Read the rest of Laura Helmuth's series on longevity.
The fundamental structure of human populations has changed exactly twice in evolutionary history. The second time was in the past 150 years, when the average lifespan doubled in most parts of the world. The first time was in the Paleolithic, probably around 30,000 years ago. That’s when old people were basically invented.
Throughout hominid history, it was exceedingly rare for individuals to live more than 30 years. Paleoanthropologists can examine teeth to estimate how old a hominid was when it died, based on which teeth are erupted, how worn down they are, and the amount of a tissue called dentin. Anthropologist Rachel Caspari of Central Michigan University used teeth to identify the ratio of old to young people in Australopithecenes from 3 million to 1.5 million years ago, early Homo species from 2 million to 500,000 years ago, and Neanderthals from 130,000 years ago. Old people—old here means older than 30 (sorry)—were a vanishingly small part of the population. When she looked at modern humans from the Upper Paleolithic, about 30,000 years ago, though, she found the ratio reversed—there were twice as many adults who died after age 30 as those who died young.
The Upper Paleolithic is also when modern humans really started flourishing. That’s one of the times the population boomed and humans created complex art, used symbols, and colonized even inhospitable environments. (The modern humans she studied lived in Europe during some of the bitterest millennia of the last Ice Age.) Caspari says it wasn’t a biological change that allowed people to start living reliably to their 30s and beyond. (When she looked at other populations of Neanderthals and Homo sapiens that lived in the same place and time, the two different species had similar proportions of old people, suggesting the change was not genetic.) Instead, it was culture. Something about how people were living made it possible to survive into old age, maybe the way they found or stored food or built shelters, who knows. That’s all lost—pretty much all we have of them is teeth—but once humans found a way to keep old people around, everything changed.
Old people are repositories of information, Caspari says. They know about the natural world, how to handle rare disasters, how to perform complicated skills, who is related to whom, where the food and caves and enemies are. They maintain and build intricate social networks. A lot of skills that allowed humans to take over the world take a lot of time and training to master, and they wouldn’t have been perfected or passed along without old people. “They can be great teachers,” Caspari says, “and they allow for more complex societies.” Old people made humans human.
What’s so special about age 30? That’s when you’re old enough to be a grandparent. Studies of modern hunter-gatherers and historical records suggest that when older people help take care of their grandchildren, the grandchildren are more likely to survive. The evolutionary advantages of living long enough to help raise our children’s children may be what made it biologically plausible for us to live to once unthinkably old ages today.
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No matter how many grandmothers were around during most of human history, though, many children didn’t survive. Until the 20th century, most deaths occurred in children and infants. According to most estimates, quarter to half of them died.
We’re now on the other side of the second great demographic change in human evolutionary history. The main reason lifespan doubled in the past 150 years is that infant mortality plummeted. Just as having old people around changed human culture profoundly 30,000 years ago, having infants and children survive has fundamentally changed modern society.
If you walk through an old cemetery, you’ll see all the tiny headstones of nameless infants. Abandoned cemeteries are the most peaceful. The small Bolen graveyard in Shenandoah National Park has about 40 stones that are still legible: Infant son of John H. and Lula Hindall, Born & Died Jan. 15, 1913. Daughter of Waverly H. Bailey, age 11 days. Mollie E. Pullin, Age 7 Years, Gone Home. Some cemeteries are full of infants buried next to mothers who died in childbirth. It’s like strolling through the medieval wing of an art museum: Everywhere you look is Madonna and Child, Madonna and Child.
Parents knew they couldn’t expect infants to live. In the United States and other parts of the world, infants often weren’t named immediately; a tradition in China and other parts of Asia is to name a child only after 100 days. According to some interpretations of Jewish law, if a baby dies before 30 days, it never really lived. Was this meant to keep parents from getting too attached to their children?
People certainly grieved when they lost a child. In the haunting words of an Alabama cotton tenant: “You ain’t never seen trouble till you lose a young’un.” He had lost seven. An analysis of poems written by parents who had lost children from the 16th century on reveals plenty of grief.
But overall, parents’ relationships with their children were fundamentally different than they are in much of the world today. “It was very difficult to invest emotionally because at least half of them would die,” says S. Jay Olshansky, a longevity researcher at the University of Illinois at Chicago. French historian Philippe Ariès popularized the notion that childhood is a modern invention and that until recently children weren’t as coddled or precious as they are today.