Whether it’s a sea of faces at a school reunion or distant family at a wedding, our ability to remember people we met years ago can come in handy. Now it appears that our evolutionary cousins have a similar skill.
Researchers found bonobos and chimpanzees can remember peers they have spent time with in the past, even if separated by decades. What’s more, this recognition seems to be influenced by whether they got along well with each other – or not.
“These results represent some of the longest long-term memory yet found in non-human animals. It is also one of the very first studies to show that monkeys’ memories can be shaped by their social relationships,” said Dr Laura Lewis, the first author of the research based at the University of California, Berkeley.
“This is surprising because the length and nature of this social memory is so similar to our own human long-term memory.”
Lewis added that previously the longest known memory in non-human animals was in dolphins, which can remember the vocalizations of others for 20 years, while bonobos have been found to remember vocalizations of previous group mates for up to five and a half years.
Write in the Proceedings of the National Academy of SciencesLewis and colleagues reported how they made their discovery by showing 26 bonobos and chimpanzees side by side photographs of other members of their species.
Two images were shown at a time, one depicting an individual they had not previously met, and the other showing a former groupmate who had either died or been relocated at least nine months earlier. During the process, the team monitored the gaze of the monkeys.
The results indicate that the monkeys spent longer on average looking at images of former group mates than strangers, although this finding was strongest for the 12 monkeys at the Kumamoto Shrine in Japan, which are most used to screen-based eye-tracking experiments.
“In the most extreme case, bonobo Louise did not see her sister Loretta or cousin Erin for more than 26 years [years] at the time of testing,” the team wrote. “Notably, she showed a strong attentional bias toward Loretta and Erin.”
The results also suggest that the monkeys looked longer at former group mates if their relationship was generally positive rather than negative.
“The positive relationships that monkeys have with others are characterized by spending more time in close proximity to each other and grooming each other. So it may be that these relationships are more salient for monkeys even after years of separation,” Lewis said.
Lewis said further work is needed to understand why this type of long-term memory may have evolutionary advantages for the monkeys, but suggested that one factor may be that when females reach reproductive age, they leave the groups they are born into to join neighboring ones. join groups. , mainly to avoid inbreeding.
“So it may be the case that long-term memory helps others with these types of social dynamics where they don’t see individuals for long periods of time,” Lewis said.
Dr. Christopher Krupenye of Johns Hopkins University, another author of the research, said that while the experiments suggested that monkeys were just as good at remembering relatives as non-relatives, this may depend on the size of the sample, or reflect that relationships outside of family also matter – indicating strong ties and even alliances between non-relatives.
“Just having a rich model of your social world is critical, regardless of whether the individual is [family],” he said.
