A piece on evolutionary and social explanations for large increases in average human life span in the Paleolithic period is currently doing the rounds. Quoting from the Betterhumans version:
A dramatic increase in longevity that took place during the early Upper Paleolithic Period, around 30,000 BC, could explain humanity's evolutionary success.
"Increased longevity, expressed as number of individuals surviving to older adulthood, represents one of the ways the human life history pattern differs from other primates," say the researchers. "We believe it is a critical demographic factor in the development of human culture."
Details of how longevity increases over the course of human evolution provides a wealth of information on how human social networks developed.
The number of people living to older adulthood would have allowed early modern humans to pass down specialized knowledge from one generation to another.
Old age would have also promoted population growth and strengthened social relationships and kinship bonds.
The presence of grandmothers, for example, confers an important evolutionary advantage as they transfer knowledge and other resources to their daughters and their daughters' offspring.
An increase in the number of relatively old people therefore likely gave modern humans a competitive edge that ensured their evolutionary success.
Of course, "older" in this context means making it to 30. Romanticized notions of prehistory obscure the fact that life back then was nasty, brutish and short. Randall Parker has comments - serious and otherwise - at FuturePundit:
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 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 longer still more 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?
The important point to take away from this is that the presence of more relatively older, wiser people enables a more successful society to emerge. This was true back then, and it is still true today - one more reason for us to strive to extend the healthy human life span.