In Vienna in the 1920’s, the followers of Freud and Adler debated whether sex or power is the fundamental human motivation. That debate continues today, with different contestants. On the one side, we have neo-Darwinian evolutionary psychologists, who think that reproductive fitness is the ultimate explanation of all human behavior. On the other, we have neo-Nietzschean feminists and postmodernists, who think that the will to power is the main human motive. The Darwinians are miffed when the postmodernists describe sex in terms of power relationships. The postmodernists get incensed when the evolutionists evaluate power relationships in terms of the numbers of babies produced.
An especially heated argument has broken out over the meaning and causes of rape. Since Susan Brownmiller made the crime of rape a central part of feminist theory with her 1975 book Against Our Will, many social scientists and feminists have come to view rape strictly as a crime of violence, with no element of sexual desire -- and, in the larger scheme of things, as one way that patriarchal societies keep women in their place. But throughout the 1990’s, evolutionary psychologists have increasingly urged that rape be seen as a male reproductive strategy.
One recent salvo from the Darwinian side is the controversial book A Natural History of Rape: Biological Bases of Sexual Coercion (MIT Press, 2000), by the biologist Randy Thornhill and the anthropologist Craig T. Palmer. They argue that rape is a biological phenomenon with a reproductive agenda, and they are scornful and contemptuous of Brownmiller and others who prefer to see it as a cultural phenomenon with a political agenda.
Thornhill and Palmer base their story about rape on the Darwinian notion that males and females have different reproductive priorities and strategies. A female mammal invests a lot of time and energy in bearing and rearing babies. A male invests far less, and as a result can have more offspring than a female. Because female reproductive investment is a relatively limited resource, males compete for it. (That’s why they grow all those horns, antlers, and other weapons.) A male’s best strategy is to impregnate as many females as possible and drive other males away from them. Conversely, a female’s best strategy is to choose one mate carefully, with an eye to general quality and to any specifically male traits that will make her sons successful competitors.
In species where males help rear the offspring, both sexes compete for mates, because each sex is a resource for the other. A female of such a species should try to mate with a good provider (to minimize the drain on her own resources) and prevent him from having any other mates (to avoid diluting his investment in her offspring).
Does all that sound familiar? Men, the theory implies, can be expected to be pugnacious and competitive; women, meek and nurturant. Men are interested in women as sex objects; women see men as meal tickets. Men want to sleep around; women want to keep them at home. All those implications match our stereotypes about how men and women typically behave. As the old doggerel has it:
Hoggamus higgamus, Men are polygamous; Higgamus hoggamus, Women, monogamous.
To a postmodernist, the fact that the evolutionary psychologists’ theory corresponds so well with our cultural stereotypes shows that the psychologists’ pretended scientific objectivity masks an underlying political agenda. To an evolutionary psychologist, it proves that our stereotypes reflect biological reality.
Thornhill and Palmer’s arguments, which they have been working up for many years in various learned journals, have evoked widespread outrage among feminists and social scientists. It’s easy to see why. After a quick reading of their book, you might think that they are saying that rape is adaptive, that the impulse to rape is genetically determined, and that men have a special part of their brains devoted to raping women.
A closer look, however, reveals that those ideas are just being floated as speculations. Thornhill believes them, but Palmer doesn’t. Thornhill sees the urge to rape as an adaptation -- a useful reproductive subroutine that contributes to overall male fitness and is generated by a module in the male brain that evolved specifically to foster rape. Palmer, on the other hand, suspects that rape is just a side effect of the simultaneous arousal of sexual desire and the urge to dominate others.
Despite their differences, Thornhill and Palmer agree that the rapist’s behavior ultimately has to be understood in terms of Darwinian theory, as a product of natural selection. Rape sometimes results in offspring. Therefore, Thornhill and Palmer reason, any genes that make men more likely to rape women can in theory confer selective benefits. For a man who can’t compete successfully in the race for mates, rape may be the only reproductive strategy available; and even the fittest men may find that an occasional rape increases their lifetime baby-making score. It makes sense, the authors conclude, to think that human rape may be a male adaptation -- and to go on collecting data to test that hypothesis.
