New research suggests that men from polygamous cultures outlive those from monogamous ones.
Virpi Lummaa, an ecologist at the University of Sheffield, suggested that after accounting for socioeconomic differences, men aged over 60 from 140 countries that practice polygamy to varying degrees lived on average 12% longer than men from 49 mostly monogamous nations.
The research looks to solve the long-standing puzzle of life expectancy in human biology.
A phenomenon called the grandmother effect seeks to explain why women are able to live so long after the menopause””unlike nearly all other animals.
Lummaa says for every 10 years a woman survives past the menopause, she gains two additional grandchildren. It seems that doting on and spoiling grandchildren aids their survival, as well as furthering some of their grandmother’s genes.
By contrast, men can reproduce well into their 60s and even 70s and 80s, leading most researchers to assume this explained their longevity.
However, Lummaa and colleague Andy Russell wondered whether other factors explained the long lifespan of men, such as a grandfather effect.
The team tested this possibility by analyzing church-gathered records for 25,000 Finns from the 18th and 19th centuries, when people tended to move little, no one practiced contraception and the Lutheran Church enforced monogamy.
During this era, only widowed men were allowed to remarry, and if they had children with their new wife, they fathered more kids, on average, than men who married once.
“Ultimately, remarried men don’t end up with any more grandchildren. If anything the presence of a grandfather was associated with decreased survival of grandchildren,” Lummaa said.
“Perhaps the children of the first mother lose out on food and resources that go to the second mother’s kids. It’s kind of the Cinderella effect,” Lummaa added.
A finding supported by previous research showed even fathers with only one wife provided no benefit to their grandchildren.
After ruling out the grandfather effect, Lummaa and Russell next wondered whether the constraints of human physiology explain male longevity.
They suggested that male longevity might be a consequence of biological selection for long-lived women.
The researchers then compared the lifespan of men from polygamous countries with those from monogamous nations.
The team then scored 189 countries on a monogamy scale of one to four – totally monogamous to mostly polygamous, taking into account a country’s gross domestic product and average income to minimize the effect of better nutrition and healthcare in monogamous Western nations.
“Our monogamy score is a crude first stab, and we’re working to find multiple ways to assess marriage patterns,” Lummaa said. She also added that the conclusions could evaporate under further analysis.
The study suggests that if female survival is the main explanation for male longevity, then monogamous and polygamous men would live for about the same length of time.
However, it seems that fathering more kids with more wives leads to increased male longevity. Men, then, live long because they’re fertile well into their grey years.
This could be both a social and genetic explanation.
Men who continue fathering kids into their 60s and 70s could take better care for their bodies because they have mouths to feed. But evolutionary forces acting over thousands of years could also select for longer-lived men in polygamous cultures.
Chris Wilson, an evolutionary anthropologist at Cornell University in Ithaca, New York, who attended the talk, said the new study is a valid hypothesis and a good prediction.
But he believes the care and attention of several wives who depend on the social status of their ageing husband could explain everything.
“It doesn’t surprise me that men in those societies live longer than men in monogamous societies, where they become widowed and have nobody to care for them.”
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