Gene Study Shows One Letter Divided Black From White
RICK WEISS
Washington Post, 12/18/2005
WASHINGTON - Scientists said Thursday that they have discovered a tiny genetic mutation that largely explains the first appearance of white skin in humans tens of thousands of years ago, a finding that helps solve one of biology's most enduring mysteries and illuminates one of humanity's greatest sources of strife.
The work suggests the skin-whitening mutation occurred by chance in a single individual after the first human exodus from Africa, when all people were brown-skinned.
That person's offspring apparently thrived as humans moved northward into what is now Europe, helping to give rise to the lightest of the world's races.
Leaders of the study, at Penn State University, warned against interpreting the finding as a discovery of "the race gene."
Race is a vaguely defined biological, social and political concept, they noted, and skin color is only part of what race is - and is not.
In fact, several scientists said, the new work shows just how small a biological difference is reflected by skin color. The newly found mutation involves a change of just one letter of DNA code out of the 3.1 billion letters in the human genome.
"It's a major finding in a very sensitive area," said Stephen Oppenheimer, an expert in anthropological genetics at Oxford University, who was not involved in the work. "Almost all the differences used to differentiate populations from around the world really are skin deep."
The work also reveals for the first time that Asians owe their relatively light skin to different mutations. That means that light skin arose independently at least twice in human evolution.
Several sociologists and others said they feared that such revelations might wrongly overshadow the prevailing finding of genetics over the past 10 years: that the number of DNA differences between races is tiny compared with the range of genetic diversity found within any single racial group.
Even study leader Keith Cheng said he was at first uncomfortable talking about the new work, fearing that the finding of such a clear genetic difference between people of African and European ancestries might reawaken discredited assertions of other purported inborn differences between races - the most longstanding and inflammatory of those being intelligence.
The discovery, described in Friday's issue of the journal "Science", was an unexpected outgrowth of studies Cheng and his colleagues were conducting on inch-long zebrafish. Having identified a gene that, when mutated, interferes with its ability to make its characteristic black stripes, the team scanned human DNA databases to see if people have similar gene.
To their surprise, they found virtually identical pigment- building genes in humans, chickens, dogs, cows and many others species, an indication of its biological value.
They got a bigger surprise when they looked in a new database comparing the genomes of four of the world's major racial groups. That showed that whites with Northern and Western European ancestry have a mutated version of the gene.