by Aristotle, as captured by his concept of ‘hypothetical necessity’—see principally Physics II.9. 22 I discuss this concept of ‘stability’ and its consequences in more detail in Chapter 6. 23 Cf. Chapter 1, §1.3–1.4. 24 Given that there exist morphological modules responsible for the production of fundamentally “basic” organismal features which are highly conserved among entire Domains (e.g. those underpinned by ‘homeobox’ GRNs), it is a consequence of my theory that every natural kind will have some proportion of its essential properties in common with every other—these being, as it were, ontological traces of their shared evolutionary origins. Typically then, a natural kind’s being “higher up” on the evolutionary ladder will be correlated with its having a greater number of essential properties; and likely, a greater number of unique such properties. 25 Cf. Chapter 3. 26 For more on the concept of ‘generative entrenchment’, see Schank and Wimsatt (1986), and Wimsatt (2001). 27 Cf. Chapter 4, §4.5. 28 Interestingly, this conception of ‘formal constraint’ has recently been characterised by some authors as the contemporary equivalent of Aristotelian ‘formal causation’; see, for instance, El-Hani and Pereira (2000), Deacon (2006), Moreno and Ruiz-Mirazo (2011), and Tabaczek (2013). 29 Although he is commonly understood otherwise, in my estimation, Aristotle too denied such an identification. An attentive and fine-grained reading of his biological works reveal, as James Lennox (1987, 2001 2017) has very ably illustrated, that his categories of genos and eidos were not only principally typological, rather than taxonomical, but that they were employed to model the very fact that members of a single natural kind could exhibit significant qualitative and quantitative variation among their shared, morphologically ‘generic’ features. While a detailed examination of the ways in which this metaphysical framework is mirrored in my theory of natural kinds would take the current discussion too far afield, the observant reader will find that the spirit of this Aristotelian paradigm pervades the present chapter.

The Essence of Natural Kinds  115 30 For this reason, ‘natural kinds’ could be considered on analogy with the conceptual middle of the taxonomic tree, low enough to secure a certain amount of morphological specificity for their members, but high enough to encompass the presence of significant morphological variability among those members. 31 This sort of research, which the progenitor of the very term ‘morphology’ and a prominent early proponent of a typological perspective on organismal form, Johann Wolfgang von Goethe (1749–1832), described as “der spekulative geist”, is perhaps now being made more tractable by the contemporary methodological framework of ‘morphometrics’ now employed within the field of evolutionary developmental biology to trace the developmental constraints which causally underpin the ‘variational modalities’ of organismal sub-systems. See Hallgrimsson et al. (2012), Wagner (2014), and Brigandt (2015); for recent empirical case studies, see Young et al. (2010), and Rasskin-Gutman and Esteve-Altava (2014).

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The Essence of Natural Kinds  117 Wimsatt, W. (2001). Generative Entrenchment and the Developmental Systems Approach to Evolutionary Processes. In S. Oyama, P. Griffiths, & R. Gray (Eds.), Cycles of Contingency: Developmental Systems and Evolution (pp. 219–238). Cambridge, MA: The MIT Press. Young, N., Wagner, G., & Hallgrimsson, B. (2010). Development and the Evolvability of Human Limbs. Proceedings of the National Academy of Sciences, 107(8), 3400–3405.

6 An Evolutionary Ontology

An Evolutionary OntologyAn Evolutionary Ontology

Priority, Modality, and the Natural State

In the previous chapter, the final pieces of my neo-Aristotelian theory of biological natural kind essentialism were put in place. According to my theory, the essence of a natural kind consists of a collection of dispositional properties—μ-dispositions—which are causally responsible for the specified production of the morphological profile which its members possess. In line with the intrinsically teleological nature of essential properties on my account, the characteristic causal-cum-modal role of the essences of natural kinds is to function as the ‘dynamical baüplan’ of organismal morphology: they establish organism-wide ‘morphospaces’ whose generatively privileged curvatures shape and constrain the various possible (and typical) developmental fates of their members. In laying the metaphysical foundations for and constructing the ontological architecture of my theory throughout the previous chapters, we’ve seen the ways in which it is uniquely unaffected by some of the most common and prominent objections that stem from the supposed incompatibility of any theory of its ilk with the conceptual cornerstone of the modern biological sciences—the theory of evolution. In particular, by casting its central focus on the causal mechanisms of morphogenesis in sharper relief (in Chapter 2), I’ve argued that neither the extrinsic individuation of taxonomical categories—via, for instance, the interbreeding or phylogenetic relations among groups of organisms—nor the mind-dependent structure of the ‘taxonomic tree’—qua its status as a fundamentally contingent heuristic artefact—pose any special problem for a neo-Aristotelian theory of biological natural kind essentialism. Moreover, through examining in more detail the precise relation it posits between the ‘form’ and ‘matter’ of natural kinds (in Chapter 5), I’ve argued that neither the genotypic variation which underwrites the processes of natural selection, nor the phenotypic diversity among organism populations which further perpetuate and/or result from those processes are problematic for my theory. The response to these latter worries has, however, made a particular Aristotelian theme at work within my theory of essence more prominent— one which has historically been understood to be at best inherently inimical to and at worst entirely incompatible with the principles of contemporary

An Evolutionary Ontology  119 evolutionary biology: the metaphysical priority of the unchanging over the changing. In this chapter, I examine the principal theoretical implication of this theme—a commitment to the so-called natural state model—and its intersection with the theory of evolution. I argue that the case for their unavoidable irreconcilability in three central areas—fundamentality, intrinsicality, and modality—has been significantly overstated: rather than being strictly necessary, I show that their dissonance is instead conditional upon the utilisation both of a particular explanatory framework as an authoritative guide to evolutionary ontology and an idiosyncratic interpretation of that Aristotelian metaphysical motif. By way of demonstrating the conceptual compatibility of the new science of evolutionary developmental biology (evo-devo) with the metaphysical commitments of my theory, I argue that these conditions are ones the neo-Aristotelian essentialist is not obliged—on either scientific or philosophical grounds—to accept. In so doing, the aim of this final chapter is to serve as a compelling coda for the claim that, properly understood, ‘essence’ belongs in the age of evolution.

6.1 The Natural State Model: Being, Backwards In the previous chapter, I argued that my neo-Aristotelian theory of natural kind essentialism can sufficiently answer the worries that the no such set objection raised in connection with the collective empirical datum of evolutionary biology concerning the prevalence of both genotypic and phenotypic variation among organism populations. It might yet be reasonably asked however whether, its theoretical virtues aside, the metaphysical framework entailed by that answer correctly matches-up to the one ostensibly constitutive of evolutionary biology. For note that, as the previous chapter has especially made clear, the tenets of my theory taken together make a particular metaphysical commitment concerning fundamentality. As an Aristotelian form of essentialism, that theory entails that what is fundamental about the world—and is thus primitively explanatory with respect to the biological realm—is stability, or invariance: for it posits, as we have seen (in Chapters 3 and 5), that unchanging, shared sets of kind-defining intrinsic capacities lie at the ontological “ground floor” of the causal architecture responsible for organismal ontogenesis. Consequently, that theory thereby designates variation as non-fundamental: for it posits, as we have seen (in Chapters 4 and 5), that the wide range of property mosaics peppered throughout the morphologies of the organisms that populate the natural world are principally the causal products of and thus constitute phenomena which must be explained by reference to their invariant natures or essences. This claim of metaphysical priority—a declaration of the “dominance” of the unchanging over the changing—has, however, long been viewed as one the most serious errors of biological essentialism. For because this claim

