Strange Science: Menstruation Causes Prejudice?

A new study suggests that depending on where they are in their menstrual cycles, women have very different reactions towards strange men. At their most fertile, women are more suspicious of men they see as outside of their social or racial group and who they perceive as being physically threatening. Which means that prejudice could, at least partially, be a byproduct of our biology.

Researchers from Michigan State University asked 252 college-age women–224 of whom were white and 28 of whom were black–to complete an online test in which they quickly associated traits like muscularity with photos of men of both races. They also asked a smaller pool of women to complete a similar test, this time asking them to wear a t-shirt that was either red, blue or yellow and then evaluate men who were also assigned one of those three color groups.

The researchers found that when they were at their most fertile, women were increasingly biased against men in a group different from their own–whether it was according to race, as in the first experiment, or according to t-shirt color, as in the second. Notably, this was only true of women who indicated that they saw the men as physically threatening.

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What the small study suggests is that in addition to learned biases, there could be something about women’s biology that leads them to protect themselves against men who they believe pose a risk to them, sexually, at the time when they are most “at risk” of getting pregnant. In other words, when women are more likely to conceive a child, they are biologically driven to be more discriminating about who they are going to mate with. Without necessarily realizing it, they protect themselves against men who they believe endanger that choice.

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