Abstract
Dance is an icon of human expression. Despite astounding diversity around the world’s cultures and dazzling abundance of reminiscent animal systems, the evolution of dance in the human clade remains obscure. Dance requires individuals to interactively synchronize their whole-body tempo to their partner’s, with near-perfect precision. This capacity is motorically-heavy, engaging multiple neural circuitries, but also dependent on an acute socio-emotional bond between partners. Hitherto, these factors helped explain why no dance forms were present amongst nonhuman primates. Critically, evidence for conjoined full-body rhythmic entrainment in great apes that could help reconstruct possible proto-stages of human dance is still lacking. Here, we report an endogenously-effected case of ritualized dance-like behaviour between two captive chimpanzees – synchronized bipedalism. We submitted video recordings to rigorous time-series analysis and circular statistics. We found that individual step tempo was within the genus’ range of “solo” bipedalism. Between-individual analyses, however, revealed that synchronisation between individuals was non-random, predictable, phase concordant, maintained with instantaneous centi-second precision and jointly regulated, with individuals also taking turns as “pace-makers”. No function was apparent besides the behaviour’s putative positive social affiliation. Our analyses show a first case of spontaneous whole-body entrainment between two ape peers, thus providing tentative empirical evidence for phylogenies of human dance. Human proto-dance, we argue, may have been rooted in mechanisms of social cohesion among small groups that might have granted stress-releasing benefits via gait-synchrony and mutual-touch. An external sound/musical beat may have been initially uninvolved. We discuss dance evolution as driven by ecologically-, socially- and/or culturally-imposed “captivity”.
Highlights
Dance is an icon of human expression
There seem to exist no parallel behaviours among our closest relatives, the great apes, calling into question how and why this trait emerged within the terminal branch of our phylogenetic tree and subsequently evolved so expansively[7,8,9]
Whether seen as an evolutionary by-product, or adaptation to promote social cohesion for religion or war, speculation abounds on possible scenarios for the emergence of rhythmic entrainment in the human clade
Summary
Dance is an icon of human expression. Despite astounding diversity around the world’s cultures and dazzling abundance of reminiscent animal systems, the evolution of dance in the human clade remains obscure. Dance requires individuals to interactively synchronize their whole-body tempo to their partner’s, with near-perfect precision This capacity is motorically-heavy, engaging multiple neural circuitries, and dependent on an acute socio-emotional bond between partners. Evidence for conjoined full-body rhythmic entrainment in great apes that could help reconstruct possible proto-stages of human dance is still lacking. In natural or naturalistic conditions, nonhuman primates engage in rhythmic behaviours[16,17,18,19], some of which can be compared, at a purely mechanical level, with the use of music instruments[20,21] Analyses of these behaviours have been seldom done in light of dance evolution and rarely adopted accurate measures of rhythm and synchrony, with only a few exceptions in the field[22]. And Bahkahri, two captive chimpanzees (Pan troglodytes) at St Louis Zoo (Missouri, USA), engaged in coupled bipedalism, one following the other in near contact, to a Conga line in humans (Fig. 1, see Supplemental Material for video links)
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