Gabriela-Alina Sauciuc

Rhythmic patterning is a widespread structural trait of animal (including human) communication. Concomitantly, a key role of communication functions to convey and induce emotion. The expression and modulation of emotion is also hypothesised to be a key mechanism underlying the evolution of rhythmic synchronisation in humans. Despite the centrality of both rhythm and emotion to human and nonhuman communication, a systematic treatment of the link between them is currently lacking. In this chapter, we bridge these two areas of research by reviewing findings from human and animal studies. These studies how rhythmic properties encode and communicate emotional states and how variations in these properties influence the emotional states of receivers. Taken together, this review of literature demonstrates that the main rhythmic parameter currently evaluated in emotion research is temporal rate (often referred to as frequency rate), which is reliably associated with levels of emotional arousal in all surveyed taxa. We discuss a range of neurobiological mechanisms that could link rhythm and emotion. We also identify several avenues for future research that address current limitations, such as the overwhelming focus on the acoustic modality and frequency rate, while other communication modalities and rhythmic feature remain understudied.

In this concluding chapter, we focus on outlining the next frontier in research on rhythm cognition and rhythmic communication (RCC), synthesising conceptual, methodological, comparative, and applied directions, as they emerge from the contributions to the Nature Beats volume . While consensus has grown regarding the composite nature of rhythmic competence and the need for integrated quantitative approaches, the field remains marked by conceptual heterogeneity and inconsistent operational criteria. To advance RCC research, the chapter identifies pressing needs for conceptual clarity, methodological standardisation, and ecologically grounded definitions of rhythmic phenomena across modalities and species. We also highlight future research trajectories for major theoretical frameworks, including the Vocal Learning–Beat Perception and Synchronisation hypothesis, Gradual Audiomotor Evolution hypothesis, Neural Resonance Theory, socio-ecological hypotheses of synchrony, and evolutionary accounts linking rhythm to social bonding and stress regulation. A bottom-up, species-specific, and comparative approach is advocated to capture the full structural and functional diversity of RCC and to evaluate mechanisms spanning neural oscillations and functional connectivity, biomechanics, development, reward systems, and environmental constraints. Finally, the chapter emphasises the translational value of RCC research. Rhythm-based interventions hold promise for educational, clinical, welfare, conservation, and human-animal interaction contexts. By integrating mechanistic, evolutionary, and applied perspectives, future research can uncover the biological principles underlying rhythmic behaviour and its central role in communication, cognition, and sociality across the animal kingdom.

Historically, rhythmic capacities in animals have been systematically studied in few taxa, like fireflies and crickets, while other behaviours have been considered rhythmic but lack de facto rigorous analysis, such as chimpanzee “rain dance”. Emerging fields like animal rhythm often suffer from data scarcity, leading to premature theories that overemphasize limited data and confuse the absence of evidence with evidence of absence. Species are assumed to have negligible or no rhythmic capacities when in fact they have only received negligible or no empirical effort. To understand rhythm behaviour and its evolution across lineages and under different conditions (including along the human lineage), it is therefore crucial that rhythm is comprehensively described, characterized, and analysed across the widest taxonomic span possible. It is necessary to proactively seek out new, unnoticed and overlooked animal rhythms. This chapter presents a list of everyday animal behaviours that offer intriguing and promising opportunities to study rhythm and synchronization across taxa. Our aim is to invite and guide renewed efforts towards new insights about rhythm and its evolution in the animal world.

Humans and animals communicate with rhythmic behaviours that vary greatly in terms of temporal parameters and patterns. In this chapter, we discuss the neuromuscular architecture underlying rhythmic behaviours and address factors that constrain their rhythmic properties. In Part I of the chapter, we provide background regarding the building blocks of rhythmic communication from the muscles to the brain and then illustrate how these building blocks are coordinated within a single system (e.g., locomotor appendage apparatus, vocal articulatory apparatus, etc.) and across relevant systems (locomotor, respiratory, and vocal). In Part II, we illustrate how variations in anatomical design and physiological function constrain rhythmic production, in particular properties such as temporal rate, stability, versatility, and pattern complexity. We also provide examples of putative mechanisms that influence rhythm perception across species. By reviewing and discussing these aspects of the neuroethology of rhythmic communication, we hope to infuse current mechanistic theorizing on the evolution of rhythmic competence(s) with novel insights from research that, historically, has had less weight in this area of study. We also hope that the design of future experimental studies aimed at testing evolutionary hypotheses will benefit from increased awareness of how variations in aspects of muscular and vocal tract design, along with “low-level” neural mechanisms, shape rhythmic communication.

Across human cultures, rhythmic movement appears to be consistently associated with the induction of altered states of consciousness (ASCs), yet research on the topic remains scarce. In this chapter, we examine the potential role of rhythmic movement in ASC induction and its significance for understanding the evolution of dance and music. We discuss the cross-cultural spread of the association between rhythmic movement (e.g. dancing, chanting, breathwork, etc.) and various categories of ASCs and outline four major classes of neurobiological mechanisms that may underlie this association. First, rhythmic movement can accelerate or decelerate breathing and, thus, modulate autonomic activity towards sympathetic or parasympathetic dominance. Second, these can be psychologically amplified through expectation and fear priming. Third, rhythmic practices can induce vestibular perturbations that distort proprioception and multisensory integration. Fourth, through neural entrainment and neural resonance, rhythmic movement can affect brain oscillatory dynamics, as well as the strength and nature of functional connectivity. Building on these mechanistic considerations, we also review emerging comparative evidence that rhythmic movement may induce altered proprioception, arousal and social attunement in the nonhuman great apes, paralleling some of the ASC features reported in humans. We discuss rhythmic stereotypies (e.g. rocking, pacing) as potential analogues of rhythm-based ASC inductors, with implications for understanding the neural circuits involved. Socially synchronised rhythmic behaviours in apes further suggest evolutionary roots for collective ASC practices. These findings underscore potentially deep phylogenetic origins of rhythm-induced state changes and call for integrative research bridging neurobiology, comparative psychology and evolutionary theory to elucidate the role of rhythm in shaping minds across species.

