A new simulation suggests the rise of grandmothering explains why human life spans are so much longer than those of chimpanzees and other non-human apes. By taking a theoretical society with apelike life spans and adding grandmas, researchers were able to double everyone's length of life.
The findings, reported today (Oct. 23) in the journal Proceedings of the Royal Society B, support the grandmother hypothesis. This hypothesis aims to explain why human females, unlike other primates and mammals, outlive their reproductive years. Perhaps, the idea goes, grandmothers took on the duty of caring for their grandchildren, allowing their own children to have more offspring. Families where people lived long enough to grandmother thus would have had a genetic advantage, allowing longevity to spread through natural selection.