Viewed through the lens of evolutionary psychology, altruism takes some explaining. In a dog eat dog world, it seems like a risky, indulgent habit. Yet we are only alive today because our distant ancestors were successful at reproducing – and the fact many of us have inherited their altruistic tendencies suggests that being altruistic gave them some kind of survival or reproductive advantage.

One idea is that altruism is advantageous because it is often reciprocated. Another is that altruism is a “costly signal” that tells potential sexual partners you would make a good mate – if you’ve the freedom to be charitable, this suggests you must be capable and resourceful. Supporting this “costly signal” account, plentiful past research has shown that signs of altruism increase both men’s and women’s attractiveness to the opposite sex.

Now an article in the British Journal of Psychology has followed through on this logic to find out whether more altruistic people aren’t just more attractive, but actually have more sex. This is an important test because as Steven Arnocky and his colleagues explain, “… it is actual mating outcomes which ultimately contribute to the evolution of particular phenotypes”. Stated differently, if the more altruistic of our forebears were not only perceived as more attractive, but also had more sex, this would help explain why many modern humans have inherited the inclination to be altruistic.

One of the best indicators we have of whether our more altruistic forebears were likely to have had more sex is to see if, today, more altruistic people continue to have more sex than less altruistic people. That’s what Arnocky and his team aimed to discover through two studies involving young adult Canadians.

They first asked 192 unmarried women and 105 unmarried men to describe their own altruistic tendencies, such as whether they give money to charity, donate blood, help people across the street and so on. They also asked them questions about their sexual history and their desirability to the opposite sex.

Men and women who scored higher on altruism said they were more attractive to, and received more interest from the opposite sex. Men, but not women, who scored higher on altruism also tended to report having had more sexual partners in their lifetime, and also more casual sexual partners specifically. Focusing on just those participants in a current long-term relationship, the more altruistic men and women in this group reported having more sex in their relationship over the last 30 days.

Results from Study 1. Green dashed line=male participants; red=female. Figure from Arnocky et al, 2016.

Of course this first study was limited by its reliance on participants’ descriptions of their own altruism. Perhaps people who have more sex are simply inclined to brag more about being altruistic. To overcome this problem, a second study involving 335 undergrads featured a test of actual altruistic tendencies by giving participants the opportunity to donate to charity their potential $100 winnings for taking part in the study.

The participants also answered questions about their sexual history, and this time there were measures of their narcissism and their tendency to give socially desirable answers (this last scale essentially involved participants rating statements about themselves – e.g. “I never regret any decisions” – as true or not, and it was possible to tell from the answers if someone was painting an unrealistically positive image of themselves).

Even factoring out the narcissists and higher scorers on the social desirability scale, the second study found that actual altruistic tendencies correlated with having more sex. Among men only, this included having had more sexual partners in the past, and among men and women, having had more casual sex partners in their lifetime, and more sex partners in the past year.

The researchers said their findings add to past research on hunter-gatherer tribes that have shown men who hunt and who share more meat among non-relatives also tend to have more sex. The new results also converge with past evidence suggesting that altruistic men and women are seen as more desirable.

“The present study provides the first empirical evidence that altruism may tangibly benefit mating in humans living in Western industrialised society,” the researchers said, “and that sex differences might exist with respect to the utility of altruism for mating, whereby it is a more effective signal for men than for women.”

One big caveat, acknowledged by the researchers – these results are correlational so it’s not clear which way the causal juices are flowing. An alternative interpretation of the results is that having more sex and sexual partners encourages people to feel generous towards others and be more altruistic. We’ll have to await longitudinal research that charts people’s sexual habits and altruism over time to settle this question, though the idea that altruism leads to more sex is certainly consistent with the past evidence suggesting altruistic behaviour causes increases in a person’s desirability.

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Arnocky, S., Piché, T., Albert, G., Ouellette, D., & Barclay, P. (2016). Altruism predicts mating success in humans British Journal of Psychology DOI: 10.1111/bjop.12208

Post written by Christian Jarrett (@psych_writer) for the BPS Research Digest.

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