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Researchers have long been puzzled by the fact that non-human primates don't seem to enjoy music. They almost always prefer silence to pieces by Mozart or other composers, past studies have found. However, a psychologist and a cellist have now created music that monkeys can groove to, according to a paper recently published online in Biology Letters.

Charles Snowdon, PhD, of the University of Wisconsin, Madison, sent University of Maryland cellist David Teie a variety of calls made by cotton-top tamarins: Quick dissonant bursts of sound made by agitated monkeys, and slower vocalizations that rise in pitch as they get quieter, made by relaxed monkeys—all about three octaves higher and twice as fast as human speech.

Teie then composed a few short pieces that pulled out the musical elements of monkey calls. In two pieces, he played very high, consonant, whistle-like notes set to a slow beat, mimicking the relaxed monkey calls. In two others, he played short, high-pitched, clashing notes against a fast beat, based on the animals' threat and alarm calls.

When Snowdon played Teie's relaxing music for the monkeys, they were more social and foraged for food. When he played the exciting music, they showed increased movement and anxious activity, shaking their heads and scent-marking.

However, when Snowdon played music that humans find relaxing, including Barber's "Adagio for Strings" and "The Fragile," by Nine Inch Nails, the animals' behavior did not change. And when he played music that humans find arousing, including "Of Wolf and Man" by Metallica and "The Grudge" by Tool, the animals, oddly, became more relaxed, though their responses weren't as strong as they were for the mellow monkey music.

The results suggest that music may have deep evolutionary roots, and that dissonance, tempo and pitch contour are among the elements that form the basis for this primitive language. However, different species interpret these musical building blocks in their own ways, says Snowdon.

"The emotional part of music may have very early origins and occur well before humans came on the scene," he says.

—S. Dingfelder