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. Defined as the use of tools to provide clear practical benefits to individuals, well-documented examples of material culture include nut-cracking and termite fishing 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. 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.