A considerable increase in early human life span may have been a key factor in shaping modern civilization, according to a new fossil study published July 5, 2004, in the Proceedings of the National Academy of Sciences.
Scientists at the University of Michigan and University of California, Riverside, analyzed the ratio of older to younger adults in 750 hominid tooth samples from successive time periods, assessing the significance of differences in rates of molar wear. Their findings showed that the number of people surviving to an older age more than quadrupled during the early Upper Paleolithic Period around 30,000 BC, when Homo sapiens was becoming established in Europe.
In the study, the researchers defined “old” to be at least double the age of reproductive maturation. “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.
The jump in longevity may have been a key factor in the shaping of modern civilization. Larger numbers of older people provided distinct evolutionary advantages such as tighter social relationships and kinship bonds, as well as allowing greater efficiency in the accumulation and transmission of more specialized knowledge from older, experienced individuals to younger generations. This so-called “grandmother hypothesis” posits that grandmothers are useful because of the knowledge they pass on to reproductive-age daughters and their daughters’ offspring.
Longer life span would also have increased the number of years available for reproduction, working to promote population expansion, and creating social pressures that led to the growth of trade networks, increased mobility, and more complex systems of cooperation and competition.
“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,” the study’s co-authors wrote.
—Dean S. Cunningham, MD, PhD