There have been many attempts to determine what it means to be human. At one time, biologists suggested that humans were the only tool users. However, many different animals use tools. Some scientists thought humans were the only animals that had language. But we now know that many animals use sophisticated communication systems similar to language. It would be an ironic twist if the thing that makes us most distinctly human is our relation to other animals, but as far as we know, humans are the only animals that keep other animals as pets.

Humans have had relationships with animals for as long as there have been humans. The human record, from prehistoric through the classical and modern periods and in every culture, is filled with examples of animals helping to shape our understanding of ourselves. Animals figure in our traditions, in our religions...