August 22, 2000
By NATALIE ANGIER
Scientists say that while it may be easy to tell at a glance whether a person is Asian, African or Caucasian, the differences dissolve when one looks beyond surface features and scans the human genome for DNA hallmarks of "race."
ADD YOUR THOUGHTS
The Science of Differences
If racial labels have "little or no biological meaning," what is the best way to address racial differences, politically or scientifically?
In these glossy, lightweight days of an election year, it seems, they can't build metaphorical tents big or fast enough for every politician who wants to pitch one up and invite the multicultural folds to "Come on under!" The feel-good message that both parties seek to convey is: regardless of race or creed, we really ARE all kin beneath the skin.
Yet whatever the calculated quality of this new politics of inclusion, its sentiment accords firmly with scientists' growing knowledge of the profound genetic fraternity that binds together human beings of the most seemingly disparate origins.
Scientists have long suspected that the racial categories recognized by society are not reflected on the genetic level.
But the more closely that researchers examine the human genome — the complement of genetic material encased in the heart of almost every cell of the body — the more most of them are convinced that the standard labels used to distinguish people by "race" have little or no biological meaning.
They say that while it may seem easy to tell at a glance whether a person is Caucasian, African or Asian, the ease dissolves when one probes beneath surface characteristics and scans the genome for DNA hallmarks of "race."
As it turns out, scientists say, the human species is so evolutionarily young, and its migratory patterns so wide, restless and rococo, that it has simply not had a chance to divide itself into separate biological groups or "races" in any but the most superficial ways.
"Race is a social concept, not a scientific one," said Dr. J. Craig Venter, head of the Celera Genomics Corporation in Rockville, Md. "We all evolved in the last 100,000 years from the same small number of tribes that migrated out of Africa and colonized the world."
Dr. Venter and scientists at the National Institutes of Health recently announced that they had put together a draft of the entire sequence of the human genome, and the researchers had unanimously declared, there is only one race — the human race.
Dr. Venter and other researchers say that those traits most commonly used to distinguish one race from another, like skin and eye color, or the width of the nose, are traits controlled by a relatively few number of genes, and thus have been able to change rapidly in response to extreme environmental pressures during the short course of Homo sapiens history.
And so equatorial populations evolved dark skin, presumably to protect against ultraviolet radiation, while people in northern latitudes evolved pale skin, the better to produce vitamin D from pale sunlight.
"If you ask what percentage of your genes is reflected in your external appearance, the basis by which we talk about race, the answer seems to be in the range of .01 percent," said Dr.
Harold P. Freeman, the chief executive, president and director of surgery at North General Hospital in Manhattan, who has studied the issue of biology and race. "This is a very, very minimal reflection of your genetic makeup." ...
By contrast with the tiny number of genes that make some people dark-skinned and doe-eyed, and others as pale as napkins, scientists say that traits like intelligence, artistic talent and social skills are likely to be shaped by thousands, if not tens of thousands, of the 80,000 or so genes in the human genome, all working in complex combinatorial fashion.
The possibility of such gene networks shifting their interrelationships wholesale in the course of humanity's brief foray across the globe, and being skewed in significant ways according to "race" is "a bogus idea," said Dr. Aravinda Chakravarti, a geneticist at Case Western University in Cleveland.
... Dr. Eric S. Lander, a genome expert at the Whitehead Institute in Cambridge, Mass., admits that, because research on the human genome has just begun, he cannot deliver a definitive, knockout punch to those who would argue that significant racial differences must be reflected somewhere in human DNA and will be found once researchers get serious about looking for them. But as Dr. Lander sees it, the proponents of such racial divides are the ones with the tough case to defend.
"There's no scientific evidence to support substantial differences between groups," he said, "and the tremendous burden of proof goes to anyone who wants to assert those differences."
Although research into the structure and sequence of the human genome is in its infancy, geneticists have pieced together a rough outline of human genomic history, variously called the "Out of Africa" or "Evolutionary Eve" hypothesis.
By this theory, modern Homo sapiens originated in Africa 200,000 to 100,000 years ago, at which point a relatively small number of them, maybe 10,000 or so, began migrating into the Middle East, Europe, Asia and across the Bering land mass into the Americas. As they traveled, they seem to have completely or largely displaced archaic humans already living in the various continents, either through calculated acts of genocide, or simply outreproducing them into extinction.
Since the African emigrations began, a mere 7,000 generations have passed.
A mere 7,000 generations?
And because the founding population of émigrés was small, it could only take so much genetic variation with it.
As a result of that combination — a limited founder population and a short time since dispersal — humans are strikingly homogeneous, differing from one another only once in a thousand subunits of the genome.
"We are a small population grown large in the blink of an eye," Dr. Lander said.