120  An Evolutionary Ontology constitutes a commitment to the so-called natural state model of organismal ontogenesis, it is nearly universally understood as standing in direct conflict with the contemporary cornerstone of our understanding of the biological realm—namely, the theory of evolution and the process of natural selection. What then precisely is the natural state model and in which respects is it incompatible with evolutionary theory? In Ernst Mayr’s (1976: 27) popular (and overtly Platonic) phrasing, according to the natural state model, “[t]here are a limited number of fixed, unchangeable ‘ideas’ underlying the observed variability [in nature], with the eidos (idea) being the only thing that is fixed and real, while the observed variability has no more reality than the shadows of an object on a cave wall”; here the Platonic eidoi are the analogical correlates of the essences of natural kinds which underlie the morphological heterogeneity prevalent among organism populations. This formulation is rather incendiary, but one can see how my theory appears at the very least to be consistent with it, given that differentiation of property possession among members of the same natural kind is on that theory conceptualised as coming about via various “accidental” (in the Aristotelian sense) exploitations of their commonly possessed, unvarying set of essential properties.1 Prima facie, the natural state model’s posit of the existence of “fixed” sets of properties at the “ground floor” of one’s ontology of the biological realm appears to be straightforwardly inconsistent with an important datum about evolution—namely, that it is a process which fundamentally relies upon the prevalence of variation, not stability. In this way, by the lights of evolutionary theory, the natural state model’s ontological perspective looks to be functionally backwards for, as Stephen J. Gould (1985: 160–161) put it, “[v]ariation is the raw material of evolutionary change [which] represents the fundamental reality of nature, not an accident about a created norm”. From the perspective of the principles of evolutionary theory, then, the claim that the biological world contains unchanging sets of properties represents not only a highly improbable state of affairs, but one whose underlying ontological assumptions are a functional non-starter, given that the existence of a substantial amount of variation among (purported) members of the same natural kind is arguably the sine quo non of the process of natural selection itself.2 However, even if, for the sake of argumentative charity, we were to grant that there exist such stable sets of properties, the problems for the natural state model are far from over. For, as Elliot Sober (1980) has convincingly argued, even if there were a stable and unchanging set of properties shared among members of a sufficiently delineated natural kind, those properties appear incapable of playing the role required of them. On my theory, the essence of a natural kind is comprised of an intrinsic set of goal-directed properties which dynamically orient its bearers toward the production of a specific ‘morphological profile’. This normative, teleological aspect of organismal development is mirrored in the parlance of the natural state

An Evolutionary Ontology  121 model according to which the essence of a natural kind is causally productive of an intrinsically privileged morphology, one which represents the ‘natural state’ of the members of that kind, with variations on this natural state representing destructive deviations being traceable to the pervading un-natural causal influences of an organism’s environment. The claim that organismal morphology is intrinsically directed to proceed along a particular set of developmental pathways, however, appears to be in conflict with the reality of a phenomenon now widely understood to play a vital role in the evolutionary process—phenotypic plasticity: for the picture that phenomenon paints is plausibly one wherein the qualitative and quantitative specificities of an organism’s morphology are principally the products of extrinsic, broadly environmental influences.3 Given this phenomenon, what ought we to make of the sense of ‘natural’ at work within the natural state model? Should we understand the natural state of an organism qua the causal product of an intrinsically goal-directed set of capacities as somehow constituting an environment-independent morphology—one whose natural “purity” is, rather unfortunately, consigned to a fate of continual corruption by the sheer ubiquity of ecological contingencies? Or perhaps, if we are to understand the natural state of an organism as consisting of an intrinsically privileged form of its morphology we should, in accepting that organismal morphology is causally correlated with the presence of extrinsic factors, declare one sort of environment as being “more natural” than every other—i.e. whichever sort is correlated with/results in the development of the “correct” form of that morphology. Needless to say, both of these options look inordinately ad hoc, and their implausibility only further undercuts the credulity of the natural state model: in light of the phenomenon of phenotypic plasticity, its claim that the essences of organisms function as the intrinsic, goal-directed developmental directives from which morphological variation ultimately derives seems altogether untenable. Indeed, from the perspective of evolutionary theory, whatever stability such sets of properties themselves enjoy, and whatever degree of normative invariability they subsequently bestow upon the groups of organisms which possess them must essentially be the mere residual by-products of the fundamentally extrinsic and accidental adaptive “forces” of natural selection. For according to Mayr’s (1961) widely accepted distinction between ‘proximate’ and ‘ultimate’ causation, even if such sets were to exist and perform the proximate role required of them by the natural state model, their very presence would be, in the final analysis, ultimately a matter determined by the influence of biotic/abiotic environmental pressures and the propogatory fluctuations of intra-population interbreeding.4 In other words, in an ontology of the biological realm suitably informed by evolutionary theory, stability, or invariance must be a metaphysically derivative phenomenon: its instances, to borrow a well-known phrase from Francis Crick (1968), simply “frozen accidents”, little more than artefactual silt shaped by the perpetual ebb and flow of selective processes.

122  An Evolutionary Ontology The natural state model’s metaphysical commitments concerning the fundamentality of invariance, the intrinsicality of ontogenesis, and the modality of morphology thus appear to undergird an ontology of the biological realm which is radically backwards: its assignment of priority and privilege effectively inverts the implicit “order of being” constitutive of evolutionary theory. Its theoretical merits notwithstanding, the conceptual competency and empirical credibility of my theory of biological natural kind essentialism in the context of contemporary evolutionary biology crucially depends upon this charge being sufficiently dismissed.

6.2 Evolutionary Ontology: A Tale of Two Syntheses The natural state model, and by implication, my neo-Aristotelian theory of biological natural kind essentialism, looks to be in trouble: if its metaphysical commitments conflict with those of a properly formed evolutionary ontology, its viability is in serious question. The severity of this charge stems from the fact that the conflict between the natural state model and evolutionary theory appears to be axiomatic—there is an incongruity here grounded not in a discrepancy among mere peripheral matters, but in an inconsistency between core principles. But does the rejection of the natural state model really follow from the very axioms of evolutionary theory? Properly evaluating that claim requires getting clearer on which principles are meant to occupy that position and why they deserve to do so. The arguments of the previous section are premised on the notion that those axioms have important implications for what constitutes a proper ‘evolutionary ontology’. But of course, evolutionary theory doesn’t explicitly posit any particular ontology of the biological realm, nor does it appear to implicitly prescribe any proscriptive guidelines with respect to constructing such an ontology. Its aims, after all, are principally hermeneutical: it offers an explanatory framework with which to interpret empirical data, rather than a set of ontological categories with which to classify that data. Plausibly, then, the principles that are axiomatic of evolutionary theory are those that concern the fundamental structure of that framework—e.g. what it grants explanatory prowess to, what it regards as explanatorily superfluous, etc. What then does the fundamental structure of that framework consist in? Likely the most common answer among both evolutionary biologists and philosophers of biology is that this structure is best broadly captured by the set of principles encapsulated in what’s known as the ‘Modern Synthesis’.5 The Modern Synthesis, which arose in the early 20th century as a result of the pioneering work of a number of biologists (chief among them perhaps being R. A. Simpson, Theodosius Dobzhansky, Ernst Mayr, George Gaylord, and Julian Huxley), is an ideological perspective on the nature of evolutionary theory in which the genomic basis of heritable morphological modification and the populational propagation mechanisms of

An Evolutionary Ontology  123 Darwinian natural selection are operatively integrated within an overarching explanatory framework with which to interpret the presence (and absence) of both organismal form and function. According to most developed form of the Modern Synthesis, utilising the collective work of R. A. Fisher, J.B.S. Haldane, and Sewall Wright, this framework’s explanatory aims are best achieved by employing the methodology of statistical analysis to track changes in the distributions of gene frequencies within and among organism populations. From the perspective of the Modern Synthesis, then, organismal morphology is essentially an adaptive by-product of undirected populational variation—a mere reflection of selective pressures filtering the random rippling of gene pools. Note that if the principles of the Modern Synthesis correctly characterise the explanatory structure of evolutionary theory, the shaping of organismal morphology is fundamentally an extra-organismal affair. To properly explain and sufficiently account for organismal morphology, according to the Modern Synthesis, appeal must be made primarily to populations and the environmental “forces” which act upon them—for it is these factors, rather than any intrinsic, intra-organismal ones, which function as the significantly determinative “difference-makers” of morphological differentiation. On this understanding, it is the extrinsic processes of natural selection in which an organism is an inadvertent participant that have causal and creative control over its morphological constitution: whatever the ‘proximate’ contribution of its developmental architecture to that morphology may be, it must be ‘ultimately’ relegated to the ranks of theoretical irrelevancy.6 Thus in the guise of the Modern Synthesis, evolutionary theory conceptualises organisms as intrinsically inert participants in the formation of their own morphologies, it being a process in which they are passively “pushed” and “pulled” by the predominant pressures within their respective populations. In this way, from the perspective of the Modern Synthesis, the “modality of morphology” is a fundamentally undirected and contingent phenomenon which has no genuinely intrinsic, intra-organismal basis—for which morphological forms an organism could have and which it must have are permitted and proscribed by the combination of intrinsic chance and extrinsic accidents. On the one hand, the key intrinsic factors which are given explanatory weight in the Modern Synthesis’ explication of organismal morphology are the resultants of randomness: the genomic mutations which provide the “raw material” of the selective processes which shape that morphology are not dynamically driven in the pursuit of any privileged direction. On the other hand, any directives which can be said to govern or guide the development of organismal morphology are, according to the Modern Synthesis, dictated by the contingencies of environmental contexts: the course that the selective processes which shape that morphology follows in any particular instance consists in a population’s navigation of whichever extrinsic, ecological pressures have managed to achieve a sufficient measure of proximal predominance.

