We highlight the emerging sexual differences and the mating strategies of men and women, how they came about and why. Reinforcing the power of our primal animal origins, we follow our first upright, two-legged ancestors as they stumble out of the once luscious jungles and bountiful forests to confront the challenges of the African savanna. Keeping an animated eye on Lucy, the legendary, two-legged, 3.5 million-year-old proto-human, we ponder how this momentous change of address indelibly altered the sexual bargain. On the desolate and dangerous savanna, women needed a partner—especially when pregnant and nursing—and men, as always, required a purpose. A sexual bargain loomed on the horizon.

We also discover how the need to forage and hunt, to negotiate and sustain intimate relationships has, over the ages, propelled human evolution toward increasing levels of specialization, advanced reasoning and abstract thinking. In concert with flexible, highly adaptive bodies, our brain's expanding capacity drove us to the front of nature's pack. But there was one thing missing, one giant step that would kick off an explosion of innovation and courtship: we had to learn how to speak. From what men and women seek in a mate, to the primal instincts lurking behind our intimate desires, Chapter 2 unravels the natural foundations and vibrant history of the sexual partnership, revealing the primal motives still reverberating behind our most intimate desires.