System of Classification

Aristotle developed the first system of classification of animals. He based his classification system off of observations of animals, and used physical characteristics to divide animals into two groups, and then into five genera per group, and then into species within each genus. Aristotle's two major groups of animals are dependent on whether or not they have "red blood." Animals with red blood correspond to vertebrates, and animals without red blood correspond to invertebrates.

Here is a diagram showing Aristotle's classification of animals into ten genera: