In a book surrounded by vitriolic controversy since its publication in February, 2000, Drs Randy Thornhill (Department of Biology, University of New Mexico) and Craig Palmer (Department of Anthropology, University of Colorado) describe a theory of rape that is based upon a paradigm derived from evolutionary biology: specifically, the relatively new field of evolutionary psychology. The reasons for the resulting controversy are many, not the least of which is, of course, the disturbing nature of the subject and its many potential implications, not only for matters of law and jurisprudence but also for issues of gender politics and human sexuality—themselves topics of considerable controversy. In addition to the above sources of contention, Thornhill and Palmer (hereafter ‘T &P’) explicitly challenge much of the established dogma explaining the motivations of the rapist as described in much of the criminological and social sciences literatures. They argue against the dominant view that rape is not sexually motivated but is driven primarily by a desire to dominate and control women. Rather A Natural History of Rape develops a central hypothesis that raping behavior is intimately and causally related to the evolutionary history of sexual behavior in Homo sapiens, especially males, and therefore involves sex as a major motivational element.

The first two chapters of the book present an overview of evolutionary theory as it potentially pertains to causes of behavior thus laying the evolutionary psychological foundation for their arguments. This is probably the most conceptually difficult portion of the book and, while T&P are very lucid in their exposition, some prior familiarity with evolutionary biology and/or evolutionary psychology is very helpful. The concepts of natural selection vs. other causes of genetic change (genetic drift, mutation) over time are described, and the authors emphasize the importance of natural selection as the only process that can account for the evolutionary development of complex design—including the complex design features of the human brain. These features of the brain are described, in a manner consistent with the primary tenets of evolutionary psychology, as having a “special purpose” in nature acting to promote the acquisition (through environmental interaction) of specific “behavioral strategies” that are functional from an evolutionary perspective in that they tended to (at least in ancestral environments) promote the organism’s Darwinian fitness, i.e. tending to result in more of the organisms genes appearing in the next generation.

As might be anticipated from the above, the authors develop a theory that rape itself may represent either just such a specific behavioral strategy or is a by-product of another. Although obviously recognizing the crucial role for genes in the development of behavior, T&P emphasize that evolutionary approaches to behavior are not based upon genetic determinism, as is often assumed, but rather recognize that learning and environmental factors are critical to the development and selection of behavioral strategy. The authors assert that understanding the evolutionary basis of raping behavior may enable us to appreciate those factors that may promote this reprehensible behavioral strategy and thus, by altering or avoiding those same factors, eliminate or reduce the frequency of rape

In anticipation of objections that raping behavior may represent a “natural” evolutionarily functional (at least for our ancestors) behavioral strategy, T&P also take considerable care to define and urge avoidance of what they see as a major source of resistance to evolutionary explanations of human behavior: The Naturalist Fallacy—the idea that if a behavior or trait arises naturally—it must therefore be seen as morally good or desirable. The idea equating the natural with the good does have considerable ongoing cultural currency (despite having been undermined by philosophical ethics) and indeed has resulted in evolutionary explanations of human behavior being seen as excusing or even condoning socially reprehensible actions. In addition, evolutionary psychology continues to labor in the shadow of the Nazis and the forced sterilizations of the eugenics movements—both related misuses of evolutionary theory related to conflation of the natural with the morally prescriptive.

Finally, other evolutionary issues explored include an emphasis on the use of gene level selection (traits evolve as a result of benefiting the reproduction of the individual’s genes) rather than group selection (traits evolve due to their benefit to a group of individuals) in understanding evolutionary change and the importance of considering functional behavioral strategies in the context of ancestral rather than modern environments. Behaviors that were adaptive for our hunter-gatherer ancestors may not be adaptive for the denizens of urban sprawl.

Following their exposition of key evolutionary ideas, T&P go on to apply these ideas to the evolution of human sexuality. The sexes are seen in evolutionary terms as pursuing substantially different and potentially conflicting reproductive strategies stemming largely from the significant disparity in minimum investment for a successful reproductive event. Women are noted to have a much greater obligatory investment and far greater potential associated vulnerability associated with reproduction relative to men. In addition, the reproductive life-span is itself significantly shorter in women. The result of these disparities is said to have resulted in males tending to demonstrate reproductive strategies emphasizing maximizing numbers of mating opportunities over quality of mate or at least pursuing a sort of “dual strategy” wherein the male invests for a period of time more in one woman while still taking advantage of extra-pair bond matings whenever possible. Females, however, are, as a result of the greater obligate investment and greater degree of associated vulnerability likely to be significantly more selective with regard to mates emphasizing both genetic quality as well as a willingness on the part of the male to invest in her and her offspring.

While both authors agree that the ultimate causes of raping behavior are rooted in gender differences in reproductive strategies, the two acknowledge a basic difference in their respective conceptions of the nature of the relationship. Palmer believes that rape is a horrific “by-product” of a male disposition to “opportunistic” sexuality while Thornhill asserts that rape may be an adaptation, activated under certain conditions, that functions to promote reproduction by “by-passing” the obstacle of female mating selectivity as described above. The evidence supporting each position is reviewed but is described as being inadequately definitive.

T&P then go on to describe the detailed analysis of a large data set on rape victims and some of the results are distinctly counter-intuitive. For example, women with less overt physical injury were reported as experiencing more emotional distress than women with more obvious physical injury. This finding is described as consistent with issues related to potential high levels of male sexual jealousy in the women’s regular partners and an associated tendency to disbelieve that a rape actually occurred (as opposed to a consensual coupling). This high level of sexual jealousy is itself a predicted feature of male sexual psychology derived from evolutionary psychology and is thus consistent with T&P’s approach.

After developing their conception of the evolutionary basis of rape, T&P then devote an entire chapter to comparing this approach with what they describe as “the Social Science Explanation” i.e., rape is not sexually motivated but is motivated by a wish to maintain male dominance of women. The final chapters of the book address a variety of issues including legal matters including rape punishment, prevention of rape through educational interventions, and finally, evolutionarily informed treatment of rape victims. This last appears to consist primarily in anticipating the potential for anxiety in relation to potential changes in the victim’s sense of control over her own reproductive life and impacts in the way her value is perceived by her regular sexual partner (mate).

On the whole, I found A Natural History of Rape to be a very well written and well-argued exposition of an evolutionary psychological theory of rape. I believe this book is an important contribution to the literature on this deeply disturbing aspect of human behavior and deserves a wide audience. While the book is capable of being understood by any reasonably educated person willing to make the effort, some background in evolutionary biology would certainly be helpful and minimize the risk of misunderstanding the central arguments, and—judging from much of the criticism I have read—such misunderstandings have been common. If I were to identify any problem with this otherwise excellent book, I would locate it in their treatment of the traditional social science explanations of rape. While the traditional de-sexualization of rape does not fair well before the authors’ arguments, T&P do adopt a tone that is perhaps excessively polemical with the potential result that their otherwise well argued positions may tend to be dismissed as essentially politically motivated resulting in their ideas receiving less of a fair hearing than they deserve.