Darwin would not be proud.

After all these years we're supposed to have been evolving, the male of the human species still feels that when females are few, he must court them by competitively displaying superior plumage -- the green in his wallet. Research led by a University of Minnesota professor found that the scarcer single women are in a city, the more -- and more impulsively -- men will start spending.

"We looked at the ratio of single men to women in more than 140 cities across the U.S., and the fewer women there are, the more credit cards and consumer debt there are," said Vladas Griskevicius, an assistant professor of marketing at the U's Carlson School of Management. His specialties are consumer behavior and evolutionary psychology. "This is no shocker for economists, because it follows the rules of supply and demand."

Titled "The Financial Consequences of Too Many Men: Sex Ratio Effects on Savings, Borrowing, and Spending," the study will be published this month in the Journal of Personality and Social Psychology.

Heterosexual male subjects were asked to read news articles claiming that their cities had a smaller mating pool, then decide how much of their salaries they would save each month as well as how much they would be willing to pay for with credit cards. When they assumed there were fewer women to go around, their savings dropped by more than 40 percent, and their credit borrowing rose by nearly 85 percent.

In another experiment, men were offered the choice of accepting $20 right away or waiting a month and getting $30. They then viewed groups of photos, some featuring many men and few women, some the opposite, and some with even numbers of both. If they noticed fewer women in the pictures, the men would snap up that immediate $20 rather than hold out for a higher profit later.

Women subjects' impulsivity levels, on the other hand, did not change as sex ratios fluctuated. But when they had a larger playing field to choose from than the guys, they did expect the men to shell out more for gifts and dates. With all the progress we've made in reconsidering gender roles, can the truth really be this Neanderthal?

"Neither the men nor women were consciously aware of what they were doing," said Griskevicius. "They just reflexively do this in their heads. It always surprises me how much humans share with other animals, even though we think all our decisions are carefully thought out. When people hear about these results, they say 'No, we're so far above this, I'm an individual who decides what I do and when and how I do it all on my own.' But life is not an Excel spreadsheet. Not everything we do is deliberate."

If the study's results reflect reality, the unattached ladies of Minneapolis have an edge; we have 111 single men for every 100 single women (the local gap is slightly larger than the national figure of 106 to 100). Bucking our state's rep for frugality, Minneapolis men were willing to go slightly above the average in debt.

Women: better odds in Vegas

To improve the odds of being lavished with diamonds and dinners, try Las Vegas, Griskevicius said: "Women can really clean up, although they might not get the kind of guy they want."

On most college campuses, men have the advantage, since more women nationwide are currently enrolled. But they might have better luck at MIT or CalTech, which have more men, he said.

Darwin might not be proud that men are still motivated more by the primal than the prime rate. But he wouldn't be surprised, either.

Kristin Tillotson • 612-673-7046