Time of the Month Matters: Increased Racial Bias and the Menstrual Cycle

Can racial bias be affected by the time of the month?  According to a study in an upcoming issue of Psychological Science, a journal of the Association for Psychological Science, a woman’s menstrual cycle can affect not only her mood but may cause a racial bias as well.

Psychologist Carlos David Navarrete from Michigan State University and his colleagues have been studying the evolutionary preference toward mating–that is, women only mate with the “in-group” of males and shun anyone from the “out-group.” It turns out this bias has been modified in the present day to include skin color.

In the times of our ancestors, the out-group members posed a greater threat of sexual assault towards women than in-group members, naturally causing women to hold more negative attitudes toward the out-group when they were most vulnerable to assault and conception. The scientists tested if this theoretical bias exists today towards African-American males by white American women.

Researchers gave women a questionnaire asking about their normal menstrual cycle and then predicted the time of their peak fertility phase. They then asked women to rate their vulnerability to sexual coercion, predicting that those at the peak of fertility who believed themselves unable to fight off a sexual assault would be the most racially biased. The women also were given tests dealing with stereotypes to predict their unconscious bias, as well as a declarative test, allowing them to describe their vocal attitudes towards African-Americans.

The psychologists modified photographs of seminude males by increasing their muscle size or varying their skin color. They then presented the photos to the women and asked them to rate the men in attractiveness, and separately, to rate how scary each male looked.

Women at the peak fertility phase of their cycle carried more racial bias towards the photos in each task by rating the African-American photos to be less attractive and more threatening. This evolutionary bias toward a perceived societal group is not just an evolutionary leftover, the psychologists concluded; it is still active in women today.