Aristotle's Biology Was Not Essentialist
D.M. Balme
In Gotthelf and Lennox, eds., Philosophical Issues in Aristotle's Biology
Cambridge, 1987

"To account for animal features, Aristotle tells us to distinguish those that are for the sake of something from those that arise necessarily from the matter. (GA V 778a29-b19; PA I 640a33-b4) Eyes are for something; but their color is owed only to their matter and the movements of matter. Therefore the eyes are to be included in the animal's 'definition of being', (GA V 778a32-35) while their particular color is not. He makes the same distinction between features included in and excluded from the form (eidos): neither color nor sex is included in form by itself, but both are due to the matter in the composite form-in-matter. (Metaphysics I 1058b2). (BALME-1987a, p. 294) [PSA: this might provide an Aristotelian case against sexism and racism.]

"The fundamental difference between animals, he suggests, is the difference in their natural heat. Because of this, they differ in their perfectedness. Then, given that each animal has a basic capability determined by its heat, the next determinant is environment and lifestyle, which together explain functions and organs." (BALME-1987a, p. 300)

"[W]hy do animals differ? ... His answer is the double explanation, 'necessity' and 'the better'. Given the necessary limitations of heat and environment, each animal form is the best possible: that is, the form which brings it the most functional advantage, what Aristotle often calls 'the useful'." (BALME-1987a, p. 301)

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