Chimpanzee drumming shows rhythmicity and subspecies variation

Rhythmic percussion is present across human cultures and has been proposed as one of the earliest evolved forms of musical expression.1 Key features of human rhythmic percussion include individual and regional variation, as well as structural features widespread across musical cultures, such as the use of non-random timing and isochrony (i.e., evenly spaced note onsets).2,3,4,5 Comparative studies of drumming in our ape relatives contribute to understanding the evolutionary origins of human rhythmic percussion. In this context, large, diverse datasets allow testing for species-level universals and regional variation. Chimpanzees and bonobos, like humans, drum on instrumental substrates.2,6,7,8,9 Wild chimpanzees drum on resonant tree buttresses, showing individual variation during traveling and resting contexts, and often integrate drumming into their long-distance pant-hoot vocalizations.6,7,8 But whether wild chimpanzee drumming shows structural musical features and regional variation in rhythm or in its integration within pant-hoots remains unknown. We show that wild chimpanzees drum with non-random timing and isochrony, providing evidence that rhythmic drumming on instrumental substrates may have been present in our last common ancestor.2 Furthermore, we found subspecies-level regional rhythmic variation, showing that western chimpanzees drum isochronously, while eastern chimpanzees drum by alternating shorter and longer inter-hit intervals. Western chimpanzees also produce more drumming hits, drum at a faster tempo, and integrate drumming earlier in the pant-hoot vocalization, typically during the rhythmic build-up phase. Chimpanzee buttress drumming shows both species-level structural features of human musicality and stable subspecies regional differences across diverse ecologies.