So how did women get their curves? Why do they have breasts, while other mammals only develop breast tissue while lactating, and why do women menstruate, when virtually no other beings do so? What are the reasons for female orgasm? Why are human females kept in the dark about their own time of ovulation and maximum fertility, and why are they the only animals to experience menopause?

David P. Barash and Judith Eve Lipton, coauthors of acclaimed books on human sexuality and gender, discuss the theories scientists have advanced to explain these evolutionary enigmas (sometimes called...