Studies in History and Philosophy of Biological and Biomedical Sciences 44 (2013) 714–723

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Finding Ernst Mayr’s Plato Jack Powers Department of Philosophy, Minnesota Center for Philosophy of Science, University of Minnesota, Minneapolis, Minnesota 55455, USA

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Article history: Received 16 August 2011 Received in revised form 23 August 2013 Available online 14 October 2013 Keywords: Plato Ernst Mayr Essentialism Typological thinking Teleology Louis Agassiz

a b s t r a c t Many biologists have accepted Ernst Mayr’s claim that evolutionary biology undermined an essentialist or typological view of species that had its roots in Platonic philosophy. However, Mayr has been accused of failing to support with textual evidence his attributions to Plato of these sorts of views about biology. Contemporary work in history and philosophy of biology often seems to take onboard Mayr’s account of Plato’s view of species. This paper seeks to provide a critical account of putative inconsistencies between an evolutionary view of species and Platonic philosophy with renewed attention to the Platonic texts in light of recent Plato scholarship; I argue that claims that Plato held an essentialist view of species inconsistent with evolutionary biology are inadequately supported by textual evidence. If Mayr’s essentialist thesis fails, one might think that the intuition that Platonic philosophy is in tension with Darwinian evolution could nonetheless be accounted for by Plato’s apparent privileging of a certain sort of teleological explanation, a thesis that Mayr suggests in his 1959 paper on Louis Agassiz. However, this thesis also faces difficulties. Ernst Mayr’s Plato is more likely to be found in the writings of anti-evolutionary 19th century biologists like Mayr’s frequent target, Agassiz, than in a cautious reading of the Platonic dialogues themselves. Interlocutors in discussions of the history of biological thought and classificatory methods in biology should be cautious in ascribing views about biology to Plato and using terms like ‘‘Platonic essentialism.’’ Ó 2013 Elsevier Ltd. All rights reserved.

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1. Why beat a dead Horse? In relaying a narrative of the rise of their discipline, evolutionary biologists commonly characterize Darwin’s account of evolution by natural selection as a revolution that overthrew long-standing ideas about the biological world inherited from the ancient Greeks.1,2 Often the narrative suggests that the establishment of evolutionary thought undermined ‘‘essentialism’’ or ‘‘typological thinking’’ that purportedly has its roots in Platonic philosophy. Ernst Mayr’s account is archetypal: Without questioning the importance of Plato for the history of philosophy, I must say that for biology he was a disaster. His inappropriate concepts influenced biology adversely for centuries . . . First [among the deleterious concepts], essentialism . . . .(Mayr, 1982, p. 87)

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Mayr claims further that Darwin, ‘‘replaced typological thinking with population thinking.’’ Typological thinking no doubt had its roots in the earliest efforts of primitive man to classify the bewildering diversity of nature into categories. The eidos of Plato is the formal philosophical codification of this form of thinking. According to it there are a limited number of fixed, unchangeable ‘ideas’ underlying the observed variety, with the eidos (idea) being the only thing that is fixed and real while the observed variety has no more reality than the shadows of an object on a cave wall, as it is stated in Plato’s allegory. The discontinuities between these natural ‘ideas’ (types), it was believed, account for the frequencies of gaps in nature . . . Since there is no graduation between types, gradual evolution is basically a logical impossibility for the

E-mail address: [email protected] See Hodge & Radick (2003) for a critique of the notion that there was a unified Greek philosophy of nature to which Darwin was responding. A similar view was developed by John Dewey in 1909. See Hodge & Radick (2003) and Dewey & Hickman (2007).

1369-8486/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.shpsc.2013.09.007

J. Powers / Studies in History and Philosophy of Biological and Biomedical Sciences 44 (2013) 714–723

typologist. Evolution, if it occurs at all, has to proceed in steps or jumps . . . For the typologist, the type (eidos) is real and the variation an illusion, while for the populationist the type (average) is an abstraction and only the variation is real. No two ways of looking at nature could be more different (Mayr, 1976, pp. 27– 28).3,4 ‘‘Platonism,’’ ‘‘typological thinking,’’ and ‘‘essentialism’’ continue to be terms of derision in biological theorizing, and labeling disfavored projects as essentialist is a common rhetorical tactic. As Love (2009) puts it, ‘Typological thinking’ is not something you want to get caught doing in evolutionary biology. It involves committing the cardinal sin of ignoring variation and a tacit appeal to essentialism, which is metaphysically incompatible with population thinking, the very foundation of understanding life from an evolutionary perspective (Mayr, 1959b; cf. Ghiselin, 1997). Or so one version of the story goes (p. 52). But with the reintegration of developmental and evolutionary biology, evo–devo, ‘‘typological thinking’’ has enjoyed new attention. Attempts are ongoing to reconstruct defensible forms of epistemological practices endogenous to developmental biology that make use of idealizations and exemplars in biological explanation (e.g., the vertebrate limb), and focus less on or abstract away from variation (Love, 2009, p. 51). These attempts often take pains to quarantine such epistemological practices from objectionable ‘‘Platonic’’ or ‘‘essentialist’’ metaphysics. Mayr’s characterization of the views of Plato and their putative inconsistency with gradual evolution thus lurks in the background of these renewed debates. Further, treatments of Plato in other areas of the history and philosophy of biology often seem to accept a picture of Plato consonant with Mayr’s whereby, e.g., ‘‘the true beings are immaterial Forms’’ and ‘‘Plato looked above to the Form Horse.’’ (Hodge & Radick, 2003, p. 249)5,6 Criticisms of Mayr’s view of Plato have not been lacking. Winsor (2006) has labeled Mayr’s characterization of pre-Darwinian biologists and systematists as engaging in essentialist projects as ‘‘a fiction.’’7 Sober (1980) points out some of the ways that essentialism is not undermined by evolutionary biology. David Kitts has accused Mayr of failing to carefully identify and document with textual evidence those aspects of the Platonic view putatively inconsistent with Darwinian evolutionary thinking about species.8 In his analysis of the Platonic dialogues, Kitts failed to find a ‘‘consistent and unambiguous’’ view of plant and animal kinds as unchanging entities imbued with essential properties (Kitts, 1987, pp. 326–327). Plato does offer via the characters of his dialogues conjectures of and suggestions about forms of plants and animals in some works. However, I will argue any stronger conclusion of the sort that Plato is committed to a view of forms that is at odds with evo-

