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2004-07-06
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Old Is Young, Study Finds: Longevity Evolved Late For Humans
ANN ARBOR, Mich. -- Researchers at the University of Michigan and the
University of California at Riverside have discovered a dramatic
increase in human longevity that took place during the early Upper
Paleolithic Period, around 30,000 B.C.
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In their study of more than 750 fossils to be published July 5 in the
Proceedings of the National Academy of Sciences, anthropologists Rachel
Caspari and Sang-Hee Lee found a dramatic increase in longevity among
modern humans during that time: the number of people surviving to an
older age more than quadrupled.
Caspari, an assistant research scientist at the U-M Anthropology Museum,
said this increase in the number of relatively old people likely had a
major impact, giving modern humans a competitive edge that ensured their
evolutionary success.
For the study, the researchers analyzed the ratio of older to younger
adults in hominid dental samples from successive time periods: later
australopithecines, Early and Middle Pleistocene Homo, Neandertals from
Europe and Western Asia and post-Neandertal Early Upper Paleolithic
Europeans. They used a new analytical resampling technique allowing them
to assess the significance of differences in rates of molar wear.
In the study, they defined "old" to be at least double the age of
reproductive maturation, which is also the time when the third molars
typically erupt. "While the age of reproductive maturation may have
varied in early human groups, if it were 15, then age 30 would be the
age at which one could theoretically first become a grandmother,"
Caspari noted.
Other scientists have argued that the presence of grandmothers confers
an important evolutionary advantage since they heavily invest their
knowledge and other resources in their reproductive-age daughters and
their daughters' offspring.
By calculating the ratio of old-to-young individuals in the samples from
each time period, the researchers found a trend of increased
survivorship of older adults throughout human evolution. It's not just
how long people live that's important for evolution, but the number of
people who live to be old, Caspari and Lee pointed out.
The increase in longevity that occurred during the Upper Paleolithic
period among modern humans was dramatically larger than the increase
identified during earlier periods, they found. "We believe this trend
contributed importantly to population expansions and cultural
innovations that are associated with modernity," they wrote.
A large number of older people allowed early modern humans to accumulate
more information and to transmit specialized knowledge from one
generation to another, they speculated. Increased adult survivorship
also strengthened social relationships and kinship bonds, as
grandparents survived to educate and contribute to extended families and
others. Increased survivorship also promoted population growth, the
authors explain, since people living longer are likely to have more
children themselves, and since they also make major contributions to the
reproductive success of their offspring.
"Significant longevity came late in human evolution and its advantages
must have compensated somehow for the disabilities and diseases of older
age, when gene expressions uncommon in younger adults become more
frequent," the authors noted.
"There has been a lot of speculation about what gave modern humans their
evolutionary advantage," Caspari said. "This research provides a simple
explanation for which there is now concrete evidence: modern humans were
older and wiser."
###
For more information on the U-M Anthropology Museum, visit:
http://www.umma.lsa.umich.edu/
For the Proceedings of the National Academy of Sciences, visit:
http://www.pnas.org
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/This story has been adapted from a news release issued by University Of
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