Behavioral and brain rhythms in the millisecond-to-second range are central in human music, speech, and movement. A comparative approach can further our understanding of the evolution of rhythm processing by identifying behavioral and neural similarities and differences across cognitive domains and across animal species. We provide an overview of research into rhythm cognition in music, speech, and animal communication. Rhythm has received considerable attention within each individual field, but to date, little integration. This review article on rhythm processing incorporates and extends existing ideas on temporal processing in speech and music and offers suggestions about the neural, biological, and evolutionary bases of human abilities in these domains.Commonalities Underlying Rhythm in Music, Speech, and Animal Communication?Across all cultures in the world, humans synchronize to and move with musical rhythms. Similarly, we seem to neurally synchronize with rhythm in speech, which captures our attention, regularizes speech flow, may emphasize meaning, and facilitates interaction with others [1]. However, compared to music, rhythm in speech is more difficult to define and commonalities across the two domains remain elusive. Discrepancies between these domains begin with the fact that, while rhythmic behavior is often based on quasi-periodic repetition of steady intervals, for musicologists and linguists alike a simple periodicity-based definition is incomplete. One conceptual obstacle arises from conceiving human rhythmic behavior as a single monolithic entity rather than a multi-component phenomenon [2,3]. Clearly defining and empirically differentiating sub-components of rhythmic phenomena across domains (our first comparative task) will allow researchers to specify similarities and differences. We can then attempt to integrate insights from comparative animal work to help resolve the biological and evolutionary foundations of human rhythm cognition (our second comparative task). HighlightsMusical rhythm constitutes the sum of multiple constituent behavioral and neural features.A comparative multi-component view on rhythm in music, speech, and animal communication reveals similarities and differences and may be key to understanding rhythm evolution.Rhythm production and perception may be anchored in social synchronization across domains and species.A wider comparative perspective, which incorporates insights from not only primates and birds but also cetaceans, pinnipeds, amphibians, and insects, can inform our understanding of rhythm evolution.

A central goal of biomusicology is to understand the biological basis of human musicality. One approach to this problem has been to compare core components of human musicality (relative pitch perception, entrainment, etc.) with similar capacities in other animal species. Here we extend and clarify this comparative approach with respect to rhythm. First, whereas most comparisons between human music and animal acoustic behavior have focused on spectral properties (melody and harmony), we argue for the central importance of temporal properties, and propose that this domain is ripe for further comparative research. Second, whereas most rhythm research in non-human animals has examined animal timing in isolation, we consider how chorusing dynamics can shape individual timing, as in human music and dance, arguing that group behavior is key to understanding the adaptive functions of rhythm. To illustrate the interdependence between individual and chorusing dynamics, we present a computational model of chorusing agents relating individual call timing with synchronous group behavior. Third, we distinguish and clarify mechanistic and functional explanations of rhythmic phenomena, often conflated in the literature, arguing that this distinction is key for understanding the evolution of musicality. Fourth, we expand biomusicological discussions beyond the species typically considered, providing an overview of chorusing and rhythmic behavior across a broad range of taxa (orthopterans, fireflies, frogs, birds, and primates). Finally, we propose an “Evolving Signal Timing” hypothesis, suggesting that similarities between timing abilities in biological species will be based on comparable chorusing behaviors. We conclude that the comparative study of chorusing species can provide important insights into the adaptive function(s) of rhythmic behavior in our “proto-musical” primate ancestors, and thus inform our understanding of the biology and evolution of rhythm in human music and language.

Music exhibits some cross-cultural similarities, despite its variety across the world. Evidence from a broad range of human cultures suggests the existence of musical universals 1 , here defined as strong regularities emerging across cultures above chance. In particular, humans demonstrate a general proclivity for rhythm 2 , although little is known about why music is particularly rhythmic and why the same structural regularities are present in rhythms around the world. We empirically investigate the mechanisms underlying musical universals for rhythm, showing how music can evolve culturally from randomness. Human participants were asked to imitate sets of randomly generated drumming sequences and their imitation attempts became the training set for the next participants in independent transmission chains. By perceiving and imitating drumming sequences from each other, participants turned initially random sequences into rhythmically structured patterns. Drumming patterns developed into rhythms that are more structured, easier to learn, distinctive for each experimental cultural tradition and characterized by all six statistical universals found among world music 1 ; the patterns appear to be adapted to human learning, memory and cognition. We conclude that musical rhythm partially arises from the influence of human cognitive and biological biases on the process of cultural evolution 3. Percussion instruments may have provided the first form of musical expression in human evolution. Great apes, our closest living relatives, show drumming behaviour 4 , which they can learn socially 5 , producing some human-like rhythmic sequences 6. Percussive behaviour may therefore have already been present in our ancestors some million years ago, before the split between the human and Pan lineages 2. Archaeological findings also suggest that the first human musical instrument might have been percussive, as also attested in modern hunter-gatherer societies around the world 7. This makes rhythm a particularly apt musical dimension for reconstructing crucial steps in the evolution of music. Six rhythmic features can be considered human universals, showing a greater than chance frequency overall and appearing in all geographic regions of the world. These statistical universals 1 are:

Sensitivity to dependencies (correspondences between distant items) in sensory stimuli plays a crucial role in human music and language. Here, we show that squirrel monkeys (Saimiri sciureus) can detect abstract, non-adjacent dependencies in auditory stimuli. Monkeys discriminated between tone sequences containing a dependency and those lacking it, and generalized to previously unheard pitch classes and novel dependency distances. This constitutes the first pattern learning study where artificial stimuli were designed with the species' communication system in mind. These results suggest that the ability to recognize dependencies represents a capability that had already evolved in humans’ last common ancestor with squirrel monkeys, and perhaps before.