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lutionary biology faces difficulties illuminated by recent Plato scholarship. While we may be entitled to say that statements made by characters in Platonic dialogues are suggestive of essentialism and typological thinking of the sort that Mayr attributes to Plato, we are not clearly well-supported in saying that Plato held such views. Another case for Plato’s philosophy being in tension with the explanatory standards of evolutionary biology can be made with respect to Plato’s putative privileging of teleological explanation (in the sense of explaining the natural world as the result of planning on the part of an intelligent agent).9 However, I will argue that that there is a plausible interpretation of Plato’s teleological demands that renders such tension only apparent. One might reasonably wonder why investigating whether there is tension between Plato’s philosophy and Darwinian evolution is a worthwhile thing to do. Even if there were such tension, surely it would be silly to fault Plato for a lack of prescience about a theory that would not be fully articulated until the 19th and 20th centuries. But it seems as though Plato has been so faulted.10 I follow Grene in thinking it important ‘‘both for the sake of historical accuracy and out of respect for the transcendent thinkers of our tradition, to pay serious attention to the works (and words) of those philosophers who are all too glibly cited as having done this or that to science, or religion, or what you will, in this case, to biology.’’ (1989, p. 69) Plato’s view of nature and terms like ‘‘Platonic essentialism’’ continue to show up in discussions of the history of biological thought and classification in biology. This essay is intended to sound a cautionary note for workers in these areas; Plato’s views on species and nature generally are less obvious than the picture received from Mayr implies. I will suggest that Mayr’s Plato is easier to find in the writings of evolutionary theory’s most formidable 19th century bogeyman, Louis Agassiz, than in a critical reading of the Platonic dialogues. I will close with a few general comments about the Platonic dialogues and claims about entailment relationships among Darwinian evolution and certain views in philosophy and theology. 2. The essential properties of Ernst Mayr’s Plato Essentialism about biological species is a view putatively held by Plato whereby being a member of a species entails the possession of the properties or features that constitute the essence of that species, what it is to be a member of that species. These are properties that (1) all and only members of that species have, that (2) explain why they are members of that species, and that (3) allow us to differentiate members from non-members. We might refer to these three requirements of essential properties respectively as the all and only requirement, the explanatory requirement, and the diagnostic requirement.11,12 Mayr often appears to identify

3 Mayr offers here a questionable interpretation of the allegory of the cave. On a standard view, the shadows on the cave wall are images of (e.g., art and poetry representing) the various natural objects and artifacts. The variety found in nature, according to the allegory, is thus more real than the shadows on the cave wall (Republic, 514–539). 4 Mayr often uses ‘‘essentialist’’ and ‘‘typologist’’ (and their cognates) synonymously. Plato’s eidos is associated with both. See Winsor (2006). 5 These quotations are suggestive of popular views about forms accepted among both scholars and lay-readers of Plato, but neither is uncontested. The first quotation is consonant with claims about forms as presented in, e.g., the Timaeus, but as we will see, it is not clear if or in what sense Plato endorsed the view presented there. The second quotation makes controversial assumptions about what Plato took to be the scope and location of forms; see Harte (2008). 6 See also, for example, Amundson (1998)’s characterization of ‘‘Platonic Idealism.’’ 7 But the debate about the degree to which key pre-Darwinian systematists were or were not involved in essentialist projects continues. See Stamos (2005). 8 In reply, Mayr (1988) cites Popper’s (1945) treatment of Plato. Grene (1989) is among those unimpressed by Popper’s treatment. Klosko (1996) is also critical. 9 There are other ways in which ‘‘teleology’’ has been used in biology; On one sense of ‘‘teleology’’ (where purposes are given by natural selection), it is correct to say that Darwin was a teleologist (Lennox, 1993). 10 See, for example, Mayr (1959a, p. 173) where one reason for the respective successes of Darwin and Wallace and the failures of 19th century German zoologists is their differential acceptance of the ‘‘lofty fallacies’’ about the nature of species found in Plato’s philosophy, where the ‘‘lofty fallacies’’ seem to be a cluster of views that Mayr sees as antithetical to common descent. 11 As Sober (1980, p. 354) notes, a disjunctive list of the spatiotemporal locations of all the members of a species would satisfy the all and only requirement, but would fail to vindicate essentialism because such a list would fail to satisfy the explanatory requirement. 12 Essentialism about species as traditionally construed is said to have looked for properties intrinsic to member organisms, typically morphological character states. See Wilson, Barker, & Brigandt (2007).

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the Platonic eidos and idea with these sorts of essences.13 The reason a horse is a horse is because of Horse (where Horse is the form or essence of that species). The problem for this essentialist view is said to arise once we realize, per Darwin, that species change over time. Species change (into other species), but essences (or forms) don’t change (Love, 2009, p. 54; Mayr, 1976, pp. 27–28; 1982, p. 87). Thus, so the argument goes, essentialism is incompatible with gradual evolution. Typological thinking is said to be the closely related error of taking these essences, idealizations, or ‘‘types’’ to be real, and minimizing the significance or denying the reality of variation found in nature among members of species. Mayr’s ‘‘population thinking’’ treats idealizations as abstractions describing the statistical norms of the real variation among species but denies reality to such idealizations. Variation is central to the Darwinian evolutionary account (as the heritable variation that makes possible differential survival and reproduction), but taken as unreal or illusory on the typological account (Love, 2009, p. 54; Mayr, 1976, pp. 27–28; 1982, p. 87). Ascribing essentialist or typological views (and their putative consequences) to Plato commits one to at least the following two claims. The first is that Plato thought that there were forms (whatever these turn out to be) or essences for the different species of plants and animals. The second is that the Platonic view entails that such forms are inconsistent with at least certain sorts of changes or variation in the particulars to which the relevant form corresponds. In the following sections, I will ask how well these ascriptions are supported by Platonic texts and recent scholars’ interpretations thereof. But first I will consider two competing hypotheses for interpreting the relevant textual evidence. 3. Reading Socratic dialogues: two views about a puzzle That Socrates seems to advance a claim is not necessarily reason to ascribe the view implicit in the claim to either the character Socrates or to Plato. There is an apparent tension between what the character Socrates says he does in the Apology and what we see him do in certain other dialogues, notably the Republic and the Phaedo (Peterson, 2008, p. xv). According to the Apology (29d–32d), the Socratic project is primarily one of examining others’ beliefs and the entailments thereof with respect to living well through a method of question and answer. This behavior is modeled in e.g., the Euthyphro, where Socrates examines Euthyphro’s beliefs and commitments about piety and shows them to be inconsistent. The Socrates of the Apology disavows having knowledge of anything of much importance (other than knowledge of his own ignorance) (21b). In the Republic and the Phaedo, however, we have a Socrates apparently articulating and endorsing (unusual) views about the nature of the best state, forms, life after death, etc., and leaving these views largely unexamined. It is a puzzle why Socrates behaves so differently in different dialogues, and engages in behavior that seems in tension with his own account of what he does as a matter of course in the Apology (Peterson, 2011, pp. 1–3). On the account offered by Gregory Vlastos as fundamental to his interpretation of Plato, to make sense of so drastic a departure from what Plato had put into his portrayals of Socrates from the Apology to the Gorgias, we must hypothesize a profound change in Plato himself. If we believe that in any given dialogue Plato allows the persona of Socrates only what he (Plato) at that time considers true, we must suppose that when that persona discards [dialectical question and answer] as the right method to search for the