124  An Evolutionary Ontology Thus the conceptual strictures of the Modern Synthesis demand that whatever ‘stability’ might be found among organismal morphology throughout the phylogenetic trajectory of a particular population must be a merely residual record—nothing more than the incidental afterimage of the chaotic contingencies constitutive of its selective history. This characterisation is in fact mirrored in the explanatory structure of the Modern Synthesis, which is in a certain sense “blind” to such stability: because natural selection does not (and cannot) operate upon that which is invariable within interbreeding populations, to explain, or account for organismal morphology requires an appeal to facts concerning variation—in genetic mechanisms within those populations, in pressures exerted by their environment, etc. The unchanging features of organismal morphology, then, while perhaps pertinent to the historical tracing of lineage relations, are essentially artefactual irrelevancies: their presence is not only fundamentally accidental, but explanatorily impotent.7 If the axioms which constitute the explanatory framework of evolutionary theory provide the conceptual scaffolding upon which an evolutionary ontology must be constructed, and those axioms are derived from the principles of the Modern Synthesis, it’s clear that the natural state model must be seen as resting on rather shaky ground: the fundamental structure of that framework—what it grants explanatory prowess to, what it regards as explanatorily superfluous, etc.—offers it no firm foundation. For that structure, as evinced earlier, entails that if there is a ‘natural state’ of an organism, it consists in its being the fundamentally ineffectual instrument of extrinsic and accidental environmental inconstancies. Conciliatory phraseology aside, this conception of a ‘natural state’ quite clearly constitutes a rejection of the core tenets of the natural state model—prima facie, it prescribes an ontology of organisms with which that model is profoundly at odds. What are we to conclude then? If the axioms of evolutionary theory entail that its metaphysical hierarchy represents an erroneous inversion of the “order of being”, should not the natural state model be considered scientifically suspect, if not entirely empirically unsound? Yes, unquestionably so: any proposed philosophical system that hopes to correctly capture the nature of the biological world which stands in conflict with the well-attested postulates of evolutionary theory ought to be regarded as essentially specious. Does the acceptance of evolutionary theory thus necessarily entail the rejection of the natural state model? As we have seen, if one understands that theory as being constituted from the principles of the Modern Synthesis, their incompatibility is all but unquestionable. Note, however, that this is a form of hypothetical, rather than strict, necessity: that rejection follows on the assumption that evolutionary theory is embodied by those principles. If one is to dismiss the natural state model on the grounds that it is irreconcilable with evolutionary theory, presumably this “weaker” form of necessity would need to be strengthened—a feat minimally achieved if it can be shown that the aforementioned assumption has no reasonable

An Evolutionary Ontology  125 alternatives. While performing this task might have once been considered fairly trivial, that is plausibly no longer the case: for the Modern Synthesis is no longer the most modern synthesis, and its explanatory framework no longer the only operative underpinning of evolutionary theory. Indeed, as I will illustrate in what follows, the more “modern synthesis” at the heart of contemporary evolutionary developmental biology, or ‘evo-devo’ posits an explanatory framework whose implications for an evolutionary ontology are not inimical to, and are in fact supportive of, the core tenets of the natural state model. When viewed through the explanatory prism of evo-devo, the dissonance between evolutionary theory and that model’s metaphysics is effectively dissipated. Although the conceptual roots of evo-devo reach far back into the history of the biological sciences, it bloomed into a reasonably well defined and widely respected discipline only rather recently in the latter half of the 20th century.8 This relatively late occasion is not accidental, and its many contributing factors came together in the context of the growing sense of dissatisfaction with the explanatory prowess of the Modern Synthesis framework prevalent among evolutionary biologists reaching somewhat of a breaking point: the omnipotence of the mechanisms of natural selection to account for organismal morphology enshrined in the ‘adapationist’ paradigm of the Modern Synthesis was now being continually thrown into serious question. As the evident inability of its explanatory framework to sufficiently account for a wide range of morphological phenomena—including, but not limited to, the discernible biases in character variation within phylogenetic trajectories, and the origin, prevalence, and persistence of homological structures in both parallel and convergent phylogenies—became increasingly apparent, an essential oversight within the Modern Synthesis perspective emerged: its systematic neglect of the developmental architecture responsible for organismal ontogenesis. In fact, as many have now noted, this ignorance is not the result of mere happenstance, but instead reflects the core commitments of the Modern Synthesis: in that framework, the causal structure of development is effectively “black boxed”—for whatever happens betwixt ‘gene’ and ‘form’ has no explanatory role to play in the statistical analysis of gene frequencies within organism populations.9 Indeed, that box, already darkened by the explanatory axioms of the Modern Synthesis, had cause to remain unilluminated— the methodological failings inherent in the formulation of Ernst Haeckel’s ‘biogenetic laws’, and the virulent rejection of the vitalist principles associated with the organism-centred analyses of the ‘rational morphologists’ (e.g. Driesch, Goethe, Owen, von Bertalanffy, et al.) inspired a not insignificant amount of reticence among biologists toward research which might shed light upon it.10 Recently, however, due to significant technical and technological advances in experimental embryology (accelerated in no small part by the innovatory work of Wilhem Roux and Hans Spemann), conducting comparative analyses of morphologically salient developmental systems

126  An Evolutionary Ontology across distinct organism populations has become a task both tangible and tractable—and with the opening of that “black box”, a fundamental reevaluation of the viability of organism-centred analyses of evolutionary phenomena has followed. The explanatory framework of evo-devo—an operative synthesis of the study of development with the study of evolution—effectively collapses the classic division between ‘proximate’ and ‘ultimate’ causation: its central focus is on the role that the generative mechanisms of organismal morphology play within the process of evolution. Evo-devo’s bestowal of evolutionary significance to developmental factors not only notably expands the conceptual reach of evolutionary theory but also courts a fundamental shift in its explanatory emphases: the selective forces of an organism’s environment and their adaptive influence upon the allele dynamics of its populational gene pool are relegated from their reign and the generative capacities of intra-organismic developmental architecture positioned in a place of primacy. In other words, as Gerd Müller (2007: 947) puts it, in stark contrast to the stratagem of the Modern Synthesis, “evo-devo moves the focus of evolutionary explanation from the external and contingent to the internal and inherent”. As I see it, this ideological contrast is one principally drawn along the lines of the distinction between ‘categorical’ and ‘dispositional’ properties.11 The attentive reader will have noted that the Modern Synthesis essentially conceptualises the developmental systems of organisms—and thus organisms themselves—as operating categorically with respect to their role in the process of evolution: as fundamentally passive participants in that process, they place no modal constraints upon its proceedings, their contributions therein the mere happenstance resultants of their being pushed and pulled by the contingencies of their extrinsic causal contexts. From the perspective of evo-devo, however, the developmental systems of organisms play a dispositional role within that process. For its explanatory framework makes principal appeal to the prowess of the intrinsic “generative rules” of those systems to provide the potentiality for morphological variation upon which the vagaries of their environment and the processes of natural selection may subsequently act; these systems are, in other words, conceptualised as causally responsible for that variation (as per Chapter 4).12 Evo-devo thus recognises these systems’ vital role in shaping the “modality of morphology”: their dynamical architecture not only establishes ‘developmental constraints’ which proscribe the quantitative and qualitative limits of the characters they are capable of producing but also permissively privileges the developmental trajectories with which the ‘evolvability’ of those characters is endowed; the role these systems play in the process of evolution is, in other words, a richly teleological one (as per Chapters 4 and 5).13 Consequently, the explanatory framework of evo-devo views the shape and structure of phylogenetic lineages not as an aleatory artefact, but as a reflection of the generative dynamics of developmental systems causal underwriting

