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OP-ED CONTRIBUTOR
A Family Tree in Every Gene
By ARMAND MARIE LEROI
http://www.nytimes.com/2005/03/14/opinion/14leroi.html?th=&pagewanted=print&position=

[L] ondon — Shortly after last year's tsunami devastated the lands on the 
Indian Ocean, The Times of India ran an article with this headline: "Tsunami 
May Have Rendered Threatened Tribes Extinct." The tribes in question were the 
Onge, Jarawa, Great Andamanese and Sentinelese - all living on the Andaman 
Islands - and they numbered some 400 people in all. The article, noting that 
several of the archipelago's islands were low-lying, in the direct path of the 
wave, and that casualties were expected to be high, said, "Some beads may have 
just gone missing from the Emerald Necklace of India."

The metaphor is as colorful as it is well intentioned. But what exactly does it 
mean? After all, in a catastrophe that cost more than 150,000 lives, why should 
the survival of a few hundred tribal people have any special claim on our 
attention? There are several possible answers to this question. The people of 
the Andamans have a unique way of life. True, their material culture does not 
extend beyond a few simple tools, and their visual art is confined to a few 
geometrical motifs, but they are hunter-gatherers and so a rarity in the modern 
world. Linguists, too, find them interesting since they collectively speak 
three languages seemingly unrelated to any others. But the Times of India took 
a slightly different tack. These tribes are special, it said, because they are 
of "Negrito racial stocks" that are "remnants of the oldest human populations 
of Asia and Australia."

It's an old-fashioned, even Victorian, sentiment. Who speaks of "racial stocks" 
anymore? After all, to do so would be to speak of something that many 
scientists and scholars say does not exist. If modern anthropologists mention 
the concept of race, it is invariably only to warn against and dismiss it. 
Likewise many geneticists. "Race is social concept, not a scientific one," 
according to Dr. Craig Venter - and he should know, since he was first to 
sequence the human genome. The idea that human races are only social constructs 
has been the consensus for at least 30 years.

But now, perhaps, that is about to change. Last fall, the prestigious journal 
Nature Genetics devoted a large supplement to the question of whether human 
races exist and, if so, what they mean. The journal did this in part because 
various American health agencies are making race an important part of their 
policies to best protect the public - often over the protests of scientists. In 
the supplement, some two dozen geneticists offered their views. Beneath the 
jargon, cautious phrases and academic courtesies, one thing was clear: the 
consensus about social constructs was unraveling. Some even argued that, looked 
at the right way, genetic data show that races clearly do exist.

The dominance of the social construct theory can be traced to a 1972 article by 
Dr. Richard Lewontin, a Harvard geneticist, who wrote that most human genetic 
variation can be found within any given "race." If one looked at genes rather 
than faces, he claimed, the difference between an African and a European would 
be scarcely greater than the difference between any two Europeans. A few years 
later he wrote that the continued popularity of race as an idea was an 
"indication of the power of socioeconomically based ideology over the supposed 
objectivity of knowledge." Most scientists are thoughtful, liberal-minded and 
socially aware people. It was just what they wanted to hear.

Three decades later, it seems that Dr. Lewontin's facts were correct, and have 
been abundantly confirmed by ever better techniques of detecting genetic 
variety. His reasoning, however, was wrong. His error was an elementary one, 
but such was the appeal of his argument that it was only a couple of years ago 
that a Cambridge University statistician, A. W. F. Edwards, put his finger on 
it.

The error is easily illustrated. If one were asked to judge the ancestry of 100 
New Yorkers, one could look at the color of their skin. That would do much to 
single out the Europeans, but little to distinguish the Senegalese from the 
Solomon Islanders. The same is true for any other feature of our bodies. The 
shapes of our eyes, noses and skulls; the color of our eyes and our hair; the 
heaviness, height and hairiness of our bodies are all, individually, poor 
guides to ancestry.

But this is not true when the features are taken together. Certain skin colors 
tend to go with certain kinds of eyes, noses, skulls and bodies. When we glance 
at a stranger's face we use those associations to infer what continent, or even 
what country, he or his ancestors came from - and we usually get it right. To 
put it more abstractly, human physical variation is correlated; and 
correlations contain information.

Genetic variants that aren't written on our faces, but that can be detected 
only in the genome, show similar correlations. It is these correlations that 
Dr. Lewontin seems to have ignored. In essence, he looked at one gene at a time 
and failed to see races. But if many - a few hundred - variable genes are 
considered simultaneously, then it is very easy to do so. Indeed, a 2002 study 
by scientists at the University of Southern California and Stanford showed that 
if a sample of people from around the world are sorted by computer into five 
groups on the basis of genetic similarity, the groups that emerge are native to 
Europe, East Asia, Africa, America and Australasia - more or less the major 
races of traditional anthropology.

One of the minor pleasures of this discovery is a new kind of genealogy. Today 
it is easy to find out where your ancestors came from - or even when they came, 
as with so many of us, from several different places. If you want to know what 
fraction of your genes are African, European or East Asian, all it takes is a 
mouth swab, a postage stamp and $400 - though prices will certainly fall.

Yet there is nothing very fundamental about the concept of the major 
continental races; they're just the easiest way to divide things up. Study 
enough genes in enough people and one could sort the world's population into 
10, 100, perhaps 1,000 groups, each located somewhere on the map. This has not 
yet been done with any precision, but it will be. Soon it may be possible to 
identify your ancestors not merely as African or European, but Ibo or Yoruba, 
perhaps even Celt or Castilian, or all of the above.

