Decades-Long Social Memory in Apes: Louise Reunites with Sister After 26 Years

A Johns Hopkins team used infrared eye-tracking with 26 apes across Europe and Japan and found that chimpanzees and bonobos gazed longer at former companions than strangers; one bonobo, Louise, now 46, recognized her sister Loretta after 26 years apart, the longest documented nonhuman social memory, suggesting apes remember bonds for much of their lifespans and that memory relates to positive past relationships, with welfare implications for housing and breeding decisions.