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Race is an unscientific concept, experts say



   

    

Natalie Angier, New York Times


We truly are all kin beneath the skin, many scientists are concluding.

The more closely 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 young on an evolutionary scale, and its migratory patterns so wide, restless and rococo, that it has not had a chance to divide 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 Corp. in Rockville, Md.

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 unanimously declared that there is only one race -- the human race.

Most scientists in the field say that those traits most commonly used to distinguish one race from another, such as skin and eye color, or the width of the nose, are traits controlled by a relatively few number of genes, and have changed rapidly in response to extreme environmental pressures during the short history of Homo sapiens.

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 0.01 percent," said Dr. Harold Freeman, the chief executive, president and director of surgery at North General Hospital in New York City, who has studied the issue of biology and race. "This is a very, very minimal reflection of your genetic makeup."

Science to the rescue

In Freeman's view, the science of human origins can help to heal any number of wounds, and that, he says, is sweet justice.

"Science got us into this problem in the first place, with its measurements of skulls and its emphasis on racial differences and racial classifications," he said. "Scientists should now get us out of it."

Yet a few researchers continue to insist that among the three major races, there are fundamental differences that extend to the brain. Dr. J. Philippe Rushton, a psychologist at the University of Western Ontario and author of "Race, Evolution and Behavior," is perhaps the most tireless proponent of the belief that the three major races differ genetically in ways that affect average group IQ and a propensity toward criminal behavior. He asserts that his work reveals east Asians to have the largest average brain size and intelligence scores, those of African descent to have the smallest average brains and IQs, and those of European ancestry to fall in the middle.

Many scientists have objected to Rushton's methods and interpretations, arguing, among other things, that the link between total brain size and intelligence is far from clear. Women, for example, have smaller brains than men do, even when adjusted for their comparatively smaller body mass, yet average male and female IQ scores are the same. For that matter, fossil evidence suggests that Neanderthals had very sizable brains, and they did not even last long enough to invent standardized tests.

Dr. Eric 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 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."

Strikingly homogeneous

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.

Since those emigrations began, a mere 7,000 generations have passed. And because the founding population of emigres was small, it could only take so much genetic variation with it. As a result, humans are strikingly homogeneous, differing from one another only once in a thousand subunits of the genome.

The human genome is large, though, composed of some 3 billion subunits, or bases, which means that even a tiny percentage of variation from one individual to the next amounts to a sizable number of genetic discrepancies. The question is, where in the genome is that variation found, and how is it distributed among different populations?

Through transglobal sampling of neutral genetic markers -- stretches of genetic material that do not help create the body's functioning proteins but instead are composed of so-called junk DNA -- researchers have found that, on average, 88 to 90 percent of the differences between people occur within their local populations, while only about 10 to 12 percent of the differences distinguish one population, or race, from another.

To put it another way, the citizens of any given village in the world, whether in Scotland or Tanzania, hold 90 percent of the genetic variability that humanity has to offer.

But that 90-10 ratio is just an average, and refers only to junk-DNA markers. For the genetic material that encodes proteins, the picture is somewhat more complex. Many workhorse genes responsible for basic organ functions show virtually no variability from individual to individual, which means they are even less "race-specific" than are neutral genetic markers.

Some genes, notably those of the immune system, show enormous variability, but the variability does not track with racial groupings.

Ethnic diversity

A few group differences are more than skin deep. Among the most famous examples are the elevated rates of sickle-cell anemia among blacks and of beta-thalassemia, another hemoglobin disorder, among those of Mediterranean heritage.

Both traits evolved to help the ancestors of these groups resist malaria infection, but they prove lethal when inherited in a double dose. As with differences in skin pigmentation, the pressure of the environment to develop a group-wide trait was powerful, and the means to do so simple and straightforward, through the alteration of a single gene.

Another cause of group differences is the so-called founder effect. In such cases, the high prevalence of an unusual condition in a population can be traced to a founding ancestor who happened to carry a specific mutation into a region. Over many generations of comparative isolation and inbreeding, the community, like it or not, became "enriched" with the founder's disorder. The founder effect explains the high incidence of the neurodegenerative disorder, Huntington's disease in the Lake Maracaibo region of Venezuela, and of Tay-Sachs disease among Ashkenazi Jews.

Thus Dr. Sonia Anand, an assistant professor of medicine at McMaster University in Ontario, suggests that clinicians think about ethnicity rather than race when seeking clues to how disease patterns differ from one group to the next.

"Ethnicity is a broad concept that encompasses both genetics and culture," Anand said. "Thinking about ethnicity is a way to bring together questions of a person's biology, lifestyle, diet, rather than just focusing on race."

Copyright Star Tribune. All rights reserved.

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