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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." ©
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