Natalie Angier in The New York Times:
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 therefore 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 conventional 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.
More here.