truth, this occurs only because Plato himself has now lost faith in that method. (Vlastos, 1991, p. 117) On this sort of reading, Socrates says what Plato thought at the time of the writing of a given dialogue. Any tensions between dialogues are a result of the development of Plato’s thought over the course of his career. The take home message for Plato interpretation is that on this sort of reading Plato ‘‘owns’’ whatever doctrinal statements issue from the mouth of Socrates. I will refer to this sort of interpretation as Plato-centered (Peterson, 2011). Sandra Peterson (2011) offers a different and original hypothesis about the puzzle. On her view, Socrates, throughout the diverse dialogues, even when he seems to offer rather outlandish positive views, is engaging in just the sort of examination of others that he claims to in the Apology. For Peterson, examination is itself a multi-stage activity. Its first step is revealing the interlocutor. Socrates’ awareness of what is appropriate to reveal his interlocutors occasions Socrates’ different speaking styles, tailored to different interlocutors in different dialogues. With certain interlocutors Socrates appears to be recommending teachings of which he is certain. With them he appears to be teaching in those very areas of which he disclaims knowledge in the Apology. That is because Socrates as depicted realizes that appearing to enunciate doctrine, and observing his interlocutor’s receptivity to it, is the best way of revealing for certain interlocutors their beliefs and inclinations that need to be examined. Revealing a receptive interlocutor, Socrates thereby enacts the first stage of examination. So in the doctrinal dialogues we still see Socrates living the singleminded life of examination that he attributes to himself in the Apology. (Peterson, 2011, p. 5) A reading of Plato’s Socratic dialogues that takes up this characterization of the Socratic project will not tend to see apparent cases of Socrates advancing doctrinal positions as clear evidence that these positions were held by Plato (or the character Socrates). On this view, it is plausible that it is the interlocutors rather than Socrates or Plato that ‘‘own’’ the commitments issuing from Socrates’ mouth. I will refer to this sort of interpretation as interlocutor-centered (Peterson, 2011). Vlastos’ Plato-centered methodology is a traditional and widely accepted one. However, Peterson offers a cogent and extensive argument for her view (2011). Without taking a strong position on this methodological debate, I will only claim that conclusions drawn from Plato-centered readings often need additional support in the form of reasons for rejecting an interlocutor-centered reading of the relevant passages. I will attempt to highlight places where the choice of one or the other of these interpretive hypotheses has important implications for reading passages from the texts relevant to the evaluation of Mayr’s characterization of Plato. 4. What are forms? Given that Mayr’s account of the putative inconsistency of evolutionary biology and Platonic philosophy rests in part on a set of claims about Platonic forms, the question of what forms are is a natural place to begin. Socrates in certain dialogues produces arguments to defeat proposed definitions without committing himself to the idea that the things to be defined are to be found in an eternal, unchanging, and ontologically pure realm. In other dialogues definition

13 See, for example, Mayr (1959a, pp. 172–173) where Agassiz’s views on species are said to be an ‘‘unequivocal interpretation of zoological classification in terms of Plato’s Ideas.’’

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takes more of a backseat, and Socrates does commit himself to that metaphysical view. The metaphysical view is the Theory of Forms (Dancy, 2004, p. 4). As Dancy points out, the flavor of some Socratic talk of an eidos or idea seems to suggest a rather commonplace notion of definition. Elsewhere the eidos has appeared to many to be ontologically inflated, connoting a denizen of a ‘‘Platonic heaven,’’ a world beyond our everyday experience (Harte, 2008, p. 206). One way that these two apparent sorts of forms have been treated is via a distinction introduced by Aristotle in the Metaphysics between Socratic forms and Platonic forms. For Aristotle, Platonic forms were a response to Socrates’ search for definitions for terms in ethics. The claim is that such Socratic definitions could not apply to sensible things because sensible things change, so the definitions must be of non-sensible and immutable things, Platonic forms (Metaphysics 987a32-b10, 1078b12-1079a4, 1086a37-b11; Irwin, 1999, p. 143). For now it is enough to introduce Aristotle’s distinction. I will save evaluation of claims about forms and changes in the particulars to which they correspond for Section 6. As an example of a more minimal ‘‘Socratic’’ characterization of forms, Irwin interprets the Euthyphro (5d–7d) as offering four constraints on an adequate form (eidos) or idea of piety. 1) There is one eidos for all pious things. 2) It must be a useful paradigm for deciding whether a thing is a member of the class of pious things. 3) It must be describable without reference to other disputed terms. 4) It must be explanatory of why all pious things are pious. (Irwin, 1999, p. 145) Notice that the first and second constraints together are suggestive of the all and only condition traditionally associated with essentialism, the second is an instance of the ‘‘diagnostic’’ condition, and the fourth is an instance of the explanatory condition. On a Plato-centered reading, this is some evidence for the charge that Plato held, at least at some point in his career, views about ethical terms that we might now well-characterize as essentialist, but not necessarily for the charge that he held an essentialist view of biological species. Although one might worry about the third constraint if it were applied generally (since it is plausible on pain of infinite regress that definitions must eventually run-out), there is nothing apparent about it or the other three constraints here that implies ‘‘an eternal, unchanging, and ontologically pure realm’’ or the denial of the importance of the this-worldly which Mayr attributes to Plato. In contrast, in the Phaedo, we get a picture that has been interpreted as more consonant with what the Plato literature often refers to as the Platonic theory of forms (or, more dramatically, the Theory of Forms).14 Here, on Irwin’s interpretation, Plato has Socrates say that, 1) Forms are grasped by the intellect rather than the senses (65d–66a).

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2) A form is different from any particular sensible instantiation of it because the form has properties that no sensible thing can have (74a–b). 3) Sensible things undergo change and forms are completely unchanging (78c–e). 4) The form of beauty is what makes beautiful things beautiful and cannot be identified with bright colors, symmetrical shapes, etc. (100c–d) (Irwin, 1999, p. 151). In these passages of the Phaedo, many interpreters have thought that Plato endorses a view of forms that begins to sound mysterious.15 One might have some trouble even imagining with respect to a form of beauty what sort of thing could be as divorced from sensory perception or description in terms of sensible properties as these latter four constraints seem to suggest, or what sort of convincing evidence we might have of the immutability of such a thing. This picture of the forms as mysterious is reinforced by the famous allegory of the cave and analogy of the line in Books VI–VII of the Republic. There we find suggestions of forms as entities, the objects of true knowledge, only accessible by a select few who have passed through successive stages of intellectual development and left behind the distractions of the senses. But Peterson (2011) argues that we should not be too quick to give Socrates or Plato ownership, in either the Phaedo or the Republic, of any grandiose claims about forms or who has access to them. Rather, in the Phaedo, Socrates is charged with convincing Cebes and Simmias by way of ‘‘law-court-style persuasive defense’’ of the reasonableness of not fearing death; the object is persuasion, not truth-seeking or an exposition of Socrates’ views, and Socrates is therefore entitled to enlist in his persuasive speech any premises that Cebes and Simmias already hold or are prepared to give assent to, regardless of the reasonableness of these premises (2011, pp. 172–177). For example, with respect to the claim about entities that are graspable by intellect alone at 65d–66a, Socrates, at 65c, elicits Simmias’ assent to the claim, on the authority of the poets, that the senses are deceptive. Although Simmias’ assent is eager, it is far from clear that the character Socrates, or Plato for that matter, endorses this premise.16 After gaining assent to the claim that the ‘‘Just itself’’ and other forms are known, and assuming that the senses and the intellect are the only two ways of gaining knowledge, the claim that these forms are known by the intellect rather than the senses follows by eliminative inference. But there is a case to be made against any strong supposition that either Plato or Socrates endorses the premises on which this inference is based. It is not clear that Socrates or other characters in the dialogues always use eidos in what might be called the ‘‘technical sense,’’ i.e., referring to either ‘‘Socratic definitions’’ or reified non-material ‘‘Platonic’’ entities. Peterson argues that we can often best understand the use of ‘‘eidos’’ or other apparent form-talk (e.g., ‘‘itself by itself’’) as mere qualification, a way to specify what it is that the character wishes to discuss, as in the claim, ‘‘I want to discuss shampoo itself, not pet shampoo or medicinal shampoo.’’ (Peterson, 2008, p. 383) This interpretation is deflationary with respect to ascriptions of grand metaphysical commitments to either the character Socrates or to Plato.17 Referring to a passage in the Repub-

