Orangutans, the most arboreal of the great apes, have been found by researchers at the University of Warwick to generate more and more varied consonant-like sounds than their African ground-dwelling relatives (gorillas, bonobos and chimpanzees).
While African apes are genetically quite similar to humans, they do not seem to share any of our vocal patterns. Great apes appear to have developed various vocal repertoires due to their arboreal compared to terrestrial lives, with tree-dwelling apes like orangutans producing a wide and diverse inventory of consonant-like calls. The findings of this study are in line with the theory that our evolutionary ancestors spent more time in the trees than was originally thought.
Associate Professor of Psychology at the University of Warwick Dr. Adriano Lameira looked into the history of human speech and found that all vowels are voiced sounds and all consonants are silent.
For decades, scientists have looked to non-human primates for insights on the development of language and speech in humans. However, non-human primates’ calls are made up almost entirely of vocalized vowels. Consonants are the building blocks of every language in the world, therefore this begs the issue of their genesis, as Dr. Adriano Lameira puts it.
The laryngeal structure of primates has been analyzed in relation to human vowel usage as the only focus of existing theories of speech evolution.
This, however, does not explain how voiceless, consonant-like sounds spread throughout the world’s languages.
Dr. Lameira compared patterns of consonant-like vocal production in the vocal repertoire of three major great ape lineages that exist currently from a once-diverse family, including orangutans, gorillas, bonobos, and chimpanzees, to understand the origins of human speech and the root-cause of consonant sounds in the human lineage.
Unlike other primates, but like any human language, great apes have both consonant and vowel sounds in their call repertoires. Consonant noises are used inconsistently by great apes in the wild.
In the wild, gorillas, chimpanzees, and bonobos don’t employ a vast range of consonant-like noises according to the researchers.
To provide one example, it has been discovered that certain populations of gorillas employ a call that sounds like a consonant whereas other populations do not. Some chimpanzee groups make a series of calls consisting of a single or double consonant when doing a specific task, such as grooming, whereas other groups seldom make such calls.
However, like humans, wild orangutans utilize the same set of consonant-like calls across all groups and for a variety of actions. Smacking, clicking, kiss-sounds, spluttering, and raspberry are all part of their extensive vocal repertoire.
Professor Lameira has spent the last 18 years studying orangutans in the wild and suggests that the apes’ arboreal lifestyle and diet may provide an explanation for the depth and complexity of their consonant-like calls.
All apes are expert scavengers because they forage for food from their surroundings. They’ve figured up clever ways to get at items that are normally hard to get at, such the piths of plants and the nuts that grow inside of them. Orangutans, in contrast to ground-dwelling apes like gorillas and chimpanzees, spend much of their time in the trees, where they must continually utilize at least one limb to maintain their balance while they forage for food high in the treetops.
Orangutans are able to utilize their mouths as a fifth hand for holding food and manipulating tools because of the increased control they’ve evolved over their lips, tongue, and jaw as a result of this limitation. Dr. Lameira claims that orangutans’ exceptional fine oral neuro-motoric control is an integral feature of their biology because of their well-known ability to peel an orange using only their lips.
The study supports the idea that our ancestors’ time spent in the trees may have been a necessary step in the development of consonants and, by extension, the development of human speech.
Specifically, the article “Arboreal origin of consonants, and thus, ultimately, speech,” has been published in Trends in Cognitive Sciences.
Arboreal origin of consonants, and thus, ultimately, speech, Trends in Cognitive Sciences (2022).