Do my friends make me look fat ?
Stigmatizing female promiscuity -- a.k.a. slut-shaming -- has often been blamed on men, who have a Darwinian incentive to discourage their spouses from straying. But they also have a Darwinian incentive to encourage other women to be promiscuous. Dr. Vaillancourt said the experiment and other research suggest the stigma is enforced mainly by women.
"Sex is coveted by men," she said. "Accordingly, women limit access as a way of maintaining advantage in the negotiation of this resource. Women who make sex too readily available compromise the power-holding position of the group, which is why many women are particularly intolerant of women who are, or seem to be, promiscuous."
Indirect aggression can take a psychological toll on women who are ostracized or feel pressured to meet impossible standards, like the vogue of thin bodies in many modern societies. Studies have shown that women's ideal body shape is to be thinner than average -- and thinner than what men consider the ideal shape to be. This pressure is frequently blamed on the ultrathin female role models featured in magazines and on television, but Christopher J. Ferguson and other researchers say that it's mainly the result of competition with their peers, not media images.
"To a large degree the media reflects trends that are going on in society, not creates them," said Dr. Ferguson, a psychologist at Stetson University. He found that women's dissatisfaction with their bodies did not correlate with what they watched on television at home. Nor were they influenced by TV programs shown in laboratory experiments: Watching the svelte actresses on "Scrubs" induced no more feelings of inferiority than watching the not-so-svelte star of "Roseanne."
But he found that women were more likely to feel worse when they compared themselves with peers in their own social circles, or even if they were in a room with a thin stranger, like the assistant to Dr. Ferguson who ran an experiment with female college students. When she wore makeup and sleek business attire, the students were less satisfied with their own bodies than when she wore baggy sweats and no makeup. And they felt still worse when there was an attractive man in the room with her.
"Sexual competition among females seems to increase due to circumstances that tend to be particularly common in affluent societies," Dr. Ferguson said.
In traditional villages, people married at an early age to someone nearby, but young men and women in modern societies are free to postpone marriage as they search long and far for better options. The result is more competition because there are so many more rivals -- and there's no longer any scientific doubt that both sexes are in to win it.