Monkey See, Monkey Remember?

Christopher Krupenye ’11 proves humans’ closest relatives can recognize friends they haven’t seen for decades.

By Amy Martin

he 15 chimpanzees who live at Scotland’s Edinburgh Zoo—Louis, Lucy, Eva, Sophie, Lianne, Heleen, Qafzeh, Kilimi, Rene, Paul, Frek, Edith, Liberius, Velu and Masindi—see more than 1,500 visitors every day. For the most part, they ignore their human admirers and simply go about their everyday chimp lives.

But when scientist Christopher Krupenye ’11 and his research colleagues arrive at the zoo, the reaction is noticeably different. The chimps they’ve met during previous visits will come right over, gesture and even try to communicate with these particular humans.

“Everyone I know who works with apes has had this experience where you go back to these places, sometimes years later, and it’s very apparent that the individuals that you bonded with are behaving very differently toward you than they are toward the average visitor to the zoo. They seem excited to see you,” Krupenye says.

“That experience has given us the impression that they must remember us, that we have this relationship that’s transcending these long periods of absence.”

But can great apes really recognize individuals they haven’t seen for years? How long does that social memory last? And what might that tell us about the origins of social memory in humans?

Those are the types of questions that have been driving Krupenye’s research into the social and cognitive abilities of humans’ closest relatives for more than a decade. After earning a Ph.D. in evolutionary anthropology from Duke University, he completed postdoctoral research at the Max Planck Institute for Evolutionary Anthropology, the University of St. Andrews and Durham University. In 2022, he joined the faculty at Johns Hopkins University, where he is an assistant professor of psychological and brain sciences and director of the Social & Cognitive Origins research group.

To prove his hunch that great apes do remember individuals, Krupenye teamed up with other researchers from around the world to conduct a study with the chimpanzees and bonobos at the Edinburgh Zoo, the Planckendael Zoo in Belgium and the Kumamoto Sanctuary in Japan.

“All of our research is voluntary and noninvasive,” Krupenye says. “The apes we work with live in normal social groups. When we want to do studies, the keepers call them by name into a testing area. If they want to come in, they do. And they usually do—they seem to really enjoy it.”

In this case, while the apes sipped diluted juice from a straw, Krupenye and his team tracked their eye movements as they looked at side-by-side photographs of two members of their own species—a former groupmate who had either left the zoo or died and an individual completely unknown to the ape.

“If they don’t recognize the former groupmate, they should treat them the same as the stranger, and we should see equal attention or random attention to the two pictures,” Krupenye explains. “But if they do recognize those individuals, then we expect them to spend more time looking at their former groupmates, just as you might if you passed someone you recognized on the street and did a double take.”

The researchers found the apes did indeed look significantly longer at the individuals they’d once known. And while that didn’t surprise the scientists, they were excited to find that the social memory lasted a very long time—one bonobo, 46-year-old Louise, even recognized her sister, Loretta, and her nephew, Erin, even though she hadn’t seen either of them in 26 years.

How richly can animals understand others’ minds? Can apes or dogs take others’ perspectives? Do they know what others can see or know or believe? What information and relationships are they keeping track of?

Christopher Krupenye ’11

That finding represents the longest non-human social memory ever documented, which generated significant media buzz when the research was published in the scientific journal Proceedings of the National Academy of Sciences in December.

“We really didn’t have any sense of how long their memories would last. It could have been that they remember for a few years, but then if they’re not likely to see the individual again, there might not be any value in retaining that memory and we might have seen a drop off,” Krupenye explains. “So we were really surprised to find they hold onto these memories for so long—potentially for their entire lives.”

The researchers were also interested to find that the apes looked longer at the individuals who were their closest social partners—the friends and relatives with whom they had positive relationships.

“This suggests that they really are distinguishing them as individuals, that they have some way of keeping track of the quality of their social relationships, even over many years,” Krupenye says.

“Apes prefer to spend time with certain individuals; they groom them to build camaraderie. Sometimes they support each other in coalitionary aggression, in which they work together to team up against a rival. These relationships matter very much, so it does make sense that they retain this type of information. But there had been almost no research on that question.”

