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Primate Brains Shed Light On The Evolution Of Human Speech

One feature of humans that really sets us apart from our primate relatives is our ability to talk. While apes and monkeys can produce vocalizations to communicate, these are no way near as complex or numerous as those used in human speech. Now, a new study has looked into the link between brain structure and vocal repertoire in primates, producing some interesting results.

A question that scientists have long been trying to answer is why can’t non-human primates talk? We know that humans and primates have slightly different versions of the FOXP2 gene, which is essential to the development of language, so that likely plays a role. But how might our brain wiring add to the story?

Researchers from Anglia Ruskin University and Stony Brook University set out to investigate, publishing their findings in Frontiers in Neuroscience. They collected data on the vocal repertoires and group size of a variety of primates – group size was taken into account because sociability is a likely driving force in the evolution of speech. They also looked at data on the volumes of various brain regions, and how large they were relative to overall brain size for each species.

The least vocal of the primates was found to be the proboscis monkey, which only produces four distinct calls. At the other end of the scale were the great apes, with the bonobo claiming the most vocalizations – a total of 38.

The researchers looked at the vocalizations of 34 primates, the proboscis monkey had the fewest. Kjersti Joergensen/Shutterstock

The team found a significant link between range of vocal repertoire and relative size of three brain regions known as cortical association areas. Interestingly, overall brain size had no effect.   

“Cortical association areas are found within the neocortex and are key to the higher cognitive processing capacities considered to be the foundation for the complex forms of behavior observed in primates,” lead author Dr Jacob Dunn explained in a statement. The areas are responsible for voluntary control of behavior.

“We also found a positive relationship between the relative volumes of the cortical association areas and the hypoglossal nucleus in apes, both of which are significantly bigger in these species. The hypoglossal nucleus is associated with the cranial nerve that controls the muscles of the tongue, thus suggesting increased voluntary control over the tongue in our closest relatives.”

Therefore, it seems that the most vocal primates – like chimps and bonobos – have brains that are better adapted to controlling the production of vocal sounds than those of their less chatty counterparts.

This has implications in terms of our own evolution – perhaps the human brain rewired over time to become more adept at controlling the body’s vocal apparatus. Many people attribute our vocal abilities to our superior intelligence, but perhaps this is not the case. Other primates are still pretty smart anyway – a group of monkeys in Panama recently entered the Stone Age, after all.   

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