Sci. Aging Knowl. Environ., 14 July 2004
Long in the Tooth
Paleolithic hominids outlived their predecessors, dental wear suggests
R. John Davenporthttp://sageke.sciencemag.org/cgi/content/full/2004/28/nf66
Whether it's the latest band or the newest fashion fad, young people are usually the ones on the cutting edge. But a new study suggests that old people helped foster early human ingenuity. Populations from tens of thousands of years ago had a higher proportion of old individuals than did previous populations, researchers surmise based on tooth wear. Because these ancestors created more sophisticated tools and art than did their predecessors, the rise of modern culture might have required a mature population.
Some researchers suggest that humans evolved to survive past their reproductive years because grandparents benefit families by providing care for young and passing on vital knowledge (see "Invest in the Future, Invest in Yourself"). But experts aren't sure how the hominid life span changed over time. Anthropologists can pin down how old people were when they died because particular teeth emerge from the gums at different times in life. They calculate the rate of wear and use it to assign approximate ages to particular skeletal samples. In the new study, anthropologists Rachel Caspari of the University of Michigan, Ann Arbor, and Sang-Hee Lee of the University of California, Riverside, gauged longevity in several ancient hominid populations.
The researchers gathered 768 tooth samples from four groups of hominids: australopithecines, who roamed the Earth about 2 million years ago; early members of the genus Homo, whose tooth samples ranged from 250,000 to 2 million years old; Neandertals, who were represented by teeth that were between 35,000 and 130,000 years old; and Upper Paleolithic Europeans, whose samples were between 18,000 and 30,000 years old. The team deduced, based on tooth wear, the proportions of old and young people in each population. By calculating rates of wear for each group separately, the researchers accounted for differences in diet and other local factors that influence tooth deterioration. The more recent the group, the higher the ratio of old to young individuals. The elderly were particularly abundant in the Upper Paleolithic sample. Caspari notes that this group exhibited many more signs of modern human culture than did previous groups. The demographic change might have helped the population grow and transfer knowledge between generations, events that might have sparked the creative revolution. In turn, "as societies that foster the survival of older folks are more successful, the more older people will continue to survive," she says.
"They've taken something that's oftentimes very complicated, given the nature of anthropological data, ... and looked at it in an uncomplicated way," says paleoanthropologist Robert Hoppa of the University of Manitoba in Winnipeg, Canada. "It argues nicely that there's an increase in adult survivorship as we go through evolutionary time from early hominids to early modern humans." Anthropologist Hillard Kaplan of the University of New Mexico, Albuquerque, cautions that the bone samples might not reflect the distribution of ages in the living populations--for instance, a society might treat the corpse of a young person differently than that of an older one. Still, he says, "I think they've found something important." Perhaps thousands of years ago, older people annoyed the young with their newfangled music.
July 14, 2004
Science of Aging Knowledge Environment. ISSN 1539-6150