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Designer Genes: Women May Stray When Ovulation Peaks

January 10, 2006

Study suggests infidelity could be part of evolutionary call for desirable mates

Women who feel an urge for sex outside of their marriages might be hearing an evolutionary call to improve the species.

New research suggests that during ovulation, when women are ready to conceive, nature may encourage them to look beyond their male partners for a better gene pool, but only if they don’t find their mates sexually attractive.

“The mating market is driven by supply and demand, and therefore not all women will attract long-term mates offering good genes,” the study authors stated. Women innately deduce that a man they find sexy has better genes to pass on to a baby.

“Ancestrally, these women may have benefited from a strategy in which they secured investment from a long-term mate and obtained genetic benefits from extra-pair partners,” the study added.

But the researchers, from the University of California, Los Angeles, and the University of New Mexico, also contend that men who are generally less attractive to women tend to guard their ovulating wives with particularly attentive and possessive behavior.

“What is at stake is not just the loss of face or the loss of love,” said co-author Martie G. Haselton, an assistant professor of communication studies and psychology at UCLA. “This is about Darwinian prosperity. Males who did not successfully guard their mates are not our ancestors.”

Study co-author Steven W. Gangestad, a psychologist at the University of New Mexico, said studies he has worked on have shown that women prefer men whose faces, voices, odors and demeanor are deemed masculine. It makes sense then that they should be particularly inclined toward such men when they are ovulating, particularly if their usual partner is something less than a 10 on the stud scale.

It makes sense physiologically as well, said Dr. Irwin Goldstein, founder and former director of the Institute for Sexual Medicine at the Boston University School of Medicine. Women who are ovulating have a higher level of testosterone, which causes heightened desire, he said, adding they are now ready and willing to conceive.

If your libido is high and you require a partner to express that libido, you have to find a person who is sexually functional, Goldstein said. Couples influence each others’ experience. Scientifically, a woman’s sexual physiology is linked to the man’s performance, so during ovulation she may seek a man who appears ready to get the job done, he said.

The study, reported in the current issue of Hormones and Behavior, was based on responses from 38 coeds from a large unnamed U.S. university. They were asked to rate their partner’s sexual attractiveness and submitted 35 diary-like entries rating the strength of their attractions to men other than their mates and the frequency with which they flirted or otherwise acted out those attractions.

For a second study, Haselton recruited 43 women who similarly rated their partner’s sexual attractiveness on a day near ovulation and on a non-fertile day.

Those findings, to be published in Evolution and Human Behavior, confirm the first study, Haselton said.

“We aren’t saying that women are genetically programmed to be unfaithful,” said Gangestad. “They aren’t robots following genetic instruction. You have psychology, biology that is some product of selection. But relationships are mixtures of loving aspects and conflicts, and this is a part of conflict. Infidelity itself is a choice.”

More information

For more on female reproduction, visit the U.S. National Institutes of Health.