Wednesday, May 21, 2014

The Biology of Musical Rhythm

Patel AD (2014) The Evolutionary Biology of Musical Rhythm: Was Darwin Wrong? PLoS Biol 12(3): e1001821. doi:10.1371/journal.pbio.1001821
Abstract: In The Descent of Man, Darwin speculated that our capacity for musical rhythm reflects basic aspects of brain function broadly shared among animals. Although this remains an appealing idea, it is being challenged by modern cross-species research. This research hints that our capacity to synchronize to a beat, i.e., to move in time with a perceived pulse in a manner that is predictive and flexible across a broad range of tempi, may be shared by only a few other species. Is this really the case? If so, it would have important implications for our understanding of the evolution of human musicality.
The last section of the article:
The range of species capable of human-like synchronization to a beat is currently an unsolved mystery. Apart from further research on parrots and nonhuman primates, which other animals should be tested for this ability? In terms of vocal learners, further work is needed to find out whether the capacity to synchronize to a beat is latent in all vocal learners (e.g., including bats), or only in a subset of vocal learners who also have other key traits. Parrots, for example, can imitate nonvocal gestures and are also deeply social creatures who may have a propensity for coordinated movement with social partners [59]. It may be that these other traits are necessary, in addition to vocal learning, to create the capacity for human-like synchronization to a beat [15],[47],[48]. If this is the case, then only vocal learners with these other traits, such as dolphins [60], may be able to synchronize to a beat in a human-like fashion.

In terms of vocal nonlearners, one animal of particular interest is the domestic horse (Equus ferus caballus), a vocal nonlearning animal that (unlike sea lions) has no close vocal-learning relatives. In favor of Darwin's views on musical rhythm, there are anecdotal accounts of horses spontaneously synchronizing their gait to the beat of music, even when they have no rider (who could unintentionally give them cues to the beat). This makes them an ideal test case for Darwin's view, since the vocal learning hypothesis predicts that they lack human-like capacities for synchronizing to a musical beat. Using new methods for testing synchronization to music in horses ([61]–[63], Movie S1), this prediction can now be tested.

Stepping back to a larger view, studies of beat-based processing in other animals are part of a small but growing body of cross-species research on music processing (e.g., [16],[17],[26],[49],[50],[64]–[78]). Such research is in its infancy, but is worth pursuing because it provides an empirical approach to studying the evolutionary history of human musicality. Specifically, it can help identify which aspects of our nonlinguistic auditory processing are broadly shared with other species, which aspects are shared with just a few other species, and which are uniquely human. It is important to note that such work is essentially Darwinian in its approach. That is, even if Darwin was wrong about the widespread nature of musical rhythm processing, the cross-species approach to evolutionary studies that he championed will undoubtedly lead us to a deeper understanding of the biological roots of human music.

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