In 2015, as a university researcher at the North Carolina Zoo, Laura Lewis befriended a male chimpanzee, Kendall. Every time she visited the chimpanzees, Kendall would gently hold her hands and inspect her nails.
Lewis then left all summer to study baboons in Africa. When he returned, he wondered if Kendall remembered her face. As soon as he entered her compound, Kendall ran up to her and made a gesture asking to look at her hands.
“The feeling I had was that he remembered me clearly after four months of absence,” said Lewis, now a comparative psychologist at the University of California, Berkeley. “But he didn’t have the data to prove it.”
Now he thinks he has them. In a new study, Lewis and his colleagues have shown that chimpanzees and bonobos can remember the faces of other apes they haven't seen in years. A bonobo recognized a face after 26 years—a facial memory record beyond our species.
Together with his advisor, Chris Krupenye, now at Johns Hopkins University in Maryland, Lewis studied 26 apes at the Edinburgh Zoo in Scotland, the Kumamoto Sanctuary in Japan and the Planckendael Zoo in Belgium.
At each facility, the researchers moved a computer up to the fence of the apes' enclosure to show them images of animals. A straw attached to the fence allowed the apes to drink juice while they carefully viewed the images.
After giving the apes a few months to get used to the arrangement, Lewis and his colleagues began their experiment. While the animals drank juice, the computer displayed pairs of ape faces for three seconds at a time. In each pair, one face was a stranger and the other an old companion the ape had not seen in years.
The scientists used an infrared camera to record the animals' eye movements. If the apes did not remember their old companions, the scientists anticipated that they would spend equal time on each image.
However, the apes consistently spent more time looking at their former companions.
Louise, a 46-year-old bonobo from Kumamoto Shrine, demonstrated the oldest memories. Until 1992, she had lived at the San Diego Zoo with her sister and her nephew. She was then transferred to the Cincinnati Zoo in Ohio before arriving at the Kumamoto Sanctuary in 2014.
In 2019, researchers found that Louise looked longer at the faces of her long-lost relatives than at apes she didn't know, even after being separated more than 26 years ago.
Lewis noted that tracking eye movements only offers a limited glimpse inside the apes' minds: “We can't fully characterize what their memories are like.”
However, researchers actually found a clue that suggests good memories may stay strong over the years. The apes spent a little more time looking at the faces of animals they once had positive experiences with.
Lewis speculates that apes could benefit from these memories. For example, a female bonobo commonly leaves her mother's group to join another group for the rest of her life. If the two groups bump into each other years later, she could form an alliance with old acquaintances.
The experiment does not limit the duration of the animals' memories. They may remember faces as long as we do. In one study, some people who looked at photos from their high school yearbooks could correctly name their classmates 48 years after graduating.
Lewis noted that chimpanzees, bonobos and humans have a common ancestor who lived about 7 million years ago. Early humans may have developed long-term memories as their societies became more complex.
“In our human evolution, we have faced environments in which we live socially, but not close to each other all the time, and populations are increasingly separated,” he noted.
Clive Gamble, an archaeologist at the University of Southampton in England, who was not involved in the study, said the evolution of language may have strengthened lasting social memories, as people told stories about acquaintances they had not seen in years.
“We just tapped into our common ancestry and then turned up the volume,” he explained.
By: CARL ZIMMER
THE NEW YORK TIMES
BBC-NEWS-SRC: http://www.nytsyn.com/subscribed/stories/7044713, IMPORTING DATE: 2023-12-26 22:15:05
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