An Evolutionary Ontology  127 of a directed exploration of “morphological space” over evolutionary time: according to its ‘structuralist’ perspective, morphological homology echoes organismal ontology.14 Evo-devo is thus a science of dispositions: it posits that the central participants in the process of evolution are systems whose intrinsic dynamical structure both delivers and delimits its possible directions, thereby actively undergirding the regularities which non-accidentally pattern its actual paths.15 In the context of this chapter’s discussion, this observation is not trivial. For note that the metaphysical commitments which characterise the natural state model—concerning the fundamentality of invariance, the intrinsicality of ontogenesis, and the modality of morphology—all broadly align with those of a dispositional ontology: these are properties which function as the intrinsically causal basis of end-directed, context-dependent state-change (as discussed in Chapters 3–5). Given that the construction of a proper ‘evolutionary ontology’ is to be constrained by the explanatory structure of evolutionary theory, what one takes that structure to consist in has important consequences—and the contrast in the choice between the Modern Synthesis and evo-devo in this respect could not be clearer.16 If evolutionary theory must characterise organismal morphology as an essentially extrinsic and accidental phenomenon, its categorical conception of organisms is inconsistent with the metaphysic of the natural state model. If, on the other hand, evolutionary theory characterises organismal morphology as an intrinsic and non-contingent phenomenon, its dispositional conception of organisms is perfectly compatible with that model’s metaphysic. The evident availability and well-attested viability of this latter characterisation makes one thing particularly plain: a theory of the biological realm qualifying as sufficiently scientifically informed by the strictures of evolutionary theory need not entail its rejection of the natural state model.

6.3 The Nature of Essence The alignment of the metaphysical commitments of the natural state model with the axioms evolutionary theory is especially important in the context of my theory. Of course, one can affirm that evo-devo, in virtue of offering an explanatory framework which makes appeal to dispositional properties, is not inimical to that model without thereby accepting that model: alignment is one thing, entailment another. However, in my neo-Aristotelian theory of biological natural kind essentialism, dispositional properties occupy the centre stage, and explicating what the ‘natural state’ amounts to in that theory cannot be done without them. As I illustrate next, this is not inconsequential: it underlies the philosophical compatibility of my theory with an ‘evolutionary ontology’.17 The apparent inconsistency between the concept of a ‘natural state’ and the principles of such an ontology stems from the former’s representing an organism’s privileging of a particular morphology in an environment-independent

128  An Evolutionary Ontology fashion in a way which renders variation an effectively derivative and incidental phenomenon.18 By the lights of my theory, however, this conflict can be shown to be largely the result of a metaphysical misunderstanding. It’s certainly true that, according to that theory, the essence of a natural kind is comprised of dispositional properties which dynamically direct the process of morphological development. But although that theory declares the causal privileging of organismal ontogenesis to be the primary function of these properties, the nature of this privileging is teleologically complex. As we have seen (in Chapter 4), in their role as causally responsible for organismal morphology, the generative competency of μ-dispositions to produce particular morphological features cannot be captured by their production of a single, qualitatively and quantitatively precise instance of that feature. Instead, those properties causally undergird the production of an expansive, teleologically textured morphospace, and their manifestations are thus necessarily multi-dimensional (as discussed in Chapters 4 and 5). There are many important implications of this conception of essential properties, but the most pertinent one is this: because the essence of a natural kind is defined by a set of determinable developmental morphospaces, particular collections of determinate end-states within those topologies cannot possibly capture the richly comprehensive morphological terrain which the ontological division of ‘natural kind’ carves out.19 Accordingly, the objection that, in stark contrast to the picture painted by the process of evolution wherein the vagaries of selection plausibly rule out any instance of organismal morphology as being “more natural” than any other, an organism’s membership to a specific natural kind necessarily entails its generatively privileging a particular morphology simply misses its mark. On my theory, there’s no sense in which any of the particularised manifestations of a kind-defining, organism-wide morphospace is “more natural” than any other: each represents a set of possible permutations of the morphological architecture afforded by the dynamical capacities of its collection of μ-dispositions.20 Thus the only ‘natural state’ to which the metaphysics of my theory of biological natural kind essentialism is committed is one of specified morphological potentiality: what is “of the nature” of a natural kind is its functioning as a dynamically plastic and multifaceted developmental template for its members’ ontogenesis (as described in Chapter 5). Furthermore, according to the theory I have proposed, while it’s certainly true that the modality of morphology is conceptualised as being a fundamentally intra-organismal affair, it is not an environment-independent one. As we have seen (in Chapter 4), in virtue of the causal primacy of μ-dispositions, the essence of a natural kind intrinsically shapes and constrains the various possible and typical courses of its members’ morphological development. However, as illustrated in the explication of those properties’ role as causally responsible for organismal morphology, this does not thereby render ontogenesis an exclusively internal process: on the contrary, given its functional-cum-mediatory station as the causal channel

An Evolutionary Ontology  129 of state-transition, performing the role of responsibility necessarily requires the polygenic “input”, or influence of extrinsic causal factors. Indeed, on my theory, it is “of the nature” of kind-defining essential properties to contain within them the generative potential for environmentally dependent variation on their associated morphological structures.21 The intrinsic natures of those properties may determine the expanse and extent of that capacity, but the causal role they perform in the process of ontogenesis ensures that it is one which cannot be exercised in a context-independent fashion. Does the ontological framework of the theory of biological natural kind essentialism, in stark contrast to the ordo entis seemingly entailed by the evolutionary process, render morphological variation a non-fundamental and derivative phenomenon? My theory certainly declares that phenomenon to be ontologically ‘derivative’ in an important sense: as we have seen (in Chapter 5), according to that theory, the intra-organismal actualisation and subsequent inter-organismal allocation of such variation is principally the environmentally tokened causal product of the intrinsic generative potential of the μ-dispositions which comprise the essences of natural kinds. At the same time, however, there is a significant sense in which this very aspect of my theory, upon closer inspection, designates morphological variation a fundamental and non-derivative phenomenon. For although the essences of natural kinds may function as centres of ontological invariability, on my theory, their “stability” does not render them static—indeed, as outlined earlier, the dynamic capacity for specified variation is an intrinsic and fundamental aspect of the properties which comprise the essences of natural kinds. In this way, the metaphysical invariability which characterises the essences of natural kinds on my account is best conceptualised as a form of ‘homeodynamism’, rather than homeostasis.22 Because the essences of natural kinds consist of collections of μ-dispositions, what must essentially “remain the same” in members of the same natural kind is not the production of any particular morphology, but the possession of a particular set of dynamical capacities which undergird an expansive generative repertoire for the production of a wide range of environmentally correlated morphologies. Notably, while the former, homeostatic conception of essence might entail a metaphysic which necessitates a kind-wide morphological uniformity of the sort which would effectively relegate intra- and inter-organismal variation a statistically insignificant, if not impossible occurrence, the same cannot be said for the latter, homeodynamic conception. Thus according to my theory of biological natural kind essentialism there is a nuanced sense in which variation represents, as Gould (1985: 160–161) put it, “the fundamental reality of nature”—indeed, the viability of that theory depends on that being the case. As should by now be evident, although the metaphysics of my theory align with those implicit in the natural state model, the particular fashion in which they do so is rather unique—and with dispositional properties

130  An Evolutionary Ontology at its conceptual centre, that theory plausibly avoids the problematic consequences which might plague other theories of its ilk. Properly understood, its proposed ontological underpinning of the ‘natural state’ which accompanies the essences of natural kinds provides a picture of the biological world which both allows and accounts for the process and products of evolution. For, contrary perhaps to other more primitive forms of natural kind essentialism, the metaphysical framework of the theory I have offered provides an ontologically operative foundation for the adaptive evolution of organisms—a plausibly indispensable requirement for any properly formed ‘evolutionary ontology’. As Denis Walsh (2006) has recently illustrated, and in accordance with the aforementioned synthesis principles of evo-devo, the process of ‘adaptive evolution’ (minimally) requires that organismal ontogenesis exhibits two key features: stability and mutability. On the one hand, the survival and subsequent propagation of organisms— something without which the evolutionary process could quite clearly not occur—requires that their developmental architecture be sufficiently ‘stable’: the functional integrity of the intricate dynamics of those systems must be suitably “buffered” against the potentially disruptive influences engendered by its environment in such a way that the proper performance of its particular generative role is not substantially subject to every contingent whim of its ever-changing causal context. Organismal ontogenesis, in other words, must be considerably and consistently resilient to alteration. On the other hand, however, the differential divergence of organismal morphology in accordance with variations in environmental pressures—something without which the evolutionary process (qua a ‘selective’ process) could quite clearly not occur—requires that those same systems be sufficiently ‘mutable’: they must be capable of producing functionally viable dynamical “solutions” to the causal demands engendered by changes in their environmental conditions.23 Plausibly, then, any metaphysical framework of the biological world that is to be designated as genuinely able to undergird an ‘evolutionary ontology’ must in some way possess the theoretical resources to adequately account for both of these requirements. I contend that if, as I have proposed, the neo-Aristotelian essences of the natural kinds to which organisms belong are comprised of collections of μ-dispositions, these requirements are easily met—for from these properties flow both a power to change (mutability) and a limit on change (stability). In fact, both of these aspects are grounded in the central metaphysical feature of those properties—their teleological directedness. As we have seen, that directedness encompasses a complex, multi-dimensional capacity, one captured by the topologically textured mapping of an entire morphospace. As earlier illustrated (in Chapter 3, §3.3 and Chapter 4, §4.5), the geometrical curvatures of that space—the width, depth, and slope of the channels which flow into its low-lying basins—reflect the dynamical ground of both its persistent and pleonastic production of particular developmentally privileged end-states: they reflect, in other words, the shape of the intrinsic

