Posted in the
Sacramento Bee
August 22, 2000
Race is only skin deep, DNA scientists believe
By Natalie Angier
New York Times
Scientists have
long suspected that the racial categories recognized by society are not
reflected on the genetic level. But 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.” Scientists say the human species is so
evolutionarily young, and its migratory patterns so wide and restless, that it
has 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 Cilera Genomics Corp. 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.”
Venter and scientists at the
National Institutes of Health recently announced they had mapped the entire
human genome and unanimously declared there is only one race – the human race.
Venter and other researchers say
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.
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 P.
Freemen, who has studied the issue of biology and race. “This is a very, very
minimal reflection of your genetic makeup.”
Unfortunately for
social harmony, the human brain is exquisitely attuned to difference in
packaging details, prompting people to exaggerate the significance of what has
come to be called race, said Dr. Douglas C. Wallace, a professor of molecular
genetics at Emory University School of Medicine in Atlanta.
“The criteria that people use for
race are based entirely on external features that we are programmed to
recognize,” he said. “And the reason we’re programmed to recognize them is that
it’s vitally important to our species that each of us be able to distinguish one
individual from the next. Our whole social structure is based on visual cues,
and we’ve been programmed to recognize them, and to recognize individuals.”
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 traits like intelligence, artistic talent and social
skills are likely to be shaped by thousands, of not tens of thousands, of the
80,000 or so genes in the human genome, all working in complex combination.
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. “The differences that we see in skin color do
not translate into widespread biological differences that are unique to groups.”
A handful of scientists continue to
insist there are fundamental differences among the three major races that extend
to the brain. Dr. J. Philippe Rushton, a University of
Western Ontario
(Canada) psychologist and author of “Race, Evolution and Behavior,” may be 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.
But 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. And fossil evidence suggests Neanderthals had sizable brains, yet they did
not even last long enough to invent standardized tests.
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 he sees it, proponents of such racial divides have a
tough case to defend.
“There’s no scientific evidence to
support substantial differences between groups,” Lander said, “and the
tremendous burden of proof goes to anyone who wants to assert those
differences.” |
