[Paleopsych] WP: Scientists Find A DNA Change That Accounts For White Skin

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Fri Dec 30 19:30:47 UTC 2005

Scientists Find A DNA Change That Accounts For White Skin

[Another warning against racism, the previous one coming from National 
Public Radio, while the Times' account had no warning at all.

[Actually, it's the Times that has changed. Generally speaking (having 
read the Times since 1962 and the Post since 1969) the Times is more 
liberal than the Post when it comes to new programs to uplift the 
despised, the downtrodden, and the dispossed, whereas the Times is more 
conservative in cautioning against the potentials for depredations and 
inroads on civil liberties than the Post. No surprise this last, since the 
Post published in a government town.

[It's on the matter of racial differences that the Times, or certainly 
Nicholas Wade, has become more open minded.]

By Rick Weiss Washington Post Staff Writer Friday, December 16, 2005; A01

Scientists said yesterday 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 that 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 -- the complete instructions for making a 
human being.

"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 raises a raft of new questions -- not least of which is why white 
skin caught on so thoroughly in northern climes once it arose. Some 
scientists suggest that lighter skin offered a strong survival advantage 
for people who migrated out of Africa by boosting their levels of 
bone-strengthening vitamin D; others have posited that its novelty and 
showiness simply made it more attractive to those seeking mates.

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, in each case affecting 
populations with the facial and other traits that today are commonly 
regarded as the hallmarks of Caucasian and Asian races.

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 long-standing and inflammatory of those being 

"I think human beings are extremely insecure and look to visual cues of 
sameness to feel better, and people will do bad things to people who look 
different," Cheng said.

The discovery, described in today's issue of the journal Science, was an 
unexpected outgrowth of studies Cheng and his colleagues were conducting 
on inch-long zebra fish, which are popular research tools for geneticists 
and developmental biologists. 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 a similar gene resides in 

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.

Skin color is a reflection of the amount and distribution of the pigment 
melanin, which in humans protects against damaging ultraviolet rays but in 
other species is also used for camouflage or other purposes. The mutation 
that deprives zebra fish of their stripes blocks the creation of a protein 
whose job is to move charged atoms across cell membranes, an obscure 
process that is crucial to the accumulation of melanin inside cells.

Humans of European descent, Cheng's team found, bear a slightly different 
mutation that hobbles the same protein with similar effect. The defect 
does not affect melanin deposition in other parts of the body, including 
the hair and eyes, whose tints are under the control of other genes.

A few genes have previously been associated with human pigment disorders 
-- most notably those that, when mutated, lead to albinism, an extreme 
form of pigment loss. But the newly found glitch is the first found to 
play a role in the formation of "normal" white skin. The Penn State team 
calculates that the gene, known as slc24a5, is responsible for about 
one-third of the pigment loss that made black skin white. A few other 
as-yet-unidentified mutated genes apparently account for the rest.

Although precise dating is impossible, several scientists speculated on 
the basis of its spread and variation that the mutation arose between 
20,000 and 50,000 years ago. That would be consistent with research 
showing that a wave of ancestral humans migrated northward and eastward 
out of Africa about 50,000 years ago.

Unlike most mutations, this one quickly overwhelmed its ancestral version, 
at least in Europe, suggesting it had a real benefit. Many scientists 
suspect that benefit has to do with vitamin D, made in the body with the 
help of sunlight and critical to proper bone development.

Sun intensity is great enough in equatorial regions that the vitamin can 
still be made in dark-skinned people despite the ultraviolet shielding 
effects of melanin. In the north, where sunlight is less intense and cold 
weather demands that more clothing be worn, melanin's ultraviolet 
shielding became a liability, the thinking goes.

Today that solar requirement is largely irrelevant because many foods are 
supplemented with vitamin D.

Some scientists said they suspect that white skin's rapid rise to genetic 
dominance may also be the product of "sexual selection," a phenomenon of 
evolutionary biology in which almost any new and showy trait in a healthy 
individual can become highly prized by those seeking mates, perhaps 
because it provides evidence of genetic innovativeness.

Cheng and co-worker Victor A. Canfield said their discovery could have 
practical spinoffs. A gene so crucial to the buildup of melanin in the 
skin might be a good target for new drugs against melanoma, for example, a 
cancer of melanin cells in which slc24a5 works overtime.

But they and others agreed that, for better or worse, the finding's most 
immediate impact may be an escalating debate about the meaning of race.

Recent revelations that all people are more than 99.9 percent genetically 
identical has proved that race has almost no biological validity. Yet 
geneticists' claims that race is a phony construct have not rung true to 
many nonscientists -- and understandably so, said Vivian Ota Wang of the 
National Human Genome Research Institute in Bethesda.

"You may tell people that race isn't real and doesn't matter, but they 
can't catch a cab," Ota Wang said. "So unless we take that into account it 
makes us sound crazy."

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