It's a bit long but clearly written and well argued. An excerpt:
Humans are naturally polygamous
The history of western civilization aside, humans are naturally polygamous. Polyandry (a marriage of one woman to many men) is very rare, but polygyny (the marriage of one man to many women) is widely practiced in human societies, even though Judeo-Christian traditions hold that monogamy is the only natural form of marriage. We know that humans have been polygynous throughout most of history because men are taller than women.
Among primate and nonprimate species, the degree of polygyny highly correlates with the degree to which males of a species are larger than females. The more polygynous the species, the greater the size disparity between the sexes. Typically, human males are 10 percent taller and 20 percent heavier than females. This suggests that, throughout history, humans have been mildly polygynous.
Relative to monogamy, polygyny creates greater fitness variance (the distance between the "winners" and the "losers" in the reproductive game) among males than among females because it allows a few males to monopolize all the females in the group. The greater fitness variance among males creates greater pressure for men to compete with each other for mates. Only big and tall males can win mating opportunities. Among pair-bonding species like humans, in which males and females stay together to raise their children, females also prefer to mate with big and tall males because they can provide better physical protection against predators and other males.
In societies where rich men are much richer than poor men, women (and their children) are better off sharing the few wealthy men; one-half, one-quarter, or even one-tenth of a wealthy man is still better than an entire poor man. As George Bernard Shaw puts it, "The maternal instinct leads a woman to prefer a tenth share in a first-rate man to the exclusive possession of a third-rate one." Despite the fact that humans are naturally polygynous, most industrial societies are monogamous because men tend to be more or less equal in their resources compared with their ancestors in medieval times. (Inequality tends to increase as society advances in complexity from hunter-gatherer to advanced agrarian societies. Industrialization tends to decrease the level of inequality.)
This isn't a guidebook for behavior but deductions based on science. While polygamy offends most of us, the driving evolutionary force behind it is hard to deny. Some will argue that our intellect and ingrained values should be enough to counteract these primal impulses and they often are but understanding why we think and act is invaluable. Another excerpt on the Clinton-Lewinsky affair:
...The question many asked in 1998—"Why on earth would the most powerful man in the world jeopardize his job for an affair with a young woman?"—is, from a Darwinian perspective, a silly one. Betzig's answer would be: "Why not?" Men strive to attain political power, consciously or unconsciously, in order to have reproductive access to a larger number of women. Reproductive access to women is the goal, political office but one means. To ask why the President of the United States would have a sexual encounter with a young woman is like asking why someone who worked very hard to earn a large sum of money would then spend it.
Note, I do not quite grasp the logic behind #6 (Why Beautiful People have Daughters) but I think I will buy this book when it comes out in September.
HT: Jonah at NRO.