After years of sparring with their critics, Thornhill and Palmer have ready answers for all the standard objections to the evolutionary approach.
Some of their critics say that anyone who claims that rape has a biological basis must secretly approve of rape, because anything that is part of human nature has to be okay. Thornhill and Palmer rightly dismiss that argument as an example of the naturalistic fallacy.
Other critics say that seeking a biological basis for rape justifies it as inevitable. Thornhill and Palmer retort that genetic determinism is a myth. Noting that every behavior results from an interaction between genes and environment, they argue that understanding the interaction should help us find ways of controlling the behavior -- not lead us to give up on it.
One common criticism of evolutionary psychology notes that its explanations bear little resemblance to actual human motives. That is certainly true in this case: Men who rape women don’t usually have babies in mind, and women don’t resist rapists out of a desire to defend their female reproductive strategies. But Thornhill and Palmer dismiss that objection, and criticize the social sciences in general for failing to distinguish between proximate and ultimate causes. That distinction is essential to any Darwinian explanation of behavior. A tomcat on the prowl for females is not trying to make kittens. But the reason why tomcats want what they want -- the ultimate, evolutionary cause of their sexual urges -- is that copulation results in offspring.
In that respect, men are not different from tomcats. Human appetites, including the wish to dominate others, may be the proximate cause of rape and other human behaviors; but Darwinian theory implies that natural selection has made our appetites what they are because having those particular appetites contributes to successful reproduction. Here, I think Thornhill and Palmer are right, and their critics are missing the point.
But it seems to me that Thornhill and Palmer have themselves omitted an important element of Darwinian theory. The fact that rape sometimes results in offspring doesn’t say anything about its adaptive value. Natural selection isn’t simply a matter of successful reproduction, but of differential reproductive success -- not just making babies, but making more babies than the competition. If rape is adaptive, rapists should have more babies than nonrapists.
An example from another primate species may make that clearer. Adult male orangutans come in two sizes: big and small. (The difference may have a genetic basis; you can distinguish between the two types even with juvenile orangutans, from the size of their teeth.) In the wild, each big male patrols a territory containing two or more females. On the infrequent occasions when a female becomes interested in sex, she solicits it from the resident big male. But most of the copulations that occur are forced on unreceptive females by small males, who prowl around the edges of a territory waiting for a chance to rush in and rape a female -- hastily, before the big male comes running in response to her screams.
You might think that being a small rapist is an adaptation -- a viable reproductive option for puny male orangutans that can’t compete with the big guys. But primate biologists have not jumped to that conclusion. They are holding off until they get some data on the numbers of offspring sired by small rapists. If the small-rapist strategy yields fewer offspring on average than the big-male strategy, it can’t be an adaptation -- because it can’t be produced or maintained by natural selection.
Similar issues occur in the human case. In the arithmetic of reproduction, rape has a lot of negatives as well as positives. A rapist runs the risk of being injured or killed by victims, their friends or relatives, or the police. And because women (unlike female cats and orangutans) understand the causal link between copulation and childbirth, they have ultimate control over the rapist’s reproductive success. Raped women can, and often do, respond by taking deliberate countermeasures -- abortion, infanticide, or child neglect and abuse -- to kill or handicap the rapist’s offspring and deny him any reproductive advantage. Thornhill and Palmer have little to say about those issues.
To argue that rape is an advantageous male strategy, you have to show that the minuses in the reproductive equation have on the whole been outweighed by the pluses throughout human history -- that is, that rapists have sired more offspring on the average than similar men who didn’t rape. It’s not evident that they have, and it’s not clear that there is any way to settle the question.
For me, the most offensive parts of A Natural History of Rape were the authors’ Darwinian explanations of women’s resistance to rape. Females, they claim, resist rape not because it violates their bodies, but because it violates their reproductive strategy -- that is, it keeps them from gaining a competitive edge over other females through their choices of mates. According to the authors, "[t]he females who outreproduced others and thus became our ancestors were individuals who were highly distressed by rape.” Thornhill and Palmer suggest that the cuts and bruises a woman gets when she resists rape may serve a reproductive function: Showing evidence that she resisted sex with another man may keep her male provider from ditching her as an unreliable mate and a bad reproductive investment.
