Did you know that grandmothers are almost uniquely human? The only other species with grandmothers might be elephants and killer whales. Grandfathers? I don’t know of any species, but humans, that have grandfathers, not even chimpanzees.
Hawkes, a professor of anthropology at the University of Utah, has extensively studied the Hadza, a group of hunter-gatherers in Tanzania who eat a lot of wild foods such as berries and tubers. While young children can pick berries themselves, older women in the community are the ones pulling up the bulbous root vegetables, which would be difficult for young kids.
Hawkes found a correlation between how well children grew and their mother’s foraging work, until the mother had another kid. Then, their growth correlated with “grandmother’s work,” she says. “There were the data right in front of us.”
These observations, which Hawkes and collaborators began in the 1980s, have helped fuel the Grandmother Hypothesis, the idea that grandmothers step in to feed young children and perform other motherly duties so that mothers can focus their own energy and resources on having more children at shorter intervals. The result is that a grandmother enables the birth of more descendants, leaving more copies of her genes in subsequent generations. In prehistoric times, the theory goes, grandmothering led to the spread of genes corresponding to slower aging in women relative to their predecessors, which increased expected lifespans in general.