In 2022, Johns Hopkins researchers found that bonobos and chimpanzees can remember former companions; one bonobo recognised her sister after 26 years apart

A bonobo named Louise at a sanctuary in Japan helped document the longest-lasting social memory recorded outside our species. When shown a photograph of her sister Loretta, whom she had not seen in more than 26 years, Louise stared intently at the familiar face and barely glanced at a stranger beside it, suggesting apes can retain memories of family and friends for much of their natural lifespan.The findings come from a Johns Hopkins University team led by comparative psychologist Christopher Krupenye and lead author Laura Simone Lewis, and the results were published in the Proceedings of the National Academy of Sciences. The experiment used infrared eye-tracking cameras to measure exactly where 26 chimpanzees and bonobos living across zoos and sanctuaries in Europe and Japan focused their attention when shown paired photographs on a screen.