New research from the University of Warwick has revealed that orangutans, the most arboreal of the great apes, produce consonant-like calls more often and of greater variety than their African cousins living in the soil (gorillas, bonobos and chimpanzees).
This contrasts with the expectation that, while closely related to humans, African apes should have call repertoires that more closely resemble our speech. Arboreal versus terrestrial lifestyles appear to have caused great apes to develop different vocal repertoires, with large and varied inventories of consonant-like calls originating from arboreal apes such as orangutans, rather than apes living on the ground. The study suggests that our own evolutionary ancestors may have lived a more arboreal lifestyle than previously thought.
Dr Adriano Lameira, an associate professor of psychology at the University of Warwick, has studied the origins of human spoken language, which is universally made up of vowels that take the form of voiced sounds, while voiceless sounds take the form of consonants. .
Non-human primates have been studied for decades in search of clues to the evolution of speech and language in our species. However, the calls of non-human primates are composed mainly or exclusively of vowel-like vocal sounds.
This raises questions about the origin of all the consonants that make up all the languages of the world.
Until now, existing theories on the evolution of speech have focused exclusively on the connection between the laryngeal anatomy of primates and the human use of vowels.
This, however, does not explain how voiceless, consonant-like sounds have become a fundamental part of every language spoken in the world. »
Dr Adriano Lameira, Associate Professor of Psychology, University of Warwick
To understand the origins of human speech and the root cause of consonants in the human lineage, Dr. Lameira compared the consonant-like voice production patterns in the vocal repertoire of three great ape lineages that survive today. from a once diverse era. family – orangutans, gorillas, bonobos and chimpanzees.
Unlike other primates, but like any spoken human language, great ape call repertoires consist of both consonant-like and vowel-like calls. However, there are inconsistencies in the use of consonant sounds by great apes in the wild.
“Wild gorillas, chimpanzees and bonobos don’t use a wide variety of consonant-like calls,” he explains.
“Gorillas, for example, have been found to use a particular consonant-like call, but this is only prevalent in some gorilla populations and not others. Some chimpanzee populations produce one or two consonant-like calls associated with a single behavior, such as while grooming, but these same grooming calls are rare in other chimpanzee populations.
“Wild orangutans, however, use consonant-like calls universally and consistently across different populations and for multiple behaviors, much like humans do with speech. Their vocal repertoire is a rich display of pops, clicks, kissing sounds, spitting and raspberries. »
Professor Lameira has observed orangutans in their natural habitat for the past 18 years and says their arboreal lifestyle and feeding habits could help explain the complexity and sophistication of their consonant-like calls.
“All monkeys are accomplished extractive foragers. They have evolved complex mechanisms to access protected or hidden foods like nuts or plant piths, which often requires meticulous use of hands or tools. Apes such as gorillas and chimpanzees need ground stability to be able to successfully manipulate these foods and use tools, however, orangutans largely live in trees and access their food in the canopy. , where at least one of their limbs is constantly used to provide stability among the trees.
“It is because of this limitation that orangutans have developed greater control over their lips, tongues and jaws and can use their mouths as a fifth hand to hold food and maneuver tools. Orangutans are known to peel an orange with just their lips so their fine oral neuro-motor control is far superior to that of African great apes, and it has evolved to be an integral part of their biology,” says the Dr. Lameira.
Research suggests that living in trees may have been a pre-adaptation to the emergence of consonants and, by extension, the evolution of speech in our human ancestors.
The article, Arboreal origin of consonants, and therefore, ultimately, of speech, was published in Trends in cognitive science.