A new study has found that the combination of physical attractiveness and prosociality greatly boosts a person’s desirability as a romantic partner. But the combination of these traits produces “more than the sum of its parts,” according to the researchers.

“There has been some great research done by psychologists to help us understand human mating and in particular the individual traits that are valued by both men and women, however in reality these traits will be assessed as a whole when we make judgements of the desirability of a potential partner,” explained study author Daniel Farrelly, a senior lecturer at the University of Worcester.

“Therefore we wanted to see how both men and women assess potential mates when the latter vary in levels of two characteristics that are well established in mate choice research; physical attractiveness and prosocial behaviours (e.g. altruism and trustworthiness). Furthermore we were interested to see if these assessments varied according to the length of relationship sought, or the different forms of prosocial behaviour.”

The study, which was published in the British Journal of Psychology, asked German university students to watch 20-second clips of people of the opposite sex and rate their desirability as either a short-term sexual partner or long-term romantic partner.

The study used two economic games — the dictator game and the trust game — to establish the respective altruism and trustworthiness of the people being rated.

In the dictator game, one person (the dictator) is asked to share money with another person — who can only passively accept what is offered. In the trust game, one person (the trustor) decides whether to share money with another player (the trustee.) The trustor can then receive extra money, but only if the trustee gives him some money back in return.

For each person being rated, participants were provided with made-up information on the target’s decision in one of the games.

The researchers found that both altruism and trustworthiness were preferred in long-term partners. But this was is especially true for people who were already physically attractive.

People with prosocial traits who were also physically attractive were preferred the most. But the effects of prosociality and physical attractiveness wasn’t simply additive.

“In other words, as we found there were synergistic effects of being both physically attractive and prosocial, which meant that such individuals were viewed as more desirable than would be expected from just the sum of the two desirable traits,” Farrelly explained to PsyPost. “Also, this effect was most important for seeking long term partners, where having both traits will be much more valued and desired compared to short term partners for both men and women.”

The findings indicate that “we make decisions on who we consider desirable not just on which attractive characteristics they have, but on how these characteristics can combine to make a potential partner more desirable than expected,” Farrelly said.

The study, like all research, has some limitations. The study only examined university students of a relatively young age, for example, which could limit the generalizability of the results.

“There are a number of interesting questions that arise from this research. Firstly, it would be interesting to see how other forms of prosocial behaviour, other than altruism and trustworthiness, play a role in human mating, such as fairness,” Farrelly told PsyPost.

“Secondly, this research concentrated on heterosexual mate choice, and it would be very useful and interesting to investigate the same effects in homosexual mate choice decision-making.”

“Finally, an investigation of real world mating behaviour where such characteristics and others are directly assessed when we really do choose potential partners, will help our understanding of the rich tapestry of human mating greatly!”

“One of the intriguing findings of our study was how different forms of prosocial behaviours (altruism and trustworthiness) were valued in different ways by men and women that we predicted based on their potential adaptive value in mate choice,” Farrelly noted.

The context had a much stronger impact for men than for women. For men, trustworthiness had very little influence in the context of short-term relationships, but a strong influence in the long-term context.

“The majority of research to date on prosocial behaviours in mate choice have paid little attention to how different forms of these behaviours may produce different effects, however this research highlights how important it is for distinctions to be made, and that future research can explore how other prosocial behaviours (such as fairness, heroism, and true altruism) may be viewed differently in human mate choice due to the different adaptive roles they may have there,” Farrelly added.

The study, “The synergistic effect of prosociality and physical attractiveness on mate desirability“, was co-authored by Daniel Ehlebracht, Olga Stavrova, and Detlef Fetchenhauer.