An Evolutionary Ontology  131 constraints which furnish the process of organismal ontogenesis with the requisite degree of generative robustness, or stability. At the same time, however, in representing the causal responsibility of μ-dispositions (as described in Chapter 4), these morphospaces also reflect the dynamic plasticity of the generative prowess of these properties to produce a wide array of environmentally correlated, quantitatively and qualitatively distinct permutations on their generatively specified morphological features: they reflect, in other words, the rich polygenic capacity for pleiotropic morphological variation which furnishes the process of organismal ontogenesis with the requisite flexibility, or mutability. In this way, according to my neo-Aristotelian theory of biological natural kind essentialism, the ontogenetic “balancing act” between stability and mutability which serves as an operative prerequisite for the process of adaptive evolution arises naturally, as it were, from the very nature of organisms: on that theory, and in alignment with the aforementioned theoretical emphases of evo-devo, it is the dynamical nature of essence typified by (to borrow Goethe’s phrasing) this “beautiful concept of power and limit” which itself grounds and gives rise to Darwin’s “endless forms most beautiful”.24 Thus in this respect, the conception of the ‘natural state’ implicit in my theory is underpinned by a metaphysical framework which is not in conflict, but instead perfectly consistent with the theoretical parameters of a properly formed ‘evolutionary ontology’. Indeed, as I’ve illustrated throughout this chapter, the conflict between the natural state model and an evolutionary ontology is, in the end, only apparent: it is an antagonism conditional upon the acceptance both of a particular explanatory framework as correctly characterising evolutionary theory and a particular construal of that model’s metaphysical commitments. Neither of these conditions, as I have shown, are ones the neo-Aristotelian essentialist is required to accept. The new explanatory framework of evo-devo and the concordant disposition-based essentialism of my theory together offer an alternative appraisal of the scientific and philosophical viability of natural kind essentialism in the age of evolution.

Notes 1 In the Aristotelian sense, a property is ‘accidental’ if it “flows from” and is causally grounded in the essence of an entity. See Gorman (2014) for a recent discussion. 2 Cf. Wilson (1999: 190) and Okasha (2002: 197). 3 On the evolutionary importance of phenotypic plasticity, see West-Eberhard (2003) and Fusco and Minelli (2010). 4 This distinction was discussed in the context of the explanatory role of taxonomical categories in Chapter 2, §2.3. 5 The depiction of the Modern Synthesis presented next assumes the reader’s general familiarity with the subject and is meant to highlight certain themes pertinent to the current discussion rather than serve as an exhaustive description of its theoretical nuances. For an excellent collection of papers on the subject, see Mayr and Provine (1998).

132  An Evolutionary Ontology 6 The characterisation of natural selection as being ‘causal’ and/or ‘creative’ is admittedly contentious—the latter perhaps particularly so. Interestingly, both Dobzhansky and Huxley were unafraid to place emphasis upon the “creativity” of natural selection in the process of evolution (Depew and Weber 2017) and, more recently, Stephen J. Gould (1977: 44) described that creativity as constituting the very “essence of Darwinism”; see Beatty (2016) for an excellent historical discussion on the subject. Whether and in what sense selective processes are genuinely ‘causal’ is the subject of a long-standing and substantial debate in the philosophy of biology—see Matthen and Ariew (2002) and Otsuka (2016). For the purposes of the present discussion, the appellations ‘causal’ and ‘creative’ are only utilised to highlight the privileged explanatory prowess of that process with respect to organismal morphology in the context of the Modern Synthesis, and so I here take no stance on these nuanced interpretive issues. 7 I borrow the metaphor of the ‘blindness’ of the Modern Synthesis from Amundson’s (2005: 169–189) discussion of ‘Mendelian blind spots’ in population genetics. 8 In what follows, I offer only a brief summary—rather than an exhaustive retelling— of the historical advent of evo-devo: the interested reader is encouraged to consult Laubichler and Maienschein (2007) and Amundson (2005) for more in-depth examinations of both the genesis and consequences of this event. Furthermore, in service to its dialectical aims, this section’s discussion highlights only a few central themes of evo-devo, which is today a rather broad church encompassing a multitude of conceptual emphases and research programmes: for more comprehensive overviews, see Minelli and Fusco (2008) and Love (2015). 9 The Modern Synthesis’ theoretical disinterest and dismissal of organismal developmental systems was first described as “black boxing” by Hamburger (1980), though he viewed it as an incidentally necessary by-product of its explanatory aims, and thus not problematic per se. The diminished role of developmental systems in the explanatory structure of the Modern Synthesis and its reinvigoration in the origins of evo-devo is expertly surveyed in Amundson (2005). 10 Cf. Allen (2007). 11 Cf. the initial characterisation of this distinction in Chapter 3, §3.1. 12 The ‘intrinsicality’ of the capacity of developmental systems to produce heritable morphological variation is reflected in Gunter Wagner’s (2014) apt characterisation of evo-devo as a theory of ‘variational structuralism’, and in the sentiments of Hendrikse et al. (2007) that the “proper focus” of evo-devo is the ‘evolvability’ of such systems. 13 For more on the integrated dual modal role which developmental systems play in organismal ontogenesis in the evo-devo framework, see Brigandt (2007, 2015), Amundson (1994, 2005), and Hendrikse et al. (2007). 14 This perspective on the phylogenetic record conceptually mirrors the dispositionalist understanding of ‘laws of nature’ as patterns of regularities shaped by the intrinsically causal natures of properties—see Mumford (2004). For more on evo-devo and ‘structuralism’, see Amundson (2005). 15 I’ve previously elsewhere explored these themes in some detail—see Austin (2017b) and Austin and Nuño de la Rosa (2018). 16 Although this stark ideological contrast reflects the existence of a deep divide between the explanatory emphases of the two frameworks, their associated research programmes do not operate on distinct dominions—they are, after all, largely united in their explanatory aims: the origin and preservation of organismal morphology, the causal structures underlying the phylogenetic record, etc. Most evo-devo researchers view the discipline as an extension of the Modern Synthesis, or else a novel, though non-exclusionary synthesis of that synthesis

An Evolutionary Ontology  133 with the study of developmental mechanisms—see Müller (2007), Hall (2012), and Pigliucci and Müller (2010). 17 This section closely tracks the discussion of this topic found in Austin (2017a). 18 As discussed earlier in §6.1. 19 Cf. Chapter 5, §5.3. 20 The same goes, mutatis mutandis, for the notion of ‘perfection’ of the sort typically associated with the rational morphologists. Goethe, for instance, maintained that some organism’s expressions of a particular morphological feature were “more perfect” than others—‘perfection’ being largely coextensive with ‘most developed/articulated’ (Lenoir 1987). On my view, it would be more apt to describe every particularised form of a specific morphological feature as imperfect—in the sense that, as outlined in Chapter 5, §5.3, each is necessarily a limited expression of the generative potential of the μ-disposition which causally undergirds the production of that feature. 21 Cf. Chapters 4 and 5. 22 This conception of ‘homeodynamism’ might also usefully be employed in explicating the metaphysical ground of the ‘diachronic unity’ of individual organisms— see Austin and Marmodoro (2017). 23 Such solutions may be subsequently propagated within organism populations by the process of ‘genetic assimilation’ (Waddington 1942), or ‘genetic accommodation’ (West-Eberhard 2003), and promote the appearance of significant evolutionary novelties. See Pigliucci and Murren (2003), and Moczek et al. (2011). 24 This phrase is featured in Goethe’s poem ‘The Metamorphosis of Animals’ (1806). The colourful description of the products of evolution is, of course, Darwin’s own, in On the Origin of Species (1859).

