What is it about?
In this study we show that chimpanzees and bonobos, humans’ closest-living phylogenetic relatives, likely remember groupmates for a decade or longer and that their social relationships may also shape their long-term memory. We used a special non-invasive camera for tracking where apes looked as they viewed images of members of their species. Apes spent much more time looking at pictures of former groupmates than at pictures of strangers, suggesting that they recognized their past social partners, even partners they hadn’t seen for over 26 years! We also demonstrate that chimpanzees and bonobos may remember the quality of their past social relationships: apes looked the longest at individuals with whom they had the most positive relationships, individuals we might call their friends.
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Photo by Francesco Ungaro on Unsplash
Why is it important?
As humans, we have remarkable memory for others that lasts decades, incorporates important information about social relationships, and is shaped by our emotions. Other animal species like Japanese macaque monkeys, sheep, and elephants also have long-term memory for others that can last years – and dolphins can remember others for up to 20 years. However, up until now only one other animal on the planet – ravens – have been shown to incorporate information about relationship quality into their long-term memory. Nonhuman apes are very social and thus should also benefit from robust knowledge about current, past, and potential future social partners and relationships. Our results represent the longest-lasting social memory found in any nonhuman animal species, and demonstrate that humans’ closest great ape cousins may also incorporate information about social relationships into their long-term social memory. Our research suggests that important properties of human social memory are shared with other apes, and may have provided the foundation for the emergence of complex cooperative relationships that operate across long distances, time-scales, and group boundaries—such as intergroup trade.
Perspectives
Many of us who study great apes often have to travel, sometimes long distances, to work with our study species. We work with these animals for months, and then may spend large amounts of time away from them before we are able to return to study them again. The authors of this paper, as well as many other great ape researchers, had the intuition that the apes with whom we worked seemed to remember us when we returned after long periods away. But we needed to test this hypothesis and felt that the best way to do so was by investigating years-long memory for groupmates from whom apes were separated for various reasons (death, female dispersal patterns, etc.). We were delighted to be able to design a fairly simple looking-bias task to determine that they do recognize groupmates even after years and sometimes decades apart. We hope our work inspires future research to understand the full extent and nature of great ape and other nonhuman animal long-term social memory.
Laura Lewis
Read the Original
This page is a summary of: Bonobos and chimpanzees remember familiar conspecifics for decades, Proceedings of the National Academy of Sciences, December 2023, Proceedings of the National Academy of Sciences,
DOI: 10.1073/pnas.2304903120.
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