Language and culture are often seen as unique characteristics of human beings. In this book the author argues that our ability to use a wide array of emotions evolved long before spoken language and, in fact, constituted a preadaptation for the speech and culture that developed among later hominids. Long before humans could speak with words, they communicated through body language their emotional dispositions; and it is the neurological wiring of the brain for these emotional languages that represented the key evolutionary breakthrough for our species.

How did natural selection work on the basic ape anatomy and neuroanatomy to create the hominid line? The author suggests that what distinguished our ancestors from other apes was the development of an increased capacity for sociality and organization, crucial for survival on the African savanna. All apes display a propensity for weak ties, individualism, mobility, and autonomy that was, and is today, useful in arboreal and woodland habitats but served them poorly when our ancestors began to move onto the African plain during the late Miocene.

The challenge for natural selection was to enhance traits in the species that would foster the social ties necessary for survival in the new environment. The author suggests that the result was a development of certain areas of the primate brain that encouraged strong emotional ties, allowing our ancestors to build higher levels of social solidarity. Our basic neurological wiring continues to reflect this adaptive development. From a sociological perspective that is informed by evolutionary biology, primatology, and neurology, the book examines the current neurological bases of our emotional repertoire and their implications for our social actions.