Aristotle on biology, by Lennox
One cannot understand how any aspect of biology developed until one understands Aristotle's contribution and inspiration to it. In my own area, Aristotle is responsible for the development of a logic of investigation (one hesitates to call it "science" as yet) that is the logic of diairesis, or division. The conception of "species" as the smallest group of related individuals comes directly from Aristotle (the term "species" is a Latin translation of the Greek term eidos, from which we also get "idea"). But there were some limitations to the way Aristotle tried to apply this taxonomic notion - it relied on the referents of terms already being natural. Lennox has this to say:
The notion of an "essence" (in Aristotle's terminology, the "what-it-is-to-be-that-thing") is supposed to resolve this. Essential properties were those that a thing needed to have in order to be that kind of thing, but doing science by definition turned out in the longer run to be unsatisfactory (although this didn't become apparent until the 15th century or so), and the empirical turn that followed sat uncomfortably with Aristotle's scientific enterprise.
What is clear from the practice of the History of Animals is both the value of division and its limitations. Division by itself does not provide you with the axes of division; rather they are presupposed. Division does not give you animal kinds; as we saw in the previous section, one needs to turn to PA I 4 and HA I 6 for Aristotle's thoughts on how those kinds are established. Something besides division is needed in order for a researcher to recognize theoretically significant kinds. Why group animals together based on their possession of four legs and the ability to produce living offspring (rather than eggs)? Certainly each of these traits is the product of a division, one of modes of locomotion and one of modes of reproduction. But those divisions do not tell you that animals with four legs that bear living young constitute a scientifically significant group.
A second limitation of division is its indifference to the distinction between causally fundamental characteristics and proper attributes, to use the language of the Analytics. Yet, being able to distinguish these is absolutely fundamental to Aristotelian science. A careful comparative study of the History of Animals, on the one hand, and works such as On the Parts or On the Generation of Animals again provides insight into how Aristotle understands and deploys this distinction in his actual scientific practice. And as we have seen above, Aristotle draws explicit attention to its importance for his biological investigations in a number of key texts within those investigations themselves. To study in detail the interplay between definition, causal demonstration and division in the biology is to see Aristotle working through just those problems which form the central question of Posterior Analytics II—how precisely are definition, causal demonstration and division related to one another in the quest for, and achievement of, scientific understanding?
Modern biology generally tends to avoid using definitions as a way to solve scientific problems, but Aristotelian approaches are endemic. A recent proposal to classify genes according to what is basically the Aristotelian diairesis, the Gene Ontology Project, is gaining ground in part because database structures are basically just diairetic logics. It is useful at explicating much of what we do know but haven't explored yet. But I fear it will constrain investigation in ways we don't expect.