It was recently shown that rhythmic entrainment, long considered a
human-specific mechanism, can be demonstrated in a selected group of
bird species, and, somewhat surprisingly, not in more closely related
species such as nonhuman primates. This observation supports the vocal learning hypothesis
that suggests rhythmic entrainment to be a by-product of the vocal
learning mechanisms that are shared by several bird and mammal species,
including humans, but that are only weakly developed, or missing
entirely, in nonhuman primates. To test this hypothesis we measured
auditory event-related potentials (ERPs) in two rhesus monkeys (Macaca mulatta),
probing a well-documented component in humans, the mismatch negativity
(MMN) to study rhythmic expectation. We demonstrate for the first time
in rhesus monkeys that, in response to infrequent deviants in pitch that
were presented in a continuous sound stream using an oddball paradigm, a
comparable ERP component can be detected with negative deflections in
early latencies (Experiment 1). Subsequently we tested whether rhesus
monkeys can detect gaps (omissions at random positions in the sound
stream; Experiment 2) and, using more complex stimuli, also the beat
(omissions at the first position of a musical unit, i.e. the ‘downbeat’;
Experiment 3). In contrast to what has been shown in human adults and
newborns (using identical stimuli and experimental paradigm), the
results suggest that rhesus monkeys are not able to detect the beat in
music. These findings are in support of the hypothesis that beat induction
(the cognitive mechanism that supports the perception of a regular
pulse from a varying rhythm) is species-specific and absent in nonhuman
primates. In addition, the findings support the auditory timing dissociation hypothesis,
with rhesus monkeys being sensitive to rhythmic grouping (detecting the
start of a rhythmic group), but not to the induced beat (detecting a
regularity from a varying rhythm).
Is it music what makes us humans?
Alright, the title is a blunt cliché admittedly. But that is what a new study on rhesus monkeys has found: that our intelligent cousins from India cannot discern the beat, the regularity that makes up a rhythm. Human babies can instead and so is the case of some birds.
Henkjang Honing et al., Rhesus Monkeys (Macaca mulatta) Detect Rhythmic Groups in Music, but Not the Beat. PLoS ONE 2012. Open access → LINK [doi:10.1371/journal.pone.0051369]
Sadly for the enthusiasts of “complex modern behavior”, who’d love to draw an absolutist line between before and after of being humans, music leaves no or almost no remains, so their line, even if it might exist in blurry or whatever other state, cannot be identified in the archaeological record.