In Western cultures, some combinations of musical notes are perceived as pleasant, or consonant, and others as unpleasant, or dissonant. The cover shows superimposed frequency spectra of two musical intervals, one consonant (the perfect fifth) and one dissonant (the tritone). The composite frequency spectrum of the consonant interval forms a subset of the harmonic series (integer multiples of a common fundamental frequency, indicated by the black line segments). By contrast, the frequency spectrum of the dissonant interval is inharmonic. The aesthetic contrast between consonance and dissonance is commonly thought to be biologically determined and thus to be universally present in humans. Josh McDermott and colleagues put this idea to the test by conducting experiments in remote areas of the Bolivian Amazon rainforest, working with the Tsimane�, an indigenous society that has remained relatively isolated from Western culture. They found that the Tsimane� rated consonant and dissonant chords and vocal harmonies as equally pleasant. By contrast, Bolivian city- and town-dwellers preferred consonance, albeit to a lesser degree than US residents. These findings suggest that the preference for consonance over dissonance is not universal, and probably develops from exposure to particular types of polyphonic music.