14 Peterson (2008), on the basis of the heterogeneous characterizations of forms in the various dialogues, wants to resist language (i.e., ‘‘the Platonic theory of forms’’) that ‘‘suggests that there is one determinate, recurrent collection of principles about forms.’’(p. 386) See also Annas (1981) for arguments in favor of caution in the use of such language. 15 Vlastos (1969) sees Plato as here introducing what he calls the ‘‘full-blown theory of Plato’s Middle Period’’ where forms are ‘‘immutable, incorporeal, divine’’ and ‘‘cannot be known by sense experience, but only by ‘recollection.’’’ (pp. 298–299) 16 Peterson diagnoses the eagerness of Simmias and Cebes to accept premises suggesting that the ‘‘true philosopher’’ denies the body and the senses as resulting from their Pythagorean sympathies, sympathies that Socrates is free to exploit in making his persuasive speech (2011, pp. 172–183). 17 For instance, Peterson (2008) argues that interpreting Socrates as using eidos in the non-technical sense in some potentially confounding arguments in the Parmenides makes clearer the strength of Socrates’ refutation of Zeno early in the dialogue and relieves us of having to say ‘‘that Socrates invokes a non-helpful and gratuitous new technical theory.’’ (p. 388)

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lic where Socrates is often interpreted as introducing forms in a technical sense, Peterson says that, the word ‘‘forms’’ (eidon) at 476a is not inevitably a technical term. An ordinary speaker could agree to what Socrates says. The literal meaning of eidos is ‘‘that which is seen’’ or ‘‘appearance.’’ It is what is presented to the viewer. Similarly for idea, which occurs at 479a. ‘‘Aspect’’ seems to me an approximate equivalent in English. Proposing to have a conversation about an aspect of things seems to me a natural and ordinary thing to do. The use of a phrase such as ‘‘the beautiful itself’’ or ‘‘the beautiful by itself’’ is a natural way to start a conversation about a specific aspect of something. One might naturally in conversation want to focus on a single aspect such as beauty that many beautiful things share. Similarly, there is no reason to take ‘‘share’’ (476d) to be some mysterious technical term. To say in ordinary discussion that several things share beauty is simply to say that they are all beautiful. (2011, pp. 127–128)18 In addition to Peterson’s interpretation of the eidos as a non-technical attention-focusing device, we have seen a distinction between two rough sorts of characterizations of forms (as technical terms) with respective sets of constraints, with the second characterization (the so-called Platonic theory of forms) seemingly entailing greater metaphysical and epistemological commitments, but we don’t yet have picture of what forms are. What forms are is one of the fundamental questions in Plato scholarship. One view is that forms are theoretical entities in the sense that they have explanatory roles to play, as in the fourth constraint on forms in each of the sets of characterizations offered above (Harte, pp. 193–194). Whether these theoretical entities should be understood as more ordinary (‘‘Socratic’’) definitions or as peculiar and mysterious (‘‘Platonic’’) beings is contested. I will proceed with a characterization of forms of the sort that Socrates offers in the Phaedo at (75c–d) as ‘‘the things on which we put as a seal this mark ‘what is,’ and about which we ask and answer in our questions and answers.’’ That is, we should proceed by thinking of forms as explanatory definitions (as sets of properties) that are the answers to questions about what things are.19 Whether it is reasonable to read Plato as being committed to forms being anything more than this will hopefully become clearer as we proceed, but I hope to have already destabilized the notion that he is so committed on the basis of certain interpretations of famous passages in, e.g., the Phaedo and the Republic; these interpretations are not uncontested. Notice that there is no apparent tension between a characterization of forms as explanatory definitions and an evolutionary view of species. If there are, for Plato, forms of plants and animal species, then whatever properties we use to answer questions about what these things are (including properties derived from our best evolutionary theories) could plausibly be incorporated into the relevant form.20 5. Is there a zoo in the realm of the intelligible? It is apparently necessary for the conclusions that Mayr draws about Plato that Plato thought there were forms of animals. As Kitts notes, ‘‘there is scarcely a claim about the forms that has not been subject to intense debate among classicists and philosophers.’’ Kitts agrees with Cornford that Plato never answers the

