A novel research has shown that men from polygamous relationships seem to live longer than those from monogamous ones.
After accounting for socioeconomic differences, men aged over 60 from 140 countries that practice polygamy to varying degrees lived on average 12 percent longer than men from 49 mostly monogamous nations, says Virpi Lummaa, an ecologist at the University of Sheffield, UK.
The latest research might solve a long-standing puzzle in human biology: Why do men live so long? This question only makes sense after asking the same for women, who - unlike nearly all other animals - live long past the menopause.
One answer seems to be a phenomenon called the grandmother effect. For every 10 years a woman survives past the menopause, she gains two additional grandchildren, Lummaa says.
It seems that doting on and spoiling grandchildren aids their survival, as well as furthering some of their grandmother's genes. Men, by contrast, can reproduce well into their 60s and even 70s and 80s, and most researchers assumed this explained their longevity.
But Lummaa and colleague Andy Russell wondered whether other factors explained the long lifespan of men, such as a grandfather effect.
To test this possibility, the team analysed church-gathered records for 25,000 Finns from the 18th and 19th centuries.
People tended to move little, no one practiced contraception and the Lutheran Church enforced monogamy. Only widowed men could remarry, and if they had children with their new wife, they fathered more kids, on average, than men who married once. But ultimately remarried men "don't end up with any more grandchildren," Lummaa says.
"If anything the presence of a grandfather was associated with decreased survival of grandchildren," New Scientist quoted Lummaa, as saying.
Perhaps, Lummaa adds, 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.
Even fathers with only one wife provided no benefit to their grandchildren, a finding supported by previous research. With the grandfather effect ruled out, Lummaa and Russell next wondered whether the constraints of human physiology explain male longevity.
In the same way that men have nipples that evolved for women to nourish their young, male longevity might be a consequence of biological selection for long-lived women.
To answer this question, the researchers compared the lifespan of men from polygamous countries with those from monogamous nations.
Using data from the World Health Organization, Lummaa and Russell scored 189 countries on a monogamy scale of one to four - totally monogamous to mostly polygamous.
They also took into account a country's gross domestic product and average income to minimise the effect of better nutrition and healthcare in monogamous
ummaa stressed that their monogamy score is a crude first stab, and they are working to find multiple ways to assess marriage patterns. The conclusions could evaporate under further analysis, she adds.
If female survival is the main explanation for male longevity, then monogamous and polygamous men would live for about the same length of time. Instead, 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.
The study has been presented at the International Society for Behavioral Ecology's annual meeting in Ithaca, New York. (ANI)