This book investigates the evolutionary origins of human intelligence by proposing that the brain functions as a biological signal of fitness, analogous to the elaborate plumage of a peacock. Christopher Wills, a professor of biology, utilizes principles of evolutionary genetics and comparative anatomy to argue that human cognitive development was driven by sexual selection and the accumulation of past survival successes. He posits that the brain's rapid expansion was not merely a tool for survival, but a mechanism for signaling genetic quality and social competence. The text synthesizes research from anthropology, genetics, and neurology to construct a framework for understanding the runaway nature of human mental evolution.

This work is regarded as a provocative contribution to evolutionary psychology that challenges traditional adaptationist views of the human mind. The text provides a dense, theory-driven exploration of biological signaling that remains accessible to readers interested in the intersection of genetics and human behavior.