A Natural History of Rape: Biological Bases of Sexual Coercion.

• Author: Lloyd, Elisabeth A.
• Position: Review

A NATURAL HISTORY OF RAPE: BIOLOGICAL BASES OF SEXUAL COERCION. By Randy Thornhill and Craig T. Palmer. Cambridge: MIT Press. 2000. Pp. xvi, 251. $28.95.

It is clear where the opposition is coming from -- it's coming from ideology.... Most of the ideology is coming from certain feminist groups. It's not feminism, per se, that's against us. It is certain groups of feminists that are against the application of science for dealing with this problem. That is a socially very irresponsible position. (1) Throughout A Natural History of Rape, coauthors Randy Thornhill (2) and Craig Palmer (3) resort to what is known among philosophers of science as "The Galileo Defense," which amounts to the following claim: I am telling the Truth and doing excellent science, but because of ideology and ignorance, I am being persecuted. (4) The authors have repeated and elaborated upon this defense during the sizable media flurry accompanying the book's publication in February 2000. (5)

Now, history has accepted this defense from Galileo. But in order for it to work for Thornhill and Palmer, of course, they must be telling the Truth and doing excellent science. In this Review I shall argue that the Galileo defense is impotent in the hands of Thornhill and Palmer because of glaring flaws in their science.

1. THEIR CLAIMS

   Thornhill and Palmer present two alternative evolutionary explanations for the existence of human rape. They claim that rape behavior must either have evolved through a process of natural selection -- that it must be a specific adaptation -- or it must be the byproduct of some underlying traits which must themselves be adaptations.

   Their main arguments for these theses all rest on a hypothesis about the evolution of sex differences: that because women bear the brunt of the effort in reproduction -- through pregnancy, nursing, and infant care -- they have evolved to be very selective about their mates. Men, on the other hand, by virtue of the possibility of being able to reproduce with the minimal investment of mere ejaculation, have evolved to seek out as many mates as possible, and to copulate with no intention of co-parenting or providing. This has led to such traits of male sexuality as the desire for casual sex, the seeking out of a wide variety of mates, and a stronger disregard for the particular features of a given mate. Hence, female and male "reproductive strategies" differ: women choose mates carefully, whereas men seek multiple mates. (6)

   Here is how each of Thornhill and Palmer's two theses about rape relies on this picture of evolved male sexuality. They call their first hypothesis -- that men have evolved, through natural selection, a specific tendency toward rape behavior -- the "rape-specific" hypothesis. On this view, men who had trouble attaining sexual access to females -- especially because of low status or evidence of inferior genetic make-up -- must have resorted to rape in order to satisfy their sexual urges to mate with a larger number of women. This trait, a disposition to rape behavior, helped get these males' genes into the human gene pool by increasing mate number, and thereby increasing the frequency of "rape genes" in the population, through the process of natural selection. In other words, the reproductive problems facing our human ancestors were very specific, and thus the mechanism that "solved" these problems -- i.e., the tendency to rape itself -- is also specific. Therefore, the rape-specific adaptation hypothesis is favored.

   Evolution by natural selection occurs when individuals of one type of genetic makeup (genotype) reproduce more successfully than individuals of other types of genetic makeup, resulting in a change within the whole population of the proportions of each type. In order for natural selection to work in favor of a particular genotype, the genotype must be associated with a trait that is inheritable and that increases the organism's reproductive success. In this case, the rapists would succeed reproductively while men who were otherwise genetically equivalent but who were not rapists would have failed at reproducing. The long-term effect of this pattern of reproductive success on human demographics would thus have been the increasing frequency of the rapist type within the human population.

   When a trait evolves (or is "chosen") through natural selection, it is called an evolutionary adaptation. Thus, the primary hypothesis defended in Thornhill and Palmer's book is that rape is an evolutionary adaptation -- that it evolved because rape behavior itself was reproductively superior to nonraping behavior.

