Societies where monogamy is the norm are safer than polygamous ones, according to a new Canadian study. 
Researchers at the University of British Columbia found that polygamous cultures have higher levels of robbery, rape, kidnapping, fraud and murder even when taking into account poverty levels.
The higher levels, says the researchers, is accounted for partly by the bigger pools of unmarried men found in polygamous societies.
The study suggests that institutionalised monogamous marriage is rapidly replacing polygamy because it has lower levels of inherent social problems.
Professor Joseph Henrich, one of the report’s authors, said that the crimes were primarily driven by pools of unmarried men, a result of some men taking multiple wives. Professor Henrich was an expert witness in a recent Canadian case which upheld the law against polygamy.
He said: “Our findings suggest that institutionalised monogamous marriage provides greater net benefits for society at large by reducing social problems that are inherent in polygamous societies.”
He added: “The scarcity of marriageable women in polygamous cultures increases competition among men for the remaining unmarried woman.
“The greater competition increases the likelihood men in polygamous communities will resort to criminal behaviour to gain resources and women.”
He added that polygamy was outlawed in 1963 in Nepal, 1955 in India (partially), 1953 in China and 1880 in Japan.
According to Henrich, monogamy’s main cultural evolutionary advantage over polygyny is the more egalitarian distribution of women, which reduces male competition and social problems.
By shifting male efforts from seeking wives to paternal investment, institutionalised monogamy increases long-term planning, economic productivity, savings and child investment, the study finds. Monogamy’s institutionalisation has been assisted by its incorporation by religions, such as Christianity.
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 finds. These benefits result from greater levels of parental investment, smaller households and increased direct “blood relatedness” in monogamous family households,
The study, entitled The Puzzle of Monogamous Marriage, was published in the journal Philosophical Transactions of the Royal Society.
A polygamous family in America is currently trying to overturn their state’s law against bigamy.
Kody Brown and his four ‘wives’ claim that Utah’s bigamy law is unconstitutional because it violates their right to privacy.
Their lawyers are using Supreme Court rulings, such as a case from 2003 when judges ruled that homosexual acts in private were protected by the US constitution, to argue against the law.
In November a judge in Canada upheld the country’s ban on polygamous marriages, but the case is likely to be appealed.
Canada legalised same-sex marriage in 2005 and polygamist supporters say it is therefore unfair to ban polygamy.
