Study subjects read prepared articles that described their local population as being predominantly male or being half male-half female. Then they were asked how much money they’d save and how much they’d spend using credit cards each month. When the men believed there were fewer women, they predicted they’d save 42 percent less money and were willing to spend 84 percent more on credit cards than when the sexes were at equal numbers.

Participants also looked at photos of groups where the gender ratios varied or balanced. Men who were led to believe that women were scarce were more likely to take a $20 gift today than wait for $30 in a month.