'Single mutation led to language'

A controversial new theory suggests that the power of speech and language resulted from a single mutation in the brain of one man who lived many tens of thousands of years ago.

The idea has been put forward by Professor Tim Crow, a respected psychiatrist from Oxford University, UK.

He believes this chance event could help to explain why modern humans, or Homo sapiens, have come to dominate the planet.

He told a conference of fossil experts, geneticists and anthropologists in London on Tuesday that one individual could have been born with a freak mutation on his Y chromosome - the bundle of DNA in cells that is possessed by men only.

This mutation, he said, could have triggered a series of other biochemical changes that eventually resulted in the specialisation of the two halves of the human brain and the development of the power of speech.

Decisive advantage

"The theory is that some chromosomal change occurred," he told the BBC. "We know quite a lot about the chromosomes of man and chimpanzees and other apes, and in many respects they are extremely similar. But there are small differences and the question is whether one of those differences is relevant to the differences we see between man and the chimps."

He said the theory could be tested with modern methods of genetic investigation.

It is thought that Homo sapiens started to appear in Africa around 150,000 years ago and most anthropologists agree that we certainly had some form of language by 30,000 years ago. But precisely when and how this skill was first developed is a mystery.

These are important questions because they may help explain why H. sapiens flourished at the expense of all other human-like creatures such as the Neanderthals. A sophisticated form of communication, and the organisational abilities that would have come from it, could have given H. sapiens the decisive advantage over his rivals.

Professor Chris Stringer, who works at the Department of Palaeontology, Natural History Museum, UK, is intrigued by Professor Crow's ideas but is cautious about crediting the development of language to a single biochemical event.

'Bones and stones'

He believes that language is more likely to have formed gradually over a long period of time.

"Obviously, my concern is with the prehistoric record and the trouble is that things like language and brain structure do not fossilise in a way that can be readily studied. It's all bones and stones. We have to look at that record and try to interpret when language began - and the experts are divided.

"When we get to people like the Neanderthals, who are now extinct, some people argue that they did share some of our features and were possibly starting to symbol and probably did have a degree of language."

Professor Crow believes that the mutation also left humans vulnerable to mental illnesses such as schizophrenia and manic depression. These conditions involve the breakdown of the brain's ability to deal with language and so must somehow involve the brain's language processing skills.

"With the capacity for language came great diversity, and part of that diversity relates to how the brain is organised. And I think that is somehow related to our predisposition to serious mental disorders, language delays, and dyslexia. All these things may be related to the specialisation of the brain for language."