question of ‘‘the extent of the world of forms.’’ (Cornford, 1957, p. 9; Kitts, 1987, p. 324) On one view, there are forms for each group of things to which we give a common name. ‘‘We are in the habit, I take it, of positing a single idea or form in the case of the various multiplicities to which we give the same name.’’ (Republic 596a) Socrates’ statement is often taken as evidence on a Plato-centered reading that Plato wanted to posit forms for a wide range of objects, presumably including the kinds of plants and animals, since we give members of these kinds a common name. However, Smith (1917) proposes that the passage should be interpreted rather as a claim about there being a one-to-one relationship between a form and the group of particular things to which it applies; i.e., if there is a form of X, there is just one form of X. Read in this way, 596a does not make a claim about how broadly forms are posited, or what forms there are (Harte, 2008, p. 200).21 On an interlocutor-centered reading of 596a, even if the passage does entail a claim about the scope of forms, it is not clear that Socrates or Plato owns the claim. Immediately preceding the above passage at 595c Socrates and Glaucon explicitly enter into a question and answer mode of discourse. Socrates solicits assent to the procedure and his interlocutor grants it. In Alcibiades I (113a–b), Socrates and Alcibiades agree that it is the answerer who has possession of the answers in such discussions (Petersen, 2011, p. 8). On a Plato-centered reading, seemingly supporting the view that Plato is not strongly committed to positing forms for all things to which we give a common name, Socrates in the Parmenides is skeptical about forms of mud and dirt. More salient here, Socrates is ambivalent on the question of whether or not there is a form for human beings (Parmenides, 130c). On a Plato-centered reading, supporting an interpretation of Plato as positing forms for artifacts, animals, and objects generally, the allegory of the cave in Book VII of the Republic has the puppeteers ‘‘carrying all kinds of artifacts.’’ Among these are ‘‘statues of people and other animals.’’ (514b–c) Socrates later says that, ‘‘The visible realm should be likened to the prison dwelling and the light inside to the power of the sun.’’ (517b) If we are to analogize in this way, and the sun outside of the cave is the form of the good, it seems to suggest, following the analogy, that visible artifacts and objects (including plants and animals) also have forms. In Book X of the Republic, Socrates seems to say that there is a form of bed and a form of table. That there are forms for such common classes of artifacts suggests a more global scope for forms. Socrates, after referencing forms for beds and tables, analogizes the creation of ‘‘all the plants that grow from the earth [and] all animals’’ to the creation of beds and tables. On a Plato-centered reading, a few further considerations give some evidence that Plato was inclined to posit forms for a wide range of objects, including biological kinds. First, in the Philebus at 17e, Socrates says that, ‘‘every investigation should search for the one and many. For when you have mastered these things in this way, then you have acquired expertise there, and when you have grasped the unity of any other things there are, you have become wise about that.’’ If the various species are, for Plato, rightly considered objects of investigation and expertise, such talk of searching for the one and many of ‘‘other things there are’’ suggests that Plato thinks there is a particular unifying eidos for the various species. In the Apology at 25b, Socrates suggests that there is exper-

18 Vlastos (1969) see this participation or sharing relationship between forms and things that instantiate them, at least in the Phaedo, as more complicated and less easily characterized, a ‘‘one-way ontological dependence relation’’ of which Plato ‘‘has yet to reach a clear-cut conception.’’ (p. 301) 19 I see this characterization as consonant with Irwin’s view of forms as objective explanatory properties (1999, p. 149). 20 If our best evolutionary theorizing tells us that species are differentiated on the basis of relational properties like phylogeny or interbreeding capacity, the resulting view might well be a non-traditional sort of ‘‘relational essentialism’’ about species. See Griffiths (1999), Okasha (2002), and LaPorte (2004). 21 As Harte (pp. 200–201) notes, the scope of forms may also be tied to a distinction between objects of contemplation that require rational inquiry for understanding and those that do not. The need to attend to this interpretive possibility is echoed by Kitts (1987, p. 324) on the basis of claims made by Socrates in the Republic at 523.

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tise of horses and ‘‘all other animals.’’ And finally, a passage in the Meno also seems suggestive of essential properties for bees. Meno and Socrates take it as a matter of course that Meno would be able to tell Socrates ‘‘in which [bees] are all the same and do not differ from one another.’’ (72b) However suggestive these passages might be, drawing strong conclusions about Plato’s views from their content arguably requires the rejection of an interlocutor-centered interpretation and the reasoned acceptance of a Plato-centered interpretation for the relevant passages. Whether and how this can be done for these passages are interesting questions. Peterson argues that we should see the doctrinal statements in at least the above passages from the Republic as reflecting the views of Socrates’ interlocutors rather than the character of Socrates or Plato (Peterson, 2011, pp. 147–165). If Plato has commitment to forms of plant and animal species, the creation story of the Timaeus seems a natural place to look for it. In Timaeus’s account, we find a distinction between the created world of becoming and the eternal world of being (forms). Timeaus introduces the demiurge as architect and creator of the world of becoming. The demiurge takes as his templates for sensible things in the world of becoming the unchanging forms of the world of being (28b–31b). Perhaps in some tension with the supposition that Plato thinks that there is simply one form for each type of animal and plant, the Timaeus provides us with reason to entertain the idea that Plato posited a single form for all biological entities, Living Thing, a complex form that (somehow) encompasses the forms of all the animals (92c).22 There is of course the controversial question of to what extent Plato endorsed the story offered by Timaeus. Given that Plato put the story in the mouth of a character other than Socrates we might think on a Plato-centered interpretation that Plato wanted to distance himself from the account.23,24 However, Timaeus is careful to offer, at Socrates’ suggestion, a prayer to the gods and goddesses that his speech does not go too far astray. Our attribution of any commitment on Plato’s part to statements made by Timaeus should additionally be tempered by Timaeus’ characterization of what Johansen calls ‘‘the standards of cosmological argument.’’ (Johansen, pp. 470–471) Again, in Timaeus’s account, he introduces a distinction between the created world of becoming (in part, likenesses of forms) and the eternal world of being (forms). Timaeus seeks to provide an account of the principles governing the former (Johansen, 2008, pp. 463–467). Timaeus says that, ‘‘The accounts are of the same kind as the very things of which they are interpreters.’’ (29b–c) According to Johansen, From this principle, it follows that if this account is of being, and being is ‘‘stable and certain and transparent to rationality,’’ the account should have the same or related attributes; whereas if the account is of a likeness, then the account should be likely . . . likelihood for accounts of likeness is both the maximum and minimum to which they should aspire. (2008, p. 471) Accounts of being are to be approached through dialectic, as a search for that which is ‘‘stable, certain, and transparent to rationality.’’ Accounts of becoming are, on the contrary, are merely likely opinions whose standard is not transparency to reason, but the

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acceptance of wise men suited by ‘‘nature, education, and experience’’ to thoughtfully consider cosmology (Johansen, 472; 20a–b). Thus, even if we take it that Plato did endorse the creation story of the Timaeus, and the account of forms there and their relationship to plants and animals, we should be careful about what we take that endorsement to mean; perhaps at most the endorsement consists of granting the story the epistemic status of ‘‘likely.’’ The story is a defeasible account acceptable to those who have made a serious study. We have seen here that although characters in Plato’s dialogues do make comments suggesting forms (at least as explanatory definitions) for plants and animals, any attempt to give Plato ownership of these remarks faces challenges. (And we should keep in mind the possibility that some of the some uses of form-talk in the treated passages may also be interpreted as non-technical attention-focusing markers. Where this is the correct interpretation, the claim that Plato thought there were forms of plants and animals seems trivial.) It is not obvious that Plato consistently thought there are (technical sense) forms of plants and animals, and it is also unclear what such a belief on Plato’s part might entail. In the following section I explore some of the ways that one might think that evolution is in tension with at least certain interpretations of Platonic form-based essentialism about species. 6. How hard is it to make evolution a problem for Plato? Assuming that Plato did hold a view of biological species that could be well-described as essentialist, we can still ask if and how such a view is undermined by or inconsistent with gradual evolution. I am proceeding here with an intuitive sense of what it would mean for Plato’s views to be inconsistent with evolutionary biology; the question is roughly whether Plato believes something (e.g., about forms of plants and animals) that entails (logically implies) that species are immutable.25 Mayr claimed that evolution undermined essentialism in biology because it showed species to be dynamic and temporary phenomenon rather than static. ‘‘[G]radual evolution is basically a logical impossibility for the typologist.’’ (Mayr, 1959b, p. 2)26 However, Sober points out that the transmutation of elements does not seem to undermine essentialism in chemistry. That nitrogen can be changed into oxygen does not mean that there are not essential properties of nitrogen and oxygen. Similarly, that Homo sapiens evolved from an ancestral hominid species does not necessarily mean that the two species do not each have essential properties. While some historical essentialists (e.g. Agassiz) did advance static doctrines of species, others (e.g. the later Linnaeus) accepted that new species at least occasionally arose from other species (Sober, 1980, pp. 355–356). Does Plato’s putative essentialism of biological kinds fall prey to this stasis objection? There is indication in the Timaeus that Plato entertained the idea that biological kinds (of some sort) could emerge from other kinds. At 77b, Timaeus says that domestic plants came to be by the action of the art of agriculture upon wild plants; ‘‘But at first the only kinds were wild ones, older than our cultivated kinds.’’ Whether the wild and domesticated plants are different varieties, different species, different higher-order kinds, or variations of the same higher order-kind (or whether Plato made

