Why Lessons From Chimp Mothers Last a Lifetime

A grooming study suggests the powerful influence of moms (human ones, too)



See the column on the Wall Street Journal site


My mother taught me how to cook, learn my times tables and read with a critical eye—and, in the social realm, how to mind my manners and reach out to others.

But maternal mentors are hardly exclusive to humans. Vervet-monkey moms show their infants their own way to clean off fruit, while chimpanzee mothers teach their toddlers just which stick is best for termite-fishing and how to use rocks to crack nuts. Some bottlenose-dolphin mothers show their young how to find sponges to protect their sensitive snouts while scouring the sea floor for treats—a safety measure that resonated with the mother in me.

New evidence shows that some mammal mothers—specifically, chimps—also transmit to offspring their unique style of socializing. (In contrast, nonhuman primate fathers rarely get involved in teaching children.) The new research focuses on grooming, a primary feature of an ape’s social life.

Chimp grooming does double duty: Picking through another animal’s fur controls parasites and also establishes a trusting social bond. Grooming can be a relaxing pastime, a come-on or a way to forge alliances. As with human social behavior, chimps do it in different ways.

In what primatologists call “high-arm grooming,” two chimps groom each other face-to-face, each with one arm raised in the air. Using their opposite hands to comb through each other’s fur, the pair might be clasping their raised hands aloft or leaning their forearms together overhead. Either way, chimps of both sexes practice this unique grooming style well into adulthood.

While male chimps stay where they are born all their lives, most females migrate to new groups at adolescence. Wherever they end up, the ones from the high-arm, hand-holding community then teach this endearing posture to their own progeny. “It’s a social custom inherited from mother to offspring and not known in any primate before,” said Richard Wrangham, a professor of biological anthropology at Harvard. He and his team observed this unusual behavior among wild chimps living in the Kanyawara community of Uganda’s Kibale National Park.

As described last month in the journal Current Biology, the researchers analyzed 932 photos of high-arm grooming among 36 wild chimps, half of them female. The team had expected that when the adolescent female chimps immigrated to a new community, they would conform to its customs. Teenagers like to fit in, after all.

But a close look at which chimps held hands showed that what mattered is how mom did it. “We’ve got individuals up to 40 years old who are following the maternal pattern,” Dr. Wrangham told me, adding that even after the mother dies, her offspring keep doing things her way.

Intriguingly, hanging out with other family members or peers made no difference in grooming style—regardless how close the relationship or how much time the animals spent together. That makes sense, given that primate mothers are crucial to the education and survival of their offspring. In a 2006 study of wild chimps in Tanzania’s Gombe National Park, the amount of time spent watching mom fish for termites correlated with how skilled 6-year-old chimps became at that task. Female children copied their mothers more faithfully and so became more efficient learners.

Human mothers also have a uniquely powerful effect on their children’s behavior. As mammals and primates, they take time to coach their young ones, who then copy what they do. I’m not discounting the importance of fathers, but it looks like we belong to a large evolutionary family that learns enduring lessons at our mothers’ feet.