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Is Rape an Evolutionary Trait?

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Dr. Wendy Walsh: The registered sex offender who abducted Jaycee Lee Dugard and kept her captive for 18 years had a prior record of rape. From my perspective, rape seems pretty darned common in our culture -- 46 registered sex offenders in my busy neighborhood alone, and yes, I'm raising girls.


My neighborhood's statistic made me start to wonder exactly why it seems to be so common, and by extension, if rape is natural, if somewhere back in our ancient past, it made evolutionary sense for men to mate with as many women as possible, even those who didn't want to knock boots. According to some experts, a rapist "gene" may have helped evolution
-- that is, if men could procreate with both willing and unwilling women, it indicated fitness. In doing so, they would also be passing on the gene that provided a penchant for forced sex. Therefore, might a rapist's defense become, "My genes made me do it?"

Not so fast, buddy. The rape gene theory was expounded in a 2000 book co-authored by biologist Randy Thornhill, called "A Natural History of Rape: Biological Bases of Sexual Coercion." But in June of this year, a Newsweek article came out debunking the entire notion. According to Newsweek's Sharon Begley, anthropologist Kim Hill at Arizona State University had a hunch that sloppy projections had been made about the fitness of rape. Although anthropologists still study a few hunter/gatherer societies today, few have ever seen a rape. That doesn't mean the gene wasn't selected for increased reproduction, though.

Hill and some colleagues decided to do a calculation using the example of the Aché, a traditional hunter/gatherer tribe living in Paraguay. Focusing on the case of one 25-year-old male Aché, they mathematically projected how rape would affect his evolutionary journey. Essentially, they calculated a rapist's costs and benefits, and the likelihood that his genes would survive. They were also generous with their calculations -- for one thing, they assumed that the subject would only rape women of child-bearing age, when in actuality, women of all ages are raped. The calculations included a demerit point system -- the man would lose fitness points for things like getting killed by a rape victim's relative, having the child abandoned by the rape victim, the likelihood that conception would happen at all based on a woman's reproductive cycle, and even if being a rapist in a small community would affect the likelihood that others would share their food with him. I, for one, don't have any of the sex offenders in my neighborhood over for barbecue.

And ... drum roll please ... the final math, from Begley's Newsweek article: "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,' Hill said. '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.'"

From the mouths of scientists: If you are a rapist, you can't blame your genes. It's your own damn fault. Well, actually it's probably the fault of some receptive biology mixed with a bad childhood. But it's your own damn fault if you fail to seek help.

Psychologists view rape not as an act of sex, but as an act of power and control. The average profile of a rapist is a man of small stature with low income, indicating that he has less access to women than his taller, richer counterparts, but still doesn't mean the rape is linked to sex drive. It is usually linked to rage. Plenty of rapists torture and humiliate women without ever having an erection. The technical term for this is called "stuffing." Don't try visualizing this.

Rape is no more natural than serial killing. It is a fluke that occurs when a biological predisposition meets an environment that provides just the right (or wrong, in this case) stimulation. And it is tragic every time it happens.

next: Family, Friends Mourn as Jackson Is Laid to Rest
5 comments so far | Post a comment now
ashley September 4, 2009, 4:29 AM

How about this for a theory: Like murderers, they are possessed by devil spirits. That’s what my parents would say anyways.

Bjørn Østman September 6, 2009, 12:00 AM

Rape nevertheless increased Garrido’s fitness.

Erik February 1, 2010, 1:46 PM

I just googled around and found your article. I will get Hill’s article, but from the Newsweek article, there seems to be two things wrong with the theory. Firstly, rape commonly occurs in war, “raping and pillaging” and here babies are indeed produced as 200 000 Germans prove.
Secondly, and this is something you touch upon in your article, “The average profile of a rapist is a man of small stature with low income, indicating that he has less access to women than his taller, richer counterparts…”.
This is the other example where Hill’s fitness calculations are wrong. These men have close to zero chance of reproducing in a loving relationship. Rape in this case is what I believe you Americans call a “Hail Mary” pass. A 10% chance of reproducing is still more than 0%. If rape then occurs within the group and the man is killed by relatives, he has still improved his chances of reproducing.

Golf September 14, 2010, 10:38 AM

In related news, a cheetah wouldn’t cheat on his wife, but a Tiger Wood.

Jeanna Sebald December 2, 2010, 8:02 PM

I was surprised just how much on this I did not fully understand. Appreciate your sharing this information. I’ll be certain to return here to find if you have any kind of fresh information.

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