Play two notes that are three steps away on a musical scale, like C and the F-sharp above it, and you have what’s called the Devil’s Interval. It has long been used to symbolize tension, sinister forces, and outright evil, from Wagner's Gotterdammerung to the music of Black Sabbath to the Simpsons theme song. It’s a great example of dissonance—a sound that seems unpleasant, tense, and jarring. By contrast, consonant notes, like the octave or perfect fifth (C and the G above it) sound pleasant and agreeable, like the notes belong together.

To Western ears, the difference between consonance and dissonance is stark, and we greatly prefer the former to the latter. Since the ancient Greeks, scholars have wondered why. Many musicologists and composers have assumed that the preference is cultural: Western listeners learn to love consonant sounds because of how they are used in Western music.

By contrast, many scientists have suggested that this preference is universal and innate. After all, there’s something special about pairs of consonant notes: their frequencies can be expressed as simple whole-number ratios. In an octave, that ratio is 2:1. In a perfect fifth, it’s 3:2. You can’t express dissonant notes in the same way. “The combinations that sound pleasant to Westerners have this particular mathematical relationship,” Josh McDermott from MIT, who studies hearing and music. “It’s not arbitrary, which is partly why people thought that there had to be a biological basis.”

That’s certainly what McDermott thought when he first started studying music 15 years ago. But he has since changed his mind.

Five years ago, he and his colleagues started working with the Tsimané (pronounced ‘chee-mah-nay’)—an Amazonian society with barely any exposure to Western music. And they, to McDermott’s surprise, don’t care about consonance or dissonance. They can tell the difference between the two kinds of sounds, but they rate both as being equally pleasant.

“This puts the final nail in the coffin of biological accounts of consonance,” says Sandra Trehub from the University of Toronto, who was not involved in the study. “We become progressively attuned to the music of our culture, which makes it seem ‘natural’. Other cultures with different musical systems consider their music equally ‘natural’.”

Until now, studies of consonance and dissonance, like many other areas in psychology, have been restricted to WEIRD people—that is, those from Western, Educated, Industralized, Rich, and Democratic nations. “There’s been very little data from people from other cultures,” says McDermott. So when anthropologist Ricardo Godoy contacted him and offered him a chance to work with the Tsimané, he leapt at the chance.

The Tsimané live in remote villages in the Amazon rainforest, with no electricity or tap water. They have no televisions and limited access to radios, so they only encounter Western culture during their brief forays to nearby towns. Indeed, to get to them, McDermott had to fly to La Paz, Bolivia, drive along dirt roads into the Amazon, and paddle up-river in a canoe.

He worked with 64 Tsimané villagers, asking them to rate the pleasantness of synthetic tones and recorded notes, all played through headphones. When he did the same for US citizens, they preferred consonant chords over dissonant ones. So did city-dwellers from La Paz and residents of a rural Bolivia town, albeit to a weaker extent. But the Tsimané? They didn’t care. A few years later, McDermott’s team repeated the study with a different group of 50 villagers, this time playing them pitch-shifted recordings of their singing peers. Again: no preference.

It’s not that the Tsimané misunderstood the task; they predictably preferred laughter over gasps, just like Western listeners. It’s not that they can’t distinguish between consonant and dissonant intervals, either. They could; they just didn’t prefer one over the other.

There’s other evidence for this in other cultures, albeit not through experiments. Trehub says that scientists have long ignored ethnomusicologists’ descriptions of cultures that make deliberate use of dissonant intervals, like Balinese musicians who seem to intentionally “mistune” their instruments, or Croatian duettists who sing the same melody one semitone apart. “They’ve also ignored Western music history with its changing perspectives on consonance and dissonance,” she adds. “And they’ve celebrated studies that report preferences for consonant sounds in infancy, implying innateness, while ignoring studies that fail to find such preferences.”

But if the Western preference for consonance isn’t rooted in biology, then why do the frequencies of these sounds relate to each other with such clean mathematical precision? “The Greeks were really into ratios,” says McDermott. “All their theories of aesthetics related to ratios. It’s possible they started making music that way and we’ve been stuck with it ever since.”

But Daniel Bowling from the University of Vienna isn’t ready to throw out the biological accounts yet. He notes that while the Tsimané didn’t prefer consonant chords over dissonant ones as a whole, they showed some leanings towards specific intervals like the perfect fifth.

Besides, he argues that framing the debate in terms of nature versus nurture is wrong. The two act together. Although aesthetic tastes vary around the world, they operate under constraints—there are no musical traditions based on high-pitched screeching sounds, for example, because we’re all strongly attracted towards tones. Bowling argues that we also have a weaker attraction to consonant tone combinations, which can be developed through exposure to music where such tones are common. “The claim that the human perception of tonal beauty is free from biological constraint on the basis of a lack of full blown Western consonance preferences in one Amazonian tribe is misleading,” he says.

McDermott concedes that it’s possible people are born with a preference for consonance, that either disappears or doesn’t manifest. “We can’t exclude that,” he says. “But our results show that the presence of that preference relies on being exposed to music that has it.”

This is an old debate, says Diana Deutsch from the University of California, San Diego. In 1631, the French philosopher and mathematician Rene Descartes wrote a letter to Marin Mersenne, the ‘father of acoustics’, saying: “As to what renders [consonances] more agreeable, that depends on the places where they are employed; and there are places where even diminished fifths and other dissonances are more agreeable than consonances, so that one could not determine absolutely that one consonance is more agreeable than another.”

“I believe that Descartes would have been pleased with the present findings,” says Deutsch.

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