The Paradox of Isochrony in the Evolution of Human Rhythm

Abstract

Isochrony is crucial to the rhythm of human music. Some neural, behavioral and anatomical traits underlying rhythm perception and production are shared with a broad range of species. These may either have a common evolutionary origin, or have evolved into similar traits under different evolutionary pressures. Other traits underlying rhythm are rare across species, only found in humans and few other animals. Isochrony, or stable periodicity, is common to most human music, but isochronous behaviors are also found in many species. It appears paradoxical that humans are particularly good at producing and perceiving isochronous patterns, although this ability does not conceivably confer any evolutionary advantage to modern humans. This article will attempt to solve this conundrum. To this end, we define the concept of isochrony from the present functional perspective of physiology, cognitive neuroscience, signal processing, and interactive behavior, and review available evidence on isochrony in the signals of humans and other animals. We then attempt to resolve the paradox of isochrony by expanding an evolutionary hypothesis about the function that isochronous behavior may have had in early hominids. Finally, we propose avenues for empirical research to examine this hypothesis and to understand the evolutionary origin of isochrony in general.

Rhythm in speech and animal vocalizations: a cross‐species perspective

“…With respect to measuring vocal rhythms, transition probabilities can be used in the temporal domain (see Ref. ), with the caveat that time is continuous, so some discretization is necessary. For instance, one could calculate the transition probability from short to long call durations and vice versa (Fig.…”

“…(D) A probabilistic finite state machine, which can also generate durational patterns as those seen in A and summarized in the transition matrices in C. Figure reproduced verbatim from Ref. , an Open Access article distributed under the terms of the Creative Commons Attribution License (CC BY).…”

“…Figure reproduced verbatim from Ref. , an Open Access article distributed under the terms of the Creative Commons Attribution License (CC BY).…”

Cultural transmission of melodic and rhythmic universals: 4 experiments and a model

“…We also see a gradual increase in mirrored elements, which suggests that the emerging melodies contain arched contours (a common musical universal). In addition, drumming sequences became more isochronous (Ravignani & Madison, 2017), and composed of few (categorically distributed) alternating inter-beat intervals, related by small integer ratios. Patterns transformed by between-participants transmission show similar properties to those emerging from within-participant transmission (i.e.…”

Beat perception in a non-vocal learner: Rats can identify isochronous beats

“…The origins of rhythm in music and language seem to be intertwined and may share evolutionary pathways (Fitch, 2006(Fitch, , 2013Patel, 2006Patel, , 2010Ravignani and Madison, 2017). The development of song in birds and speech in humans follows similar sensorimotor phases and parallel periods of vocal learning (Marler, 1970(Marler, , 1976, an ability that allows animals to imitate and modify the vocalizations learned from other individuals thanks to specific neural connections (Jarvis, 2006(Jarvis, , 2007.…”