Evolution and Rape

The Objectivist
Rape and Evolution
Dunkirk-Fredonia Observer
October 19, 2009

The way in which we think is the result of how our brains are wired. Evolution tells us that the way in which our brains are wired is in part the result of the way in which wiring patterns affected reproductive success over millions of years of our history. Evolution provides an insightful look into this history. It can be troubling in that it suggests that many of our violent and ugly desires are at least in part genetic. Perhaps the best example of this is rape.

Men and women often use different reproductive strategies. In animals like human beings where offspring depend on their parents for years, females must invest significant time and bodily resources in order to reproduce and raise their offspring. In contrast, men can father many more offspring with much less time and bodily resources. This gives them an incentive to have as many mates as possible. This is not true for females. The male reproductive strategy explains why males more strongly desire casual no-string-attached sex than do females. On this account, then, the male reproductive strategy was hard wired into their brains through their genes. This same account also explains why males desire rape-sex when females do not.

In A Natural History of Rape: Biological Bases of Sexual Coercion, biologist Randy Thornhill and anthropologist Craig T. Palmer defend the notion that rape is a behavioral pattern that evolved because it was genetically advantageous. Their argument rests on several types of evidence. It should be noted that their arguments are highly controversial.

First, Thornhill and Palmer argue that the theory fits cleanly with the presence of rape in our closest relatives and across human cultures. They note that male rape of females is found in our closest relatives (chimpanzees, gorillas, and orangutans). They claim that it is also found in every human society. In addition, they note, it is widespread in the animal kingdom. Mammals, birds, and insects all engage in coerced copulation. Whenever you see a behavioral pattern that is found in our closest relatives and in all human societies, there is good reason to believe that it is either an evolutionary adaptation or a by-product of one.

Second, Thornhill and Palmer note that the theory explains how victims are chosen. Rape victims are overwhelmingly in their peak reproductive years (13-35, mean age 24). This is what one would expect of a behavior that is favored because it led to increased reproduction. This age distribution differs from other violent crimes. It also is not what one would have expected if rape victims were picked for their physical vulnerability. Thornhill and Palmer also assert that rape is a relatively effective way of producing conception. They claim that roughly 5% of rape victims become pregnant.

Third, Thornhill and Palmer point out that the notion that rape is an evolutionary adaptation explains the way in which rape is often carried out. In particular, it explains why rapists usually do not cause gratuitous injury to victims. That is, they rarely inflict a serious or fatal injury that would preclude conception or birth. Thornhill and Palmer note that it explains why it is more likely that a rape victim will more likely suffer a vaginal rape, rather than an oral or anal one, if she is in her fertile years than if she is not. Again, all of this fits with the notion that rape was encoded because of its contribution to reproductive success.

Fourth, the researchers point out that the desire for rape appears to be fairly widespread in males. They note that studies indicate that many normal men (for example, college students and community volunteers) are significantly sexually aroused by depictions of coercive sex, including ones that involve physical aggression. Again, this is what we would expect if rape where an evolutionary adaptation because it would allow for opportunistic reproduction.

This theory has striking implications. Feminist writer Susan Brownmiller and numerous other feminist writers have claimed that rape is not motivated by sexual desire, but by hostility toward women or by a desire to control them. This theory does not fit the data. In particular, the theory is unable to explain why such desires have led to a targeting of victims and means of victimizing them that is so closely tied to reproduction. It fits poorly with the observation that rapists favor women in their reproductive years and statistically in time in which they are at their peak attractiveness. It fits uneasily with the similar pattern of rape in human beings and their closest ape relatives. The theory runs aground on studies that indicate that most rapists cite sexual desire as a cause of their actions.

The theological view that human beings are created by God in his own image also fits poorly with this data. After all, it is hard to imagine why God would want his most prized creation to walk around with such evil and destructive desires. Even if God wanted to make it hard for humans to be moral by tempting them, it is hard to believe that he couldn’t have picked a less cruel way of doing so.

The theory also has implications for what to expect of men, especially young men in their peak sexually competitive years. It tells us that we can expect a significant number of them to have rape-thoughts and -desires. This likely includes the seemingly kind-hearted college-aged male who is your son, grandson, nephew, son-in-law, etc. Whether the most effective way to stop men from acting out on these desires is to strengthen criminal penalties, educational programs that focus on making men aware of these desires and the need to control them, discouraging women from dressing in provocative ways, or other means is in part an empirical question and not one that can be answered by common sense. For example, the penalties for rape are already quite strong (in the U.S. in 1992, the average rapist was sentenced to 11.8 years and served 5.4 years).

In any case, there is a dark side to man and one that is hard-wired into him.