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Thursday, Feb. 26, 2004
Sex (selection) and the City
By ROWAN HOOPER
It's colloquially well known that women can feel competition from other women, as this scene from "Sex and the City" shows:
Charlotte: "I just know no matter how good I feel about myself, if I see Christy Turlington, I just want to give up!"
Miranda: "Well, I just want to tie her down and force-feed her lard, but that's the difference between you and me."
While Charlotte wants to bow out of the mating game altogether, Miranda wants to force her competitors to become obese, with the implication that they would then be out of the mating game.
The exchange illustrates what Darwin called sexual selection: The selection pressures exerted on individuals in the struggle to find a mate. Darwin described two processes: male-male competition and female choice. They explain why males have evolved elaborate structures either for fighting other males (like the horns on a stag beetle's head) or for attracting females (like the peacock's tail).
But the "Sex and the City" episode highlights a different aspect of sexual selection. In this case it is women who are competing, not men. That's because sexual selection doesn't always mean males compete and females choose. If the conditions are right, males can be choosy about who they mate with (yes, really) and females may compete among themselves. In New York City, where there is reportedly a shortage of heterosexual men, women may be more than usually competitive.
While the writers of "Sex and the City" recognize this, and female-female competition had been reported in other animals such as baboons, no one had formally reported on the process in humans until last week, in a paper in the Royal Society journal Biology Letters.
Maryanne Fisher, from York University in Toronto, Canada, compared how women in periods of high and low fertility rated the attractiveness of other women's faces. She found that women in a highly fertile/high estrogen period of their menstrual cycle rated other women's facial attractiveness significantly lower than women in a less fertile/low estrogen period of the cycle.
"Evolutionary theory predicts female intrasexual competition will occur when males of high genetic quality are considered a resource," said Fisher, concurring with what could be called the "Sex and the City hypothesis."
To test the hypothesis she selected 104 first-year students (57 women and 47 men) to take part in her test. In her selection, Fisher excluded females who were pregnant, were using or had used oral or intravenous contraceptives in the previous three months, had used antidepressant drugs, missed an ovulatory cycle in the last 12 months or were not heterosexual. Likewise, nonheterosexual males were also not allowed in the test.
The students were shown a set of photographs of 35 female and 30 male faces and asked to rate the attractiveness of the faces. Each face was presented in a random order on a laptop computer and the students used a seven-point scale from "extremely unattractive" to "extremely attractive." Ratings and response times were recorded. In addition the women students indicated where they were in their ovulatory cycle.
Women's rating of male facial attractiveness remained almost identical during periods of high and low fertility. Interestingly, in both cases women's rating of male facial attractiveness was much lower than their rating of women. And the average rating of men's facial attractiveness by men themselves was slightly higher than the women's average rating of males.
But how does running down the looks of another woman help in sexual competition? What happened to the idea of sisterhood?
"One potential strategy for competition is competitor derogation using tactics to make a rival inferior to oneself," said Fisher. "Devaluing the facial attractiveness of a same-sex rival would indicate this phenomena occurring and it was further hypothesized that during periods of high fertility -- when the potential for conception and competition for a 'good mate' was greatest -- women would be most critical of a rival's appearance."
And Fisher's results appear to support this conclusion.
"The theory of intrasexual competition in women has been controversial, but this study shows that women's perceptions of potential rivals' attractiveness is considerably altered depending on the state of their own fertility. This demonstrates a potential intrasexual competitive process," said Fisher.
Fisher hopes to extend the work into a social context. "It would be interesting to study what women say about each other in a normal, social environment and how this changes with the state of their fertility," she said. "Women are very willing to talk about these things and volunteer readily for these studies."
Any plans Fisher may have had to augment her academic wages with a consultancy role on "Sex and the City," however, will come to nothing. The award-winning series finishes this year. But then again, there's talk of taking it to the big screen.
A book of a selection of these Natural Selections columns translated into Japanese, "Nou to sekkusu no seibutsugaku (Evolution, Sex and the Brain)," is published by Shinchosha on Feb. 27. Rowan Hooper is a researcher at Trinity College Dublin. He welcomes comments at firstname.lastname@example.org