A growing body of research suggests that these life stages—which last far longer in humans than in any other animal—are responsible for the remarkable success of our species.

On the surface, children and elders appear to contribute less to society than the middle-aged do. But a growing body of research suggests that these life stages—which last far longer in humans than in any other animal—are responsible for the remarkable success of our species.

Psychologist Alison Gopnik recently published an essay on this subject at Aeon. Unlike our closest relatives, chimpanzees, who are self-sufficient by around age 7, humans remain dependent on their elders for nearly two decades. And while chimp females bear young throughout adulthood and then die around 50, women are often vigorous for decades after 50, though reproduction ceases by then.

It’s not a coincidence that humans have evolved both a protracted childhood and a protracted elderhood, Gopnik argues. A long childhood is necessary to fully develop the large, intricate brains that enable us to create, communicate, and cooperate once we’re grown. And post-reproductive elders ensure that there are enough carers around for these needy, immature kids.