Chimps and bonobos recognize familiar faces even after decades apart

In experiments, primates paid special attention to images of old friends

Two chimpanzees near each other hold hands while perched on a wooden structure in front of green leaves

Remembering friends, family and other social acquaintances is something people regularly do. Now there’s evidence that other types of apes also have this recognition of others that persists after years of absence.

Courtesy of Laura Simone Lewis

Chimpanzees and bonobos have great memories for familiar faces.

Research now suggests that these apes can recognize members of their own species. Not just day to day or month to month. These animals recognized others even after more than 26 years apart. That sets a new record for the longest known social memory in any non-human animal. Until now, the record was held by dolphins. They can recognize each other’s voices after 20 years apart.

Researchers shared the new findings December 18. The work appeared in the Proceedings of the National Academy of Sciences.

illustrated text reads "Wild Things: A graphic tale" with animals drawn around the letters
Text: Chimps and bonobos have great memories for faces . Written by Maria Temming. Illustrated by JoAnna Wendel. Image: Two chimps are on neighboring branches of a tree. The chimp on the left, hanging from their branch, says, “We’ve met before, right? No, no, don’t tell me…Loretta?” The chimp on the right, sitting on their branch, smiles and scratches their head.
Text (above image): Humans’ closest living relatives, chimpanzees and bonobos, are very social creatures. Image: Two zoo enclosures are shown side by side. The left enclosure has a plaque that reads “chimpanzees.” Inside, two chimps sit on a wooden plank suspended on the trunk of a tree, while another chimp hangs with both hands from a rope. The right enclosure has a plaque reading bonobos. Inside, a mom and baby bonobo sit together on a wooden plank suspended from a tree, while two other bonobos sit together on a nearby tree branch. Text (below image): “They have different friendships and relationships and family members,” says Laura Simone Lewis. She is a researcher at the University of California, Berkeley, who studies apes. Apes are a group of animals that include chimps, bonobos, gorillas, orangutans and humans.
Text (above top image): Chimps and bonobos might groom or play with their friends, or eat or sleep near them. Top image: two chimps sit together on the branch of a tree. One is picking bugs off the other. The chimp who is getting groomed has their eyes closed and is saying, “Oooh, yeah, right there!” Text (above bottom image): And sometimes chimps and bonobos fight their own kind for dominance, mates or food. Bottom image: Two chimps on a branch are fighting with each other over a banana. The chimp holding the banana is saying, “Mine!” The other chimp is saying, “Gimme!”
Text (above image): Chimps and bonobos also interact with the scientists who study them. Lewis first got curious about their ability to remember faces in 2015, after she took a break from working with the chimps at the North Carolina Zoo for the summer. Image: Lewis holds up her hand to wave at a chimp inside a zoo enclosure through the glass. The chimp holds their hand over their heart and has an exclamation point over their head. Text (below image): “When I did return four months later,” Lewis says, “it seems like they remembered me… They would come over to the side of their enclosure close to me.” But did the chimps really recognize her, Lewis wondered. And would they recognize each other after months or years apart?
Text (above image): To find out, Lewis and her colleagues recently ran an experiment with 15 chimps and 12 bonobos who lived in captive settings in Scotland, Belgium and Japan. “The animals [could] choose when to come up and participate or leave whenever they want,” Lewis says. The team enticed apes to sit down and stay a while with a juice sipping station. Image: A bonobo sits at the edge of an enclosure, looking through a glass panel at a computer sitting on a desk outside the enclosure. The bonobo smiles as it sips juice through a long tube.
Text (above image): While drinking juice, each ape viewed side-by-side photos on a computer screen: a member of their species they once lived with vs. an ape they’d never met. Image: A bonobo sits at the edge of their enclosure, looking through a glass panel at the computer screen. The screen shows two apes side by side that have slightly different facial features. Lewis stands near the computer with a clipboard. Text (below image): An infrared camera below the screen tracked how long the ape looked at each picture.
Text (above image): The chimps and bonobos looked about 14 percent longer at images of apes they once lived with than unfamiliar apes. This hinted that the animals recognized their past group mates—even though they hadn’t seen those apes for long stretches of time, ranging from 9 months to more than 26 years. Image: A chimp sipping juice through a long tube stares at a computer screen. It is thinking, “Wow, long time no see!” Text (below image): Chimps and bonobos looked especially long at pictures of their former friends. “We were just excited and almost relieved like, ‘Oh my gosh, our intuition was correct!’” Lewis says. “Yes, they can recognize individuals they haven’t seen for years, even decades.”
Text (above image): Humans can recognize faces they haven’t seen for nearly 50 years. Finding out that chimps and bonobos have similarly long-lasting social memories hints that our last common ancestor did too. Image: A family tree shows how different species of primates branched off from each other over the course of their evolution. These species include: lemurs, tarsiers, new world monkeys, old world monkeys, lesser apes, orangutans, gorillas, chimps and bonobos, and cartoonists (humans). The branches separating monkeys from apes divided about 25 million years ago, when the last common ancestor of monkeys and apes lived. The branches separating chimps and bonobos from humans diverged about 6 to 9 million years ago, when the last common ancestor of humans, chimps and bonobos lived.
Text: The discovery also raises many new questions. Do chimps and bonobos remember specific events that took place with old familiar faces? Do they mis friends and family who have passed away or moved to other zoos? Image: Two bonobos hang out in an enclosure. One bonobo, laying on its back on the branch of a tree, has a thought bubble imagining them with another bonobo holding their face. The other bonobo in the enclosure is laying back on the grass, with a thought bubble imagining another bonobo with hearts around it.
Text (above image): And what other primates might also have such great memories for familiar faces? Image: A girl sits on a bench outside a zoo enclosure with a plaque reading “orangutans.” Inside the enclosure, two orangutans sit side-by-side, looking at each other.
JoAnna Wendel

Maria Temming is the Assistant Managing Editor at Science News Explores. She has bachelor's degrees in physics and English, and a master's in science writing.

JoAnna Wendel is a freelance science writer and cartoonist in Portland, Ore. She loves to make comics about all types of science, but she especially loves drawing planets, invertebrates and sea creatures. When she's not drawing, JoAnna is probably reading, hiking or hanging out with her cat, Pancake.