Progression of Animals

Progression of Animals (or On the Gait of Animals; Greek: Περὶ πορείας ζῴων; Latin: De incessu animalium) is one of Aristotle's major texts on biology. It gives details of gait and movement in various kinds of animals.

Aristotle's approach to the subject is to ask "why some animals are footless, others bipeds, others quadrupeds, others polypods, and why all have an even number of feet, if they have feet at all; why in fine the points on which progression depends are even in number." It is a good example of the way he brought teleological presumptions to empirical studies.