Here, too, there is no doubt. We are not naturally monogamous. Anthropologists report that the overwhelming majority of human societies either are polygynous or were polygynous prior to the cultural homogenization of recent decades. They also suggest that individuals are mildly polygynous, having evolved in a system in which one man maintains a harem. This, incidentally, helps explain the persistent sex appeal of successful, dominant men, whether they be high-ranking politicians, movie or rock stars, glamorous athletes or wealthy entrepreneurs. Power, as Henry Kissinger once noted, is the ultimate aphrodisiac. At the same time, women can and do seek additional sex partners, even when already mated. Thus, monogamy -- when it occurs -- is shot through with EPCs, not just among birds. Otherwise, why would men have such a powerfully developed tendency for sexual jealousy?

Why, then, does monogamy occur at all? Maybe it's like Winston Churchill's observation that democracy is the worst possible form of government except for all the others that have been tried. At least monogamy is a great equalizer (in theory). It assures that in a species with equal numbers of males and females, no one need be left out. But at the same time, it cannot and does not prevent individuals of either sex from looking elsewhere.

Imagine a society of rigid social monogamy in which women nonetheless seek to be inseminated by the best possible males. Such males are rare, and likely to be already taken. So women might well adopt a kind of ratcheting-up tactic, in which they pair with the best man they can get, and thereby obtain his child-rearing assistance as well as whatever additional material resources he can provide, while also making themselves available for men further up in the hierarchy -- probably charismatic men like Jesse Jackson.

Such a motivation need not be conscious. In fact, a woman who has an affair with an attractive married man may intentionally avoid becoming pregnant. The point is that part of the underlying sexual motivation for the affair likely derives from these factors.

When right-wing Christian moralists worry that family values are under assault, they don't know how right they are! Monogamy, perhaps the poster child of family values, is under profound assault -- but not from any progressive, gay or feminist agenda. Rather, nature is the culprit.

We are imbued by Western culture with monogamous ideals. Yet, like other living things, we're often compelled by our biology to depart from monogamy. Neither men nor women are the primordial purveyors of extra-pair copulations, yet EPCs have dogged and delighted human beings throughout recorded history, and doubtless before. It takes two to do the EPC tango. And human beings love to dance.

Private Life Romance, relationships, and the personal side of Table Talk