Chimpanzee culture extends beyond matrilineal family units

The “grooming handclasp” (GHC) is one of the most well-established cultural traditions in chimpanzees. A recent study by Wrangham et al. [1] reduced the cultural scope of GHC behavior by showing that GHC-style convergence is “explained by matrilineal relationship rather than conformity” [1]. Given that we have previously reported cultural differences in GHC-style preferences in captive chimpanzees [2], we tested Wrangham et al. [1]’s alternative view in the chimpanzee populations that our original results were based on. Using the same outcome variable as Wrangham et al. [1] – proportion high-arm grooming featuring palm-to-palm clasping (PPC) – we found that matrilineal relationships neither explained within-group homogeneity nor between-group heterogeneity, thereby corroborating our original conclusion that GHC can represent a group-level cultural tradition in chimpanzees