22 Sellars (1959) interprets Living Thing as whole whose parts are the forms of particular animals. Seeing Living Thing as a complex form that contains simpler forms seems broadly consonant with the definition by division activity that we see (or see referenced) in the Sophist, Republic, Euthyphro, Gorgias, Protagoras, and Meno. Peterson (2011, p. 213) draws attention to these episodes. 23 Johansen (2008, p. 3) thinks it plausible that Plato put the creation story of the Timaeus in the mouth of a character other than Socrates in order to preserve coherence across the dialogues; the Socrates of the Apology disavows having done natural philosophy at 19c. 24 However, Lennox (1985) is among those who see the Timaeus as fulfilling ‘‘the fondest wishes of the Socrates of Phaedo 97–99,’’ i.e., wishes for teleological explanations (p. 208). 25 See Sober (1980) for objections to Mayr’s account for its failure to distinguish local from global essentialism and problematic language with respect to ‘‘reality’’ and ‘‘abstraction.’’ (pp. 350–355) 26 I interpret Mayr as using ‘‘typologist’’ synonymously with ‘‘essentialist’’ here. See Winsor (2006).

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any such distinctions here) is unclear, but in any case, the remarks are suggestive of transmutation. Further, the eugenics program as given in the Republic (459–461e) suggests that Plato was aware of the changes that could be induced in population lineages through artificial selection. The breeding ‘‘lottery’’ is meant to improve the guardians of Callipolis through the same process that improved the lineages of Glaucon’s hunting dogs and fighting birds; only the ‘‘best’’ men and women are to be paired and allowed to have offspring.27 Against attributing a stasis view to Plato, on a Plato-centered interpretation, it sometimes seems to be a necessary property of the world of becoming (which includes plants and animals) that it be able to become worse. In Book III of the Republic at 381b, Socrates says that those things that are most good are least susceptible to change, but this seems to suggest that even good things (in the world of becoming) are somewhat susceptible to change. Socrates seems to think that the degeneracy of just cities (and presumably analogous soul types) is inevitable (Republic Book VIII, 546). In light of these considerations, I hesitate to say that Plato rejected the idea that kinds could emerge from other kinds; as I see it, we cannot say with any certainty that his (purportedly essentialist) view is subject to the stasis objection to essentialism. If the stasis objection fails, Sober says that a more plausible view of the undermining of essentialism by evolutionary biology is the one advanced by Hull (1965). It is a consequence of gradual evolution that species boundaries are vague. Essentialism holds that there are essential properties endemic to each species. The essentialist requirement is thus seen as inconsistent with the continuities of biological entities. But given vague species boundaries, this requirement on species seems as implausible as demanding a specific number of hairs to delineate baldness from non-baldness. Sober says that the force is taken out of Hull’s argument when one considers that historical pre-Darwinian essentialists were aware of line-drawing (sorites) problems. E.g., Aristotle acknowledges the problem in History of Animals (5888b4 ff.), but nonetheless maintains his (per Sober) essentialist view. Sober sees this as a coherent position. There is nothing to prevent the essentialist from maintaining that there are vague properties essential to a given species. Sober does concede to Hull however that essentialism has historically been associated with a theory of definition in which vagueness is forbidden (Sober, 1980, p. 356). Gradual evolution would present a serious difficulty to biological essentialism wedded to a vagueness-proscribing theory of definition. Does Plato likely subscribe to a theory of definition that proscribes vagueness in a way susceptible to Hull’s argument? There are some reasons to think so. The Meno is in part an exploration of what Plato takes to be an adequate definition. At 73d, Socrates wants to add an additional qualifier to Meno’s definition of justice, suggesting that Socrates wanted more specificity. In the Euthyphro, Socrates’ questioning has the consequence of specifying Euthyphro’s definition of piety; Euthyphro begins by claiming that the pious is what is loved by the gods, and then must specify that the pious is what is loved by all the gods. Although Definitions was probably not written by Plato, the definitions therein were plausibly the sort of definitions pursued by at the Academy (perhaps as subjects for debate) under Plato’s direction and subsequently. In Definitions, ‘‘definition’’ is defined as ‘‘something said, comprised of genus and differentia.’’ (414d) It is not clear to me how much this sort of definition would admit of

the vagueness of properties that gradual evolution would seemingly require of an essentialist definition of species, or what the exact relation is between the definitions in Definitions and the forms found in the dialogues. With these qualifications in place, however, in Definitions the only species defined is man: ‘‘wingless, two-footed, flat-fingernailed animal; the only being capable of acquiring rational knowledge.’’ (415a)28 The focus on particular and at least somewhat well-specified biological character states suggests that Plato (or at least his students) did aspire to exclude vagueness from species definitions. Since it is possible that other beings may someday evolve the capacity for rational knowledge, it appears that the truth of evolution undermines this particular essentialist definition (though perhaps the deities were already a counter-example to this definition during Plato’s time) if we take it that what is wanted is a species definition that is necessarily rather than conditionally true. It is plausible then on a Plato-centered reading (and assuming that Definitions can tell us something about the degree of specificity sought in Platonic species definitions) that Hull’s argument has shown how a putatively Platonic essentialist view of the nature of species is incompatible with Darwinian evolutionary thought about the gradual evolution of species. Making this case stronger seems to require at least giving textual evidence for Plato’s having ownership of the moves towards specificity of definitional properties evidenced in the Meno and Euthyphro and historical evidence for associating the content of Definitions with Plato. Mayr’s argument for tension between gradual evolution and Plato’s essentialism probably fails. The stasis argument plausibly succeeds in highlighting a tension between a stasis-committed essentialism and evolution, but there are reasons against thinking that Plato held a view that is susceptible. Hull’s vagueness argument seemingly succeeds in giving a reason for thinking that essentialism along with a theory of definition that proscribes vagueness is incompatible with gradual evolution. There are some reasons to think that Plato might have held this sort of view of definition, but the case is rather weak in the absence of further work. 7. But what about the teleology? There is another contender for making sense of the intuition that there is a tension between modern evolutionary biology and Plato’s philosophy. There is an apparent preference, e.g. in the Phaedo (95e–105c), on Plato’s part for teleological explanation in the sense of explaining the features of the natural world in terms of the plan of a benevolent intelligent agent.29 Lennox (1985) says that, Plato puts forward two models of explanation which he clearly feels are preferable to those put forward by the ‘natural investigators.’ One of these types of explanation is teleological in nature . . . there is a persistent exploration of a model of skillful craftsmanship, a major theme of the Gorgias, Cratylus, Republic X, Timaeus, Statesman, Sophist, and Philebus. (p. 196) Even if attributing a considered view to Plato about teleology being a necessary part of all good explanations is perhaps premature, it is clear that this mode of explanation is a recurring feature of his thought. Mayr argues that Agassiz bases his anti-evolutionary views in part on belief in a Platonic ‘‘rational plan of the universe.’’ (1959a, p.168)

