Anne Peterson

Homology is a biological sameness relation that is purported to hold in the face of changes in form, composition, and function. In spite of the centrality and importance of homology, there is no consensus on how we should understand this concept. The two leading views of homology, the genealogical and developmental accounts, have significant shortcomings. We propose a new account, the hierarchical-dependency account of homology, which avoids these shortcomings. Furthermore, our account provides for continuity between special, general, and serial homology.

The Extended Evolutionary Synthesis (EES), given the significance it places on evolutionary developmental biology, has been associated with Aristotles hylomorphism. But how deep does this association run? In the context of his biological writings Aristotle zeroes in on two methodological principles alongside his hylomorphic ontology – principles of particular significance for the biological arena. One of these principles denies the Empedoclean claim that the order of explanation is exhausted by the temporal order of development or, in Aristotles terms, the order of material causes. The second denies the Democritean claim that animals and their parts can be exhaustively explained in terms of static, structural forms – forms are dynamic and active, indeed interacting with the order of material causes. Focusing on the post-Darwinian concept of homology, I argue that the debate between Empedocles, Democritus, and Aristotle on the proper methodology for investigating animal parts is far from obsolete. First, the EESs preferred developmental account of homology was articulated in response to recognizably Empedoclean and Democritean implementations of the prominent alternative historical account of homology. Second, despite key contextual differences, the developmental account is not merely superficially hylomorphic; it embodies the very methodological principles that Aristotle associates with hylomorphism in his own biological writings.

Socrates and Plato are one in species, but diverse in number. What accounts for their diversity in this sense? This question lies at the center of a longstanding controversy over what has been called the principle of individuation. Though multiple questions have been investigated using the terminology of individuation, the author’s focus here is on the question of what, for Aristotle, explains the numerical diversification of cospecific organisms, along with the two mainstream answers to this question: that their diversity derives from the diversity of their matter, or that it derives from the diversity of their forms. She argues that if we take Aristotle’s metaontology as our starting point for investigating this question, both of the mainstream views falter for the same reason. Aristotle’s analyses of the concepts of unity and diversity support the conclusion that the diversity of cospecific organisms is underived.

Aristotle insists that the organic matter composing an organism depends for its being and becoming upon the living organism whose organic matter it is. An evolutionary context may at first seem to secure autonomy for an organism’s organic matter: after all, in such a context not only can organisms in divergent taxa have the same trait, but a trait can remain the same through thoroughgoing changes in its form, function, composition, and organismic context over evolutionary time. The biological homology concept attempts to capture this mysterious relationship of trait sameness. However, accounts of biological homology that have dominated the contemporary scene face compelling problems—these problems, I will argue, arise from their exclusion of the organism as an explanatory locus for the being and becoming of biological traits. An evolutionary framework in fact supports an account of homology that retains these two aspects of Aristotle’s views on organic matter.

In his account of epistēmē, the highest level of understanding attainable in philosophical inquiry, Aristotle articulates standards for the ideal explanations that confer this level of understanding. I argue that Aristotle's key standard for epistēmē is of central importance for the biological homology concept. The explanatory shortcoming that results from violating this standard has been vaguely articulated in recent literature on homology; Aristotle's account offers a more neutral and precise formulation of the shortcoming and its antidote. Further, the risk for this shortcoming has heightened with recent accounts of homology grounded in genetics, increasing the contemporary relevance of Aristotelian epistēmē.

The traditional concept of prime matter – a purely potential substratum that persists through substantial change and serves to constitute the generated substance – has played a dwindling part in Aristotelian scholarship over the centuries. In medieval interpretations of Aristotle, prime matter was thought to play these two roles in all substantial changes, not only in changes at the level of the four elements. In more recent centuries, traditional prime matter was relegated only to the context of substantial changes between the four elements. And in the last few decades of Aristotelian scholarship, it has become common either to downplay or even to eliminate prime matter’s role in elemental changes too. I will support the traditional concept of prime matter by showing that it aligns Aristotle’s view of elemental change with one of the central constraints on matter imposed in his Physics to a degree that cannot be achieved on the non-traditional interpretations: the need for matter to be in potentiality in a way that avoids the two problematic extremes of mere persistence, on the one hand, and destruction, on the other. This point will be supported by Aristotle’s rejection of both monism and pluralism in On Generation and Corruption. Second, I will argue that Aristotle calls for precisely the same kind of potentiality in a very different context: his critique of Anaxagoras’s view of matter in the Generation of Animals. Here the very same problematic extremes of mere persistence and destruction that plague the alternate views to traditional prime matter also plague the dominant views on the matter for animal generation. Especially since Aristotle takes living things to be paradigmatic substances, these comparisons suggest that the apparent idiosyncrasies of elemental transformation which have motivated interpreters to depart from traditional prime matter may not be so idiosyncratic after all. And if that is so, it may be that the problem lies not so much with traditional prime matter as with our assumptions about how persistence and constitution work in substantial change according to Aristotle. In the end, this line of argument opens the door to three new potential interpretations of the matter for substantial generation in Aristotle, interpretations which align with his concept of potentiality and – to varying degrees – with traditional prime matter as well.

How should we understand the relationship, for Aristotle, between matter, form, and hylomorphic composite? Are matter and form distinct from each other, so that each hylomorphic unity harbours a plurality within it, or would such a plurality undermine the unity of the composite? A recent strand of argument in both Aristotelian and contemporary literature on hylomorphism has concluded that no genuine unity can be composed of a plurality. I will argue that the objection motivating this conclusion falls away as improperly formulated in light of Aristotle's metaontology—in particular, his thesis that unity is indeterminate. The genuine objection threatening hylomorphic unity is one that Aristotle himself formulates as a central concern in his Metaphysics: no substance can be composed of substances. He answers this genuine objection in his appeal to the actuality/potentiality distinction, and in Metaphysics VIII.6 he reminds us why no more basic problem of hylomorphic unity arises. Against the backdrop of Aristotle's metaontology, hylomorphic unity cannot be undermined by the plurality, just as such, of matter and form.