Parts of AnimalsAristotle
About Parts of Animals
is Aristotle's most systematic work of comparative anatomy and his clearest statement of teleological explanation in biology. Book I lays out the method: the natural philosopher must explain not just what the parts of animals are made of (material cause) but what they are for (final cause). Nature does nothing in vain. Each organ exists for the sake of some function, and understanding an animal means understanding how its parts serve its way of life.
Books II through IV catalog the parts themselves, organized not by species but by tissue type and organ system: uniform parts (blood, bone, fat, marrow) and non-uniform parts (heart, liver, lungs, hands). Aristotle moves between precise observation and functional analysis. The elephant's trunk is both a breathing organ and a hand; its size requires a snorkel when the animal crosses deep water. Horns, teeth, and claws serve as instruments of defense, and nature distributes them according to a principle of compensation: what is given to one organ is taken from another.
The work stands at the origin of comparative biology. Aristotle did not have a theory of evolution, but his method of explaining organic structure through function, his attention to the correlation of parts, and his insistence that the biologist must study the whole organism rather than just its material composition set terms that anatomists and natural historians followed for two millennia.