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During Fertile Days, Women Are on the Prowl, Study Finds


For the last decade, the scientific community has investigated how a woman's ovulation--which is concealed, cryptic and undetectable unlike that in most other animals--influences her behavior and, by extension, that of her partner. In the latest volley of research, it appears that when a woman is in the fertile phase of her menstrual cycle, she is most likely to find other men sexually alluring and to fantasize about men other than her spouse or lover. Men, in turn, appear to sense their women's surging sexual urges. As a woman's eye wanders, her man may send flowers, call to see if she is really where she said she would be, try to occupy her time and grow more attentive.

The University of New Mexico researchers who conducted the study, which appears in the current issue of the journal Proceedings: Biological Sciences, have hypothesized that these modern-day reproductive urges and strategies are left over from the mating rituals of our ancient ancestors. Women, they theorize, may be scanning the gene pool for the Superman of genetic health in hopes of bearing the most robust offspring. At the same time, these women's mates are working to fortify bonds to ward off sexual interlopers.

Fifty-one women from 18 to 34 years old filled out questionnaires concerning their sexual desires, their behavior and their partners' behavior during the high-fertility phase of their cycle (five to seven days before ovulation) and once during the low-fertility phase of their cycle. Ovulation detection kits were used to determine the phases. The women were asked how much they had engaged in each of 35 behaviors or feelings in the previous two days on a four-point scale. The questionnaire asked about strong sexual attraction to the primary partner, sexual arousal by the sight of someone very physically attractive other than the primary partner, flirting with someone other than a current partner and sexual activity.

"Women did not fantasize about their primary mate any more during the high-fertility phase of their cycle than during other times in their cycle," said Steven Gangestad, professor of psychology at University of New Mexico in Albuquerque, lead author of the study. "But there was a 60% to 85% increase in women's ratings for attraction to and fantasies about people other than their partner in their high-fertility phase.... We don't know if this happens for all women."

The jump in fantasies about men other than a current lover "impressively supports our hypothesis" that women in their highest stage of fertility are shopping around for the best genetic benefits for their potential offspring, said Christine Garver, a University of New Mexico doctoral student in psychology and co-author of the study. "The results indicate that maybe ovulation may not be completely concealed. It would be nice to know exactly how the mechanism works but we don't." Strangely, the women reported that while they felt more sexual in their fertile phase and initiated sex more often with their primary partner, they did not feel more sexual interest in him.

"Women have reported having greater sexual desire during ovulation for the last 30 years," said Gangestad. "Women feel more sexual and it appears that they find themselves attracted to men other than their partner but they are not necessarily going to pursue it."

To determine whether men changed their behavior during their partner's fertile period, 27 of the women filled out a questionnaire about their primary partner's behavior. The most dramatic and complex results had to do with vigilance or, in the parlance of evolutionary psychology, "mate guarding" behavior. Women reported that their men were more attentive, called or checked up on them unexpectedly, looked through their personal belongings, tried to monopolize their time and were motivated to please them. Women in nonexclusive relationships indicated that their partners were particularly vigilant in their high-fertility phase.

But just what behavioral or biological cues men are responding to is unclear. Gangestad, who with University of New Mexico psychologist Randy Thornhill has studied how women's menstrual cycles affect behavior for the last decade, said that it could be women are tipping men off in subtle ways. It may have to do with how a woman dresses, said Gangestad. Or women may be openly gazing at other men, or flirting conspicuously. Yet another possibility is as a woman initiates sex more, her partner spends more time with her. And, say researchers, it's conceivable that men are hard-wired to detect when a woman is ovulating.

"I don't think men or women have any conscious awareness that they are behaving any differently," said Garver. "I don't think that men are aware and thinking, 'Oh, my partner is ovulating now so I think that she is interested in other men.'"

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