July 06, 2004
Life Expectancies Increased In Upper Paleolithic Period

By examining dental information derived from molar wear patterns a pair of anthropologists has been able to show that human life expectancy increased during the Upper Paleolithic Period.

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.

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.


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."

Here is my FuturePundit speculation on this report: the lengthening of lifespans created a selective pressure for higher intelligence. When people started living longer they accumulated more knowledge. The increase in available knowledge increased the value of having a high cognitive ability to sort through, analyze, and apply that knowledge. A smarter person can notice more and learn more useful lessons from an accumulation of life experiences than can a less intelligent person. So genetic mutations that lengthened lifespans may have led to selection for mutations that increased intelligence. Then the selection for higher intelligence likely increased the value of living even longer which would have fed back into selecting for longer lifespans.

But important questions remain unanswered: Did any Upper Paleolithic civilizations collapse from spiralling taxes enacted in a futile attempt to meet unfunded pension liabilities? Were massive human migrations across the continents driven by a desire to escape from old age pension taxes?

Update: Managing to live for 30 years was enough to classify someone as "old" in the Upper Paleolithic.

They judged the age of specimens by examining wear to teeth and classified "old" as twice the age of sexual maturity - roughly 30 years.

Share |      Randall Parker, 2004 July 06 03:49 PM  Trends, Human Evolution

back40 said at July 6, 2004 7:37 PM:

One comment I read in a newsgroup by an evolutionary biologist questioned the interpretation of these findings as having any bearing on genetics since humans were already capable of living their 3 score and ten if only they didn't meet an untimely end. They credited cultural and technological evolution rather than biological evolution.

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