Thursday, July 23, 2009

Birds do it, bees do it...

...even educated fleas do it.

What do they do? They cheat on their mates.

Presidents do it, preachers do it, even -- oh dear! -- teachers do it.

Democrats do it. Republicans pompously preach against it, but they do it too.

All those philandering politicians in the American news lately may be following a script written in their DNA. Natural selection, it would seem, favors the male who spreads his genes by fathering as many progeny as possible, and favors the female who picks the best possible genes for her offspring. Advantages can accrue to both males and females who cheat on a mate. In the animal kingdom, fidelity is the exception rather than the rule. Only about ten percent of apparently monogamous birds and mammals are faithful to their partners. Even among those traditional paragons of marital virtue, the bluebirds, females sometimes slip away for a brief fling.

Among our closest animal kin, the primates, infidelity is the rule. Males tend to look for liaisons with lots of young, nubile partners. Females are generally less promiscuous, but when they do have affairs they go for partners with power, access to resources, or prestige. Only females already paired with powerful males tend to be faithful.

All of which sounds terribly familiar.

If natural selection favors adultery, and if it is the nature of human males (and sometimes females) to cheat, then where did our monogamous ideal come from? This is one of those questions that evolutionary biologists love to answer. Most make a case for a maximum selective advantage for those individuals who combine a stable partnership with a little something on the side. Such individuals get the best of both worlds -- genetically speaking.

I like to think our ideal of monogamous fidelity springs not from our genes but from the same cultural tendencies as the Sermon on the Mount and Jeffersonian democracy: The notion that in the best society, everyone -- not just the most powerful males and most nubile females -- have equal access to life, liberty and a warm body in bed.