Everyone knows the racier the car, the racier the hormones.

Now, researchers at the University of Minnesota have brought scientific precision to that age-old observation, which turns out to be true, but with a twist.

Sexual signalling really works -- just not necessarily as intended when a man buys the biggest TV or the flashiest car.

"Men and women both know that that's the guy who wants casual sex," said Vladas Griskevicius, assistant marketing professor at the U. "But he isn't more desirable as a marriage partner. That's not the guy you want to marry."

And while the urge to splurge is often blamed on the culture of materialism and incessant advertising, it's probably because of the basic drive to impress the ladies. Other research has shown it's just as true for men in the Amazon forests and the Australian outback who have never seen a TV.

"Flaunting their money is not too different than the way a peacock displays his tail," Griskevicius said.

What about women? For the record, they really are different.

"The anticipation of romance doesn't trigger flashy spending [by women] as it does with some men," said Jill Sundie, a research colleague who teaches at the University of Texas-San Antonio.

Just what inspires women to spend money is largely unanswered by science. But Griskevicius said the prevailing theory is that women do it to impress -- and compete with -- each other. Men don't care what kind of handbag a woman carries or how much it cost. But other women might, he said.

Mothers of young girls, of course, have known these things for eons. But the university research, which involved surveys and interviews with 1,000 young men and women in three states, provides some insights that go well beyond what economist Thorstein Veblen famously called "conspicuous consumption" in 1899. The series of studies, "Peacocks, Porsches and Thorstein Veblen: Conspicuous Consumption as a Sexual Signaling System," was published recently in the Journal of Personality and Social Psychology.

Women, they found, respond to men who spend lavishly. In one of the studies, women viewed two biographies for a man -- each 32, with a master's degree, a good job and interests in bicycling, movies and music. The only difference -- one drove a Porsche ($58,000) and the other a Honda Civic ($15,655).

The women preferred the man with the Porsche as a date -- but not for marriage. They inferred from his flashy spending that he was interested in sex without commitment, the study concluded.

Through surveys of men under 30, the most sexually active age group, the researchers also concluded that about one-third are consistent peacocks. Another third switch back and forth depending on the situation. But they tend to be problem boyfriends.

Once a peacock always a peacock, he added -- since that same group tends to be the problem husbands.

"They are the guys who cheat on their wives," Griskevicius said.

Fortunately for the institution of marriage, not all men are like that. Some choose the Honda.

paul.walsh@startribune.com josephine.marcotty@startribune.com