Rhythmicity is a composite competence that spans perceptual, motor, and socio-cognitive abilities. This is highly salient when adopting a developmental perspective, as we do in this chapter, which reviews data from humans and other singing primate taxa with a close (gibbons) or remote (indri lemurs) phylogenetic relatedness to our species. The findings we review show that rhythmicity develops as an interplay between innate maturational processes and socio-ecological influences, and that its underlying mechanisms have distinct developmental trajectories. Generally, however, perceptual skills emerge earlier than motor ones, and rhythmic proficiency improves as (possibly innate) motor rhythms are brought under increased cognitive control. We surmise that developmental primate data are essential for understanding the underlying mechanisms and adaptive benefits of human rhythmic competence and the human-definitory forms of communication and cooperation that it enables. As this kind of data is exceedingly scarce, a substantial task of future research will be to reduce this gap. We also identify substantial gaps in the developmental research with human children, including the need to go beyond auditory rhythms and investigate rhythms broadcasted in other modalities, to increase the cross-cultural representativeness of the samples, and to examine longitudinally the relationships between elements of the rhythmic composite.

The significance of the great ape heritage to the evolution of human rhythmic competence—as manifested in speech, music and dance—has been greatly underestimated in both past and contemporary research. In this chapter, we deconstruct received misconceptions about the rhythmic competence of the apes and defend the position that, contrary to the received view, the great apes likely constitute the most important model species for research on the evolution of human rhythmicity as manifested in speech, dance and music. To this end, we review data on a range of relevant aspects of great ape behaviour and cognition, including evidence of tool-assisted sound production, the production of rhythmic body movements (including rhythmic engagement and rhythmic synchronisation) and rhythmic vocalisations. We also discuss two cognitive mechanisms—relational processing and shared intentionality—that have been theorised to underlie rhythm perception and sensorimotor synchronisation in humans. For each of these behavioural and cognitive aspects, we discuss their relevance to the evolution of human speech, music and dance and highlight new avenues for future research. Understanding the evolution of these human communicative rhythms and disentangling classical evolutionary conundrums regarding the speech–music and the dance–music relationship hinge on understanding their genesis in the precursor traits of the Hominid family.

Animals communicate with a staggering diversity of rhythmic signals, yet behind all this diversity lies a small number of ethological mechanisms. In this chapter, we provide a brief review of how animals produce rhythmic signals based on these mechanisms, which span tremulation, percussion, bodily displays, stridulation, tymbalation, aerodynamic sound production (including vocalization), as well as the production of luminescent, chromogenic, and electric rhythms. We point out that these ethological mechanisms which underlie the production of communicative rhythms appear to be derived from rhythmic ‘praxic’ behaviors that initially evolved to implement vital functions such as breathing, feeding, locomotion, defense, or procreation. Based on the findings reviewed by the chapter, we identify three important areas for future research for advancing our understanding of the evolution of rhythmic communication. First, there is a massive research gap when it comes to quantifying how rhythmic signals unfold and interact across perceptual and behavioral modalities. Second, there is a need to understand how behavioral rhythms relate to—and are constrained by—their underlying neuromuscular substrates. Third, very little is known about the relationship between communicative rhythms and the praxic behaviors in which they putatively originated.

Research on the rhythmic communication (RC) of nonhuman animals is undergoing a period of great effervescence and expansion. Here, we synthesize this rapidly growing literature with the aim of mapping RC forms and usage contexts in an unprecedented diversity of taxa, spanning insects, fish, frogs, birds and mammals. We see this as a first large-scale effort toward charting the functional and structural traits of RC to identify taxon-specific and shared motifs and, thus, evolutionary trends. Our synthesis shows that all the covered taxa use RC in reproductive contexts and suggest that RC undergoes an increasing functional complexification as a function of sociocognitive complexification. By contrast, structural complexity fluctuates less at cross-taxonomic level, such that, at the production level, within each studied class or order, some species exhibit highly complex RC forms and rhythmic coordination, while others exhibit the simplest forms of RC. However, based on the current data, it remains unclear if species with complex RC structures also possess sophisticated RC perception. This chapter also reveals considerable theoretical and methodological heterogeneity in the study of animal RC and the need for cross-talks between taxon-specialized researchers toward harmonising key terms, concepts and measures to improve data comparability.

Animals communicate with a staggering diversity of rhythmic signals, yet behind all this diversity lies a small number of ethological mechanisms. In this chapter, we provide a quick review of how animal produce rhythmic signals based on these mechanisms, which span tremulation, percussion, bodily displays, stridulation, tymbalation, aerodynamic sound production (including vocalisation), as well as the production of luminescent, chromogenic and electric rhythms. We point out that these ethological mechanisms which underlie the production of communicative rhythms appear to be derived from rhythmic praxic behaviours that initially evolved to implement vital functions such as breathing, feeding, locomotion, defense or procreation. Based on the findings reviewed by the chapter, we identify three important areas for future research for advancing our understanding of the evolution of rhythmic communication. First, there is a massive research gap when it comes to quantifying how rhythmic signals unfold and interact across perceptual and behavioural modalities. Second, there is a need to understand how behavioural rhythms relate to — and are constrained by — their underlying neuromuscular substrates. Third, very little is known about the relationship between communicative rhythms and the praxic behaviours in which they putatively originated.