A Natural History of Rape: Biological Bases of Sexual Coercion is a 2000 book about rape by biologist Randy Thornhill and anthropologist Craig T. Palmer, with a foreword by psychologist Margo Wilson. Thornhill and Palmer propose that rape should be understood through evolutionary psychology, and criticize the idea, popularized by Susan Brownmiller in Against Our Will (1975), that rape is an expression of male domination that is not sexually motivated. They argue that the capacity for rape is either an adaptation or a byproduct of adaptive traits such as sexual desire and aggressiveness. A Natural History of Rape provoked controversy and received extensive criticism.
Thornhill and Palmer wrote that they wanted to see rape eradicated, and argued that improved understanding of what motivates rape would help achieve this goal, while false assumptions about the motivation of rapists are likely to hinder efforts to prevent rape. They wrote that rape could be defined as, "copulation resisted to the best of the victim's ability unless such resistance would probably result in death or serious injury to the victim or in death or injury to individuals the victim commonly protects". However, they noted that other sexual assaults, including oral or anal penetration of a man or a woman under the same conditions, can also sometimes be called rape. They suggested that theory and research in evolutionary biology and evolutionary psychology can help to elucidate the ultimate (evolutionary) causes (as opposed to primarily proximate causes) of rape by males in different species, including humans. They argued that the capacity for rape is either an adaptation, or, a byproduct of adaptative traits such as sexual desire and aggressiveness that have evolved for reasons that have no direct connection with the benefits or costs of rape.
Thornhill and Palmer identified anthropologist Donald Symons as the first author to propose, in The Evolution of Human Sexuality (1979), that rape is "a by-product of adaptations designed for attaining sexual access to consenting partners." They noted that Symons has falsely been accused of basing his arguments on the assumption that "behavior is genetically determined", even though he explicitly rejects that assumption and criticizes it at length. Thornhill and Palmer criticized explanations of rape put forward by social scientists, and Susan Brownmiller's book Against Our Will, which popularized the feminist view that rape is an expression of male domination that is not sexually motivated. They criticized arguments that rape is not sexually motivated on several grounds. In their view, concluding that rape must be motivated by the desire to commit acts of violence because it involves force or the threat of force is as illogical as concluding that men who pay prostitutes for sex are motivated by charity. They criticized the argument that rape cannot be sexually motivated because rapists do not prefer sexually attractive victims by citing evidence that a disproportionate number of rape victims are women in their teens and early twenties.
Biologist Jerry Coyne, writing for Nature, described Thornhill and Palmer's hypothesis as controversial. Thornhill and Palmer have claimed that some of the criticism it has received consists of straw man arguments, contradictions, and flawed logic. Thornhill debated the book's conclusions with Brownmiller on American public radio.
Sociologist Hillary Rose and biologist Steven Rose called A Natural History of Rape, "perhaps the nadir of evolutionary psychology's speculative fantasies", writing that while Thornhill and Palmer described forced sex among animals as rape, leading journals of animal behavior had already rejected that characterization as long ago as the 1980s, and that Thornhill and Palmer failed to address evidence showing that while forced sex among animals always takes place with fertile females, human rape victims are often either too young or too old to be fertile. The Roses also accused Thornhill and Palmer of insulting rape victims by suggesting that they might have invited sex by wearing revealing clothing, and criticized them for preferring ultimate to proximate explanations. Primatologist Frans de Waal argued in The New York Times that rape involves both sex and violence, and that while A Natural History of Rape serves as a corrective to the dogmatic view that rape is primarily about power, Thornhill and Palmer's view that rape is primarily sexually motivated is equally dogmatic. In de Waal's view, their theory could only be true if men who rape differ genetically from men who do not rape and sire more children than they could without committing rape, and there is no evidence that either of these things is true. He questioned why one-third of rape victims are young children and the elderly, too young or too old to reproduce if rape is about reproduction and why most men do not rape if rape is a smart reproductive strategy. He suggested that Thornhill and Palmer wrongly describe premature ejaculation and the ability to detect female vulnerability as rape adaptations, when other explanations for them exist.
Author Richard Morris wrote that A Natural History of Rape caused "a great deal of controversy", and that some critics objected "quite violently" to Thornhill and Palmer's ideas. Morris considered it unfortunate that the controversy obscured the fact that A Natural History of Rape was not only about rape, but was also "an endorsement of the principles of evolutionary psychology and an attack on its opponents." Eric Smith et al. (2001) criticized Thornhill and Palmer's hypothesis that a predisposition to rape in certain circumstances is an evolved psychological adaptation. They developed a fitness cost/benefit mathematical model and populated it with estimates of certain parameters (some parameter estimates were based on studies of the Aché in Paraguay). Their model suggested that generally, only men with a future reproductive value of 1/10th or less of a typical 25-year-old man would have a net positive cost/benefit fitness ratio from committing rape. On the basis of their model and parameter estimates, they suggested that this would make it unlikely that rape generally would have net fitness benefits for most men.
Psychologist Steven Pinker, writing in The Blank Slate (2002), called A Natural History of Rape "one of the most incendiary books of the last decade" and observed that its authors "brought down more condemnation on evolutionary psychology than any issue had in years". According to Pinker, attacks on A Natural History of Rape included a Feminist Majority Foundation calling the book "scary" and "regressive", and a spokesperson for the creationist Discovery Institute testifying at a U. S. congressional hearing that the book threatened America's moral fabric. Pinker endorsed Thornhill and Palmer's view that rape is sexually motivated, and criticized Hilary Rose.
Evolution, Gender, and Rape, a 2003 book edited by Cheryl Brown Travis written in response to A Natural History of Rape, compiled the views of twenty-eight scholars opposed to sociobiological theories of rape. One contributor, sociologist Michael Kimmel, criticized Thornhill and Palmer's argument that female rape victims tend to be sexually attractive young women, rather than children or older women, contrary to what would be expected if rapists selected victims based on inability to resist. Kimmel argued that younger women are the least likely to be married and the most likely to be out on dates with men, and therefore are the most likely to be raped because of opportunity arising from social exposure and marital status. Palmer and Thornhill responded in an article in Evolutionary Psychology.
David Sloan Wilson et al. (2003) argued that Thornhill and Palmer use the naturalistic fallacy inappropriately to forestall legitimate discussion about the ethical implications of their theory. According to Thornhill and Palmer, a naturalistic fallacy is to infer ethical conclusions (e.g., rape is good) from (true or false) statements of fact (e.g., rape is natural). Wilson et al. point out that combining a factual statement with an ethical statement to derive an ethical conclusion is standard ethical reasoning, not a naturalistic fallacy, because the moral judgment is not deduced exclusively from the factual statement. They further argued that if one combines Thornhill and Palmer's factual premise that rape increases the fitness of a woman's offspring with the ethical premise that it is right to increase the fitness of offspring, the resulting deductively valid conclusion is that rape also has positive effects and that its ethical status is ambiguous. Wilson et al. stated that Thornhill and Palmer dismiss all ethical objections with the phrase 'naturalistic fallacy' although "it is Thornhill and Palmer who are thinking fallaciously by using the naturalistic fallacy in this way."
Richard Hamilton (2008) criticized Thornhill and Palmer's definition of rape as the coerced vaginal penetration of women of reproductive age, suggesting that the exclusion of male rape, rape of women outside the reproductive age range, murderous rape, and non-vaginal forms of rape virtually guaranteed the confirmation of their hypothesis that rape is an evolved reproductive strategy and not a crime of violence.