CORAL GABLES, FL (December 7, 2010)— Previous research has shown that when women are in their most fertile phase they become more attracted to certain qualities such as manly faces, masculine voices and competitive abilities. A new study by University of Miami (UM) Psychologist Debra Lieberman and her collaborators offers new insight into female sexuality by showing that women also avoid certain traits when they are fertile.
The new study shows that women avoid their fathers during periods of peak fertility. The findings are included in a study entitled "Kin Affiliation Across the Ovulatory Cycle: Females Avoid Fathers When Fertile" available online in December in the journal Psychological Science, a prominent peer-reviewed scholarly journal.
Women stay away from male relatives when they are most fertile for evolutionary reasons, explains Lieberman assistant professor in the Department of Psychology at UM and the study's lead author. "Evolutionary biologists have found that females in other species avoid social interactions with male kin during periods of high fertility," said Lieberman. "The behavior has long been explained as a means of avoiding inbreeding and the negative consequences associated with it. But until we conducted our study, nobody knew whether a similar pattern occurred in women."
For the study, the researchers examined the cell phone records of 48 women in their reproductive years. They noted the date and duration of all calls with their fathers and separately, their mothers over the course of one billing period. They then identified the span of days comprising each woman's high and low fertility days within that billing period.
"Women call their dads less frequently on these high-fertility days and they hang up with them sooner if their dads initiate a call," said Martie Haselton, a UCLA associate professor of communication in whose lab the research was conducted. Women were about half as likely to call their fathers during the high fertility days of their cycle as they were to call them during low fertility days. Women's fertility had no impact, however, on the likelihood of their fathers calling them. Women also talked to their fathers for less time at high fertility, regardless of who initiated the call, talking only an average of 1.7 minutes per day at high fertility compared to 3.4 minutes per day at low fertility.
The researchers concede that the high-fertile women might simply be avoiding their fathers because fathers might be keeping (too close) an eye on potential male suitors. But their data cast some doubt on this possibility. It is more likely, they conclude, that like females in other species, women have built-in psychological mechanisms that help protect against the risk of producing less healthy children, which tends to occur when close genetic relatives mate.
"In humans, women are only fertile for a short window of time within their menstrual cycle," Lieberman said. "Sexual decisions during this time are critical as they could lead to pregnancy and the long-term commitment of raising a child. For this reason, it makes sense that women would reduce their interactions with male genetic relatives, who are undesirable mates."
The reluctance to engage in conversations with fathers could not be attributed to an impulse to avoid all parental control during ovulation. In fact, the researchers found that women actually increased their calling to their mothers during this period of their cycle, and that this pattern was strongest for women who felt emotionally closer to their moms. At high fertility, women proved to be four times as likely to call their mothers as they were to phone their fathers, a difference that did not exist during the low fertility days. In addition, women spent an average of 4.7 minutes per day on the phone with their mothers during high fertility days, compared to 4.2 minutes per day during low-fertility.
One possible explanation is that women call their moms for relationship advice, said Elizabeth Pillsworth, who also contributed to the study.
"They might be using mothers as sounding boards for possible mating decisions they're contemplating at this time of their cycle," said Pillsworth, an assistant professor of evolutionary anthropology at California State University, Fullerton. "Moms have a lot more experience than they do. Particularly for those women who are close to their mothers, we can imagine them saying, 'Hey Mom, I just met this cute guy, what do you think?'"
Either way, the findings show that women are unconsciously driven during their most fertile periods to behavior that increases the odds of reproducing and doing so with the right mate, said Haselton.
"This suggests that although human culture has in many ways changed at a rapid pace, our every day decisions are often still tied to ancient factors affecting survival and reproduction," says Haselton. "We think of ourselves as being emancipated from the biological forces that drive animal behavior. But, that's not completely true," she says. "These kinds of findings show us that a complete understanding of human behavior needs to involve these biological forces. Humans are, after all, mammals."
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