That our closest great ape relatives, like humans, can remember individuals for long periods of time and retain information about the quality of those relationships suggests that these cognitive abilities likely evolved in our common ancestors. But Krupenye wonders just how recently, noting that dolphins have been shown to recognize the vocalizations of their podmates even after 20 years, and a study on ravens found they could retain some information about the quality of their social relationships.

“We’ve all seen those videos of a soldier coming home after a few years and their dog is just flipping out excited to see them. So the same kind of anecdotal evidence that I’ve personally experienced with apes clearly exists for other animals that are much more distantly related to us,” he says. “This type of social memory may be much more widespread across other species.”

In the Department of Psychological and Brain Sciences at Hopkins, Krupenye has joined a team of scientists dedicated to investigating fundamental questions of behavior and the mind. Some of his colleagues are interested in the cognitive abilities of the youngest humans, while others are studying the role of perceptual experience in cognitive and neural developments or working at the intersection of philosophy and cognitive science. The environment has been invigorating for Krupenye, who describes his work as “inter- and extra-disciplinary” at the nexus of psychology, anthropology and biology.

“Several of my colleagues are developmental psychologists who work with infants and very young children. So we spend a lot of time thinking and brainstorming ways to test the rich, complicated cognitive abilities of creatures that can’t talk,” he says.

“Broadly, my research group is interested in how humans and other animals navigate their social world. How richly can animals understand others’ minds? Can apes or dogs take others’ perspectives? Do they know what others can see or know or believe? What kinds of things do they know about other individuals in their social group, what information and relationships are they keeping track of?”

In addition to his continued work with apes in zoos and sanctuaries (he’s currently studying whether apes track the whereabouts of groupmates even when they aren’t directly perceptible to them), Krupenye’s research teams are studying adult human cognition to more precisely pin down the differences in the cognitive abilities of humans and non-human primates.

He’s also started working with man’s best friend. In 2023, Krupenye’s Social & Cognitive Origins Group established the Canine Minds Collaborative to study dog intelligence and behavior with the help of local pet owners and their beloved pups. Interested dog owners fill out a survey, and the Collaborative then invites the dog (and owner) to the lab to participate in a series of noninvasive cognitive games and activities designed to be mentally stimulating and enjoyable while also shedding light on canine problem-solving abilities, decision-making processes, memory, attention and social behavior.

“It’s been a very exciting partnership between the university and the community, and it has provided us with a new opportunity to understand a different kind of animal mind,” Krupenye says.

“Apes are very interesting because they are our closest relatives. And all great apes are endangered, so I hope that by exposing the richness of their mental lives and how similar they are to us, people will be more motivated to care about and conserve them.

“But dogs are very cool, too, because they’re some of the only animals that really live in the human world with us, and they seem to possess a number of interesting skills for understanding human communication and human social cues.”

At Conn, Krupenye majored in biological sciences, minored in French and earned a certificate from the Goodwin-Niering Center for the Environment. He credits his former professors with supporting his interests and inspiring his academic and research career.

Now, he’s the professor.

At Hopkins, Krupenye teaches two undergraduate classes, including a lecture course, “Primate Minds,” that explores the evolutionary history and cognitive abilities of non-human primates, and a seminar, “Origins of the Social Mind,” which focuses on the abilities of the youngest humans and other animals to understand their social world.

“It’s a unique joy to be able to see students really light up when you’re sharing with them this whole domain of knowledge and inquiry they didn’t know existed,” Krupenye says. “For some students, this becomes a passion and an area that they want to pursue. It’s very exciting to be able to guide them and extend to them the opportunities to enter this field that I, too, am very passionate about.”

It’s not hyperbole to say it’s a dream come true for Krupenye, who first told the author of this piece that he hoped “to conduct research with apes and teach at the university level” in 2010, when he won a Barry M. Goldwater Scholarship during his junior year at Conn. That was one of several scholarships, including a National Science Foundation Graduate Research Fellowship, that supported Krupenye’s pursuit of his goals. Now, he’s working to make science more accessible to students from traditionally underrepresented groups.

“We’re really invested in doing what we can to make academia a more inclusive place for everyone,” he says. “It feels very special to be able to give back and mentor the next generation of folks who are excited to enter this field.”

Watch a video about Krupenye’s research at John Hopkins.