A number of studies have found that cooperative and altruistic behaviour can attract mates, while it's also been confirmed we're more likely to behave altruistically to people we want to attract.
In a 2007 study, consisting of a series of games, participants were more likely to make donations to attractive people.
A recent article in Scientific American by researchers Steven Arnocky and Pat Barclay discussed their research which questioned people on altruistic actions (for instance whether they donated blood) and their sexual history.
A general personality "inventory" was taken to control for other characteristics that might affect sexual activity.
The researchers said:
We found that people who scored higher on altruism also reported they were more desirable to the opposite sex, had more sex partners, more casual sex partners, and had sex more often within relationships
In a follow up study, participants were entered into a contest and were asked if they won, whether they'd keep the $100 prize or donate it.
In this study:
those who donated reported having more lifetime sex partners, more casual sex partners, and more sex partners over the past year.
The researchers commented:
This research combines with previous findings on the desirability of altruism and the tendency for men to compete in the realm of generosity. Indeed, one of us has a female friend who would explicitly screen potential boyfriends based on whether they had donated blood: Others, it seems, may be doing the same.
Plus, everyone loves a partner who seeks to give.
Who knew the selfish egomaniacs weren't doing so well in the bedroom?