Our biological drive to do it conflicts pretty directly with our biological drive not to get involved with other people's bodily fluids. How do we ignore the obvious grossness of sex for long enough to propagate the species? Maybe, researchers say, by turning off our disgust reflex whenever we get turned on.
Earlier studies have asked this question in a variety of ways. For example, by asking men to "self-stimulate" and then quizzing them on what sex acts or partners they'd be open to. Or by showing men erotic slideshows and then having them stick their hands into cold pea soup or buckets of condoms. Psychology researchers Charmaine Borg and Peter J. de Jong at the University of Groningen in the Netherlands—perhaps feeling less pessimistic than others about their ability to arouse a group of female subjects—decided to study the question in women instead.
The researchers gathered 90 female university students. Rather than just answering questions about distasteful things, these subjects were going to be challenged with some actual gross tasks to see how many they would do.
But first the researchers had to turn their subjects on. Well, a third of them, anyway. One group of women watched a film described as "female friendly erotica." A second group watched a movie that was meant to be non-sexually arousing—that is, heart-pounding but not steamy. These women saw footage of sky diving and mountain climbing. The third group saw a movie about a train ride, meant to not cause any feelings at all. The movies had been previously tested with a separate group to make sure they elicited the right emotions.
As the women watched their steamy, exciting, or boring movies, they were periodically interrupted by an experimenter who showed up and gave them disgusting tasks to do. There were a total of 16 challenges, ranging from picking up apparently soiled toilet paper to sticking a needle in a cow eye. The subjects didn't have to go through with any task they didn't want to, but they did have to rate how disgusting they found each one.
Out of the 16 gross-out tasks, 5 were classified as sex-related. These included touching some "used" condoms, handling "used" women's underwear, and reading aloud a sexual phrase about, um, a dog. (The researchers made liberal use of Halloween-style tools and props, including blood-colored ink, fake feces, coconut milk in the underwear, and one plastic bug. And one real worm, which they rereleased outside when the study was over.)
The groups who watched the train movie and the sky-diving movie didn't differ in their willingness to do the gross tasks, or in how disgusting they rated those tasks. But the women who watched the erotic film rated the sex-related tasks as significantly less disgusting than the other groups. They seemed to find the rest of the tasks less gross too, though the result wasn't quite significant. And overall, the erotica group completed more challenges of both kinds. The turned-on subjects completed 85% of the non-sexy tasks, for example, compared to about 66% in the other two groups.
Charmaine Borg says she was surprised to see that sexual arousal, but not general arousal (the sky-diving kind), "makes us approach stimuli that are in general so disgusting." The way subjects perceived disgusting things seemed to change when they were sexually aroused.
The study focused on a small group of young, heterosexual, dysfunction-free women. It was limited to one method of turning those subjects on (the erotic film) and an odd handful of gross, somewhat sex-related tasks. And the study relied on subjects' own ratings of their arousal and repulsion. But if it proves to be generally true that sexual arousal squelches disgust, it would explain how we manage to reproduce despite our usual instincts—which presumably evolved to keep us safe from disease-carrying stuff.
Borg is more interested, though, in women whose bodies don't let them have sex. She wonders if sexual disorders such as dyspareunia (painful intercourse) or vaginismus (involuntary clenching of the muscles around the vagina, making intercourse difficult or impossible) are rooted in problems overcoming disgust.
"Studies from our lab with women afflicted with vaginismus have shown that they experience disgust responses towards erotic stimulation," Borg says. "Sex-related stimuli appeared to elicit disgust rather than arousal." Since our usual response to disgust is to keep far away from what's causing it, she says the problem could be self-perpetuating as women start avoiding sex altogether.
Borg says her results so far are "very exciting." By carrying on her experiments in the condom-filled, fake-blood-soaked laboratory, she helps to hope women overcome their difficulties and get down to whatever business they want.
Charmaine Borg, & Peter J. de Jong (2012). Feelings of Disgust and Disgust-Induced Avoidance Weaken following Induced Sexual Arousal in Women. PLOS ONE : 10.1371/journal.pone.0044111