Once a month, millions of women change their economic behavior and become more focused on their social standing relative to other women, says a paper written by scholars from The University of Texas at San Antonio and the University of Minnesota.

Why are women such slaves to the moon? It's the ovulatory cycle, they assert, and it alters women's behavior by subconsciously motivating them to outdo other women. 

The conclusion was based on three studies, one of which had ovulating and non-ovulating women play the "dictator game." In this popular economic experiment, a person is given a fixed amount of money that she can choose to share with another person. 

"We found that ovulating women were much less willing to share when the other person was another woman. They became meaner to other women," said Kristina Durante, assistant professor of marketing at the UTSA College of Business and lead author of the paper. Non-ovulating women shared about 50 percent of the money with another woman, while ovulating women shared only half that.

Lead author Kristina Durante, University of Texas at San Antonio. Credit: Kristina Durante

In another experiment, women made product choices that could either maximize their individual gains or maximize their relative gains compared to other women. For example, women indicated if they preferred to have a $25,000 car while other women got $40,000 cars (Option A) or have a $20,000 car while other women got $12,000 cars (Option B). The study found that ovulating women preferred Option B, choosing products that would give them higher standing compared to other women.  

"What's interesting about this finding is that ovulating women are so concerned about their relative position that they are willing to take less for themselves just so that they could outdo other women," said study coauthor Vladas Griskevicius, associate professor of marketing at the University of Minnesota's Carlson School of Management.

But the studies find that ovulation doesn't always make women want more status. When women played against a man rather than a woman in the dictator game, the researchers found an even more surprising result. Whereas ovulating women became meaner to women, they became nicer to men. While nonovulating women shared about 45 percent of the money with a man, ovulating women gave 60 percent of the money to the man.

"These findings are unlike anything we have ever seen in the dictator game. You just don't see people giving away more than half of their money," noted Durante. "One possibility is that we're seeing ovulating women share more money as a way to flirt with the men."

They paper builds on their previous work that has shown how the ovulatory cycle alters preferences for romantic partners, clothing, food and even politics. Based on studies rooted in theory and research in evolutionary biology and evolutionary psychology, their findings that ovulating women jockey for position over other women is consistent with the literature on animals. For example, studies have shown that female monkeys become more aggressive toward other females when fertile.

They say their findings on women's monthly hormonal fluctuations could have important implications for consumers, marketers and researchers. Marketers especially might be able to use this information strategically by emphasizing the superiority of a given product in advertising, promotions and messages to female consumers.