In general, he said, "generosity can signal something about the person to both males and females. But women have had to worry more about guys doing the mate-them-and-dash kind of routine. They'd be slightly more concerned with character than men."
It's hard to quantify exactly how much of a difference generosity/altruism made in mate selection, Barclay said, although it might bump a person from five points to 5.5 on a 10-point attractiveness scale. "It's not going to turn a five into an eight, but it can certainly make a difference in competition with other people who are about the same level."
Why does all this matter? In the bigger picture, the research could give scientists some insight into evolution of humans. The findings add "to what we know about sexual selection in human behavior: traits that have evolved in one specific sex for the purposes of luring the other. These results suggest that altruism may very well be one of those traits that has been either evolved for, or adapted to, serve the purposes of luring a good mate," said Stan Treger, a psychology graduate student at Illinois State University.
Now to the nitty-gritty: Should you volunteer at the soup kitchen in order to attract a mate? Maybe, but don't flaunt it, Barclay warned.
"If somebody is always saying, 'Look, I'm generous, I'm really generous,'" he said, "people will be a little skeptical about why you're constantly mentioning that."
There's more on altruism at Stanford University's Center for Compassion and Altruism Research and Education.
SOURCES: Pat Barclay, Ph.D., assistant professor, University of Guelph, Ontario, Canada; and Stan Treger, psychology graduate student, Illinois State University, Normal, Ill.; February 2010, British Journal of Psychology
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