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Home | Pregnancy Timeline | News Alerts |News Archive Jan 21, 2015

Makushi Cultural Group




Some men only commit when women are scarce

Sexual supply and demand affects mate choice among the Makushi people of Guyana, South America. When women are in short supply, men are more likely to seek long-term relationships.

In line with evolutionary theory, the sexual stereotype is that women want commitment and men want flings. Charles Darwin pointed out "that males are generally the mate-getting sex and females are generally the sex more choosy about who they mate with," But a study of the Makushi people in Guyana reflects that sometimes men are more likely to seek long-term relationships, particularly when women are scarce.

Guyana has 800,000 residents, including about 13,000 Makushi living in savannas near their border with Brazil. Premarital sex is accepted and expected in order to find a partner. Marriages are usually monogamous. Extended families live in villages of 160 to 750 people, and mates tend to come from within the village. Migration has affected male to female ratios in the villages studied. Women moving to larger towns with jobs in shops, while men gravitate to mining, ranching, farming and logging outposts.

Schacht and his wife, Jacque, interviewed 300 Makushi men and women ages 18 to 45 in eight rural communities where the number of men ranged from 90 to 140 for every 100 women. Using a well-established test named the Sociosexual Orientation Inventory, Schacht spent 16 months building rapport with the villagers. He interviewed only men and Jacque only women. A coding system kept answers anonymous.

"Commitment to a relationship is influenced by the availability of partners. So 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 dominate," says University of Utah anthropologist Ryan Schacht, first author of the study published in the journal of the Royal Society Open Science. However, Schacht observes:"it's time to move away from stereotyped assumptions of men having certain behaviors and women having others with regards to relationships. Sex is one of many things that matter — partner availability matters, socioeconomic status matters, the quality of available mates matters."

Although "in general, Makushi men show a greater willingness to engage in uncommitted sex than do women, as the stereotype predicts," Schacht adds, they also found that Makushi men are more likely to want committed relationships when there are fewer women available, regardless of the woman's age. "Women by contrast appear indifferent to changes in the adult sex ratio," and prefer commitment no matter how many men are available.

"Short-term, uncommitted relationships are potentially costly to women with children and no fathers to support their children. If you're chasing partners, you're not home taking care of babies."

Ryan Schacht PhD, anthropologist, University of Utah, first author of the study

Studies of animals and people have created the concept that males benefit from multiple partners by having more offspring to pass on their genes. On the other hand, women can only pass on their genes through the long and costly investment of pregnancy and breast-feeding, then years of supervised care to insure the survival of their children — hopefully made easier with a committed partner.

Yet Schacht feels stereotypes have failed to cover the diversity of sex life as reflexed in animal studies as well as in studies of people. He cites bird species where females keep harems of males, so that males can sit on the nests. He also sites sexual diversity in humans not only seen in men with multiple mates, and females with multiple mates, but in same-sex relationships within both sexes, as well as those African cultures where men preen and wear makeup to attract female partners. Indeed, in previous research, Schacht cited higher marriage and marriage fertility rates, fewer female heads of household, and children out of wedlock when men are abundant in urban U.S. communities —adds Schacht: "All indicators of family stability increased when there were more men."

Characterizations of coy females and ardent males are rooted in models of sexual selection that are increasingly outdated. Evolutionary feedbacks can strongly influence the sex roles and subsequent patterns of sex differentiated investment in mating effort, with a key component being the adult sex ratio (ASR). Using data from eight Makushi communities of southern Guyana, characterized by varying ASRs contingent on migration, we show that even within a single ethnic group, male mating effort varies in predictable ways with the ASR. At male-biased sex ratios, men's and women's investment in mating effort are indistinguishable; only when men are in the minority are they more inclined towards short-term, low investment relationships than women. Our results support the behavioural ecological tenet that reproductive strategies are predictable and contingent on varying situational factors.

The study was funded by the National Science Foundation and Wenner-Gren Foundation.

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