Picky, Picky

Natural History, Nov, 2000 by Ellen Goldensohn

A hundred and thirty years ago, Darwin came up with the theory of sexual selection, which holds that choosy females, by consistently favoring the fittest, highest-quality males, can drive the evolution of such traits as the unwieldy antlers of elk and the gaudy tails of peacocks. Late-twentieth-century animal behaviorists and anthropologists, some of them using DNA analysis, discovered that choosiness is not the only way female animals maximize their chances of producing the most, and the healthiest, offspring.

Females also compete among themselves (an acorn woodpecker mother, for instance, may toss a rival's eggs out of their shared nest), and in supposedly monogamous species as diverse as bluebirds and humans, females quite frequently hedge their genetic bets by mating with several males.

In this issue, Tim Birkhead, a British ornithologist and evolutionary biologist, takes a look at findings (by famed entomologist William Eberhard and others) indicating that females, especially those with limited control over the act of mating itself, may exert choice in another, more hidden arena: the reproductive tract. Signals at the molecular level, for example, can trigger acceptance or rejection of a particular male's sperm. As yet, little is known about this aspect of pickiness, but as Birkhead suggests in "Hidden Choices of Females" (page 66), the possibilities are intriguing.