The human brain is specially equipped to process language but the building blocks for this biological machinery may have appeared as early as 25 million years ago in a distant ancestor, according to researchers at Newcastle University, UK. This discovery pushes back the origin of the human language pathway in the brain by at least 20 million years.
The ancient seed for millions of words
Every day, it seems like we learn that many traits we thought of as unique to humans are shared by other animals. Killer whales and dolphins have a culture (defined as the sum of a particular group’s characteristic ways of living), great apes and some monkeys understand and employ deception, New Caledonian crows manufacture and use tools, and there’s even evidence that captive chimpanzees are able to make moral judgments.
What about language? After all, we know of no other animal that can utter words, so it makes sense to draw the line and conclude that speech is exclusively tied to the human lineage (our species as well as extinct relatives like Neanderthals and Denisovans). That may be true, but that doesn’t mean non-human animals can’t ‘understand’ and use language.
Research suggests that primates, birds, cetaceans, dogs and other species are able, through extensive training, to understand human words and simple sentences. Take Kanzi, for instance, a male bonobo that was an infant when he started working with primatologist Sue Savage-Rumbaugh. After a couple of years of training with Savage-Rumbaugh, Kanzi could understand several thousand words and communicate using a special keyboard with over 400 visual symbols called lexigrams.
The ability to, at least party, understand and process some of the components of language in many non-human animals suggests that this characteristic is shared at a fundamental level — and where else but the brain.
‘Brain fossils’ and the origin of language
Previously, researchers found evidence that pointed towards a 5 million-year-old precursor of the language pathway in the brain in a common ancestor of both apes and humans.
But unlike bones, brains cannot fossilize, so how do neuroscientists make such inferences?
Their only tool at their disposal is comparing the brains of living primates and comparing them to humans, in order to infer what the brains of common ancestors might have looked like through a process that resembles reverse engineering.
The researchers at Newcastle University led by Chris Petkov relied on an open database of brain scans performed by the international scientific community. They also generated their own original brains scans, which they duly shared.
Next, they directed their attention towards the auditory regions and brain pathways of humans, apes, and monkeys.
Their investigation revealed that a segment of the language pathway in the brain interconnects the auditory cortex with frontal lobe regions, which serve important roles in processing speech and language. This pathway seems to be at least 25 million years old.
“It is like finding a new fossil of a long lost ancestor. It is also exciting that there may be an older origin yet to be discovered still,” Petkov said in a press release.
“We predicted but could not know for sure whether the human language pathway may have had an evolutionary basis in the auditory system of nonhuman primates. I admit we were astounded to see a similar pathway hiding in plain sight within the auditory system of nonhuman primates.”
The study also revealed how the language pathway changed over the years in humans. It seems like the left side of this human brain pathway was stronger and the right side appears to have diverged from the auditory evolutionary prototype to involve non-auditory parts of the brain. These characteristics are unique to humans and may be responsible for granting us speech.
“This discovery has tremendous potential for understanding which aspects of human auditory cognition and language can be studied with animal models in ways not possible with humans and apes. The study has already inspired new research underway including with neurology patients,” Professor Timothy Griffiths, consultant neurologist at Newcastle University, UK and co-author of the new study.
The findings appeared in the journal Nature Neuroscience.
Correction: an earlier version of the article stated that Kanzi the bonobo was 31 years old when he started learning lexigrams. He was, in fact, an infant at the time of doing so.
