Previous research has found that sex ratios influence mating behaviors across a wide variety of species. For instance, in environments where male guppies outnumber female guppies, females display stronger preferences for orange coloration in males. In the honey locust beetle, females increase their competitive mating efforts as they become more abundant than males. And in the European bitterling, a freshwater fish, males change mating tactics from defending territory to direct competition as the number of same sex rivals increase.
A new study published today aimed to extend these findings by investigating the effects of sex ratios in the mating behaviors of humans. To do so, a group of 108 authors from around the world (including myself) collected data across 45 countries. Around 15,000 people completed the survey that asked them about their sex (male/female) and about their ideal partner preferences on five traits: kindness, intelligence, health, physical attractiveness, and good financial prospects. Those answers were then compared to sex ratio data in each of the countries, including city-level sex ratios.
What did we find? In places where men were more numerous than women, men decreased their preferences for good financial prospects and physical attractiveness. Women, on the other hand, increased their preferences for good financial prospects and physical attractiveness in those places where men were more numerous.
The inverse relationship was found when the sex ratios were reversed. In places where women were more numerous than men, women decreased their preferences for good financial prospects and physical attractiveness. Men, on the other hand, increased their preferences for good financial prospects and physical attractiveness in places where women were more numerous.
What about kindness, health, and intelligence? The relationship between those traits and sex ratios was not as strong as that of physical attractiveness and good financial prospects. This might be because these qualities are considered more important for both men and women and therefore, their preferences may be less likely to be influenced, even when potential partners are scarce.
In conclusion, men and women both tended to report more demanding preferences for physical attractiveness and good financial prospects when they were the scarcer sex. Therefore, those who are pickier in the dating market (particularly when it comes to attractiveness and financial prospects) might be so because they have fewer competitors and more potential partners.
The study “Sex differences in human mate preferences vary across sex ratios” was published today in the academic journal Proceedings of the Royal Society B.