   Under Thornhill and Palmer's second hypothesis, which they call the "byproduct" view, evolved psychological traits such as the male desire for a wide variety of mates led accidentally to the existence of rape, but rape itself was not directly selected. That is, the act of rape is an incidental byproduct of other male sexual adaptations, "especially those that function to produce the sexual desires of males for multiple partners without commitment" (p. 60). The phenomenon of evolutionary "byproducts" is frequent in human evolution. Manual dexterity, for example, was directly selected because it was reproductively advantageous to our ancestors for making tools, etc., and is therefore an adaptation. Our use of manual dexterity in playing the piano is a byproduct of the selection on manual dexterity. It is not an evolutionary adaptation itself. Note that selection leading to evolutionary adaptation is involved in this scenario, but the trait of playing the piano is distinct from the evolutionary adaptation itself; it is an epiphenomenon.

   Thornhill and Palmer consider each of these hypotheses about the evolution of human rape -- the hypothesis that rape is a specifically selected adaptation, and the hypothesis that rape is an evolutionary byproduct of selection on other traits. Most of their attention, however, centers on the rape-specific hypothesis.

   To buttress this hypothesis, Thornhill and Palmer propose a number of subsidiary psychological adaptations that would have increased men's chance of reproductive success when attempting to rape. Proposed mechanisms include men having: (1) a special psychological adaptation that enables them to evaluate females' vulnerability to rape (p. 66); (2) a special psychological adaptation to prefer to rape women at peak fertility (p. 71); (3) a psychological adaptation to be sexually aroused by gaining physical control over an unwilling sexual partner (p. 75); (4) a psychological adaptation to rape wives and girlfriends if they believe their women are cheating on them (pp. 77-78); and finally, (5) a psychological adaptation for male paranoia about women's claims of being raped (p. 158).

   But under either evolutionary scenario women are also hypothesized to have evolved rape-related adaptations -- specifically, an adaptation for psychological anguish upon being raped. The supposition is that rape victims suffer an overall loss in reproductive success. Psychological anguish is thus hypothesized to have been an adaptation to help women guard against such reproductive loss. The psychological adaptation focuses the victim's attention on the causes of the loss and helps her avoid repetition of those causes (p. 85). The basic evolutionary assumptions here are that rape reduces a woman's reproductive success by circumventing her mate choice, that it reduces her mate's reproductive success by lowering his certainty of paternity, and that it reduces the fitness of the relatives of the victim and her mate (p. 85). In addition, reproductive losses could be expected from getting raped, insofar as the act causes physical injury, the loss of a victim's ability to use copulation as a means of obtaining material benefits from men, the interference with a victim's mate's protection of her, or a reduction in the quality or quantity of parental care given by her mate (p. 86).

   According to Thornhill and Palmer, the adaptation of psychological anguish manifests itself differently in different circumstances of rape. Women of peak reproductive age are hypothesized to experience more psychological pain than females of either pre- or postreproductive age (pp. 89-90). This is because the reproductive costs to these young women from getting raped are higher.

   In addition, Thornhill and Palmer predict that reproductive-age victims will experience more violent attacks than the pre- or postreproductive-age rape victims (pp. 91-92). The basis of this prediction lies in the hypothesis that reproductive-age women are more likely to fight back "because of the greater evolutionary historical cost to their reproductive success of being raped" (pp. 91-92), and that rapists would be more highly sexually motivated to complete the rape in reproductive-age victims because of these victims' greater sexual attractiveness relative to victims in the other two categories (p. 92).

   Other hypothesized adaptations among females include: (1) the tendency to experience decreased psychological pain as the violence of the attack increases -- this is because physical injury helps to prove to her mate that the sex really was forced and not consensual (p. 92); (2) "the absence of orgasm during rape" (p. 99); and (3) the tendency to avoid risky situations, especially during the fertile phase of her cycle (p. 100).

   Thornhill and Palmer then use the supposed existence of female psychological rape adaptations to bolster their claims for specific male psychological rape-adaptations and to counter two alternatives to their theory. One would expect to find rape behavior to be ubiquitous in human societies, if it is genuinely adaptive for men; "women's apparent adaptation to deal with rape ... implies that rape has been common enough in human evolutionary history to select for counter-adaptations in women" (p. 57). This, they claim, refutes the alternative explanation that rape results...