Bestselling author Jared Diamond explores the bizarre sexuality of humans. Why do we engage in sex primarily for pleasure rather than for reproduction and the survival of the species? Does this not contradict evolution? Why have sex with women who are pregnant or beyond menopause? After all, sex could be energy-efficient if limited to fertile days. With wit, flair, and extensive expertise, the award-winning evolutionary biologist Jared Diamond explains how human sexual behavior differs from that of other animals—and how this difference is the key to our evolutionary success.