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Old People May Hold Key to Human Success -Study
« on: 2004-07-06 08:15:21 » |
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http://www.reuters.co.uk/newsArticle.jhtml?type=scienceNews&storyID=5594537§ion=news
Old People May Hold Key to Human Success -Study
Tue July 06, 2004 05:11 AM ET
By Maggie Fox, Health and Science Correspondent
WASHINGTON (Reuters) - Old people may hold the key to human civilization, U.S. researchers said on Tuesday.
They found evidence that, around 30,000 years ago, many more people started living into old age, in turn fueling a population explosion.
Rachel Caspari of the University of Michigan and Sang-Hee Lee of the University of California at Riverside believe 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.
"We think with increases in longevity two things happened to increase survivorship," Caspari, an anthropologist specializing in evolution, added in a telephone interview.
"First, individual people have more kids because if you live longer you can continue to have kids after your kids have kids. And second, you can contribute to your extended family and increase the survival of your progeny. This can increase population size, and it can happen quite quickly."
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 different human fossils, including examples of Cro-Magnon, which are early Homo sapiens who lived in Europe, Neanderthals, an earlier type of Homo sapiens that died out about 35,000 years ago, and earlier prehumans such as Homo erectus and australopithecenes, which date back as long ago as 3 million years.
JUMP IN LONGEVITY
"What we looked at is differences in the proportion of people who were living to be older," Caspari said. Some individuals may have lived to great age, but at some point humans as a species began living longer on average than other primates and Caspari and Lee wanted to find out when and why.
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.
In primitive societies, people are often grandparents at 30, Caspari pointed out.
"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 five-fold. We didn't expect that."
Caspari and Lee rechecked their numbers and analysis.
"But then we started to think about it and thought we really shouldn't be surprised, because there is a behavioral change that took place over time at the same time," Caspari said.
"You start to see a change in symbolic behavior. You see art. You see a large number of people being buried with jewelry, with body ornaments."
Perhaps around this time people started to value and take care of the weak and the old, and in turn benefited from their help and experience, Caspari sad.
This could be when the uniquely human condition of menopause evolved and started to have an effect, Caspari said. Women not burdened by childbearing could focus on their grandchildren and other kin.
"We live in a society that is so geared toward younger people. It is nice to realize that it might be older people that make us human after all," Caspari said.
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