In 2015, the MIT scientist loaded a laptop, headphones, and a gasoline generator into a canoe and pushed off from the Amazonian town of San Borja, some 50 kilometers downriver from Santa María. Together with collaborator Ricardo Godoy, an anthropologist at Brandeis University, McDermott planned to carry out experiments to test whether the Tsimane' could discern certain combinations of musical tones, and whether they preferred some over others. The pair wanted to address a long-standing question in music research: Are the features of musical perception seen across cultures innate, or do similarities in preferences observed around the world mirror the spread of Western culture and its (much-better-studied) music?
"Particular musical intervals are used in Western music and in other cultures," McDermott says. "They don't appear to be random—some are used more commonly than others. The question is: What's the explanation for that?"
Ethnomusicologists and composers have tended to favor the idea that these musical tendencies are entirely the product of culture. But in recent years, scientific interest in the evolutionary basis for humans' musicality—our capacity to process and produce music—has been on the rise. With it has come growing enthusiasm for the idea that our preference for consonant intervals—tonal combinations considered pleasant to Western ears, such as a perfect fifth or a major third—over less pleasant-sounding, dissonant ones is hardwired into our biology. As people with minimal exposure to Western influence, the Tsimane' offered a novel opportunity to explore these ideas.
Making use of the basic auditory equipment they'd brought by canoe, McDermott and his colleagues carried out a series of tests to investigate how members of this community responded to various sounds and musical patterns. The team found that although the Tsimane' could distinguish consonance from dissonance, they apparently had no preference for one over the other. McDermott interprets the results as evidence against a strong biological basis for preference.1 "If these properties are absent in some cultures, they can't be strictly determined by something in the biology—on the assumption that the biology in these people is the same as it is in us," he says.
But the authors' publication of their results proved controversial. While some took the findings to imply that culture, not biology, is responsible for people's musical preferences, others argued that the dichotomy was a false one. Just because there's variation in perception, it doesn't mean there's no biological basis, says Tecumseh Fitch, an evolutionary biologist and cognitive scientist at the University of Vienna. "Almost everything has a biological basis and an environmental and cultural dimension," he says. "The idea that those are in conflict with one another, this 'nature versus nurture,' is just one of the most consistently unhelpful ideas in biology."
Identifying the biological and cultural influences on humans' musicality is one of various thorny issues that researchers working on the cognitive science of music are currently tackling. The field has exploded in recent years, and while many answers have yet to materialize, "the questions have been clarified," says Fitch, who was one of more than 20 authors contributing to a special issue of Philosophical Transactions B on the subject in 2015. For example, "rather than talking about the evolution of music, we're talking now about the evolution of musicality—a general trait of our species. That avoids a lot of confusion."
Researchers are beginning to break this trait into various components such as pitch processing and beat synchronization (see Glossary); addressing the function and evolution of each of these tasks could inform the broader question of where humans' musicality came from. But as illustrated by the discussions following McDermott's recent publication, it's clear just how much remains mysterious about the biological origins of this trait. So for now, the debates continue.
A mind for music?
Musical faculties don't fossilize, so there's little direct evidence of our musical past (see Time Signatures). But researchers may find clues in the much older study of another complex cognitive trait: speech perception. "Music and language are both sound ordered in time; they both have hierarchical structure; they're in all cultures; and they're very complex human activities," says Fred Lerdahl, a composer and music theorist at Columbia University. "A lot of people, including me, think that music and language have, in some respects, a common origin."
Numerous lines of evidence have supported this view. For example, Tufts University psychologist Ani Patel and colleagues showed a few years ago that patients with congenital amusia, a neurodevelopmental disorder of musical perception commonly known as tone deafness, also had difficulty perceiving intonation in speech.2 (See "Caterwauling for Science.") And fMRI scans of normally hearing volunteers listening to recordings have revealed that large areas of the brain's temporal lobes—regions involved in auditory processing—show heightened activation in response to both music and speech, compared with nonvocal sounds or silence.3 For many, these findings hint at the possibility of common neural circuitry for the processing of speech and music.
But other research points to dissociated processing for at least some components of music and language, suggesting that certain parts of the brain specialized in musicality during our evolution. Lesion studies, for example, show that brain damage can disrupt the processing of pitch in music without disrupting pitch processing in speech.4 And multivariate neuroimaging analyses with higher sensitivity than traditional methods indicate that, despite stimulating overlapping regions of the cortex, recordings of music and speech activate different neural networks.5 "People may take localization of activity as evidence for sharing," notes Isabelle Peretz, a neuropsychologist at the University of Montreal. But given the low resolution of most current methods, "that's nonsense, of course."
