Summary: Why are non-human primates unable to speak like humans? A widely-accepted theory associated it with their lack of vocal anatomy to produce human-like sounds. This was debunked, though, by recent studies upon recognizing vocal muscles similar to ours. It appears that non-human primates are speech-ready and yet do not speak still the way we do.
Perhaps, you have already seen one of those viral videos of pet dogs that seemingly muttered “I wuv (love) you”. Those dogs seemed to make a garbled speech, but still, they unfailingly fascinated people with their apparent “sweet talking“. Thus, one can truly wonder. If these dogs seem to be able to mutter a few, then, how come our closely-related apes and other primates are unable to do so? Even the more evolutionary-distant bird species, such as parakeets, mockingbirds, cockatoos, and other parrots possess the skills to mimic human language and yet our closely-related non-human primates were limited to merely grunts and hoots.
Is it because of the non-human primates’ lack of vocal anatomy?
Why non-human primates are unable to speak has long been blamed on their vocal anatomy. A long-held theory explicates that monkeys and apes are incapable of, at least, imitating human speech sounds because their vocal tract is not that intricately flexible. In a paper published in “Science” in 1969, Philip H. Lieberman and others posited that non-human primates, particularly Rhesus (or macaque) monkeys (Macaca mulatta), were unable to speak like us because of vocal tract limitations. They went as far as to say that the ability for speech as we know it is a “… linguistic endowment …” exclusive to humans.1
A recent study debunked this widely-known theory. In the article, Muscles of the Apes, it referred to the study published in Frontiers in Ecology and Evolution wherein their findings refuted such long-held theory about apes lacking the muscles associated with the vocal communication (as well as bipedalism and facial expressions). These muscles were thought of as exclusive to humans. However, with the availability of more specimens to work on to, they found that certain apes did possess these muscles yet they did not put them to use as humans did. Apparently, the apes were likely speech-ready because they, too, possess the anatomy essential for generating human speech sounds.
Is it because of the non-human primates’ lack of exposure to humans?
Is human language nature- or nurture-driven? We are aware that our language is something that we learned and acquired as we grow. Perhaps, primates would be able to acquire it as well if they could be exposed profoundly to it, thus, came the Project Nim in 1973.
Project Nim was a controversial research. It was a Columbia University psychology experiment on a chimpanzee, named Nim Chimpsky. He was taken as a child from the wild to be raised in a common human household. The research aimed to see if the chimp would be able to acquire human-like behavior and language through nurture. The chimp did learn to convey through sign language but was not successful at speaking even a single word.2
Is it because of the non-human primate’s lack of the necessary brain wiring?
Another theory surfaces to explain why non-human primates are incapable of human speech and it has to do with brain wiring. Accordingly, while non-human primates (particularly, macaques) appear to be well equipped with a speech-ready vocal tract, they do not have the adequate brain wiring that regulates the vocal tract muscles to generate human-like speech sounds. They seem to lack the proper neural control on muscles on their vocal tract and as such are not able to configure them for speech.3
It is also postulated that there might be a molecular predisposition involved, for instance, the FOXP2 (forkhead box protein 2) gene.4 FOXP2 was the first gene identified to play a role in human speech and language development, thus, was called the “language gene“. It is located in chromosome 7 and is expressed in certain cells, including the brain. Mutation of this gene causes speech and language disorder in humans.
Non-human primates do not have the gift for human-like speech because they probably do not need one. Based on recent findings, they have the anatomical features similar to ours yet they produce vocal sounds different from ours. They do have a communication prowess that they use amongst them. It may be far different from ours but it is just as remarkable. Nevertheless, exploring the intricacies of language development could help us learn more about how humans diverged from our non-primate relatives and eventually acquired one of our own.
— written by Maria Victoria Gonzaga
1 Lieberman, P. H., Klatt, D. H., & Wilson, W. H. (1969). Vocal Tract Limitations on the Vowel Repertoires of Rhesus Monkey and other Nonhuman Primates. Science 164: 1185-1187. Retrieved from
2 ‘Project Nim’: A Chimp’s Very Human, Very Sad Life. (2011). National Public Radio, Inc. Retrieved from https://www.npr.org/2011/07/20/138467156/project-nim-a-chimps-very-human-very-sad-life
3 Fitch, W. T., de Boer, B., Mathur, N., & Ghazanfar, A. A. (2016). Monkey vocal tracts are speech-ready. ScienceAdvances. Retrieved from http://advances.sciencemag.org/content/2/12/e1600723.full
4 Conger, C. (n.d.).Can chimpanzees learn human language? HowStuffWorks. Retrieved from https://animals.howstuffworks.com/mammals/chimps-learn-language.htm