Fisher (The Sex Contract, 1981)--research associate at the American Museum of Natural History, former ""house anthropologist"" for The Today Show, and one of our best science--popularizers--may find a large readership for her subject here: the influence of evolutionary biology and genetics on sex, love, marriage, divorce, and today's family. Among the more controversial ideas: that divorce rates (which regularly peak at four years of marriage) are an evolutionary legacy from when early humans formed monogamous bonds until offspring were past infancy, after which parents were free to go their separate ways; that hormones ""sex"" the fetal brain with resulting differences between males and females that may even encourage (though not determine) such apparently male psychological traits as compartmentalization and hierarchy-creation. (Fishar stresses that cultural and societal values play an important role as well: Genetic legacy provides a natural inclination, not an imperative.) While acknowledging the pain of divorce and of the splitting of families, Fisher argues that the stable, nuclear family is more a historical aberration than a norm, and that ""blended"" families, the rise of ""working"" women, and greater equality between the sexes represent a return to tradition. The author is an engaging guide on visits to hunter-gatherer cultures, singles bars, cross-cultural adolescence, chimpanzee social politics, and more. Theories based on prehistoric reconstruction, ethnographies, and comparisons with other species are bound to require large speculative leaps: Fisher's provocative ideas are no exception. Many will be convinced by her knowledgeable, persuasive, and entertaining discussion--and the more skeptical will find fascinating tidbits for thought along the way.