What is it that allows human beings to think the way we do? What enables us to communicate with one another through the use of speech? Is the difference between Homo sapiens and other apes simply a matter of degree or are we unique and discontinuous from other species? Michael C. Corballisargues that this century-old debate lies in the fact that humans are the only primates that are predominantly right-handed, a sign of the specialization of the left hemisphere of the brain for language. He attributes humans' unique abilities to a biological mechanism in the left hemisphere of thebrain called a "generative learning device" or GAD. The GAD, Corballis contends, enables us to generate a limitless number of forms and meanings from a few parsed elements, providing the basis for language and manufacture as well as mathematics, reasoning, art, music, and play. Surveying thecurrent views of evolution using evidence from archeology, linguistics, neurology, and genetics, Corballis takes us on a fascinating tour of the origins and implications of the structure of the human brain accounting for the dominance of humanity over all species.