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134  An Evolutionary Ontology Brigandt, I. (2015). From Developmental Constraint to Evolvability: How Concepts Figure in Explanation and Disciplinary Identity. In A. Love (Ed.), Conceptual Change in Biology: Boston Studies in the Philosophy and History of Science (Vol. 307). Dordrecht, The Netherlands: Springer. Crick, F. (1968). The Origin of the Genetic Code. Journal of Molecular Biology, 38(3), 367–379. Darwin, C. (1859). On the Origin of Species. London: John Murray. Depew, D., & Weber, B. (2017). Developmental Biology, Natural Selection, and the Conceptual Boundaries of the Modern Synthesis. Zygon, 52(2), 468–490. Fusco, G., & Minelli, A. (2010). Phenotypic Plasticity in Development and Evolution: Facts and Concepts. Philosophical Transactions of the Royal Society B, 365(1540), 547–556. Goethe, J. W. (1806). Goethe, Selected Poems (Vol. 1, C. Middleton, Ed.). Princeton: Princeton University Press, 1994. Gorman, M. (2014). Essentiality as Foundationality. In D. Novotny & L. Novak (Eds.), Neo-Aristotelian Perspectives in Metaphysics (pp. 119–137). London: Routledge. Gould, S. J. (1977). Ontogeny and Phylogeny. Cambridge, MA: Harvard University Press. Gould, S. J. (1985). The Flamingo’s Smile: Reflections in Natural History. New York: W.W. Norton & Co. Hall, B. (2012). Evolutionary Developmental Biology (Evo-Devo): Past, Present, and Future. Evolution: Education and Outreach, 5(2), 184–193. Hamburger, V. (1980). Embryology and the Modern Synthesis in Evolutionary Theory. In E. Mayr & W. Provine (Eds.), The Evolutionary Synthesis (pp. 97–112). Cambridge, MA: Harvard University Press. Hendrikse, J., Parsons, T., & Hallgrimsson, B. (2007). Evolvability as the Proper Focus of Evolutionary Developmental Biology. Evolution & Development, 9(4), 393–401. Laubichler, M., & Maienschein, J. (2007). From Embryology to Evo-Devo: A History of Developmental Evolution. Cambridge, MA: The MIT Press. Lenoir, T. (1987). The Eternal Laws of Form: Morphotypes and the Conditions of Existence in Goethe’s Biological Thought. In F. Amrine, F. Zucker, & H. Wheeler (Eds.), Goethe and the Sciences: A Reappraisal (pp. 17–28). Dordrecht, The Netherlands: Springer. Love, A. (Ed.). (2015). Conceptual Change in Biology: Scientific and Philosophical Perspectives on Evolution and Development. New York: Springer. Matthen, M., & Ariew, A. (2002). Two Ways of Thinking about Fitness and Natural Selection. The Journal of Philosophy, 99(2), 55–83. Mayr, E. (1961). Cause and Effect in Biology. Science, 134(3489), 1501–1506. Mayr, E. (1976). Evolution and the Diversity of Life. Cambridge, MA: Harvard University Press. Mayr, E., & Provine, W. (Eds.). (1998). The Evolutionary Synthesis: Perspectives on the Unification of Biology. Cambridge, MA: The MIT Press. Minelli, A., & Fusco, G. (Eds.). (2008). Evolving Pathways: Key Themes in Evolutionary Developmental Biology. Cambridge: Cambridge University Press. Moczek, A., Sultan, S., Foster, S., Ledon-Rettig, C., Dworkin, I., Nijhout, H. F., et al. (2011). The Role of Developmental Plasticity in Evolutionary Innovation. Proceedings of the Royal Society B, 278(1719), 2705–2713.

An Evolutionary Ontology  135 Muller, G. (2007). Evo-Devo: Extending the Evolutionary Synthesis. Nature Reviews: Genetics, 8, 943–949. Mumford, S. (2004). Laws in Nature. London: Routledge. Okasha, S. (2002). Darwinian Metaphysics: Species and the Question of Essentialism. Sythese, 131(2), 191–213. Otsuka, J. (2016). A Critical Review of the Statisticalist Debate. Biology and Philosophy, 31(4), 459–482. Pigliucci, M., & Muller, G. (2010). Evolution: The Extended Synthesis. Cambridge, MA: The MIT Press. Pigliucci, M., & Murren, C. (2003). Perspective: Genetic Assimilation and a Possible Evolutionary Paradox: Can Macroevolution Sometimes Be So Fast as to Pass Us By? International Journal of Organic Evolution, 57(7), 1455–1464. Sober, E. (1980). Evolution, Population Thinking, and Essentialism. Philosophy of Science, 47(3), 350–383. Waddington, C. H. (1942). Canalization of Development and the Inheritance of Acquired Characters. Nature, 150, 563–565. Wagner, G. (2014). Homology, Genes, and Evolutionary Innovation. Princeton: Princeton University Press. Walsh, D. (2006). Evolutionary Essentialism. British Journal of the Philosophy of Science, 57(2), 425–448. West-Eberhard, M. (2003). Developmental Plasticity and Evolution. New York: Oxford University Press. Wilson, R. (1999). Realism, Essence, and Kind: Resucitating Species Essentialism? In R. Wilson (Ed.), Species: New Interdisciplinary Essays (pp. 187–208). Cambridge, MA: The MIT Press.

Conclusion

ConclusionConclusion

This book has a singular aim: to propose a novel theory of biological natural kind essentialism—one formed from philosophical insight and informed by scientific knowledge. At the centre of this neo-Aristotelian theory are dispositional properties: in virtue of their functioning as the dynamically rich causal capacities which generatively ground and govern the ontogenesis of organismal morphology (Chapter 3), it is an organism’s possession of a specific set of these properties which ontologically demarcates it as a member of a particular natural kind (Chapter 1). According to that theory, the essences of natural kinds are typological, rather than taxonomical: they are natural collections of intrinsic properties which represent the ontological “joints” of the biological ream around which any of our ultimately successful conceptual schemas must carve (Chapter 2). Being comprised of these uniquely powerful properties, the essence of a natural kind thus performs a primary role in the directed development of organismal morphology, one which consists in the complex dynamical balancing of causal control and context-sensitivity (Chapter 4). In this role, the essence of a natural kind is not only an invariable anchor in a sea of extrinsic evolutionary contingency, but the inherent fount of the variability which non-accidentally shapes its selective waves (Chapters 5 and 6). Refined by the conceptual pressures of contemporary biology and developed within the metaphysical framework of a neo-Aristotelian ontology, an evolved essentialism is at hand. In formulating this theory, this book has unapologetically traversed an uncommon trajectory. It is, for instance, all too easy, and unfortunately entirely commonplace, to defend a theory of natural kind essentialism which principally relies on appeals to the nature of “philosopher’s kinds”—those continually and inexplicably dredged up from the metaphysically shallow depths of semantic theories of reference and shrouded in the only slightly scientific veneer of ‘microstructural essentialism’.1 Throughout this book, however, there has been no discussion of tigers, oak trees, lemons, etc., and for good reason. Firstly, the theory I have offered does not have as its aim the identification of any particular natural kinds at all: its only aim, in the true Aristotelian spirit, is to give an account of what it is to be a natural

