All of the world’s spoken languages are built from vowels and consonants, but the typical call repertoire of non-human primates skews heavily toward vowel‑like sounds. What sparked the emergence of consonants? New research on orangutan communication and the origins of human speech sheds light on this question.
Vowels form mainly through the larynx and the vocal cords, while consonants arise in the mouth with the help of supralaryngeal articulators such as the lips, tongue, palate, and jaw.
Non-human primates often produce vowel‑like noises, yet some species also generate sounds that resemble consonants. This tendency hints at abilities that may have common roots with early human speech, suggesting a shared ancestral base.
The variety and use of consonant‑like sounds differ across species, opening a window into how evolutionary mechanisms shape vocal repertoires. Studying wild populations is essential, because captive primates can learn socially and even create new consonant‑like calls.
The study, led by Adriano Lameira, associate professor of psychology at the University of Warwick, found that the most tree‑dwelling great apes, orangutans, produce more frequent and more diverse consonant‑like sounds than their ground‑dwelling African relatives: gorillas, bonobos, and chimpanzees.
This finding challenges the idea that African apes, being closer relatives to humans, would already display call repertoires more similar to human speech.
Living in trees appears to have pushed great apes to develop larger vocal repertoires, including a broader set of consonant‑like calls, according to the researchers.
tree-dwelling ancestors of humans
The study also suggests that human evolutionary ancestors may have spent more time in arboreal habitats than previously thought.
Wild orangutans in the Pongo genus use consonant‑like calls across many contexts, from nest building to mother‑offspring communication. The most common call type is a consonant‑like alarm signal.
An orangutan and her infant illustrate the forest context in which these sounds emerge, a reminder of how natural habitats shape vocal behavior.
The prevalence and diversity of consonant‑like calls is much lower in wild gorillas, chimpanzees, and bonobos. In gorillas, only a few populations have a single consonant‑like, putative cultural call.
Among chimpanzees, some populations use one or two consonant‑like calls, sometimes with subtle variants, in a single context such as social grooming.
Remarkably, wild orangutans exhibit universal, culturally shared consonant‑like calls that appear across multiple contexts, paralleling features of human speech, according to the researchers.
As noted by Lameira, existing theories of speech evolution have often linked vowel use to laryngeal anatomy, but have not fully explained how consonant‑like sounds became a core component of human language.
Working with wild orangutans for eighteen years, the researcher reports that their consonant‑like vocalizations occur in universal and consistent ways across populations and contexts, reflecting a rich repertoire of sounds such as clicks, kiss sounds, chatter, and trumpets.
The “fifth hand” of the orangutans
Their way of life—orangutans rely on their mouths as a kind of fifth hand to navigate the trees—requires constant mouth control as they hang and move among branches.
This constraint has driven orangutans to develop sophisticated control over their lips, tongue, and jaw, enabling the mouth to act as an extra tool for handling food and manipulating objects.
A female orangutan and her infant inhabit the forest, reminding us of the intimate link between behavior, anatomy, and sound production in arboreal life.
Orangutans are known to peel fruit with their lips, a testament to their advanced oral neuromotor control, which appears to be more refined than in African apes and deeply integrated into their biology.
Studies suggest that a tree‑based lifestyle may have provided the preadaptive groundwork for consonants and, by extension, the emergence of spoken language in human ancestors.
The possibility that arboreal life contributed the essential preadaptations for spoken language implies that human ancestors were more arboreal than some close relatives, even while sharing a close phylogenetic distance, according to the study.
At the same time, the invention and imitation of consonant‑like sounds by great apes in captivity indicate that the adoption of consonant‑like sounds, whose use extended to land environments, could have been shaped by developmental learning and practice.
Thus, the rich interplay of innate tendencies, epigenetic factors, and social interactions shaping infants’ language acquisition may also play a role in the early stages of pre‑speech evolution among hominins.
The article titled The Arboreal Origin of Consonants and Thus of Speech appeared in Trends in Cognitive Sciences, highlighting ongoing debates about how language may have emerged from primate vocal systems. This line of inquiry continues to refine our understanding of how speech could arise from a combination of anatomy, environment, and social learning, bridging gaps between primate vocal behavior and human language.
Reference notes: Trends in Cognitive Sciences, 2022, and related findings from the study on arboreal origins of consonants.
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This exploration reflects a growing recognition that early life in trees might have set the stage for consonants and the eventual development of human speech, underscoring the complex tapestry of biological and ecological factors shaping language across our ancestor lineages.