27 Also suggestive here are Socrates’ remarks on variation among the population of Callipolis; ‘‘For the most part, you will produce children like yourselves, but, because you are all related, a silver child will occasionally be born from a golden parent, and vice versa, and all the others from each other.’’ (Republic 414a–b) 28 See Lennox (1980) for a treatment of Aristotle’s reservations about definition by dichotomous division. 29 See, e.g., Phaedo 97c for the link between intelligence and benevolence.

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If everything in the world follows an underlying plan, it becomes the task of the naturalist to discover the a priori principles of this plan. An empirical approach toward an establishment of general principles would be a disorderly and futile method in a rational world. (p. 169) Mayr does not specify what he has in mind with respect to ‘‘empirical’’ and ‘‘a priori’’ here. I have difficulty seeing how the belief in a (divine) rational plan for the natural world leads inevitably to an anti-empirical approach. Mayr acknowledges that Agassiz did worthwhile work, work that appears to me empirical in the minimal sense of drawing conclusions about the way nature operates (with no immediate recourse to supernatural explanation) based on careful observation (1959a, p. 168). And Agassiz’s contemporary, Asa Gray, held Christian beliefs in divine creation that were apparently no barrier to his spending his career poring over dried plants (and finally drawing evolutionary conclusions) rather than searching for a priori principles (Dupree, 1988). Still, one might think that Mayr is correct insofar as evolutionary explanations might not even be the kind of explanation that would satisfy Plato. Turning again to Socrates’ autobiographical digression in the Phaedo, if the case can be made that Plato rejected natural-science-type explanations (like evolution by natural selection), key textual evidence seems likely to be found in this passage. As Vlastos puts it, The importance of this passage could hardly be exaggerated: as much is to be learned from it about Plato’s metaphysics, epistemology, and philosophy of science as from any other text of equal length in his corpus. But it is also one of the most perplexing. Scholars who have not confessed its difficulty have evidenced this difficulty just the same in the wild diversity of the interpretations they have put on it. (1969, p. 291) Indeed, this passage of the Phaedo offers one of Plato’s most extensive treatments of causation, but there is considerable disagreement about what should be made of this treatment. For our purposes, I will make use of David Sedley’s influential interpretation that reads ‘‘cause’’ in these passages as ‘‘thing responsible.’’ (1998) At 96a– 102a, the character Socrates gives an account of the development of his own views about causes. Socrates says that in his youth, he was interested in ‘‘that wisdom which they call natural science.’’ As an example of this sort of wisdom, Socrates gives the belief that the cause of a man’s growth is food and drink, because ‘‘food adds flesh to flesh and bones to bones.’’ (96d) The cause of growth here, the thing responsible, is flesh. But Socrates says that he ‘‘has no natural aptitude for that kind of investigation.’’ (96c) Socrates claims to be confused by the apparent contradictions common to these sorts of causal claims. For example, if flesh is the cause of growth, then flesh is also the cause of shrinking (e.g., of the food when flesh is removed from the food through eating), the opposite of growth (Sedley, 1998, p. 119). Flesh, it seems, for Socrates, is not correlated in the right way with growth for flesh to be the cause of growth. Sedley labels this sort of causation as ‘‘spurious cause.’’ These causes left Socrates in confusion because they are the sorts of things liable to bring about results that are in some sense opposites, e.g., growing and shrinking. Socrates, on Sedley’s view, apparently sees claims that a thing causes opposite results as highly problematic (pp. 117–118). Although this passage has led many to think that Socrates (and Plato, on a Plato-centered interpretation) rejected natural science in toto, there are some considerations that should lead us to caution in drawing that conclusion. First, on one plausible interpreta-

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tion, Socrates does not commit himself to the rejection of natural causes per se, but only points out a flaw in a certain locution used by some natural philosophers with pretenses of providing an adequate causal story.30 E.g., for Socrates, when Anaxagoras says that ‘‘air and ether and water and many other strange things’’ are the cause of the world being as it is, there is reason to doubt that we thereby have an adequate etiological account. Famously, Socrates says that such accounts are as absurd as saying that the reason that he is in prison (rather than escaping) is bones and sinews. The absurdity is apparent once we realize that bones and sinews are just as compatible with escaping as they are with staying in prison (98c– 99c). Similarly, air, ether, etc. are compatible with the world being other than how it is, and so cannot explain the actual state of the world. This does not seem to be an unreasonable criticism of a certain sort of causal claim, and it does not obviously commit one to the rejection of natural sciences; one might think that this sort of criticism might lead to more adequate explanatory standards for natural sciences. Although Socrates characterizes ‘‘that wisdom that they call natural science’’ as offering this sort of problematic causal language, the mapping of this sort of causal locution and Socrates’ objection to it onto our modern conception of natural science is not straightforward, and it is far from clear that evolution by natural selection, properly described, is subject to this criticism. In the Apology at 19c, Socrates, speaking of ‘‘studying things in the sky and below the earth,’’ says, ‘‘I do not speak in contempt of such knowledge if someone is wise in these things.’’ It is not transparent on the basis of textual evidence that the Socrates of either the Apology or the Phaedo was committed to the rejection of natural science. But even if Plato did not reject the sorts of explanations offered by what we now call natural science, perhaps Plato thought that this sort of explanation was not complete. Maybe, for Plato, even if we have an adequate account of some feature of the world in terms of natural causes, a complete explanation also requires a teleological component. Assuming that Plato was committed to considering the inclusion of a teleological component as necessary for a complete explanation, there are long-recognized philosophical reasons for thinking that such a requirement is not clearly incompatible with the truth of any particular naturalistic explanation, including evolution by natural selection. The reason for this, in short, as Descartes was wont to point out, is that we do not have access to the mind of God (Descartes and Cottingham 1985, p. 202). In a more recent instantiation of this general point, Sober (2007) concludes that intelligent design theory fails to be a serious scientific alternative to evolution by natural selection because the former (without making substantial assumptions about the intentions of God and the nature of divine action) has no clear observational predictions that differ from those of the latter. As Sober has it, ‘‘Taken alone, the statement that an intelligent designer made the vertebrate eye does not have observational consequences other than the entailment that vertebrates have eyes.’’ (p. 5) Because we do not know the intentions or modes of action of the Creator we cannot know what kind of world such a being would create or how they would do it. Therefore, it is perfectly coherent to claim, for example, that evolution by natural selection is the workmanship of a demiurge whose intentions were, as the Timaeus would have it, aimed at what is best (30a–b). The additional teleological layer of this explanation is, on contemporary notions of science, extrascientific to be sure. But the explanatory strategy is not impugned by incoherence, and if proponents of this sort of dual-level expla-

