Study Backs Evolution’s ‘Grandma Hypothesis’

Old people may hold the key to human civilization, U.S. researchers said Tuesday. They found evidence that around 30,000 years ago many more people started living into old age, fueling a population explosion.

Rachel Caspari of the University of Michigan and Sang-Hee Lee of UC Riverside think that groups in which old people survived better were more successful, in turn allowing more people to live into old age.

“There has been a lot of speculation about what gave modern humans their evolutionary advantage. This research provides a simple explanation for which there is now concrete evidence -- modern humans were older and wiser,” Caspari said.

The finding, published in this week’s issue of the Proceedings of the National Academy of Sciences, supports the so-called “grandma hypothesis,” Caspari said. This credits grandmothers with helping to raise their extended families, contributing to a group’s success.

Caspari and Lee studied 768 human fossils, including examples of Cro-Magnons, Neanderthals, and earlier prehumans, such as Homo erectus.

They divided the fossils into two groups -- adults of reproductive age, which they settled on as 15 years, and adults that lived to be twice as old, 30, based on tooth wear.

“We found this proportion of older to young adults in the fossil record increased over time,” Caspari said. “In the Upper Paleolithic that proportion just skyrocketed. It was just unbelievable. It increased fivefold.”