Newswise — Research at the University of Sheffield, published today in Nature, has solved the mystery of why women live so long after their reproductive years have ceased. Basically, grandmothers can ensure the success of their own family by helping to increase the reproductive success of their adult children, thus propagating their own genes.

Dr. Virpi Lummaa and her PhD student Mirkka lahdenperä, from the University of Sheffield and Turku in Finland, examined the family histories of women in Finland and Canada during the 18th and 19th centuries to determine why humans, unlike other animals, survive long after they are unable to reproduce. In the animal kingdom it is usual for both males and females to continue their reproductive life until they die.

The team found that the longer a woman lived after the end of her reproductive years, the more successfully her children's reproductive lives would be. These children tended to begin their families earlier, have a shorter gap between children, have a longer reproductive life and produce offspring that were more likely to survive into adulthood. The effect was equal for both sons and daughters.

The team examined the lives of almost three thousand women and took into account different ages, socio-economic status, and social and cultural differences between Finland and Canada. The link remained throughout.

Dr Lummaa explains, "We consistently found that women gained, on average, two extra grandchildren for every ten years that they lived past their reproductive life. In evolutionary terms this gives a huge benefit as it makes it more likely that women who survive long after stopping reproduction will forward more genes to the next generation. The evidence suggests that the effect is caused by the woman passing her childcare experience on to her offspring. She can also take on some of the responsibilities of childcare, making it more likely that her children will have more children more quickly."

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