The perception（知觉） that women are scarce leads men to become impulsive¹, save less, and increase borrowing, according to new research from the University of Minnesota's Carlson School of Management. "What we see in other animals is that when females are scarce, males become more competitive. They compete more for access to mates," says Vladas Griskevicius, an assistant professor of marketing² at the Carlson School and lead author of the study. "How do humans compete for access to mates? What you find across cultures is that men often do it through money, through status and through products."

To test their theory that the sex ratio affects economic decisions, the researchers had participants read news articles that described their local population as having more men or more women. They were then asked to indicate how much money they would save each month from a paycheck, as well as how much they would borrow with credit cards for immediate³ expenditures⁴. When led to believe women were scarce, the savings⁵ rates for men decreased by 42 percent. Men were also willing to borrow 84 percent more money each month.

In another study, participants saw photo arrays of men and women that had more men, more women, or were neutral. After looking at the photographs, participants were asked to choose between receiving some money tomorrow or a larger amount in a month. When women were scarce in the photos, men were much more likely to take an immediate $20 rather than wait for $30 in a month.

According to Griskevicius, participants were unaware⁶ that sex ratios were having any effect on their behavior. Merely seeing more men than women automatically led men to simply be more impulsive and want to save less while borrowing more to spend on immediate purchases.

"Economics tells us that humans make decisions by carefully thinking through our choices; that we're not like animals," he says. "It turns out we have a lot in common with other animals. Some of our behaviors are much more reflexive（反身的） and subconscious⁷. We see that there are more men than women in our environment and it automatically changes our desires, our behaviors, and our entire psychology⁸."

"The Financial Consequences of Too Many Men: Sex Ratio Effects on Savings, Borrowing, and Spending" will be published this month in the Journal of Personality and Social Psychology. Co-authors of the study include Joshua Tybur (VU University Amsterdam), Joshua M. Ackerman (M.I.T.), Andrew Delton and Theresa Robertson (University of California, Santa Barbara), and Andrew E. White (Arizona State University).