McDermott's lab recently reported more extreme dissociation. Using a novel approach to analyze fMRI data from people listening to more than 150 recordings of speech, music, nonverbal vocalizations, or nonvocal sounds, the team identified anatomically distinct pathways in the auditory cortex for speech and for music, along with other regions of the brain that responded selectively to each.6 "We find that they're largely anatomically segregated," McDermott says. "Speech selectivity seems to be located primarily lateral to primary auditory cortex, while music [selectivity] is localized mostly anterior to it."
The neural processing mechanisms themselves remain elusive, but studies like McDermott's "clearly demonstrate that you can separate the representations for speech and music," says Peretz. All the same, she notes, with current research continuing to present evidence both for and against a shared neural basis for music and speech perception, "the debate is still on."
Further clues about musicality's genetic basis could come from the study of amusia. In 2007, Peretz and colleagues reported that congenital amusia runs in families.8 And recent descriptions of high amusia incidence in patients with genetic diseases such as Williams-Beuren syndrome, a condition associated with deletion of up to 28 genes on chromosome 7, may lead researchers to additional musicality-linked genes.9 "We are making progress along these lines, but there's a lot more to be done," says Peretz. "It's really hard to do, and more expensive than neuroimaging. So we have to be patient." But it's progress worth waiting for, she adds, as an understanding of the genetics contributing to particular musical—or amusical—phenotypes could offer an entirely new perspective on the biological basis for musicality.
Meanwhile, some researchers advocate looking to related species to answer questions about the origins of human musicality. Although nonhuman primates share our ability to distinguish between consonance and dissonance, many apes and monkeys have surprisingly different auditory processing. "Things that are fundamental to music that people thought would be ancient, general aspects of how animals process sound turn out not to be, and potentially reflect specialization in our brains," says Patel. For example, the ability to synchronize movement to a beat, a capacity central to music, "doesn't come naturally to our closest living relatives," says Patel, though he adds that "it does come quite naturally to some other species," including parrots, seals, and elephants. (See "John Iversen: Brain Beats.")
Similarly, vocal learning—potentially a requirement for musicality—is known to be prevalent in several taxa, including some species of songbirds, parrots, whales, seals, bats, and elephants, but it is not well documented in any primate other than humans. (See "Singing in the Brain.") "It raises the question of why," Patel says. "What basic features of music perception are shared with other species, and what does that tell us about the evolution of those features?"
Why music?
As researchers continue to probe how humans have evolved to process music, many scientists, and the public, have been increasingly drawn to another question concerning musicality's origins: Why did it evolve at all? For some, music's universality in humans, combined with its fundamental social and cultural roles, is persuasive evidence that our musicality is adaptive. "Music is so common in all societies," says Helsinki's Järvelä. "There must be favorable alleles; it must be beneficial to humans."
But just what this benefit might be, and whether it did indeed influence our evolution, have been the objects of what Patel calls "one of the oldest debates in the book." In the late 1990s, cognitive psychologist Steven Pinker famously dubbed music "auditory cheesecake"—pleasant, but hardly essential—and argued that musicality was nothing more than a by-product of neural circuitry evolved to process language and other auditory inputs. It's become the argument to beat for researchers looking for ultimate explanations of musicality's evolution in humans, Fitch says. "Everybody seems to want to prove that Pinker's cheesecake argument is wrong," he notes. "But it's just the null hypothesis."
One adaptationist viewpoint, that traces its roots to Darwin, is that human musicality, like birdsong, is a sexually selected trait—albeit an unusual one, prevalent as it is in both sexes. Musicality is a reliable and visible indicator of cognitive ability, the argument goes, and so informs a potential mate of an individual's genetic quality. Some researchers have tried to generate testable predictions from this idea, but so far there's been little evidence in its favor. One recent study went as far as assessing the self-reported sexual success—based on indicators including the number of sex partners and age at first intercourse—of more than 10,000 pairs of Swedish twins.10 The researchers found no association between musical ability and sexual success, but cautioned against being quick to draw conclusions about the sexual relationships of our evolutionary ancestors from modern society.