Conclusion  137 kind—which collections of properties satisfy the criteria it proposes is a further, empirical matter. Secondly, and perhaps more importantly, these purported philosophical paragons of natural kind essentialism are absent from this book’s discussion because the theory it proposes owes nothing to, and borrows no justificatory support from, any of the epistemological or linguistic insights which birthed them. Indeed, not only has the construction of this theory not relied upon or in any way made use of the classificatory schematics of philosophical semantics which are typically employed in such a project, but it has also eschewed another available and all too frequently travelled avenue—namely, the simple hoisting of a metaphysical structure atop the already available taxonomic categories of the biological sciences: those divisions may represent heuristically entrenched derivations of a wealth of empirical data, but this is no justifiable pro tanto reason for any philosophical account to countenance them as carving out the mindindependent, causal structure of the natural world. In appealing to the ontological architecture of organisms, it is this structure which has been the primary focus of the theory I have offered. Note, however, that while this book has declared that structure to be fundamentally dispositional, and thus fundamentally teleological, it has not in so doing presupposed or otherwise required the operative influence of any mysterious, or un-natural powers. Although their activities are perhaps nowadays readily associated in the context of contemporary biology with those of the much maligned ephemera of vitalism—the elan vital of Bergson, the plastik natures of Cudworth, or the immaterial entelechies of Driesch—dispositional properties, properly understood, and as I have presented them, engage in no ghostly labours. Rather, on my theory, the dispositional essence of a natural kind is a collection of empirically tractable properties which perform an experimentally appreciable causal role in the ontogenesis of organisms’ morphology. Furthermore, while the teleological role which dispositional properties play functions as the conceptual fulcrum of the theory I have presented, the domain of that role is rather restricted: its scope does not extend, as perhaps one might expect from an Aristotelian theory, to the purposive realm of ‘natural ethics’.2 Teleological conceptions of “what an organism is for” with respect to either the purpose of the organism as a whole, or the purpose of its parts with respect to advantageous benefits for the organism with respect to its lifestyle or selective success have been absent from this book’s discussion. As they have been utilised in my theory, neither the acceptance of the existence of dispositional properties nor the recognition of their role in organismal development requires one to abandon any principles of naturalism. It is an integral aspect of the theory presented throughout this book that the naturalised teleological operations of the dispositional properties which comprise the essences of natural kinds have modal implications for the shape and structure of organismal morphology and thus the course of

138 Conclusion evolution. However, notwithstanding their performance of this role providing a substantial degree of intra- and inter-organismal ontological stability, the essences of natural kinds have nowhere been declared eternal, or otherwise incorrigible. In the vestigial admonishments of Heraclitus inherited from his teacher, Aristotle likely found the conceptual connection between existential duration and logical definability to be an incontrovertible necessity.3 And while I suspect that many who are apprehensive of biological natural kind essentialism are likely to assume that this connection made by its progenitor must be central to any subsequent such theory, this is not the case. In my neo-Aristotelian theory, while it is true that a significant portion of the variation and purported novelty among the denizens of the biological realm is, being metaphysically grounded in and a causal consequence of invariable essences, not understood to properly “carve at its joints”, that fact in no way entails that ‘variation’ and ‘novelty’ cannot occur in the set of existent natural kinds. In other words, the theory I have proposed does not entail that the natural kinds which now exist have always existed, or will always exist. Although empirically detecting and discerning them is in most cases a task of some considerable experimental difficulty, some ontogenetic novelties really are novelties: according to my theory, new natural kinds come into existence whenever new collections of morphospace-defining dispositions do (and mutatis mutandis for the cessation of existing kinds).4 Thus, as I hope is by now exceptionally clear, the theory of natural kind essentialism presented throughout this book neither calls for nor requires the ushering in of any sort of scientific revolution. As is proper for its being principally the product of philosophical examination, this theory should be understood metaphysically—that is, as a conceptually interpretative lens through which certain salient collections of contemporary scientific data may be classified and categorised. As evidenced throughout this book, and contrary perhaps to what one might expect from a work of its kind, accepting my neo-Aristotelian theory of biological natural kind essentialism neither necessitates a reformation of contemporary taxonomic practices nor requires a reformulation of contemporary evolutionary theory. However, while the theory I have proposed neither suggests nor requires any sort of scientific revolution in our understanding of the biological realm, that isn’t to say that it doesn’t demand an important philosophical one—for accepting that theory plausibly courts a conceptual reorientation of one’s view of what is metaphysically foundational in that realm. Firstly, one must prioritise function, or activity over form, or structure: the generative potentialities which characterise natural kinds must be realised in the mereological elements of organismal architecture, but it is those dynamical powers and their activities which ontologically define those kinds. Secondly, one must causally privilege the interior over the exterior: for although the extrinsic environment of an organism plays an important

Conclusion  139 role in the developmental specifications of its ontogenesis, it is a role fundamentally grounded in and governed by the intrinsic causal character of its kind-defining essence. Lastly, one must generally assign metaphysical precedence to invariability rather than variability: while the advent of such variation is not purely accidental, and indeed flows from the very nature of the essences of natural kinds, it is nevertheless a principally derivative and therefore non-fundamental phenomena. It is these three points which perhaps, as it were, form the essence of the neo-Aristotelian theory of biological natural kind essentialism presented in this book. Since the dawn of the “age of evolution”, this general metaphysical schema has been the perennial subject of both incredulous derision and virulent criticism. If the majority of philosophers are to be believed, biological natural kind essentialism represents an outmoded, “scholastic” enterprise— one necessarily disconnected from, and therefore hopelessly uniformed and unconstrained by, contemporary advances in the biological sciences.5 In presenting a novel form of that theory, one fashioned from the philosophical examination of empirical evidence, this book renders that characterisation fundamentally mistaken. Having adopted a fresh perspective on an ancient postulate to cultivate a theory whose roots draw from the scientific soil of contemporary research and whose blossoms are the philosophical fruit of the Lyceum, I submit that essence belongs in the age of evolution.

Notes 1 Though the practice is today widespread, see Kripke (1980) and Putnam (1975) for the canonical expressions of this approach. 2 This sort of wide-ranging teleology, itself a reflection of the intimate connection between function and form, was certainly a part of Aristotle’s metaphysics of the biological realm—see, for instance, On the Parts of Animals—and even has some recent, contemporary advocates: Crane and Sandler’s (2011) ‘axiological species concept’ is an interesting example which has some (non-teleological) similarities with my own theory. 3 See Metaphysics Ζ and On Generation and Corruption. However, some commentators—notably Balme (1972)—read Aristotle differently on this point. 4 The detection of such novelty may be aided by sufficiently precise ‘morphometric’ studies which conceptually map out the causal texture of the generative potential of organismal sub-systems. See Hallgrimsson et al. (2012) and Wagner (2014) for instances of this general approach, and its application in the recent case studies of Young et al. (2010), and Rasskin-Gutman and Esteve-Altava (2014). In contemporary evo-devo research, the task of providing a proper conceptual framework for the interpretation and subsequent detection of genuine ‘novelty’ is widely understood as being neither simple nor trivial—see the discussions in Moczek (2008), Brigandt and Love (2010), and Peterson and Müller (2013). 5 It’s worth nothing that there has rather recently been a small resurgence of Aristotelian essentialism in the context of contemporary biology, one to which this work aims to contribute. See Walsh (2006), Oderberg (2007), Devitt (2008), and Boulter (2012, 2013).

140 Conclusion

Bibliography Aristotle. (1984). The Complete Works of Aristotle (Vol. I & II, J. Barnes, Trans.). Princeton: Princeton University Press. Balme, D. M. (1972). Aristotle’s De Partibus Animalium I and De Generatione Animalium I (With Passages From II. 1–3). Oxford: Oxford University Press. Boulter, S. J. (2012). Can Evolutionary Biology Do Without Aristotelian Essentialism? Royal Institute of Philosophy Supplement, 70, 83–103. Boulter, S. J. (2013). Metaphysics From a Biological Point of View. Basingstoke: Palgrave MacMillan. Brigandt, I., & Love, A. (2010). Evolutionary Novelty and the Evo-Devo Synthesis: Field Notes. Evolutionary Biology, 37(2–3), 93–99. Crane, J., & Sandler, R. (2011). Species Concepts and Natural Goodness. In J. Campbell, M. O’Rourke, & M. Slater (Eds.), Carving Nature at Its Joints: Natural Kinds in Metaphysics and Science (pp. 289–312). Cambridge, MA: The MIT Press. Devitt, M. (2008). Resurrecting Biological Essentialism. Philosophy of Science, 75(3), 344–382. Hallgrimsson, B., Jamniczky, H., Young, N., Rolian, C., Schmidt-ott, U., & Marcucio, R. (2012). The Generation of Variation and the Develomental Basis for Evolutionary Novelty. Journal of Experimental Zoology Part B Molecular and Developmental Evolution, 318(6), 501–517. Kripke, S. (1980). Naming and Necessity. Cambridge, MA: Harvard University Press. Moczek, A. (2008). On the Origins of Novelty in Development and Evolution. BioEssays, 30(5), 432–447. Oderberg, D. (2007). Real Essentialism. New York: Routledge. Peterson, T., & Muller, G. (2013). What Is Evolutionary Novelty? Process Versus Character Based Definitions. Journal of Experimental Zoology Part B: Molecular and Developmental Evolution, 320(6), 345–350. Putnam, H. (1975). The Meaning of “Meaning”. Minnesota Studies in the Philosophy of Science, 7, 131–193. Rasskin-Gutman, D., & Esteve-Altava, B. (2014). Connecting the Dots: Anatomical Network Analysis in Morphological EvoDevo. Biological Theory, 9(2), 178–193. Wagner, G. (2014). Homology, Genes, and Evolutionary Innovation. Princeton: Princeton University Press. Walsh, D. (2006). Evolutionary Essentialism. British Journal of the Philosophy of Science, 57(2), 425–448. Young, N., Wagner, G., & Hallgrimsson, B. (2010). Development and the Evolvability of Human Limbs. Proceedings of the National Academy of Sciences, 107(8), 3400–3405.

