Orangutans that live in trees use their mouths like a fifth hand. Their lips, tongue and lower jaw have therefore developed special fine motor skills – and with them the ability to produce sounds that resemble the consonants of spoken human language. The psychologist Adriano Lameira from the University of Warwick sees this as a hint as to how the consonants might have originated.

Researchers have been searching for the origins of human speech for decades. But the calls of other primates consist mostly of sounds similar to vowels like a, e, i, o, u. “Theories have so far focused on the connection between primate laryngeal anatomy and human use of vowels.

But that doesn’t explain how the consonant-like sounds became a fundamental component of every spoken language,” says Adriano Lameira in a press release. So where do all the consonants come from – sounds like b and p, s and t?

Lameira compared the sound repertoire of humans’ closest relatives, the great apes: Their calls also contain sounds that sound like consonants, but to a different extent, the psychologist found. “Wild gorillas, chimpanzees, and bonobos do not use a wide variety of consonant-like calls,” the psychologist writes in the journal Trends in Cognitive Sciences.

Gorillas, for example, only produce one, chimpanzees one or two such calls, and that is only true for some populations. Wild orangutans, on the other hand, used these sounds—like hissing, smacking, and kissing sounds—in many different situations. “They use consonant-like calls universally and consistently across different populations and for many behaviors.”

While their African relatives – gorillas, bonobos and chimpanzees – live mostly on the ground, orangutans are at home in the trees of the Indonesian islands of Borneo and Sumatra. Lameira observed the animals in their natural environment for 18 years.

Life in the trees can explain the complexity of their calls, he says: When they search for food such as nuts or plant fibers, it requires the careful use of hands or tools and thus a stable footing. And for this, orangutans need in the trees usually more extremities than their ground-dwelling relatives.

“Because of this limitation, they have developed greater control over their lips, tongue, and jaws, and can use their mouths as a fifth tool for holding food and working with tools,” Lameira reports.

The same anatomical structures are involved in the production of consonants, whereas vowels originate predominantly in the larynx. The neuromotor control of the mouth has evolved over time as part of their biology and is vastly superior to that of African monkeys. “Orangutans can only peel an orange with their lips.”

Earlier observations already suggested that orangutans have a special talent for language: They are able to control their voice.

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The original of this article “Trees could have had a great influence on our language” comes from Spektrum.de.