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In Why Is Sex Fun?, Jared Diamond, author of Guns, Germs and Steel and The Third Chimpanzee, attempts to explain the origins of human sexual behavior. For example, why do women have sex when they aren't ovulating, and why is ovulation concealed? Why do men and women generally form long-term pair relationships? Why do women undergo menopause? Why are certain physical characteristics sexually appealing?

Diamond applies evolutionary biology to tackle these questions. He describes the sexual behavior among a variety of animals, which is entertaining in its own right while it highlights the peculiarities of human sexuality. He analyzes why the optimal reproductive strategies among people differ from the optimal strategies of other animals.

Diamond's arguments are largely successful, much more convincing than Robert Wright's evolutionary biology classic The Moral Animal. Concealed ovulation has two plausible explanations involving male behavior: (1) encouraging fathers to stay around and help provide for the baby, and (2) discouraging infanticide by the male against possible children. Diamond claims that those factors were relevant during different phases of primate evolution.

Menopause prevents older women from dying in childbirth, a major problem with large-headed human infants, and caring for children and other relatives is more likely to propagate their genes. Physical attributes that reflect greater health or genetic fitness may be more appealing, though that reasoning is rather controversial.

Overall, Why is Sex Fun? is an interesting light read, though it's not up to the caliber of Diamond's better-known books. Except for an unimpressive chapter discussing the absence of male lactation, he asks significant questions and makes reasonable speculations about their answers.
posted by Julian at 12:30 AM