BioEd Online

Is appreciation of music a uniquely human trait, or does any animal with decent hearing prefer pleasant combinations of notes? Cognitive scientists have discovered that tamarin monkeys have no taste for the consonant tones that mostly make up music, suggesting that musicality may be restricted to humans alone.

Consonant tones are combinations of sound waves whose wavelengths are simple multiples of each other. The sounds overlap to create a smooth waveform that is pleasing to our ears. But dissonant sounds are produced when the wavelengths are very slightly different, so the two waves come in and out of phase, creating an unpleasant, jarring noise.

For years, scientists have sought to explain why we prefer consonant sounds to dissonant ones. One theory is that our dislike of dissonance is related to the sensation of 'beats' that occur when the notes interfere.

Previous research has shown that macaque monkeys and songbirds can tell the difference between consonant and dissonant sounds¹. But the question of whether or not animals actually prefer consonant tones has been unanswered, until now.

Turn it up

Josh McDermott of the Massachusetts Institute of Technology and Marc Hauser of Harvard University, both in Cambridge, Massachusetts, conducted a series of musical experiments on cotton-top tamarins, a species of squirrel-sized primates.

The researchers put the tamarins into a chamber shaped in a horizontal V. They played different types of sounds in either end of the chamber, and judged which the monkeys preferred based on the amount of time they spent on each side.

McDermott and Hauser tested their set-up by running two preliminary experiments. In the first, opposite sides of the chamber played soft and loud white noise (static). The second test contrasted feeding chirps and tamarin distress calls. The cotton-top tamarins clearly favoured the softer white noise and feeding chirps, as one would expect.

Next, the scientists tested whether the monkeys found consonant sounds more agreeable than clashing notes. But the animals spent equal amounts of time on the both sides of the chamber. In contrast, the humans tested by McDermott and Hauser showed a distinct liking for consonant sounds. The results of their study are reported online in Cognition².

"This is the first time that a lack of preference for consonance has been shown in primates," says Isabelle Peretz, a psychologist from the University of Montreal, Canada, who studies music perception.

Fine tuning

McDermott cautions that more closely related primates, such as chimpanzees, might still share some sort of musical appreciation with people. But he speculates that rather than being a result of the mammalian auditory system, our enjoyment of consonant, musical tones derives from specifically human properties of our brains.

"I would place my bets on the fact that it's uniquely human," he says.

"If you want to look at the evolution of music it's important to do these types of studies," says Laurel Trainor, a neuroscientist at McMaster University in Hamilton, Canada. She adds that this research supports the idea that humans have a special preference for consonance, one of the most basic structural elements of music. This could account for the fact that as far as we know, only humans produce songs simply for enjoyment, she says.