Boys Need Not Be Boys

The design of the study is simplicity itself. A comely researcher approaches male college students and, out of the blue, propositions them. Her hunky male counterpart does the same to women students. Of the men, 75 percent typically agree to a quickie. Of the women, none do. To proponents of the view that it is men's biological nature to be promiscuous, and women's to be coy, this seems to prove their case. But does it? Scientists are now offering an alternative explanation, as Pulitzer Prize winner Natalie Angier details in her new book, "Woman: An Intimate Geography" (398 pages. Houghton Mifflin. $25). Maybe, she points out, women don't want to take a strange man back to their dorm because visions of Mr. Goodbar dance in their head. And maybe they've noticed that casual sex cheapens their status, making society think them pathetic or sullied, rather than (as it does with men) cool. Maybe women have figured the odds and opted out of sex with a stranger, guided not by their genes but by their brain.

Most of "Woman," neither a guide to women's health nor another tiresome tour through male/female differences, is a treasure chest of did-you-knows: that the X chromosome contains some 5,000 genes, while the male Y chromosome holds but a couple dozen? That lactobacilli, also found in yogurt, disinfect the vagina by making it more acidic than coffee? That the uterus makes "chemical cousins to morphine and heroin"? The tone can grate--especially Angier's view that "the female body deserves Dionysian respect." But her chapters slaying the modern sex myths called evolutionary psychology make up for it.

Evo-psych argues that, deep in our past, only people with genes for certain behaviors and drives survived and reproduced. We, their children, therefore carry those genes, too. Take the notion that men are genetically programmed to pant at the sight of female breasts because these glands signal a woman's ability to reproduce and lactate, and thus give men who are attracted to them a reproductive edge. Angier lays out the scientific evidence that neither breast size nor shape predicts a woman's reproductive fitness, and thus for a man to salivate over cleavage makes no evolutionary sense. Maybe it's a simple esthetic preference, not a functional one shaped by evolution, suggests research by biologist Nancy Burley of the University of California, Irvine. Or consider the centerpiece of evo-psychosis, that men are genetically programmed to sleep around because that reproductive strategy makes more babies. It turns out that the wham-bang strategy has no more chance of producing offspring than sex with the same woman over many months: a woman is fertile only a couple of days each cycle, and even if the guy times it right, his sperm have only a 25 per-cent chance of fertilizing her egg. Angier targets other sexual myths--like one linking testosterone and aggression--and hits a bull's-eye every time.

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