The Importance of Grandmothers

CHICAGO -- Grandmothers had played a far more critical evolutionary role than we thought in the living populations, anthropologists said on Friday in the 2009 Annual Meeting of the American Association for the Advancement of Science (AAAS).

"By living longer and having more offspring," said Rachael Caspari, a research scientist at the University of Michigan." Older people allow more information to accumulate and transfer between generations, as grandparents survive to educate and contribute to extended families."

Caspari's result derives from a series studies on Homo sapiens, namely early human beings.

By analyzing a large number of sample Neanderthal teeth and fossils, Caspari and her colleagues found that none of the Neanderthals lived beyond 35, and have a very low older-to-younger adult ratio.

In contrast, she found in another study that the early Upper Paleolithic, another species of Old Stone Age sapiens which have an extended average life cycle of 50 years old.

"The fact that significant numbers of grandparents first survived played an evolutionarily significant role in the Upper Paleolithic," she said. "The role of grandmothers was likely less important for Neanderthals."

"The role of older women is extremely valuable because of their productivity," said Caspari. "This is what you call the 'grandmother effect.'"

Neanderthals were humans' closest relatives, appearing about 300,000 years ago and living in Europe and parts of Asia until going extinct about 30,000 years ago.

On Thursday, a group of scientists in AAAC 2009 just released the genetic evidence suggesting that humans and Neanderthals are very similar, but that the two species probably didn't interbreed.

Echoing Caspari's research, Carol Ward, a professor at the University of Missouri also proposed the similar idea of "smarter mothers" at the meeting. She said: "Women who are good at negotiating with the social surroundings have gained better survival opportunities for her children, by parenting and transiting the information to her offspring."