Other evolutionary psychologists have gone even farther down that road. Some suggest that violent resistance to rape is a form of sexual selection: By putting up a fight, the victim ensures that her offspring will be descended from only the very strongest and fittest rapists. To their credit, Thornhill and Palmer reject that ugly little theory, but I couldn’t tell why; it sounds about as plausible as a lot of their own speculations.
Ever since the rise of the feminist movement in the 19th century, some people have argued that the ills of human society are mainly due to the innate wickedness of males. A Natural History of Rape falls into that tradition. Another recent book, Demonic Males: Apes and the Origins of Human Violence (Houghton Mifflin, 1996), by Richard Wrangham and Dale Peterson, argues that violence has been an overwhelmingly male phenomenon throughout human history, and that the correlation between aggression and gender has antecedents and adaptive value in the great apes. Michael P. Ghiglieri’s The Dark Side of Man: Tracing the Origins of Male Violence (Perseus Books, 1999) likewise concludes that “most men are, by nature, programmed, under specific circumstances, to employ violent solutions to their problems ... [including] rape, robbery, murder, warfare, and terrorism,” and that such behavior “is something utterly alien to most women.”
There may be some truth in those claims. Anybody who has experience with stallions, bulls, or roosters knows that the animals’ androgens make them more aggressive and harder to handle than geldings, steers, or capons. That may be as true of the males in the farmhouse as it is of those in the barnyard. But unless we shift over to asexual methods of reproduction, we are stuck with having men around. We can only try to mitigate their innate orneriness by tinkering with their environments -- and perhaps eventually with their genes -- to make them grow up as decent and sociable as possible.
The authors of these books offer a number of suggestions about how to control male behavior. But like all techniques of control, their prescriptions are concerned exclusively with proximate causes -- early experiences, cultural values, and so on. I don’t see how knowing the ultimate, evolutionary causes of the evil that men do can add anything to those prescriptions. Human nature is what it is, no matter how it got to be that way. To figure it out, we have to look at the present, not speculate about the past.
More generally, I suspect that it’s a mistake to argue about the causes of rape -- or homicide, suicide, or war. We define those acts by their properties and their effects, not by their causes, and there’s no reason to think that acts that share an effect also share a cause. For example, all homicides by definition have the same effect -- a human death -- but they don’t all have the same cause. Killing can be motivated by almost any emotion, from anger to pity. Seeking the cause of murder, war, or rape may be a fundamental mistake, like asking for the cause of things that weigh 10 pounds.
I suspect that it’s also a mistake to assume, as evolutionary psychologists do, that all human traits are either evolutionary adaptations or incidental side effects of adaptations. We know that isn’t true of the genome, and it seems unlikely to be true of every human behavior. Thornhill and Palmer defend that assumption at length, insisting that all aspects of our behavior -- including “such by-products as cosmetic surgery, the content of movies, legal systems, and fashion trends” -- can ultimately be explained in terms of differential reproduction. That seems absurd.
How, for example, can we view a suicide undertaken to avoid unendurable pain as a means of making more babies? One might argue that such suicides are a functionless side effect of certain adaptations -- say, the adaptive wish to avoid pain, plus the adaptive ability to anticipate probable outcomes. But that sort of argument explains everything and rules out nothing.
The debate between the followers of Freud and Adler back in the 1920’s was never resolved, because both schools of thought were working with theories so flexible that they could explain any imaginable human behavior. No empirical findings could tip the balance one way or the other. Watching that fruitless impasse, Karl Popper was inspired to formulate a novel philosophy of science, which claimed that a theory that explains everything and rules out nothing has no scientific standing whatever.
If evolutionary psychology is to count as a scientific explanation of human behavior, then there have to be some possible patterns of human behavior that might in principle prove it false. It remains to be seen just what those behaviors might be.
Matt Cartmill is a professor of biological anthropology and anatomy at Duke University.
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