Monkeys can recognize, solely through the observation of photographs, group companions they haven’t seen for over 25 years and respond with great enthusiasm to images featuring their friends, according to a study published in the Proceedings of the National Academy of Sciences. This research demonstrates the longest-lasting social memory ever documented outside of humans, emphasizing how human culture has evolved from shared ancestors with monkeys.
“Chimpanzees and bonobos recognize individuals they haven’t seen for decades,” said Christopher Krupenye, an assistant professor at Johns Hopkins University studying animal cognition. Krupenye, also the senior author of the study, noted, “There’s this small but significant pattern of increased attention toward individuals with whom they’ve had more positive relationships, suggesting that it goes beyond mere familiarity. Monkeys keep track of aspects related to the quality of social relationships.”
“We tend to think of large primates as beings very different from us, but the results show that these animals possess cognitive mechanisms very similar to humans, including memory,” stated Laura Lewis, a biological anthropologist and comparative psychologist at the University of California, Berkeley, and the lead author of the study. Lewis added, “I believe that’s the most interesting aspect of this study.”
The research team was motivated to investigate how long monkeys remember their peers based on experiences working with the animals. “You get the sense that they respond as if they recognize you and that, for them, you are really different from the average zoo visitor,” explained Krupenye. “They are excited to see you again,” he emphasized. “The goal of the study was, therefore, to empirically inquire whether monkeys truly have a solid and enduring memory of remembering their companions.”
The team worked with chimpanzees and bonobos from zoos in Edinburgh, Scotland, Planckendael, Belgium, and the Kumamoto Sanctuary, Japan. Researchers collected photographs of monkeys that had left the zoos or passed away, individuals participants hadn’t seen for at least nine months, and in some cases, up to 26 years. The research group also gathered information on the relationships each participant had with their former group mates, including positive or negative interactions and other relational components.