Skip to content
About the Royal Society

Men are less promiscuous when women are scarce

14 January 2015

Title: Sex ratio effects on reproductive strategies in humans

Authors: Ryan Schacht and Monique Borgerhoff Mulder

Journal: Royal Society Open Science

A study published in Royal Society Open Science finds that men are more promiscuous when there are many women and less promiscuous when women are scarce.

The study investigates how reproductive strategies in men and women might vary depending on how many men or women there are in the community.

The team interviewed 300 men and women from 8 rural communities in Guyana where the ratio of men to women varied greatly between villages. They used a 7-question test called the Sociosexual Orientation Inventory, which gives a measure of how willing a person is to engage in uncommitted sex. The team used the results to compare the promiscuity of the men and women with the abundance of each gender in the village.

Their results showed that when men are in the minority they are more willing to engage in short-term, low investment relationships and uncommitted sex than when there are many men in the community. When men outnumber women, men are less promiscuous and men’s and women’s willingness to have uncommitted sex is indistinguishable.

The scientists found that female promiscuity did not change, regardless of how many men there were in the community. It is argued that this could be because women pay higher reproductive costs than men, for example gestation and lactating. However, the team say their results reveal that men may also face steep reproductive costs that constrain their willingness to have uncommitted sex and affect their reproductive strategies when women are scarce.

‘When the pool of males is large, finding a female partner can be difficult such that existing partners become a valued resource’ say the team. Men attempt to attract and maintain a relationship with a partner because, when females are rare, it is costly to lose a partner.

‘Darwin made a famous distinction between men’s and women’s mating strategies, between choosy, coy females and ardent, promiscuous males’, say the authors. They add that the results of their study challenge these persistent views on sexual behaviour.