Menstrual Cycle May Fuel Female Bias A new study suggests genetics may be a factor in developing prejudice. Specifically, researchers discovered a women’s bias against male strangers increases when women are fertile.

The study appears online in the journal Psychological Science.

“Our findings suggest that women’s prejudice, at least in part, may be a byproduct of their biology,” said Melissa McDonald, a Michigan State University doctoral student and lead author on the paper.

Investigators studied two groups of women on how their attitudes toward men change across the menstrual cycle.

They found that fertile women were more biased against men of different races and men of different social groups than men of their own group.

Of interest is the finding that the increase in bias occurred only for women who perceived the men as physically threatening, said psychologist Dr. Carlos David Navarrete, the research team leader.

Previous research has focused on men within the same racial and social groups. In those cases, women who were fertile had more positive impressions of men who were physically imposing.

These results suggest that the same traits that fertile women find attractive in men of their same group may actually lead to more negativity against men when those traits are associated with men of a different racial or social group, McDonald said.

McDonald and Navarrete said their team’s findings are consistent with the idea that women’s prejudice may reflect the workings of an evolved psychological system that once functioned to protect them from sexual coercion, particularly when the costs are highest – that is, when women are fertile.

The bias against males may have evolved overtime as male strangers may have posed considerable risk of sexual coercion throughout human history.

“This may be deeply ingrained at psychological levels,” Navarrete said, “and may manifest itself particularly if women believe men from different racial and nonracial groups to be physically imposing and when women are most fertile.”

Source: Michigan State University