Research suggests that people who do nice things for others, often at a cost for themselves, are more sexually attractive. From an evolutionary perspective, this might be because altruism indicates that a potential mate is more cooperative and caring. Evolutionary psychologists Steven Arnocky, at Nipissing University, and Pat Barclay, at the University of Guelph, conducted a fascinating study to explore whether altruistic people really do have more sexual partners. From Scientific American:
This theory suggests that altruism may serve, in part, to convey one’s value as a mating partner, including one’s concern for others and likelihood of cooperating with future mates. Research has shown that we prefer altruistic partners, all else being equal; especially for long-term mating (the evidence for altruism being preferred in short-term mates is mixed). Not surprisingly, then, the pull to demonstrate one’s altruism can be strong. Some research has shown that men will actively compete with one another (termed competitive altruism) by making charitable donations to women. Interestingly, these charitable donations increase when the target of one’s altruism is physically attractive...
Previous findings from hunter-gatherer populations have shown that men who hunt and share meat often enjoy greater reproductive access to women. But do these links hold up in other cultural and contextual arenas, such as in contemporary North American society? To find out, we conducted a set of two studies. In our first study, undergraduate men and women completed an altruism questionnaire (involving questions like “I have donated blood”), along with a sexual history survey. Participants also completed a personality inventory, given the possibility that those with certain personality characteristics (such as being extroverted) might happen to engage in both more altruism and more sexual activity. 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 (although this latter finding was not statistically-significant after controlling for personality variables). The statistical models (including covariates) explained between 13 and 26% of variance in the sexual behavior variables. Moreover, altruism mattered more for men’s number of lifetime and casual sex partners than for women’s.
"Altruistic People Have More Sexual Partners" (Scientific American)