NATURE'S NETHER REGIONS

An exploration of sexual reproduction across species, with emphasis on the evolution of genitalia.

Dutch ecologist and evolutionary biologist Schilthuizen (Evolution/Leiden Univ.) seeks to assume the mantle of Masters and Johnson in this examination of sex in the animal kingdom. The author holds Darwin at fault for focusing on “how secondary sexual characteristics—like colorful bird plumage, the prongs on beetles’ heads, and the antlers of deer—have been shaped not by natural selection…but by sexual selection.” These secondary features serve to attract females to mate with hopeful males and only indirectly influence survival in the struggle for existence. For example, the peacock that has the grandest display of feathers is presumably healthy enough to support such an excess, as compared to a rival more poorly endowed. Darwin explicitly relegated genitalia to the role of mere mechanisms. He believed that females were aroused by male displays, and the game was on. Not so, writes Schilthuizen, who cites a 1979 discovery by an entomologist who discovered that the minuscule penis of a damselfly contained “a miniature spoon” to clean out the female's vagina and thus remove the sperm of competitors. Schilthuizen shows that this is only one example of how male and female genitalia have evolved in a battle between the sexes over which eggs would be fertilized. By closely studying the process of copulation, biologists have also observed the role of orgasm. In one experiment, the sexual responses of laboratory rats stimulated genitally appeared similar to that of “humans in the throes of orgasm.” The author suggests that the timing of female orgasm before, during or after the male sperm deposit can influence the likelihood of fertilization in all mammals, including humans.

A provocative voyage on the “vast ocean of sexual function beyond the quiet backwater that we humans find ourselves in.”