30 Though Sedley himself seems to reject the view that Socrates is merely criticizing a certain way of speaking about causation; for Sedley, for Socrates, ‘‘the aim of causal inquiry is to identify the thing responsible, no matter under what description.’’ (p. 122)

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nation have independent philosophical or theological reasons to posit such a creator, then supernatural teleological additions to naturalistic explanations may be quite reasonable. We have seen that Plato did not obviously reject what we now think of as natural science, and that the alleged teleological commitments of Plato are not obviously incongruous with belief in Darwinian evolution. But there is at least one belief about biology that is straightforwardly inconsistent with a belief in Darwinian evolution. This is the belief, held by Louis Agassiz, that species were each specially created immutably in their present form. In the next section, I will suggest that Ernst Mayr attributes anti-evolutionary beliefs to Plato in part on the basis of associating Plato with Agassiz.31 8. Plato and Agassiz: guilt by association Louis Agassiz held views that were explicitly anti-evolutionary and specifically (at least for long periods of his career) believed that species were immutable and specially created (Lurie, 1959). Mayr diagnoses Agassiz’s resistance to evolution on the basis of ways of thinking that Mayr takes to have their ultimate origin in Plato. Here are two revealing quotations from Agassiz that Mayr uses to support his thesis: Natural History must, in good time, become an analysis of the thoughts of the Creator of the Universe, as manifested in the animal and vegetable kingdoms. (Agassiz, 1857, p. 135; Mayr, 1959a, p. 171) As the community of characters among the beings belonging to these different categories arises from the intellectual connection which shows them to be categories of thought, they cannot be the result of a gradual, material differentiation of the objects themselves. (Agassiz, 1860, p. 143; Mayr, 1959a, p 173) Agassiz’s ‘‘categories of thought’’ does at least superficially sound much like popular conceptions of Platonic forms. In the second quotation, Agassiz marshals a conception of biological entities as categories of thought in an argument against Darwinian evolution. One can see how easy it would be to conclude that Plato’s eidos is inherently anti-evolutionary. Further, Agassiz, as in the first quotation, interpreted the world as a product of a divine plan, and Plato’s writings also suggest a strong interest in interpreting the world in this way. Given that Agassiz was a convinced anti-evolutionist, and his thought bears strong apparent resemblance to Plato’s with respect to its idealistic elements and its teleology, it is perhaps unsurprising that Mayr interpreted Plato as he did. But it is rash to judge the thinkers of the past based upon the views of their interpreters or those who held apparently similar views. I will close now by making a few general remarks about the Platonic dialogues and claims about the entailment relations between various metaphysical views and the theory of evolution by natural selection. 9. Losing Ernst Mayr’s Plato Plato wrote fictional dialogues with strong dramatic elements about philosophical themes. Discerning the considered philosophical positions of the authors of such works on the basis of the words and deeds of the characters in them is difficult. Plato’s dialogues are widely interpreted as being centrally about ethics, how to live the best life. Even in the case of the long cosmological monologue in the Timaeus, the project is often seen by scholars 31 32 33 34

as more edificatory than scientific.32 In cases where the dialogues deal with more metaphysical topics, i.e. forms, it is notoriously difficult to pin Plato down to a recurrent and consistent view. My own view is that it is more reasonable to read such passages as explorations of philosophical ideas and their consequences rather than treatises arguing for them. This sort of reading is amenable to appreciating what Grene (1989) has called ‘‘the inexhaustible richness and deep pluralism of Plato’s thought,’’ and also amenable to the avoidance of an unwarranted conflation of what Plato wrote with ‘‘some very general tendency that gets called ‘Platonism’ or specific doctrines of specific members of the neo-Platonic tradition.’’ (p. 69) Darwin’s theory of evolution by natural selection is about biological organisms and their histories, not philosophical ethics, religion, or metaphysics, though interpretations of his theory have been used to argue for a wide variety of views about all three. Throughout the history of the science, prominent evolutionary biologists have held wildly diverse positions on the meaning of evolution for philosophy and religion.33 This heterogeneity suggests that if there are any necessary connections between certain metaphysical, ethical, or religious views and Darwinian evolution, those connections are not apparent in any consensus-generating way to those most familiar with the science. It appears that the only sorts of beliefs that are obviously inconsistent with evolution by natural selection are beliefs about biology. Louis Agassiz held clearly and explicitly anti-evolutionary views in biology and philosophical views that recall popular interpretations of Platonic philosophy. But the fact that these sets of beliefs resided in the same infamous 19th century biologist ought not unduly influence our interpretations of the ancient philosopher, or lead us to believe that what Plato wrote is foundational to the recalcitrance of some biologists at the dawn of the evolutionary era. Ernst Mayr’s case for seeing Plato as a philosopher who held views that are strongly at odds with evolutionary biology looks suspect at best. First, there is relatively little consensus among Plato scholars about the meaning of much of Plato’s work, as the voluminous Plato literature attests. Second, even if we could say with some certainty what Plato thought or meant in his dialogues, there are reasons to deny that putatively Platonic views like certain varieties of essentialism and teleology entail any straight-forward inconsistency with the core elements of Darwin’s theory. Mayr’s essentialism narrative continues to echo through discussions of both the history of biological thought and current attempts to conceptualize important biological kind terms (e.g.,‘‘species’’ and ‘‘vertebrate limb’’).34 But for the reasons presented here, I think it time that interlocutors in these discussions, biologists and those of us in science studies, exercise more caution with respect to glib references to Plato’s view of nature and idiomatic deployment of ‘‘Platonic essentialism.’’ Acknowledgements Thanks to Lee Shepski, Clerk Shaw, Sandra Peterson, Alan Love, Greg Radick, and two anonymous reviewers for encouragement and helpful comments. References Agassiz, L. (1857). Contributions to the natural history of the United States of America, by Louis Agassiz. Brown. Accessed 22.08.13.

Mayr claims that Popper was influential in his reading of Plato. See Klosko (1996) for an assessment of Popper’s treatment of Plato. See, e.g., Lennox (1985, p. 218) and Johansen (2008, Introduction). See, e.g., McGrath (2011) and Ruse (2009). See Pigliucci (2003) and Love (2009).

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