Our ability to talk has much more ancient origins than thought, according to a brain scan study has blurred one of the key differences between monkeys and humans.
Scientists at the Max-Planck Institute for Biological Cybernetics in Tübingen, Germany, have found a "voice" area in the brain of rhesus macaque monkeys.
The find refutes the idea that the ability to speak suddenly emerged only with our most recent extinct ancestors a couple of hundred thousand years ago and pushes this ability back much further, given that we shared an ancestor with monkeys up to 30 million years ago.
Researchers have long wondered why certain fundamental characteristics of vocal communications are present in all languages, and the work published today in the journal Nature Neuroscience suggests that part of the reason is that the machinery of communication is ancient, dating back to our distant ancestors, when it likely began with expressions and calls.
The research group in the laboratory of Prof Nikos Logothetis used a non-invasive scanning technique, which has become a standard tool for understanding human brain function, to image macaque monkeys, one of our distant primate relatives.
In their study Dr Christopher Petkov and colleagues describe the discovery of a monkey "voice" area, a part of the brain that appears to be important for an individual to recognise verbal communications from other members of their species.
"We show that the function of the monkey brain during verbal recognition is very similar to what had been described in humans," he says, marking the most ancient primate brain function that supports verbal communication.
The study shows that the voice area - a part called the anterior superior temporal cortex - wasn't active to just any sound, since they played a range, including scrambled sounds and natural sounds.
Instead, this brain area preferred sounds made by animals from the same species, underlining how the coos, grunts and screams had meaning.
Hence, this brain region plays a central role in the communication between members of this species, supporting their social interactions and contributing to their survival.
In addition, the scientists also found that this voice area is sensitive to the identity of the individual that was making the calls.
Consequently, the scientists conclude that this area can support multiple verbal recognition abilities, such as helping the listener to recognise the acoustical signature or the 'voice of the species', as well as the voices of different individuals.
Many people doubt that there is much to be learned from other animals about human language. But this study strongly backs the argument that voice areas were conserved in primates over millions of years of evolution, challenging the notion that higher-level verbal communication can only be achieved by the human brain.
"This discovery in monkeys and the link to the human work is exciting because the animals are now helping us to understand how this brain area recognises voices in a way that we cannot in humans," says Dr Petkov, who led the study.
The researchers believe that their discovery will provide pathways for understanding clinical conditions such as phonagnosia, where patients show deficits in voice recognition and verbal communication prohibiting them from recognising the voice of someone that they know.