Writing about music has been compared to dancing about architecture, but bear with us.

Santa Maria is a village in western Bolivia without running water or electricity, and so remote that it can be reached only by canoeing up a tributary of the Amazon. It is home to the Tsimane’ people, who detect no difference between consonant and dissonant sounds — the relationships between notes that make, for example, ‘Eleanor Rigby’ by The Beatles sound so sad.


Dissonant chord



Dissonant chords are the unstable isotopes of Western music; they sound tense and want to revert to more stable forms. The way that composers create and resolve this tension usually invokes different moods in the listener. But not in the Tsimane’.


Consonant chord



As researchers describe in a paper this week, when they tested the musical discrimination of the Tsimane’ villagers, the listeners experienced consonant and dissonant intervals as equally pleasant (J. H. McDermottet al.Naturehttp://dx.doi.org/10.1038/nature18635;2016). This is not a deficiency of affect, because the villagers can distinguish cheerful sounds (laughter) from less cheerful ones (gasps). They also recognize physically unpleasant sonic ‘roughness’ — the beating sensation when two tones close in frequency are played at once.

The reason for the villagers’ inability to distinguish what others would call pleasant sounds from unpleasant ones might be, in large measure, one of culture. The Tsimane’ do have music, but it is purely one of melody rather than harmony. They play or sing in single lines, and do not adhere to Western scales. This seems odd to those immersed in the European musical tradition, with its clear differences between pleasant and disagreeable harmonies.

The differences are so clear, in fact, that we are inclined to think of them as innate. The mathematics behind the music seems to back this up. Consonant intervals, such as an octave, perfect fourth or perfect fifth, are integral ratios of harmonics — 2:1, 4:3 and 3:2, respectively. A reliably dissonant interval such as the augmented fourth, or tritone, has an irrational ratio of √2:1. Consonance and dissonance seem to be written into the fabric of the Universe. But the Tsimane’ results show that these structures are a human interpretation, and one that seems to be learned by experience.

The tale of the Tsimane’ should remind us that Western music was not always as richly polyphonic as it is now. In medieval times, music was as melodic as that of the Tsimane’. Chords were unknown, and so were modern musical scales. There were just eight notes, corresponding to the white notes on a keyboard. The earliest keyboard instruments had no black keys, and indeed no such thing as a musical key. Instead, there were ‘modes’, each determined by the unequal spacing of intervals, depending on which note you started from.

The Tsimane’ of Bolivia know nothing of Bernstein, let alone Birtwistle.

But then the Devil arrived, in jumps of three whole tones, in particular between F and B. This was the tritone, so obnoxious that ecclesiastical authorities described it as diabolus in musica (‘the Devil in music’) and banned it. Choristers presented with singing a tritone preferred to flatten the B, making a much more agreeable perfect fourth. Keyboard technology caught up by inserting the first black key, a B flat. The other black keys followed in time, and modal music evolved into the system of keys that we have today, followed rapidly by that most daring of innovations — polyphony.

It is fair to say that the entire edifice of Western music has been built on the tension between consonance and dissonance. The music of Beethoven and Queen’s ‘Bohemian Rhapsody’ take the listener on journeys that make sense only within that framework. Composers Harrison Birtwistle and Pierre Boulez travel routes that redefine the meaning of dissonance and (it must be acknowledged) thrill smaller audiences. Most readers of Nature, we hope, can resonate with the heartache and absolution in the song ‘Maria’ from Leonard Bernstein’s West Side Story, in which Tony sings the name of his inamorata — using a tritone that immediately resolves into a perfect fifth.

The Tsimane’ of Bolivia know nothing of Bernstein, let alone Birtwistle. Even when their traditional tunes were recorded, shifted in pitch and harmonized to make polyphonic arrangements and create consonance and dissonance, the listeners could not tell the difference between the two. One hopes that their patience wasn’t tried too sorely by outsiders playing fast and loose with their heritage (there are those of us who still bear the scars of hearing Bach murdered by The Beach Boys).

But the key finding, the resolution, the crescendo, the cadenza, the Tierce de Picardie — one is tempted to say — is that the Tsimane’ do not find the tritone any more or less pleasant than any other interval. The Devil has not reached that part of Bolivia, it seems, and the tunes of the Tsimane’ might be such as those played in Eden.