Origins of human language stretch back 25 million years

The human brain’s language pathway was previously thought to have evolved only 5 million years ago.

By James Lloyd

25th April, 2020 at 08:00

The roots of human language have been traced back 25 million years – 20 million years earlier than the previous estimate.

The discovery was made by researchers in the UK, USA and Germany by studying a connection in the brain called the ‘arcuate fasciculus’ or human language pathway. This is a bundle of nerve fibres that connects regions of the brain that are important for processing language.

If this pathway or its connected regions become damaged – through a stroke, for instance, or dementia – it can affect a person’s ability to produce or understand speech

Piecing together the origins of human language is a tricky task. Whereas palaeontologists can use fossilised bones to find out what our ancestors looked like and how they lived, brains don’t become fossilised.

This means that neuroscientists have to use brain scans of living primates, and compare these to human scans, in order to gain insights into the minds of ancient primates.

Previously, chimpanzees had been found to have their own version of the human language pathway, suggesting that a precursor to the pathway emerged around five million years ago, when the two species split from a common ancestor. But the new finding pushes back the date again.

The researchers compared brain scans of humans, chimps and rhesus macaque monkeys, and discovered that all three primate species share a segment of the pathway that links the auditory cortex – the part of the brain that processes incoming sounds – with frontal lobe regions, which in humans are important for processing speech and language.

This suggests that the pathway emerged 25 million years ago, when humans and macaques last shared a common ancestor, although the researchers say that the origins of the pathway could stretch back even further.

“It is like finding a new fossil of a long-lost ancestor,” said study leader Prof Chris Petkov at Newcastle University. “I admit we were astounded to see a similar pathway hiding in plain sight within the auditory system of non-human primates.”

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