A biological mechanism that protects against rape?

When sex researchers compare men and women's genital arousal in response to various stimuli, they generally find that men tend only to be aroused by stimuli that match their declared sexual preferences and subjective feelings, whereas women tend to be aroused by a broad array of sexual material (even involving chimps), irrespective of their declared preferences and subjective feelings. A new study by Kelly Suschinsky and Martin Lalumiere tests the claim, which will surely prove controversial, that this pattern of responding in women is an evolutionary vestige which served in the past to protect women from the genital injury that can come from unwanted sex.

'Substantial ethnographic, historical, and comparative evidence suggests that the threat of unwanted sexual activity has been considerable over human evolutionary history,' the researchers said. Their specific proposal is that women's indiscriminate genital arousal leads to lubrication which reduces the likelihood of injury occurring when unwanted sexual encounters take place.

To test this claim, Suschinsky and Lalumiere presented 15 heterosexual men and 15 heterosexual women (average age in their early twenties), all currently in a sexual relationship, with 14 two-minute audio recordings of various narratives read by a woman from her own perspective. The narratives varied in whether or not a sexual encounter occurred between a man and a woman, whether or not violence took place, and whether or not the activities were consensual.

Consistent with past research, the men's genital arousal was far more specific, tending to occur most strongly in response to a consensual, non-violent sexual encounter, which was also the scenario they said they found most arousing. By contrast, the women's genital arousal was far more uniform across all the sexual scenarios. There was one anomaly - their genital arousal to non-consensual, but otherwise nonviolent, sex was lower than for consensual, non-violent sex, but was still significantly higher than their response to neutral scenarios. Like the men, the women's subjective feeling of arousal was far more targeted, being much higher for the consensual, non-violent scenario than the others. Both sexes reported finding the violent or non-consensual scenarios unpleasant and anxiety provoking.

Suschinsky and Lalumiere said their results support what they call the 'preparation hypothesis', adding to past research showing, for example, that some women report experiencing genital lubrication during rape. The researchers acknowledged some limitations in their study. In particular, the scenarios were all told from a woman's perspective. However, they said that past research had shown men tend to find this narrative perspective particularly arousing, so this methodological imbalance is unlikely to explain the results. The researchers also acknowledged that their sample were young and sexually active, and likely to be fairly sexually liberal given that they'd volunteered for a study of this kind. 'We recommend that this study be replicated with a larger and more diverse sample,' they said.

Given the sensitivity of this research topic, and in particular the possibility that its message might be exploited to justify immoral acts, it's worth heeding the words of Mary Roach in her book Bonk:

'It is important to remember,' she writes, that 'it is the mind that speaks to a woman’s heart, not the vaginal walls... Rape offers a plangent illustration of this fact. I learned in a paper by Roy Levin that rape victims occasionally report having responded physically, even though their emotional state was a mixture of fear, anger and revulsion. ... Regardless of the mechanisms that may or may not explain a rape victim’s physical state, a rapist’s defense based upon evidence of arousal has, to quote Levin, "no intrinsic validity and should be disregarded".'

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Suschinsky, K., and Lalumiere, M. (2010). Prepared for Anything?: An Investigation of Female Genital Arousal in Response to Rape Cues. Psychological Science DOI: 10.1177/0956797610394660