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Apes Have the Right Vocal Anatomy — So Why Can't They Speak?

August 12, 2018 in Blogs

By The Conversation

Here's what evolution tells us about the complex behaviour of primates.

We all know that parrots can talk. Some people may have even seen elephantsseals, or whales mimicking speech sounds. So why can’t our closest primate relatives speak like us? Our new research suggests they have the right vocal anatomy but not the brainpower to use it.

Scientists have been interested in understanding this phenomenon for centuries. Some have argued that non-human primates didn’t have the right-shaped body parts to make the same sounds as we do, and that human speech evolved after our speech organs changed. But comparative studies have shown that the form and function of the larynx and vocal tract is very similar across most primates species, including humans.

This suggests that the primate vocal tract is “speech ready” but that most species don’t have the neural control to make the complex sounds that comprise human speech. When reviewing the evidence in 1871, Charles Darwin wrote “the brain has no doubt been far more important”.

Along with Jeroen Smaers from Stony Brook University in New York, I have been investigating the relationship between the number of different calls that each primate species can make and the architecture of their brains. For example, Golden pottos have only ever been recorded using two different sounds, while chimpanzees and bonobos use around 40.

Our new study, published in Frontiers in Neuroscience, focused on two particular features of the brain. These were the cortical association areas that govern voluntary control over behaviour, and the brainstem nuclei that are involved in the neural control of muscles responsible for vocal production. Cortical association areas are found within the neocortex and are key to the higher order brain functions considered to be the foundation for the complex behaviour of primates.

The results indicate a positive correlation between the relative size of the cortical association areas and the size of the vocal repertoire of primates. In simple terms, primates with bigger cortical association areas tended to make more sounds. But, interestingly, a primate’s vocal repertoire was not linked to the overall size of its brain, just the relative size of …read more


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