If you matched a Swiss singer against a monkey vocalist in a yodeling contest, the non-human primate would win handily, according to a study published in the journal Philosophical Transactions of the Royal Society.

It turns out apes and monkeys possess vocal membranes in their throats that humans lack. Scientists suspect these structures slowly disappeared through evolution to allow for more stable speech. So what evolutionary advantages do these throat structures provide monkeys and apes? How do these membranes work? And why do monkeys need them?

Yodeling, by definition, requires rapid back-and-forth shifts in pitch — between a low note from the chest and a high one from the throat. The study explains what gives monkeys the competitive edge.

How Monkeys Can Yodel

A team of researchers first recorded the calls of several primate species at La Senda Verde Wildlife Sanctuary in Bolivia. The recorded primates included the black and gold howler monkey (Alouatta caraya), tufted capuchin (Sapajus apella), black-capped squirrel monkey (Saimiri boliviensis), and Peruvian spider monkey (Ateles chamek).

Next, they used software to visualize and analyze the calls’ frequencies. They also performed CT scans on some primates to better understand the membrane structure in their throats. Finally, they observed how the primates used different kinds of calls, depending on the situation.

Their analysis revealed that extremely thin vocal membranes sit above folds in the larynx that allow the monkeys to introduce what the scientists call “voice breaks” into their calls. Those breaks happen because sound production oscillates between the folds and membranes. Unlike the traditional Swiss yodeler, they don’t need to shift between chest and throat for the quick pitch shifts — which resembles the classic Tarzan yell.

The mechanism is so effective that some monkeys can make what the researchers call ultra-yodels, with jumps in frequency up to five times what a human can deliver. In terms of octaves, New World monkeys can span three, while most human voices can barely extend beyond a single.

Read More: How Similar Are Humans and Monkeys?

Why do Monkeys Yodel?

Although the researchers now know what mechanisms the monkeys use to make the sounds and how they deliver such dynamic vocal range, they are still left with why?

Jacob Dunn, an evolutionary biology research at Anglia Ruskin University (ARU) in Cambridge, England and an author of the paper, hypothesizes that the monkeys leverage their larynxes for social reasons.

“This might be particularly important in primates, which have complex social lives and need to communicate in a variety of different ways,” Dunn said in a press release. “It’s highly likely this has evolved to enrich the animals’ call repertoire, and is potentially used for attention-grabbing changes, call diversification, or identifying themselves.”

Read More: Chimps May Continuously Learn as They Age, a Factor of Human Evolution

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Before joining Discover Magazine, Paul Smaglik spent over 20 years as a science journalist, specializing in U.S. life science policy and global scientific career issues. He began his career in newspapers, but switched to scientific magazines. His work has appeared in publications including Science News, Science, Nature, and Scientific American.