Index

adaptionism 121 – 126, 130 – 131 Aristotle 1 – 3, 12 – 17, 23, 39, 100 – 102,  138 baüplan 109, 118 Boolean network 47, 51 – 52, 55 – 57 causal parity thesis 67 – 68, 73, 81 – 83, 86 – 87; and informational parity 67, 72 – 73, 84; and pragmatism 68 – 72, 83 – 87 causal powers see dispositional properties causal responsibility 67, 76 – 83, 86 – 88, 91, 126; and causal primacy 76 – 79, 81; vs. causal relevance 76 – 83, 87; and dispositional properties 79 – 85, 87 – 91, 97, 101 – 110, 128 – 129 causation: causes vs. conditions 68 – 72, 85 – 86; and de re dependence 9 – 11, 43 – 44, 59, 100; and information 71 – 72, 76 – 78, 83 – 85; non-monotonicity of 11 – 12 cell fate 47 – 53, 75 Crick, Francis 121 Darwin, Charles 24 – 25, 99, 123, 131 degeneracy see robustness Delbrück, Max 100 developmental constraints 89, 104, 109, 126, 128 – 131 developmental hourglass 51 developmental modules 45 – 59, 67 – 68, 72 – 76, 83 – 91 developmental systems drift 101; and autonomisation 107 developmental systems theory 67 – 68, 73, 86 Devitt, Michael 29 – 30

dispositional properties: causal role of 16, 39 – 44, 58 – 59, 73 – 75, 78 – 85, 87 – 89, 108 – 109; and induction 42 – 44, 59, 103 – 104; and modality 41 – 44, 44, 59, 82, 89 – 91, 108 – 109; multiple realisability of 40 – 41, 106 – 108; and teleology 41 – 42, 59, 87 – 89, 103 – 105, 109 – 110, 126 – 128, 137; see also properties DNA 47, 67 – 68, 100 dunamis 3, 16, 102 dynamical systems theory (DST) 52 – 59, 88 – 91 ecological species concept 26 – 27; see also species evo-devo: and dispositional properties 119, 126 – 127, 131; and explanation 125 – 127; vs. modern synthesis 124 – 125, 127; and ontology 2 – 3, 127 – 130 evolutionary theory: explanatory framework of 98 – 99, 108, 120 – 124; and ontology 2 – 3, 119, 122 – 123, 124 – 127, 130 – 131,  138 evolvability 53, 126 form 13 – 16, 100, 102 – 105, 108 – 112 generative entrenchment 109 – 110 genetic regulatory network (GRN) 47 – 52, 68 – 73, 100 – 101, 106 – 107; expression patterns of 47 – 49, 51 – 58, 75 – 76, 82, 101; regulatory logic of 47 – 49, 52 – 57, 88 – 89 goal-directedness 14 – 16, 41 – 44, 51 – 53, 58 – 59, 87 – 91, 104 – 110, 128 – 130, 137; see also dispositional properties

142 Index Goethe, Johann Wolfgang von 125, 131 Gould, Stephen J. 120, 129 heterochrony 75 heterotopy 75 hierarchical disconnect 107 homeodynamism 129 homology 125, 127 Humean metaphysic 2 – 3, 39; see also properties hylomorphism 13 – 16, 102 – 112,  118 imaginal disc 45 – 51, 53, 75, 87 – 89,  109 information: biological information 24, 71; regulatory information 51, 58, 87 – 88, 109; Shannon information 71 – 73, 77 – 78 Intelligent Design 45 interbreeding species concept 25 – 27, 30; see also species Kripke, Saul 9 – 10, 100 laws of nature 16, 39, 125 Lewis, David 39, 69 – 70 Linnaeus, Carl 23 Locke, John 6 – 7, 10 matter 13 – 14, 102 – 112, 118; determinable vs. determinate 105, 109 – 112,  129 Mayr, Ernst 25, 29, 100, 120 – 122 microstructuralism 10, 100, 136 Mill, J.S. 68 Modern Synthesis 3, 122 – 127, 130; and categorical properties 126 – 127; and evolutionary explanation 123 – 127 morphological profile 14 – 16, 31 – 33, 44 – 45, 101 – 104, 108 – 112,  120 morphomodulatory dispositions 59, 87 – 91, 97, 104 – 112, 128 – 131 morphospace: and causal responsibility 91, 105, 130 – 131; dynamical features of 87 – 89, 91, 105 – 110, 128, 130 – 131; topological structure of 88 – 90 Müller, Gerd 126 natural kind: and induction 5 – 6, 8, 10 – 12, 15 – 16, 43 – 44, 59, 98 – 99, 103; mind-independence of 6 – 8, 23 – 28; philosophical definition of 4 – 8; realism about 4 – 7, 25 – 28

natural kind essentialism: modal fount component 9 – 14, 43 – 44, 58 – 59; necessary set component 8 – 9, 13 – 14, 98 – 99, 103 – 104, 119; real vs. nominal definitions of 6 – 8, 10 – 12, 43 – 44, 59, 99 – 102; and typology 33 – 34, 99, 110, 136 natural state model 118 – 122, 124 – 131; and evo-devo 125 – 131; and the order of being 122 – 124, 129 Okasha, Samir 26, 98 ontogenesis 31 – 33, 38, 45 – 59, 119 – 131, 137 – 139 persistence 41 – 44, 58 – 59, 91, 103, 130 – 131; see also goal-directedness phenotypic plasticity 73 – 76, 81, 87 – 89, 105, 110, 121, 131 phylogenetic species concept 26 – 27, 31; see also species Plato 6, 12, 38, 120 pleiotropy 73 – 77, 91, 131; argument from pleiotropy 73 – 77 pleonasy 41 – 44, 52, 58, 90, 103, 130; see also goal-directedness polygeny 68 – 69, 73 – 77, 91, 129, 131; argument from polygeny 68 – 73 properties: dispositional vs. categorical 16, 39 – 43, 126 – 127 proximate vs. ultimate explanations 31 – 32, 121, 123, 126; and causation 121 – 126; see also evo-devo Putnam, Hilary 10, 100 redundancy see robustness robustness 41 – 42, 52, 58, 131, 130 – 131; and induction 43 – 44, 103; and multiple realisability 41 – 42, 59; see also goal-directedness Shannon, Claude 71 Sober, Elliot 120 species: concepts 24 – 26, 28 – 32; and conceptual pluralism 25 – 28, 32; and intrinsic properties 27 – 28, 32, 98 – 99; taxonomical rank 23 – 24, 32 – 34 state-space 53 – 57, 88 – 90; developmental trajectories in 53 – 59, 88, 91, 98, 110, 126 – 127; and topological mapping 56 – 58, 88 – 91, 109 – 110; see also morphospace structuralism 127

Index  143 taxon-category vs. taxon-membership 29 – 32; see also species taxonomy 3 – 10, 22 – 28, 98, 101, 118, 137 – 138; and ontology 32 – 34, 98, 118, 137 – 138; and telos 22, 32 – 34, 110, 136 teratology 100 transcription factors 47 – 49, 51, 75 – 76, 82; and positional information 51, 72, 75

truthmakers 42 – 43; and context-sensitivity 42 – 43, 103, 105, 136; and masking 42 – 43, 103 vitalism 125, 137 Waddington, Conrad 52 Walsh, Denis 130 Woodward, James 69, 77