Think your adolescence was hard? Try being a chimp.

“Rachna Reddy. Veasey Conway/Harvard Staff Photographer Science & Tech Think your adolescence was hard? Try being a chimp. Radcliffe fellow explores vulnerable life stage we share with our closest relatives Sy Boles Harvard Staff Writer May 21, 2026 4 min read For all the diversity of the human condition, one experience is almost universally painful: Adolescence. It’s also unusual. Most other species pass from puberty to adulthood quickly, but humans linger for years in a transitional state, not quite children but not quite adults, either. Evolutionary anthropologist Rachna Reddy wants to know why. To figure it out, she studies chimpanzees and bonobos, our two closest living evolutionary relatives, who share our unusually protracted and vulnerable adolescences. “When we share a trait with both [those] species, it’s good evidence that our last common ancestor probably also had that trait,” said Reddy, a 2025-2026 fellow at the Harvard Radcliffe Institute. “Chimpanzees and bonobos in particular can really help us establish patterns that are universal in humans, so we can understand a bit more about ourselves.” In a presentation on May 13, Reddy outlined research suggesting that our long, vulnerable, and frequently difficult adolescence might serve an important purpose, evolutionarily speaking. The findings draw on a decade of fieldwork at the Ngogo Chimpanzee Project in Uganda’s Kibale National Park, where researchers have been following the same population since 1993. Like humans (and bonobos), chimpanzees live in fission-fusion societies, which means they have many overlapping relationships with members of their extended community but may also choose to spend time alone. Chimp adolescence, Reddy said, “involves a social reorientation away from caregivers and into new social bonds.” Juvenile chimps follow their mothers or adoptive caregivers until puberty, which begins between ages 8 and 12. As they venture off on their own, they make moment-to-moment decisions about whether to approach other individuals or groups. In observations, the chimps might linger, whimpering, before they approach a “party,” Reddy said — signs of uncertainty or fear, perhaps even what we might dub social anxiety. And for good reason. In childhood, chimps can expect non-family adults to cuddle, play with them, and help them if they get lost. But as soon as they hit puberty, they are met with intense aggression from those same adults. “In adolescence, chimpanzees receive threats they have never experienced before and likely never will again,” said Reddy, who is also an assistant professor at the University of Utah. Faced with that evidence, researchers wondered if young chimps would limit their exposure to violence by avoiding social situations. But they found the opposite. Adolescents actively invested in their relationships, even when those interactions seemed to make them anxious. They were also more likely to engage in grooming behavior, an important and reciprocal part of adult relationships, even when they weren’t groomed back. “It suggests that puberty in chimpanzees is really intensifying these social motivational proclivities, despite risks,” Reddy said. “It might be that having tolerance for some of that rejection and persisting despite it is really important for learning to form adult relationships.” For female chimps, the stakes are even higher. Adolescent females leave their homes and settle permanently in new groups (another rarity in the animal kingdom — in most species, it’s males who strike off solo). Researchers believe that a female chimp’s lifelong social status is largely determined in her first year in her new home. “Adolescent females are making this super high-stakes first impression, it appears,” said Reddy. Sure enough, the difference shows up in the data. Both male and female adolescent chimps engage in a behavior called peering: focused observations of adults gathering food or grooming one another. But females are much more interested than males in watching grooming, Reddy explained. “Our data suggests that a lot of this is happening in natal females before they disperse,” Reddy said. “Something is happening that really enhances their capacity to and motivation to learn about social relationships.” If humans are anything like our closest cousins, Reddy said, our own adolescence might also be the critical window that teaches us not only to compete, but to cooperate — to hold down a job, to pitch in, to introduce ourselves to those cool people at the party. “Learning to contribute is a really critical part of this stage, whether it’s in a relationship or to your community, ” she said. For more from Reddy, check out the Radcliffe Institute’s podcast, “ Born Curious .”

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