Some animals have surprisingly good social memories. The previous record holders are dolphins: as one team discovered ten years ago, they still remember their companions decades later. The Ravens also recognize old friends and enemies.
It's a foregone conclusion among ape researchers that humans' closest relatives also remember familiar individuals. You get the feeling that they recognize you, even if you haven't visited them in a long time, says Christopher Krupenye of Johns Hopkins University in a press release from his university: “To them, you are more than just a visitor normal at the zoo. . They are very excited when they see us again.” So Krupenye and a team decided to investigate how long and well great apes can actually remember others.
Fumihiro Kano A chimpanzee during a memory experiment
For the study, which has just been published in the journal Proceedings of the National Academy of Sciences, experiments were carried out with chimpanzees and bonobos in three different zoos: Edinburgh Zoo in Scotland, Planckendael Zoo in Belgium, and the Japanese Sanctuary from Kumamoto. Photos of animals that had already left the zoo or died were used. The participating monkeys had not seen the depicted people aged between nine months and 26 years. The team also collected data on the relationships between previous companions, such as whether there were many friendly interactions.
Recognized companions
In exchange for participating, the monkeys received juice. While they were drinking, two conspecifics were presented on a screen: one a stranger and one with whom they had previously been in the same enclosure. The team recorded eye movements. What was measured was where the animals looked and for how long.
Researcher's video on social memory
Chimpanzees and bonobos recognize “old friends”
Chimpanzees and bonobos looked at photos of their previous companions for much longer – regardless of how long they had been separated. The animals looked for a long time at members of their species with whom they had already had a very positive exchange, that is, they were friends, so to speak. Sometimes the animals would even stop drinking to look at the image of their once familiar.
In the most extreme case, the period of separation lasted more than two decades: female bonobo Louise had not seen her sister Loretta and nephew Erin in 26 years. The memory capacity is therefore comparable to that of dolphins.
Painful separation?
The results suggest that great apes can remember certain members of their species for decades, for a large part of their 40 to 60 years of life, the researchers write. This is comparable to people. The last common ancestor probably had an equally good social memory.
Memory of conspecifics was likely an important prerequisite for the development of human culture, study says. Many long-term relationships, such as trade between different groups, would be unimaginable without this capability. The beginnings of this can already be seen in bonobos and chimpanzees.
The study also suggests that great apes, like humans, may even miss the companions they are separated from. “The work clearly shows how fundamental and lasting these relationships are,” says Krupenye. If they are destroyed, for example by poaching and deforestation, familiar animals will likely be hit hard.