Friday, July 3, 2009

Evolutionary Psychology didn't go Anywhere.

There seems to have been a few articles trying to bash evolutionary psychology recently. They make it sound like the field has died and is being replaced by something else. In reality no such thing is happening. Simply scientists are testing evolutionary psychology and figuring out what is actually in our evolutionary interest. Here is an example using rape:

But how to test the claim that rape increased a man's fitness? From its inception, evolutionary psychology had warned that behaviors that were evolutionarily advantageous 100,000 years ago (a sweet tooth, say) might be bad for survival today (causing obesity and thence infertility), so there was no point in measuring whether that trait makes people more evolutionarily fit today. Even if it doesn't, evolutionary psychologists argue, the trait might have been adaptive long ago and therefore still be our genetic legacy. An unfortunate one, perhaps, but still our legacy. Short of a time machine, the hypothesis was impossible to disprove. Game, set and match to evo psych.

Or so it seemed. But Hill had something almost as good as a time machine. He had the Ache, who live much as humans did 100,000 years ago. He and two colleagues therefore calculated how rape would affect the evolutionary prospects of a 25-year-old Ache. (They didn't observe any rapes, but did a what-if calculation based on measurements of, for instance, the odds that a woman is able to conceive on any given day.) The scientists were generous to the rape-as-adaptation claim, assuming that rapists target only women of reproductive age, for instance, even though in reality girls younger than 10 and women over 60 are often victims. Then they calculated rape's fitness costs and benefits. Rape costs a man fitness points if the victim's husband or other relatives kill him, for instance. He loses fitness points, too, if the mother refuses to raise a child of rape, and if being a known rapist (in a small hunter-gatherer tribe, rape and rapists are public knowledge) makes others less likely to help him find food. Rape increases a man's evolutionary fitness based on the chance that a rape victim is fertile (15 percent), that she will conceive (a 7 percent chance), that she will not miscarry (90 percent) and that she will not let the baby die even though it is the child of rape (90 percent). Hill then ran the numbers on the reproductive costs and benefits of rape. It wasn't even close: the cost exceeds the benefit by a factor of 10. "That makes the likelihood that rape is an evolved adaptation extremely low," says Hill. "It just wouldn't have made sense for men in the Pleistocene to use rape as a reproductive strategy, so the argument that it's preprogrammed into us doesn't hold up."

First thing to note is that what they did is figure out what was evolutionary the best thing for members of that society to do. This is exactly what evolutionary psychology tries to do, meaning that if this study is to be taken seriously evolutionary psychology is doing just fine. All that is happening is we are fine tuning our understanding about what selective pressures are within our history.

The results are otherwise blindingly obvious. They found a society with no rapes, and found that rape wasn't an evolutionary advantage for those people. Sounds to me like the people are exactly following what you would expect based on evolutionary psychology. The rapists were bred out of that particular culture. To then say that rape is never an evolutionary advantage based on that example is quite silly though. To have any interest at all you would have to look at a situation where there were actual rapes, preferably lots of them. For example: did the Russian soldiers who raped something like a million Germans during their invasion of world war two gain an evolutionary advantage over those who abstained? Almost certainly, there were no significant costs as they would never face retribution from these women, and many of them ended up with children they never would have had otherwise. This has been true in times of war for as long as history has been recorded. Another great example would be slave masters in the south. They faced no costs, and significant evolutionary gain by being rapists.

All this study shows is that people are pretty good at evaluating costs and benefits from behavior. In a civilation like the one they studied, or ours for that matter, rape is rarely going to get you anywhere. So the vast majority of men are quite predictably not rapists.

The evolutionary psychology does have a great deal of predictive power: It explains why the vast majority of rapists are male, and vast majority of victims female. It explains why the median age of a rape victim is 23 which not coincidently happens to be right about at peak fertility (for comparison the median age of a murder victim is 29). It explains why women over 50 are only 3% of rape victims despite being a third of the population. It also happens to explain why most men are not rapists, just as it explains why some are. Sure the predictions of evolutionary psychology will change as further experimental evidence comes along. But the field as a whole will still exist, and explain a great deal.

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