Not Really, DNA Shows
By NATALIE ANGIER
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
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
"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
"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
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."
Unfortunately for social harmony, the human
brain is exquisitely attuned to differences 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
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
"The differences that we see in skin
color do not translate into widespread biological differences that are
unique to groups."
Dr. Jurgen K. Naggert, a geneticist at the
Jackson Laboratory in Bar Harbor, Me., said: "These big groups that
we characterize as races are too heterogeneous to lump together in a
If you're doing a DNA study to look for
markers for a particular disease, you can't use 'Caucasians' as a group.
They're too diverse.
No journal would accept it."
Yet not every researcher sees race as a
meaningless or antediluvian notion.
"I think racial classifications have
been useful to us," said Dr. Alan Rogers, a population geneticist and
professor of anthropology at the University of Utah in Salt Lake City.
"We may believe that most differences between races are superficial,
but the differences are there, and they are informative about the origins
and migrations of our species. To do my work, I have to get genetic data
from different parts of the world, and look at differences within groups
and between groups, so it helps to have labels for groups."
And there are a handful of researchers who continue to insist that there
are fundamental differences among the three major races that extend to the
Dr. J. Philippe Rushton, a psychologist at
University of Western Ontario in Canada 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 I.Q. 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 I.Q.'s,
and those of European ancestry to fall in the middle.
Yet many scientists have objected to his
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 I.Q. 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 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
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
Since the African emigrations began, a mere
7,000 generations have passed. 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.
"We are a little village that's grown
all over the world, and we retain the genetic variation seen in that
The human genome is large, though, composed
of three billion-odd 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
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 percent to 90 percent
of the differences between people occur within their local populations,
while only about 10 percent 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. Then there are the genes that control pigmentation and
other physical features.
These also come in a wide assortment of
"flavors," but unlike immune-related genes, are often
distributed in population-specific clusters, resulting in Swedes who look
far more like other Swedes than they do like Australian Aborigines.
A few group differences are more than skin
Among the most famous examples are the
elevated rates of sickle-cell anemia among African-Americans 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 both 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 novel
mutation into the 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 Huntington's neurodegenerative disease in
the Lake Maracaibo region of Venezuela, and of Tay-Sachs disease among
But Dr. Naggert emphasized that medical
geneticists had a much better chance of unearthing these founder effects
by scrutinizing small, isolated and well-defined populations, like the
northern Finns, the Basques of Spain, or the Amish of Pennsylvania, than
they did by going after "races."
Dr. Sonia S. Anand, an assistant professor
of medicine at McMaster University in Ontario, proposed 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," Dr. 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.
Ethnicity is about phenotype and genotype, and, if you define the
terms of your study, it allows you to look at differences between groups
in a valid way."
In investigating the reasons behind the
high incidence of cardiovascular disease among people from the Indian
subcontinent, for example, Dr. Anand discovered that Indians had
comparatively elevated amounts of clotting factors in their blood.
Beyond tallying up innate traits, she also
takes into account how Indian culture and life habits may pose added risks
for heart disease -- noting, for example, that a woman's status in India
is directly proportional to her number of belly rolls.
In Dr. Freeman's view, the science of human
origins can help to heal any number of wounds, and that, he says is sweet
"Science got us into this problem in
the first place, with its measurements of skulls and its emphasis on
racial differences and racial classifications," Dr. Freeman said.
"Scientists should now get us out of
it. They need to be leaders in promoting an evolutionary understanding of
the human race."