Gene glitch made man speak first
A freak mutation in one Stone Age man gave us language but could also be the source of depression, writes Robin McKie Sunday March 26, 2000 A single mutation in the brain of one Stone Age man provided humanity with the intellectual boost it needed to conquer the world. That change gave Homo sapiens the power of speech and language, but also came with a curse, because it left mankind vulnerable to psychoses, such as schizophrenia and manic depression. This startling idea is to be outlined on Tuesday by the Oxford University psychiatrist Professor Tim Crow at a London conference at which fossil experts, geneticists and anthropologists will debate one of evolution's most enduring mysteries: why did Homo sapiens triumph at the expense of all other types of human being? Crow believes an abrupt alteration in our brains' hard-wiring was responsible for giving us control of Earth. 'Language appeared very quickly and provided us with a unique ability to exchange complex ideas, thus giving us a powerful advantage over other types of human being,' he said. 'Mental illness is the price we pay for possessing that prowess.' One key implication of Crow's ideas for linking psychoses with language is that schizophrenia and manic depression must involve the breakdown of the brain's internal linguistic controls. People with these conditions can still speak but often believe they hear voices, or that others are controlling their thoughts. 'These psychoses clearly involve some kind of deviation in language function. That is a very important implication of this work,' Crow added. In the past decade, scientists have established that by about 100,000 years ago, different species of humans had established themselves in different corners of the globe: Neanderthals in Europe and Homo erectus in the Far East, for example. Then a new breed of upstart Earthlings appeared on the scene: Homo sapiens, who emerged out of Africa and began to spread, with remarkable speed, across the planet. Each encounter between native species and African invader appears to have been brief and one-sided, resulting in the extinction of the former - until, about 30,000 years ago, Homo sapiens was left in sole custody of Earth. Whether we indulged in 'species cleansing' or were more efficient at acquiring food and shelter is still unclear. Either way, Homo sapiens possessed a key advantage over all other forms of humanity. But what was it, and how did we acquire it? Most scientists agree this change must have involved some dramatic improvement in our linguistic skills, though they have been unable to suggest what special circumstances might have prevailed in our African homeland for natural selection to cause our ancestors to acquire complex speech. It is to this problem that Crow has proposed a dramatic solution. A freak mutation in a single, male member of early Homo sapiens was responsible. This biological change - which Crow believes can be traced to the Y chromosome, the DNA packet possessed only by men - was sufficient to trigger a cascade of biological changes that swept through our species, bringing major improvements in our linguistic ability in their wake. The specific mutation outlined by Crow is one that widened the gulf between the two hemispheres of the human brain, a gap that freed one half to take over and develop the power of speech. Research by Crow - linking variations in people's cerebral hemisphere controls of their bodies to their linguistic prowess - supports this idea. The first man to manifest this gift would probably have had the gift of the gab. 'He would have been favoured strongly for sexual selection,' said Crow. His genes would have spread quickly. This capacity for complex speech also brought major disadvantages, in particular it triggered the appearance of schizophrenia in our species. Our sophisticated language controls occasionally go wrong. 'Schizophrenia is a linguistic breakdown in which the sufferer distinguishes his thoughts from his speech output and the speech input that he receives and decodes from others,' said Crow. It is a startling way of understanding psychoses, and sparked considerable scientific interest among other researchers, especially as Crow has a reputation for individualistic brilliance. 'This is an intriguing idea, though I always hesitate about accepting single, neatly packaged explanations about our evolution,' said palaeontologist Professor Chris Stringer, of London's Natural History Museum. 'I think it is just as likely we accumulated characteristics like language in a piecemeal fashion and that there was no single, defining moment that heralded the arrival of complex speech in Homo sapiens, ' added Stringer, who will also be speaking at the conference, 'The Speciation of Modern Homo Sapiens' . 'However, this will be the first opportunity Tim Crow has had to convince anthropologists and palaeontologists about the evolutionary aspects of his ideas and he will certainly get a good hearing, albeit a lively one, I suspect.' Full text: http://www.newsunlimited.co.uk/observer/uk_news/story/0,3879,151148,00.html