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When women are scarce, Men are less promiscuous

The popularly held sexual stereotype concludes that men want as many partners as possible, and women want stability and commitment. But what men and women want from relationships also depends heavily on the supply of potential partners, according to a University of California, Davis, study.

The study found that in communities where men outnumbered women, men were much more likely to be looking for a committed, long-term relationship.

“We can think of the number of men and women in a population as a potential mating market where the principles of supply and demand hold sway and where commitment to a relationship is influenced by the availability of partners,” said Ryan Schacht, co-author of the study. “The rarer sex has more bargaining power and can get what they want because they are surrounded by available partners. If they aren’t pleased with a relationship they can move on to someone else.”

UC Davis Department of Anthropology doctoral graduate Schacht and Professor Monique Borgerhoff Mulder co-authored the study. Their paper “Explaining Sex Differentiated Behavior in Humans: Sex Ration Effects on Reproductive Strategies” is published today by Royal Society Open Science.

“A person’s gender is not the best way of determining what he or she wants in a relationship,” he said. “Men respond quite counter to simple biological models when surrounded by other men — this is when they want to settle down. We’re not saying that a person’s sex doesn’t have an impact on their view of relationships, but we need to pay attention to sex in context. We need to move away from the simplistic concept of biological propensities.”

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The study was based on interviews with 300 people in eight villages in Guyana, South America. Among the questions the subjects were asked:

  • How many partners did you have in the last year?
  • Can you imagine enjoying having casual sex with several partners?
  • How many partners do you think you will have during the next five years?

The region of Guyana where the study took place was ideal because it has a wide range of male-to-female population ratios, said Schacht. The ratio ranged from 90 men for every 100 women in one village to 140 men to 100 women in another. The pattern of women often outnumbering men was the result of women having job opportunities outside the area.

“As you get more men they are less interested in casual relationships and more in committed relationships,” Schacht said. “This preference is context dependent and has to do with supply and demand. When partners are in short supply, men have relationship preferences more in line with women than with men. This clearly highlights that our notions of sexual stereotyping need to be revised.”


Ryan Schacht, Monique Borgerhoff Mulder. Sex ratio effects on reproductive strategies in humans. R. Soc. open sci.:20152 140402;DOI: 10.1098/rsos.140402.Published 14 January 2015

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