The kind of essentialism that has been attributed to Aristotle's biology either identifies form and species, or recognizes individual forms merely as variations from a basic specific form. The essentialist holds in particular that each animal's growth is directed primarily towards the form of the species; that its essence prescribes its form; and that animal form excludes material accidents such as eye color.

These views, although apparently supported by various statements in Aristotle's logic and metaphysics, are directly opposed to some of his most mature and carefully argued theories in biology. Moreover those theories agree closely with one plausible interpretation of the disputed books Metaph. ZH. In this paper I confine myself to the biology; but I would suggest that there is ground here for supporting those who have recently been questioning the ‘essentialism’ in the logic. Here I argue that in the GA Aristotle holds that the animal develops primarily towards the parental likeness, including even non-essential details, while the common form of the species is only a generality which ‘accompanies’ this likeness. In PA he argues for teleology with the question ‘What benefits an animal of this kind?’, not with the question ‘What benefits all animals of this kind?’. He treats species as merely a universal obtained by generalization. While it is true that species-membership may help to explain the features of individuals, this is not because species is an efficient cause of individual formation, but because individuals in like circumstances are advantaged by like features.