In the fascinating book Sex at Dawn, Christopher Ryan and co-author Cacilda Jethá, MD, explore how humans' prehistoric promiscuity (perhaps similar to the bonobos') may have influenced our current attitudes toward pair-bonding, monogamy and long-lasting passion. Their thesis draws on evidence from anthropology, archeology, primatology, anatomy and psychosexuality.

As a psychologist, Ryan’s research focuses on trying to distinguish the human from the cultural. His book, he hopes, is "pointing toward a more optimistic future illuminated by our innate capacities for love, cooperation and generosity."