Inter-individual coordination in walking chimpanzees

This is the authors' abstract. We don't add key points for this paper.

Humans, like many other animals, live in groups and coordinate actions with others in social settings.1Ramenzoni V.C. Riley M.A. Shockley K. Baker A.A. Interpersonal and intrapersonal coordinative modes for joint and single task performance.Hum. Mov. Sci. 2012; 31: 1253-1267https://doi.org/10.1016/j.humov.2011.12.004Crossref PubMed Scopus (33) Google Scholar Such interpersonal coordination may emerge unconsciously and when the goal is not the coordination of movements, as when falling into the same rhythm when walking together.2Felsberg D.T. Rhea C.K. Spontaneous interpersonal synchronization of gait: a systematic review.Arch. Rehabil. Res. Clin. Transl. 2021; 3: 100097https://doi.org/10.1016/j.arrct.2020.100097Abstract Full Text Full Text PDF PubMed Google Scholar Although one of our closest living relatives, the chimpanzee (Pan troglodytes), shows the ability to succeed in complex joint action tasks where coordination is the goal,3Melis A.P. The evolutionary roots of human collaboration: coordination and sharing of resources.Ann. N. Y. Acad. Sci. 2013; 1299: 68-76https://doi.org/10.1111/nyas.12263Crossref PubMed Scopus (12) Google Scholar little is known about simpler forms of joint action. Here, we examine whether chimpanzees spontaneously synchronize their actions with conspecifics while walking together. We collected data on individual walking behavior of two groups of chimpanzees under semi-natural conditions. In addition, we assessed social relationships to investigate potential effects on the strength of coordination. When walking with a conspecific, individuals walked faster than when alone. The relative phase was symmetrically distributed around 0° with the highest frequencies around 0, indicating a tendency to coordinate actions. Further, coordination was stronger when walking with a partner compared with two individuals walking independently. Although the inter-limb entrainment was more pronounced between individuals of similar age as a proxy for height, it was not affected by the kinship or bonding status of the walkers or the behaviors they engaged in immediately after the walk. We conclude that chimpanzees adapt their individual behavior to temporally coordinate actions with others, which might provide a basis for engaging in other more complex forms of joint action. This spontaneous form of inter-individual coordination, often called entrainment, is thus shared with humans.