Chimpanzees can remember faces they haven’t seen in years – 12/19/2023 – Science

In 2015, while working as a researcher at the North Carolina Zoo (United States), Laura Lewis became friends with a male chimpanzee named Kendall. Whenever she visited the chimps, he would gently take her hands and examine her nails.

Lewis then disappeared during the following summer to study baboons in Africa. When she returned to North Carolina, she wondered if her friend would still remember her face. But as soon as she entered the place where he was, Kendall ran up to her and gestured to look at her hands.

“The feeling I had was that he clearly remembered me after four months away,” said Lewis, now a comparative psychologist at the University of California, Berkeley. “But I didn’t have the data to back it up.”

Now she says she believes she has it. In a study published this Monday (18), Lewis and five other researchers demonstrated that chimpanzees and bonobos can remember the faces of other primates that they have not seen for years. A bonobo recognized a face after 26 years — a record for facial memory, without considering our species.

Lewis and his colleagues carried out the study with 26 monkeys kept at Edinburgh Zoo in Scotland, Kumamoto Sanctuary in Japan, and Planckendael Zoo in Belgium. At each location, the researchers took a computer to the fence of the monkey enclosure and displayed images of the animals on the monitor. A straw attached to the fence allowed them to drink juice while looking at the photos.

After giving the monkeys a few months to get used to the unusual setup, Lewis and his colleagues began the experiment. While the animals drank their juice, the computer displayed pairs of monkey faces for three seconds each time. In each pair, one face was that of a stranger and the other was that of a former companion the monkey had not seen in years.

An infrared camera was used to film the movements of the animals’ eyes. If the monkeys had no memory of their former companions, scientists would expect them to spend the same amount of time looking at both images.

This, however, was not what the researchers observed. The monkeys spent more time looking at their former companions — kinship did not influence the results, as acquaintances who were not related also received more attention than strangers.

A 46-year-old bonobo named Louise from Kumamoto Shrine has been shown to have the oldest memories. Until 1992, she lived at the San Diego Zoo with her sister and nephew. It then moved to the Cincinnati Zoo before arriving at Kumamoto Sanctuary in 2014. In 2019, Lewis and her colleagues discovered that Louise looked longer at the faces of her long-lost relatives than at those of others. monkeys she had never met, even after being separated for over 26 years.

Lewis warned that tracking eye movements offers a limited view of what goes on in the monkeys’ minds. “We can’t fully characterize what their memories are like.”

But a clue found by researchers suggests that affective memories can remain strong over the years. The monkeys spent a little more time looking at the faces of animals they had positive experiences with, according to assessments by zoo keepers.

Lewis hypothesizes that monkeys might benefit from these lasting memories. A female bonobo, for example, will usually leave her mother’s group to join another group for the rest of her life. If the two groups meet years later, she may be able to form an alliance with old acquaintances.

The experiment does not impose a limit on the duration of the animals’ memories. It’s possible they remember faces as much as we do. In one study, psychologists asked volunteers to name people in photos from their high school yearbooks. Their memories began to decline after 15 years, but some volunteers were still able to correctly name classmates 48 years after graduation.

It’s hard to say how many other species have long-term memories. Jason Bruck, an ethologist at Stephen F. Austin State University in Nacogdoches, Texas, discovered that dolphins can recognize the calls of other dolphins that they haven’t heard in more than 20 years.

Bruck suspects that other long-lived animals that live in groups will also display impressive memories — if scientists have the opportunity to test them. “I believe all of these animals will have lifelong memories.”

Lewis drew attention to the fact that chimpanzees, bonobos and humans share an ancestor that lived about 7 million years ago. Early humans may have relied on the long-term memories observed in apes as a basis for the growth of their more complex societies.

“In our human evolution, we face environments where we live socially but not all the time together, and populations are increasingly dispersed,” she said.

Archaeologist Clive Gamble of the University of Southampton in England, who was not involved in the new study, agreed with this interpretation. The evolution of language may have strengthened lasting social memories, as people told stories about acquaintances they hadn’t seen in years. “We just use our common ancestry and turn up the volume.”