Aristotle (384–322 BC) studied at Plato's Academy in Athens, remaining there for about 20 years. Like Plato, he sought universals in his philosophy, but unlike Plato he backed up his views with detailed and systematic observation, notably of the natural history of the island of Lesbos, where he spent about two years, and the marine life in the seas around it, especially of the Pyrrha lagoon in the island's centre. This study made him the earliest scientist whose written work survives. No similarly detailed work on zoology was attempted until the sixteenth century; accordingly Aristotle remained highly influential for some two thousand years. He returned to Athens and founded his own school, the Lycaeum, where he taught for the last dozen years of his life. His writings on zoology form about a quarter of his surviving work. Aristotle's pupil Theophrastus later wrote a similar book on botany, Enquiry into Plants.
Aristotle argued by analogy with a woodcarving
that a thing takes its form both from its design and from the material used.
Aristotle's biology is constructed on the basis of his theory of form, which is derived from Plato's theory of Forms, but significantly different from it. Plato's Forms were eternal and fixed, being "blueprints in the mind of God". Real things in the world could, in Plato's view, at best be approximations to these perfect Forms. Aristotle heard Plato's view and developed it into a set of three biological concepts. He uses the same Greek word, εἶδος (eidos), to mean first of all the set of visible features that uniquely characterised a kind of animal. Aristotle used the word γένος (génos) to mean a kind.[a] For example, the kind of animal called a bird has feathers, a beak, wings, a hard-shelled egg, and warm blood.
Aristotle further noted that there are many bird forms within the bird kind – cranes, eagles, crows, bustards, sparrows, and so on, just as there are many forms of fishes within the fish kind. He sometimes called these atoma eidē, indivisible forms.[b] Human is one of these indivisible forms: Socrates and the rest of us are all different individually, but we all have human form.
Finally, Aristotle observed that the child does not take just any form, but is given it by the parents' seeds, which combine. These seeds thus contain form, or in modern terms information.[c] Aristotle makes clear that he sometimes intends this third sense by giving the analogy of a woodcarving. It takes its form from wood (its material cause); the tools and carving technique used to make it (its efficient cause); and the design laid out for it (its eidos or embedded information). Aristotle further emphasises the informational nature of form by arguing that a body is compounded of elements like earth and fire, just as a word is compounded of letters in a specific order.[d]