Getting to the bottom of social learning: Chimpanzees copy arbitrary behavior from conspecifics

Studying animal culture has been crucial for understanding the complexities of knowledge transmission and tracing human culture’s evolutionary origins 1 . Defined as the use of tools to provide clear practical benefits to individuals, well-documented examples of material culture include nut-cracking 2 and termite fishing 3 in chimpanzees. Additionally, there is growing interest in animal social traditions, which appear crucial for social interaction and group cohesion. We have previously documented such a tradition, in which chimpanzees copied inserting blades of grass in their ears from one persistent inventor 4 . Now, over a decade later, we have observed an unrelated group of chimpanzees where 5/8 individuals began wearing grass in their ears and 6/8 from their rectums. As of 2024, one newly introduced chimpanzee has adopted the grass-in-ear behavior. Given that the behaviors were not observed in seven other groups in the same sanctuary ( N =148), we conclude that social learning of arbitrary behavior occurred and discuss our findings considering the larger scope of animal culture.