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 survi
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Contact: Diane Swanbrow
swanbrow@umich.edu
734-647-9069
University of Michigan
5-Jul-2004