Apes and monkeys have special anatomy in their throats Voice membraneit disappeared from humans through evolution, allowing for more stable speech. However, the exact benefits these offer to non-human primates were previously unknown. New research provides important new insights Various vocal sounds It reveals for the first time how nonhuman primates and certain calls are generated.

Humans have evolved their ability to speak, but apes and monkeys, closest relatives in the animal kingdom, lack this skill.

However, they have a special anatomy in the larynx that humans have lost during their evolution: a thin, lightweight tissue membrane at the top of the crease of the voice.

Previous studies have suggested that these structures contribute to the complexity of animal vocalization, but their precise roles remain largely unclear to date.

The new study, led by researchers at Anglia Ruskin University and the University of Vienna, shows that these membranes promote rapid frequency transitions and significantly expand the range and complexity of monkey vocalization.

Scientists documented and studied the appeals of various primate species at the La Senda Verde Wildlife Sanctuary in Bolivia.Alouatta Caraya), tufted cappuchin (Sapaju Appella), black capped squirrel monkey (Saimiri boliviensis), and Peruvian spider monkeys (Atheres Chamek).

A combination of methods was used to identify two different modes of vocal fold vibration.

The first mode, which involves only the folding of the voice, produces a low-frequency sound similar to human ponation.

The second mode, which also involves the vocal membrane, results in much higher frequency oscillations, and, like human yodel, produces dramatic “mutation.”

In some cases, these shifts span octaves over 3 octaves. This goes far beyond the human ability of voice breaks, usually limited to a single octave.

“This is an attractive example of how nature offers a means to enrich animal vocalization despite the lack of language,” says Dr. Christian Herbst, a researcher at the University of Vienna.

“The production of these complex vocal patterns is almost possible by the way the animal’s larynx is anatomically shaped, and does not require the complex neural control produced by the brain.”

“These results show how monkeys can exploit new evolutionary features that can generate a wider range of calls, including these ultra-yodel,” says Jacob Dunn, a researcher at Anglia Ruskin University.

“This may be especially important for primates who have complex social lives and need to communicate in a variety of ways.”

This study further suggests that the vocal membrane also introduces vocal instability while enhancing the pitch range.

“Our research shows that the vocal membrane extends the pitch range of monkeys, but it also makes the voice unstable,” says Dr. Tecumse Fitch, a researcher at the University of Vienna.

“They may have been lost during human evolution to promote stability in the pitch of songs and speech.”

study Published in the journal Philosophical trade of the Royal Society b.

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Christian T. Herbst et al. 2025. “Monkey Yodel” – The new world’s frequency jumps far outweigh the human vocal register transition. fill. transformer. R. Soc. b 380 (1923): 20240005; doi: 10.1098/rstb.2024.0005