Humans Evolved To Live Longer Because Of Grandmothers

Lawrence LeBlond for redOrbit.com Your Universe Online

Our grandmothers being there to care of us is something we all take for granted, and we have our ancestors to thank for that. New research indicates that human longevity is what it is because of grandmothers helping with childcare at an early stage in human history. Computer simulations on evolution have helped scientists prove that humans evolved longer life spans than apes because of their grandmotherly duties.

When it comes to chimpanzees, our closest primate relatives, females rarely live beyond their 30s, usually when their fertility usually ends. Although, based on the computer data, these female primates could evolve to extend their lifespan to those on par with human levels within 60,000 years if they took on a more grandmotherly role.

Previously, anthropologists have been divided as to whether humans long lives were due to the grandmother hypothesis or the hunting hypothesis. The computer simulations now show a stronger tie to the grandmother hypothesis.

Grandmothering was the initial step toward making us who we are, said Kristen Hawkes, a distinguished professor of anthropology at the University of Utah and senior author of the new study published in todays issue of the British journal Proceedings of the Royal Society B.

In the computer experiments, simulated creatures, generally lived another 25 years after reaching adulthood, much like chimps. But after 24,000 to 60,000 years of grandmothering duties, the simulated creatures lived another 49 years, on par with human hunter-gatherers.

The grandmother hypothesis states that when grandmothers help feed their grandchildren after weaning, their daughters can produce more children at shorter intervals. This theory also indicates that children becoming younger at weaning but older when they can first feed themselves and when they reach adulthood. The hypothesis also indicates that women who take on grandmotherly duties also end up with lifespans that go well beyond menopause.

Furthermore, by allowing their daughter to have more children, ancestral females who lived long enough to become grandmothers passed their longevity genes on to their descendants, who had longer lifespans as a result.

Another suggestion, based on the simulations, is that grandmothers may have even been responsible for increasing humans brain size by allowing mother to have larger families, increasing the pressure of natural selection. Bigger brains made early humans more capable of learning better hunting techniques and clever use of hunting weapons. The increased brain size in our ape-like ancestors was the major factor in humans developing lifespans longer than apes.

Hawkes conducted her study with the aid of mathematical biologist Peter Kim, a former University of Utah postdoctoral researcher now with University of Sydney, and also James Coxworth, a University of Utah doctoral student in anthropology.

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Humans Evolved To Live Longer Because Of Grandmothers