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In one Tanzanian culture at least, women make the most of multiple mates.

In the United States and much of the Western world, when a couple divorces, the average income of the woman and her dependent children often plunges by 20 percent or more, while that of her now unfettered ex, who had been the family's primary breadwinner but who rarely ends up paying in child support what he had contributed to the household till, climbs accordingly. The born-again bachelor is perfectly positioned to attract a new, younger wife and begin building another family.

Small wonder that many Darwinian-minded observers of human mating customs have long contended that serial monogamy is really just a socially sanctioned version of harem-building. By this evolutionary psychology script, the man who skips from one nubile spouse to another over time is, like the sultan who hoards the local maidenry in a single convenient location, simply seeking to "maximize his reproductive fitness," to sire as many children as possible with as many wives as possible. It is the preferred male strategy, especially for powerful men, right? Sequentially or synchronously, he-men consort polygynously.

Women, by contrast, are not thought to be natural serializers. Sure, a gal might date around when young, but once she starts a family, she is assumed to crave stability. After all, she can bear only so many children in her lifetime, and divorce raises her risk of poverty. Unless forced to because some bounder has abandoned her, why would any sane woman choose another trot down the aisle - for another Rachael Ray spatula set? Spare me extra candlesticks, I'm a one-trick monogamist.

Yet in a report published in the summer issue of the journal Human Nature, Monique Borgerhoff Mulder of the University of California, Davis, presents compelling evidence that at least in some non-Western cultures where conditions are harsh and mothers must fight to keep their children alive, serial monogamy is by no means a man's game, finessed by him and foisted on her. To the contrary, Borgerhoff Mulder said, among the Pimbwe people of Tanzania, whose lives and loves she has been following for about 15 years, serial monogamy looks less like polygyny than like a strategic beast that some evolutionary psychologists dismiss as quasi-fantastical: polyandry, one woman making the most of multiple mates.

In her analysis, Borgerhoff Mulder, who has a doctorate in bio-social anthropology, found that although Pimbwe men were somewhat more likely than their female counterparts to marry multiple times, women held their own and even outshone men in the upper Zsa Zsa Gabor end of the scale, of five consecutive spouses and counting. And when the researcher looked at who extracted the greatest reproductive payoff from serial monogamy, as measured by who had the most children survive past the first five hazardous years of life, she found a small but significant advantage female. Women who worked their way through more than two husbands had, on average, higher reproductive success, a greater number of surviving children, than either the more sedately mating women, or than men regardless of wifetime total.

Provocatively, the character sketches of the male versus female serialists proved to be inversely related. Among the women, those with the greatest number of spouses were themselves considered high-quality mates, the hardest working, the most reliable, with scant taste for the strong maize beer the Pimbwe famously brew. Among the men, by contrast, the higher the nuptial count, the lower the customer ranking and the likelier the men were to be layabout drunks.

"We're so wedded to the model that men will benefit from multiple marriages and women won't that women are victims of the game," Borgerhoff Mulder said. "But what my data suggest is that Pimbwe women are strategically choosing men, abandoning men and remarrying men as their economic situation goes up and down."

Underestimating women

The new analysis, though preliminary, is derived from one of the more comprehensive and painstaking data sets yet gathered of marriage and reproduction patterns in a non-Western culture. The results underscore the importance of avoiding the breezy generalities of what might be called Evolution Lite, an enterprise too often devoted to proclaiming universal truths about deep human nature based on how college students respond to their professors' questionnaires. Throughout history and cross-culturally, Borgerhoff Mulder said, "there has been fantastic variability in women's reproductive strategies."

Geoffrey F. Miller, an evolutionary psychologist at the University of New Mexico, agreed. "Evolutionary psychology and anthropology really need to take women's perspective seriously in all its dimensions," Miller said. "You can construe sequential relationships as being driven by male choice, in which case you'd call it polygyny, or by female choice, in which case you'd call it polyandry, but the capacity of women across cultures to dissolve relationships that aren't working has been much underestimated."

Pimbwe equality

Pimbwe culture has been too disrupted over the years by colonialism and government interference to serve as a quaint museum piece of how our ancestors lived, but the challenges the people face are more survival-based than how to get your child into an elite preschool. The Pimbwe live in small villages, have few possessions and eke out a subsistence living farming, fishing, hunting and gathering. Virtually all Pimbwe get married at least once, Borgerhoff Mulder said, and they do it without the blessing of judge, priest or Las Vegas.

"Marriage is not formalized with any specific set of rituals," she said, "and marriages break up by one or another partner leaving."

Nor is there much formal sexual division of labor. "In terms of farming, men and women do pretty much the same tasks," she said. "The men will cook, do a lot with the kids."

Unlike in the West, where men control a far greater share of resources than women do, or in traditional pastoral societies like those found in the Middle East and Africa, where a woman is entirely dependent on the wealth of her husband and in divorce is not entitled to so much as a gimpy goat, Pimbwe women are independent operators and resourceful co-equals with men.

This does not mean that mothers can go it alone, however. Again in contrast to the contemporary West, childhood mortality remains a serious threat, and it takes the efforts of more than one adult to keep a baby alive. A good, hardworking husband can be a great asset - and so, too, may his relatives. The evolutionary theorist Sarah Blaffer Hrdy proposes that one reason the offspring of much-marrying Pimbwe women do comparatively well is that the children end up with a widened circle of caretakers.

"The women are lining up more protection, more investment, more social relationships for their children to exploit," she said. "A lot of what some people would call promiscuous I would call being assiduously maternal."

The goose, like the gander, may find it tempting to wander if it means that her goslings will fly.