Musical Rhythm, Linguistic Rhythm, and Human Evolution

This article is called “Musical Rhythm, Linguistic Rhythm, and Human Evolution”. It was written by Aniruddh D. Patel of The Neurosciences Institute
The debate in this study is over the evolutionary status of music – whether evolution has shaped humans to be musical, or whether humans adapt cognitive skills. The journal breaks down music * cognition into four parts as shown here.
Recently, the idea that human minds have been shaped by natural selection for music, first proposed by Darwin, has become widely accepted. There are skeptics, however, who believe music is an “enjoyable mental technology built from preexisting cognitive skills”. The debate can be resolved by determining whether there are fundamental aspects of music cognition which are * innate, that is being born with it, and cannot be explained as being part of cognitive abilities that have been adapted. The author concludes that as of now, there is no reason to reject the idea that * human minds have NOT been specifically shaped by natural selection for music.*
Musical rhythm is similar to speech rhythm, since they both have nice rhythmic organization. They both use pitch movements and durational lengthening, and they both start early in life. Studies have shown that the two use similar brain substrates. This is good evidence that musical rhythm is in fact an offshoot of linguistic rhythm. Musical beats occur in the context of a meter, in which some beats are stronger than others. Interestingly enough, speech is also metrically. based on stress or prominence. This suggests that the tendency to organize rhythmic sequences may originate in language.*
Beat perception and synchronization, or BPS, is a part of rhythm unique to music. It cannot be explained as a byproduct of speech rhythm. The key questions about BPS are about its innateness – its domain specificity, and its human specificity.*
Infants don’t synchronize their movements to a musical beat. This doesn’t mean innateness is false, because infants do not speak. One way to address the innateness of BPS is to look at developmental studies, in order to explore whether the brain seems prepared to acquire this ability. As for now, we don’t have enough information about BPS, including how early one can synchronize to a beat and who can attain this ability. More research is to come…*
One way to study domain-specificity of BPS is to see if brain damage that disrupts it also disrupts other nonmusical cognitive abilities. The neuropsychological literature has descriptions of people with musical rhythmic disturbance after brain damage. It also has findings that rhythmic abilities can be selectively disrupted, leaving pitch processing skills intact. Again… this topic needs more research.*
Animals do not naturally produce music, so if an animal can acquire this ability, it would mean that the ability is not part of an adaptation for music. In all the years of research and animal training, there has not been a single report of an animal being trained to tap, peck, or move in beat. Could an animal learn BPS? If so, this would mean that natural selection is not necessary for BPS.
So there is the question of which animals to study. The obvious answer would be chimps or bonobos, since they are the most closely related to humans. Also, chimps and bonobos have short bouts or rhythmic “drumming” as part of display or play behavior. So we know they are capable of making rhythmic movements on a scale of their own. Despite this, there is still question to whether or not apes are capable of BPS because of brain circuits that are involved in beat perception and motor control. * In humans, rhythms that have a regular beat are associated with the basal ganglia structure in the brain. This structure is also used for motor control and sequencing. But if just this structure were fully in charge of these things, you would expect that chimps, and other species such as rodents, would be capable of BPS. So, because of this, we can conclude that its not just one simple brain function. * This is because BPS involves a special relationship between auditory temporal intervals and patterned movement. This means that somehow or another, human evolution modified the basal ganglia in away that makes for tight coupling between auditory input and motor output.
One way this evolutionary force could have occurred is in vocal learning. This means that you learn to speak or make noise by hearing. This is common to humans, since every child learns to speak by learning. This is only common to a few animals, such as songbirds and parrots. So, humans are unique among primates in having complex vocal learning.
Neurobiological research on birds shows that vocal learning is associated with modifications to the basal ganglia, which is key in auditory input and motor output. So, we can assume that the basal ganglia in humans have also been modified by natural selection for vocal learning.
*So basically, a testable hypothesis would be that…
Having the neural circuitry for complex vocal learning is necessary for the ability to synchronize with an auditory beat. *
This hypothesis pretty much says that if you try to teach nonhuman primates, such as the chimp, to synchronize to a beat, it’s probably not going to work. But, it also says that if it doesn’t work on primates, it would still be premature to conclude that BPS is unique to humans.