Plato’s Academy, located in an Athenian olive grove, produced many scholars. Th e most famous of them by far was Aristotle (–
...). He was born at Stagirus, a Greek colony on the Macedonian coast, the son of Nichomachus, the personal physician to Amyntas III, the king of Macedonia. His father died while Aristotle was a boy, and he was raised by a guardian. In about ..., when he was , Aristotle joined Plato’s Academy and remained there for years as a pupil and later as a teacher. He left after Plato’s death and spent time in Anatolia and the island of Lesbos before returning to Macedonia in
... Amyntas had died, and the new king, Philip II, appointed Aristotle as tutor to his son Alexander, who later became Alexander the Great. Aristotle returned to Athens in about ..., where for the next years he taught at the Lyceum, a school established in the grounds of the temple to Apollo Lyceius, hence its name. Alexander died in ..., and those who opposed the Macedonians became powerful in Athens. Aristotle’s name was linked to that of a Macedo- nian general, and he was charged with impiety—a capital off ence. He avoided trial by moving to Chalcis (modern Khalkis) on the island of Euboea, north of Athens, which is where he died the following year.
Aristotle had many interests, but he devoted a great deal of his time to natural history. He established a zoo at the Lyceum, stocking it with animals captured during Alexander’s Asian campaigns, and he studied the natural history of Lesbos as well as of adjacent areas and the surrounding seas. Aristotle broke from the Platonic way of thinking. Plato had emphasized the primacy of ideas over observa- tion, which he considered illusory. Aristotle emphasized careful observation. His studies of animals involved dissection. He broke open chicken eggs at intervals between fertilization and hatching and
recorded the order in which organs developed. He recognized that sharks and rays were closely related, and he distinguished between aquatic mammals and fi shes.
In the nine books of his work Th e History of Animals, Aristotle described more than species, including species of fi sh and
species of insects. He distinguished between vertebrates and inver- tebrates, although he called them “sanguinea” (animals with blood) and “animals without blood.” He divided the animals with blood into those that bear live young and those that lay eggs. His “animals without blood” included insects, mollusks, and crustaceans with and without shells. Aristotle also wrote On the Generation of Animals, in fi ve books. Th is work describes all the diff erent ways in which ani- mals reproduce and goes into the details of reproductive anatomy.
Although Aristotle relied on observation, the conclusions he drew were often mistaken. In the third book, in trying to explain why some birds lay more eggs than others, for instance, he had the following to say about the cuckoo:
Th e cuckoo, though not a bird of prey, lays few eggs, because it is of a cold nature, as is shown by the cowardice of the bird, whereas a gen- erative animal should be hot and moist. Th at it is cowardly is plain, for it is pursued by all the birds and lays eggs in the nests of others.
A more sympathetic commentator might interpret fl eeing from pursuers and hiding its eggs in the nests of other birds as the behavior of a victim rather than a coward! In any case it is wrong, of course, for the cuckoo is a highly successful brood parasite, which is why other birds try to drive it away from their nests. Aristotle realized that ani- mals cannot be classifi ed on the basis of their reproductive method, as the following passage from the second book illustrates.
Not all bipeds are viviparous (for birds are oviparous), nor are they all oviparous (for man is viviparous), nor are all quadrupeds ovipa- rous (for horses, cattle, and countless others are viviparous), nor are they all viviparous (for lizards, crocodiles, and many others lay eggs). Nor does the presence or absence of feet make the diff erence between them, for not only are some footless animals viviparous, as vipers and the cartilaginous fi shes, while others are oviparous, as the other fi shes and serpents, but also among those which have feet
many are oviparous and many viviparous, as the quadrupeds above mentioned. And some which have feet, as man, and some which have not, as the whale and dolphin, are internally viviparous.
Aristotle distinguished animals by a moral standard based on the ratio of the four elements in them:
. . . it is those animals which are more perfect in their nature and participate in a purer element which are viviparous, for nothing is internally viviparous unless it receive and breathe out air. But the more perfect are those which are hotter in their nature and have more moisture and are not earthy in their composition.
It was not until the th century that biologists confi rmed certain of Aristotle’s observations. For example, male cephalopods (octopuses, squid, cuttlefi sh, and nautilus) possess a specialized tentacle called a hectocotylus that is used to store sperm and transfer it to the female.
During mating the hectocotylus sometimes breaks off and males usu- ally grow a new one for each mating season. Aristotle described the hectocotylus, probably relying on information from local fi shermen.
Naturalists dismissed the idea until the organ was rediscovered and named by the French zoologist Georges Cuvier (–). Aristotle also observed that in a species of dogfi sh known as the dusky smooth- hound (Mustelus canis), the young develop inside the mother’s body attached to a structure resembling a mammalian placenta—in fact, a yolk sac. Again, naturalists dismissed the idea until , when the German physiologist Johannes Peter Müller (–) verifi ed it.
Aristotle seems to have possessed boundless energy, and his con- tribution to zoology was huge. Apart from his own work, he provided guidance for his pupils in the form of lectures and encouragement to undertake research. His classifi cation of animals was often highly perceptive, but his aim was to seek the most fundamental charac- teristics, of which other characteristics were the consequences. Th is allowed him to arrange animals into a great chain of being, with those possessing the most basic features at the bottom and other ani- mals ranged above them in levels of increasing complexity. Th e chain comprised an unbroken sequence of animals, and it united every spe- cies. Th e diagram opposite shows how Aristotle arranged animals.
His chain of being remained popular until it was fi nally abandoned
in the th century as evolutionary theory rendered it irrelevant—as well as incorrect.
Aristotle accepted that every organism must perform a particular function, which meant that its basic features were usually fi xed, but he did not accept Plato’s idea that each species refl ects an idealized form. Species could change, although their capacity to do so was limited by the fact that off spring resemble their parents. He accepted that animals existed to serve humans, but in his day—and for long afterward—no one questioned that.