It is natural for a person to recognize an old acquaintance or colleague whom they have not seen for many years. However, not only humans are capable of remembering old friends. In an article published in PNAS, researchers from the University of St Andrews, Kyoto University, and other scientific institutions describe experiments with common chimpanzees and bonobos.
During the experiment, scientists looked for monkeys that had previously lived with friends, acquaintances, or family members, but then this group had broken up — someone had died or been transferred to another zoo. Monkeys that had not seen their old acquaintances for a long time were shown photographs of these acquaintances and images of other chimpanzees. The main challenge was to find such cases of separation and corresponding photographs.
Both common chimpanzees and bonobos looked at their old acquaintances longer than at strangers, which can be interpreted as a recognition process. Moreover, much depended on the nature of their relationships: if the bonds were warm, they paid more attention to such a friend than to one with whom they had conflicts in the past. One bonobo, who had not seen her family members for a full twenty-six years, nevertheless clearly recognized them in the photograph.
This raises the question of what exactly happens in the memory of monkeys. Do they react solely to appearance, or do fragments of memories about shared events remain in their consciousness? What is the role of simple curiosity in this process? Nevertheless, the results of the experiment suggest that the memory of chimpanzees about friends can be quite long-lasting (even when it comes to curiosity, it manifests specifically in relation to old acquaintances).
In fact, other animals are also capable of remembering each other well, as well as not just their kind: similar studies have been conducted on corvids, and many dog and cat owners can recount how their pets greet their owners after a long separation. However, in the case of monkeys, the main feature lies not in the act of remembering itself, but in its duration — twenty-six years is a significant period. Other animals, such as bottlenose dolphins, also exhibit the ability to remember the voices of their companions for up to twenty years.