Other hypotheses arise from research on music's far more complex and still poorly understood effects on human emotion and social bonding. University of Toronto psychologist Sandra Trehub notes, for example, that babies and young children are particularly sensitive to musical communication, and that singing comes naturally to adults interacting with them. "Caregivers around the world sing to infants," she says. "It's not a Western phenomenon, nor a class-based phenomenon. It seems to be important for caregiving everywhere."
She and her colleagues recently showed that recordings of singing, more so than speech, could delay the time it took for an infant to become distressed when unable to see another person.11 And in 2014, research led by Laurel Trainor at McMaster University found that when babies just over a year old were bounced to music, they became more helpful towards a researcher standing opposite them who had been bopping along in rhythm (handing back "accidentally" dropped objects) than to people who had been bouncing asynchronously.12
These and related findings have led some to propose that parent-infant bonding, or? social cohesion in general, provided a selective pressure that favored the evolution of musicality in early humans, though Trehub herself says she does not subscribe to this rather speculative view. "I have no difficulty imagining a time when music-like things would have been very important in communicating global notions and managing interpersonal relationships," she says. "But it's pretty hard, based on anything we look at now, to relate it to conditions in ancient times and the functions it would have served."
Indeed, the inherent challenge of studying ancient hominin behavior, combined with the complexity of the trait itself, makes explanations for musicality's evolution particularly vulnerable to "just-so" stories, says Trainor. "When you look at the effect that music has on people, it's easy to think it must have been an evolutionary adaption. Of course, it's very difficult, if not impossible, to prove that something is an evolutionary adaption."
This intractability has led some researchers to view adaptation-based lines of inquiry into human musicality as something of a distraction. "I don't think it's a particularly useful question at all," says Fitch. "It's an unhealthy preoccupation, given how little we know." Others have argued for a subtler view of musicality's evolution that avoids the search for simple answers. "The evolutionary process isn't a one-shot thing," says Trainor. "It has many nuanced stages."
Her work, for example, addresses how aspects of auditory scene analysis—the process by which animals locate the source of sounds in space—could have led to features currently viewed as critical for musicality in modern humans. But that doesn't mean that music didn't provide its own benefits once it arose. "I think parts of the long road to our becoming musical beings were driven by evolutionary pressures [for music itself]," says Trainor, "and other parts of it were driven by evolutionary pressures for things other than music that music now uses."
But most researchers agree that understanding our musical evolution will require studying musicality in more-focused and biologically relevant ways. For example, instead of asking why musicality evolved, Fitch suggests researchers investigate why humans evolved to synchronize their movements to a beat. This approach "is what's really important," says Patel. "We've had hundreds of years of speculation. Now, I think, the real advances are being made by thinking about the individual components of music cognition and looking at them in an evolutionary framework."
References
- J.H. McDermott et al., "Indifference to dissonance in native Amazonians reveals cultural variation in music perception," Nature, 535:547-50, 2016.
- F. Liu et al., "Intonation processing in congenital amusia: Discrimination, identification and imitation," Brain, 133:1682-93, 2010.
- I. Peretz et al., "Neural overlap in processing music and speech," Philos Trans R Soc B, doi:10.1098/rstb.2014.0090, 2015.
- I. Peretz et al., "Functional dissociations following bilateral lesions of auditory cortex," Brain, 117: 1283 - 1301, 1994.
- C. Rogalsky et al., "Functional anatomy of language and music perception: Temporal and structural factors investigated using functional magnetic resonance imaging," J Neurosci, 31:3843-52, 2011.
- S. Norman-Haignere et al., "Distinct cortical pathways for music and speech revealed by hypothesis-free voxel decomposition," Neuron, 88:1281-96, 2015.
- X. Liu et al., "Detecting signatures of positive selection associated with musical aptitude in the human genome," Sci Rep, 6:21198, 2016.
- I. Peretz et al., "The genetics of congenital amusia (tone deafness): A family-aggregation study," Am J Hum Genet, 81:582-88, 2007.
- M.D. Lense et al., "(A)musicality in Williams syndrome: Examining relationships among auditory perception, musical skill, and emotional responsiveness to music," Front Psychol, 4:525, 2013.
- M.A. Mosling et al., "Did sexual selection shape human music? Testing predictions from the sexual selection hypothesis of music evolution using a large genetically informative sample of over 10,000 twins," Evol Hum Behav, 36:359-66, 2015.
- M. Corbeil et al., "Singing delays the onset of infant distress," Infancy, 21:373-91, 2015.
- L.K. Cirelli et al., "Interpersonal synchrony increases prosocial behavior in infants," Dev Sci, 17:1003-11, 201
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