A memorable senior moment may have occurred toward the end of the Stone Age. Around 30,000 years ago, the number of people surviving long enough to become grandparents dramatically increased, altering the social landscape and provoking major cultural innovations, according to two anthropologists.
Their analysis of fossil teeth from human ancestors indicates that Homo sapiens from the late Stone Age—but not Neandertals or other members of our evolutionary family—exhibited a sharp rise in the population of individuals older than 30 years. Data from hunter-gatherer groups today suggest that among prehistoric H. sapiens, women first bore children at about age 15 and would have become grandmothers at around age 30, say Rachel Caspari of the University of Michigan in Ann Arbor and Sang-Hee Lee of the University of California, Riverside.
Caspari and Lee theorize that prehistoric grandparents sparked growth among Stone Age populations by caring for