In “Battle of the Sexes: Traits that help one sex but hurt the other are not sufficient for maintaining genetic variation” (The Scientist, November 17, 2011), Hannah Waters reports on the problem presented by genetic variation, seen from a strict natural selection standpoint,
If one trait has even a slight edge over another, it should quickly overtake a population; nonetheless, most populations have tremendous genetic variety. One commonly cited explanation for populations’ ability to stave off uniformity is the existence of traits that benefit one sex but handicap the other. But such sexual conflict is not enough, according to a paper published today in Science, which identified other evolutionary mechanisms that are also needed, in conjunction with clashing male and female interests, to maintain diversity.
One observation was
… whether high- or low-testosterone males reigned, the rare phenotype mated more, suggesting that a male’s success with the females depends in large part on the other males in the population—an effect known as frequency-dependent selection. That is, if high-testosterone males were plentiful, the low-testosterone males bred more frequently, and vice versa.
“It’s often the case that there’s more than one way to be a successful male,” said Cox. For example, it could be that the high-testosterone males fight with one another when they abound, making way for the low-testosterone males to steal a few minutes with a female. But when a population is comprised primarily of low-testosterone males, those with high testosterone could be more likely to catch the females’ attention.
“Could be?” Yes, it could be. Or it could be that a strictly Darwinian approach to the problem is a dead end. In the age of genetic drift and epigenetics, one ought to consider other options.
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