Matthew Gillum’s willingness to use evolutionary theory to investigate human behavior is commendable (“Evolution, not culture, deserves blame for rape,” 9/20). However, his proposed evolutionary explanation for rape suffers flaws like those of Thornhill and Palmer’s, whose work he cites. This is unfortunate, given the seriousness of the subject.

Gillum and some of his targets unproductively assume that human behavior results from either “biology” or “culture”. These are not mutually exclusive causal variables. Phenotypes result from gene-environment interactions. This applies to human anatomy and physiology — and to human behavior, for which culture provides unique environmental complexity. Gillum undoubtedly agrees with Thornhill and Palmer that arguing that evolved mechanisms influence men’s propensities to rape need not involve the “naturalistic fallacy” (i.e., claiming that rape is inevitable and justified). But committing the “biology vs. culture” fallacy allows the inference that rape is indeed immutably part of men’s “nature.” Thornhill and Palmer themselves flirt with the naturalistic fallacy in proposing that anti-rape education programs should include provisions like informing young women that wearing sexy clothes and promising sexual access invites rape because of how men’s minds have evolved to respond to such enticements (no supporting evidence offered).

Thornhill and Palmer disagree on whether “rape adaptations” (evolved psychological mechanisms predisposing men to rape in certain circumstances) exist or rape is a “byproduct” of adaptations influencing sexual desire. As Coyne noted in an excellent analysis of their substantive and methodological errors, byproduct “hypotheses” explain everything, thus nothing. Hypotheses about adaptation are testable in principle by showing that 1) traits vary; 2) they are heritable; 3) the variation results in differential reproductive success. These conditions have not been met for “rape adaptations.”

Moreover, just because we cannot experimentally test evolutionary hypotheses on humans like we can on scorpion flies does not validate the sorts of “hypothesis testing” by survey data and speculation in which Thornhill and Palmer engage. For examples, among their proposed “rape adaptations” are “psychological mechanisms that motivate men who lack sexual access to females (or who lack sufficient resources) to rape” (p. 65) and “a victim-preference mechanism designed … to maximize the reproductive benefits of rape” (p. 70). As support, they state that “rape is disproportionately committed by men with lower socioeconomic status” (p. 67), although occasional rape by “high status men with sexual access to females” complicates things. But they fail to justify assigning men to categories of relative “sexual access” based on socioeconomic status, sidestep questions about reporting bias, and ignore crucially important and hotly contested political influences on definitions of “rape” and on the willingness of legal authorities to accept women’s claims of rape. Lacking data on “reproductive benefits”, they argue that the age distribution of victims (e.g., highest rates for 16 to 24-year-olds) points towards “adaptations.” However, if men’s minds are designed to target maximally fertile women, why should 29 percent of the victims in one survey have been under 11?

Gillum, like Thornhill and Palmer, too quickly equates forced copulations in non-humans with rape. How sexual coercion influences male reproductive success in species like scorpion flies, mallards and orangutans is unclear. Surely we should not argue that men and scorpion flies share evolved psychological mechanisms. Why, then, call forced copulations in scorpion flies “rape”? As the rape prevention workers whom Gillum criticizes rightly argue (“Why we can’t divorce culture from rape,” 9/22), rape involves power relationships, violence and usurpation of control over women’s bodies by men in uniquely human cultural contexts. Asserting that arguments grounded in this uniqueness are inevitably ideologically motivated and biased is itself an ideological act: It fallaciously presumes that biological arguments are inevitably politically neutral and objective.

We might reduce arguments about evolutionary theory and human behavior if, like Sarah Hrdy and other “feminist evolutionary biologists,” we recognized that these often conflate levels of explanation. Hrdy agrees that rape expresses men’s power over women, but asks why men assert such power so pervasively. Seeing power as an end in itself is unsatisfying; asking “why” raises questions about evolutionary origins that complement those about cultural explanations.

To understand what leads to rape and how to prevent it, we cannot ignore culture, which is inextricably intertwined with biology. We cannot ethically (or practically) manipulate most potentially relevant biological factors, but we can surely change the cultural variables that are conducive to rape.

1. Thornhill, R. & C. Palmer, 2000. A Natural History of Rape: Biolgical Bases of Sexual Coercion. Cambridge: MIT Press.

2. Coyne, J. 2000. Of vice and men: the fairy tales of evolutionary psychology. The New Republic, April 23, 2000: 27-33.

3. Hrdy, S. B. 1997. Raising Darwin’s consciousness. Human Nature, 8: 1-49.

David P. Watts is a professor of anthropology. This piece is co-authored by several others in the Department of Anthropology: Stephanie Anestis (lecturer); Richard Bribiescas (associate professor); Kathryn Clancy (Ph.D. candidate); Sholly Gunter (graduate student) and Eric Worby (associate professor).