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Monogamous societies have fewer social problems than polygamous ones, UC Davis researcher says

February 10, 2012

Compared to monogamous societies, polygamous cultures see more rape, kidnapping, murder, assault, robbery, fraud, child neglect and child abuse, a new UC Davis study suggests.

The reason: When men take multiple wives, the competition for fewer available women results in greater levels of strife, the researchers hypothesize.

The findings may explain the global rise of monogamy as the dominant marriage institution in recent centuries, replacing the polygamy once practiced by 85 percent of the world’s societies, said Peter Richerson, an environmental science professor at UC Davis and co-author of the study, which appears in the January issue of the journal Philosophical Transactions of the Royal Society.

“We wanted to understand both why monogamous societies have been economically more successful in the last few centuries and why monogamy has spread to many formerly polygamous societies in the course of modernization,” he said.

Criminological data suggest that unmarried men, particularly unmarried men of lower social status with lesser prospects of attracting wives, are disproportionately responsible for violent and other seriously disruptive behavior, he said.

Polygamy continues to be practiced in parts of Africa, Asia, the Middle East and North America.

“The emergence of monogamous marriage is also puzzling because multiple marriage is mostly practiced by the economic and political elite who should be in a position to defend the practice,” Richerson said. “South African President Jacob Zuma, for example, is proud of having several wives.”

But, Richerson pointed out, what seems good for the man who has many wives does not work out as well for the rest of society.

“Our findings suggest that institutionalized monogamous marriage provides greater net benefits for society at large by reducing social problems that are inherent in polygamous societies,” he said.

By shifting male efforts from seeking wives to paternal investment, institutionalized monogamy increases long-term planning, economic productivity, financial savings and child investment, the study found.

Monogamous marriage also results in significant improvements in child welfare, including lower rates of child neglect, abuse, accidental death, homicide and intra-household conflict, the study found. These benefits result from greater levels of parental investment, smaller households and increased direct “blood relatedness” in monogamous family households, according to the researchers.

Joseph Henrich, a cultural anthropologist at the University of British Columbia, led the study, working with Richerson and Robert Boyd, a UCLA anthropology professor.

The study, “The Puzzle of Monogamous Marriage,” is available online: http://rstb.royalsocietypublishing.org/content/367/1589/657.full.pdf.

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