Scarcity of women causes men to spend more, save less

— -- A scarcity of women doesn't just dampen men's spirits — it could hurt their finances, too.

When men think they outnumber women, they borrow more, save less and make more impulse purchases, according to a study published last week by the University of Minnesota's Carlson School of Management.

University researchers asked groups of men to read news articles suggesting that their local population had either more men or 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 on credit cards for purchases.

When the articles suggested there was a surplus of men, the savings rate fell 42%, and the men were willing to borrow 84% more each month.

The study also found real-life evidence of this behavior. In Columbus, Ga., where there are 1.18 single men for every single woman, the average consumer debt was $3,479 higher than it was 100 miles away in Macon, Ga., where there were 0.78 single men for every woman.

While many commercials for male-oriented products feature beautiful women, the study's findings suggest that the image of one attractive woman surrounded by men would be more effective, says Vladas Griskevicius, professor of marketing at the Carlson School and lead author of the study. "That's what's likely to get men's testosterone ramped up," he says.

Sex ratios don't affect women's financial decisions, but they do affect their expectations of how much men should spend on them, the study found. After reading an article stating that men outnumbered them, women expected men to spend more on dinners, Valentine's Day gifts and engagement rings.

In 2010, there were eight unmarried men for every nine unmarried women in the USA, the Census Bureau says. For unmarried Americans age 15 to 49, though, there were 11 unmarried men for every 10 unmarried women.

In some parts of the country, the ratio is more pronounced. Cities such as Birmingham, Ala. and Peoria, Ill. have a higher ratio of women, while Denver and Las Vegas have decidedly more men. The lopsided ratio for Sin City might disappoint male tourists, but it's a positive for the casinos, Griskevicius says. "Having more men than women might fuel gambling behavior," he says.

The research shows that we haven't evolved as much as we think we have, Griskevicius says. "What we see in other animals is that when females are scarce, males become more competitive," he says.

Humans, though, have the ability to override these impulses, Griskevicius says. And that's a good thing, because running up big debts to attract a woman could backfire, says Gail Cunningham, spokeswoman for the National Foundation for Credit Counseling.

"If the end goal is to build a serious relationship," she says, "all the dirty financial laundry is going to have to come out."