The identification of racial origins is not a search for purity. The human 
species is irredeemably promiscuous. We have always seduced or coerced our 
neighbors even when they have a foreign look about them and we don't understand 
a word. If Hispanics, for example, are composed of a recent and evolving blend 
of European, American Indian and African genes, then the Uighurs of Central 
Asia can be seen as a 3,000-year-old mix of West European and East Asian genes. 
Even homogenous groups like native Swedes bear the genetic imprint of 
successive nameless migrations.

Some critics believe that these ambiguities render the very notion of race 
worthless. I disagree. The physical topography of our world cannot be 
accurately described in words. To navigate it, you need a map with elevations, 
contour lines and reference grids. But it is hard to talk in numbers, and so we 
give the world's more prominent features - the mountain ranges and plateaus and 
plains - names. We do so despite the inherent ambiguity of words. The Pennines 
of northern England are about one-tenth as high and long as the Himalayas, yet 
both are intelligibly described as mountain ranges.

So, too, it is with the genetic topography of our species. The billion or so of 
the world's people of largely European descent have a set of genetic variants 
in common that are collectively rare in everyone else; they are a race. At a 
smaller scale, three million Basques do as well; so they are a race as well. 
Race is merely a shorthand that enables us to speak sensibly, though with no 
great precision, about genetic rather than cultural or political differences.

But it is a shorthand that seems to be needed. One of the more painful 
spectacles of modern science is that of human geneticists piously disavowing 
the existence of races even as they investigate the genetic relationships 
between "ethnic groups." Given the problematic, even vicious, history of the 
word "race," the use of euphemisms is understandable. But it hardly aids 
understanding, for the term "ethnic group" conflates all the possible ways in 
which people differ from each other.

Indeed, the recognition that races are real should have several benefits. To 
begin with, it would remove the disjunction in which the government and public 
alike defiantly embrace categories that many, perhaps most, scholars and 
scientists say do not exist.

Second, the recognition of race may improve medical care. Different races are 
prone to different diseases. The risk that an African-American man will be 
afflicted with hypertensive heart disease or prostate cancer is nearly three 
times greater than that for a European-American man. On the other hand, the 
former's risk of multiple sclerosis is only half as great. Such differences 
could be due to socioeconomic factors. Even so, geneticists have started 
searching for racial differences in the frequencies of genetic variants that 
cause diseases. They seem to be finding them.

Race can also affect treatment. African-Americans respond poorly to some of the 
main drugs used to treat heart conditions - notably beta blockers and 
angiotensin-converting enzyme inhibitors. Pharmaceutical corporations are 
paying attention. Many new drugs now come labeled with warnings that they may 
not work in some ethnic or racial groups. Here, as so often, the mere prospect 
of litigation has concentrated minds.

Such differences are, of course, just differences in average. Everyone agrees 
that race is a crude way of predicting who gets some disease or responds to 
some treatment. Ideally, we would all have our genomes sequenced before 
swallowing so much as an aspirin. Yet until that is technically feasible, we 
can expect racial classifications to play an increasing part in health care.

The argument for the importance of race, however, does not rest purely on 
utilitarian grounds. There is also an aesthetic factor. We are a physically 
variable species. Yet for all the triumphs of modern genetics, we know next to 
nothing about what makes us so. We do not know why some people have prominent 
rather than flat noses, round rather than pointed skulls, wide rather than 
narrow faces, straight rather than curly hair. We do not know what makes blue 
eyes blue.

One way to find out would be to study people of mixed race ancestry. In part, 
this is because racial differences in looks are the most striking that we see. 
But there is also a more subtle technical reason. When geneticists map genes, 
they rely on the fact that they can follow our ancestors' chromosomes as they 
get passed from one generation to the next, dividing and mixing in 
unpredictable combinations. That, it turns out, is much easier to do in people 
whose ancestors came from very different places.

The technique is called admixture mapping. Developed to find the genes 
responsible for racial differences in inherited disease, it is only just moving 
from theory to application. But through it, we may be able to write the genetic 
recipe for the fair hair of a Norwegian, the black-verging-on-purple skin of a 
Solomon Islander, the flat face of an Inuit, and the curved eyelid of a Han 
Chinese. We shall no longer gawp ignorantly at the gallery; we shall be able to 
name the painters.

There is a final reason race matters. It gives us reason - if there were not 
reason enough already - to value and protect some of the world's most obscure 
and marginalized people. When the Times of India article referred to the 
Andaman Islanders as being of ancient Negrito racial stock, the terminology was 
correct. Negrito is the name given by anthropologists to a people who once 
lived throughout Southeast Asia. They are very small, very dark, and have 
peppercorn hair. They look like African pygmies who have wandered away from 
Congo's jungles to take up life on a tropical isle. But they are not.

The latest genetic data suggest that the Negritos are descended from the first 
modern humans to have invaded Asia, some 100,000 years ago. In time they were 
overrun or absorbed by waves of Neolithic agriculturalists, and later nearly 
wiped out by British, Spanish and Indian colonialists. Now they are confined to 
the Malay Peninsula, a few islands in the Philippines and the Andamans.

Happily, most of the Andamans' Negritos seem to have survived December's 
tsunami. The fate of one tribe, the Sentinelese, remains uncertain, but an 
Indian coast guard helicopter sent to check up on them came under bow and arrow 
attack, which is heartening. Even so, Negrito populations, wherever they are, 
are so small, isolated and impoverished that it seems certain that they will 
eventually disappear.

Yet even after they have gone, the genetic variants that defined the Negritos 
will remain, albeit scattered, in the people who inhabit the littoral of the 
Bay of Bengal and the South China Sea. They will remain visible in the 
unusually dark skin of some Indonesians, the unusually curly hair of some Sri 
Lankans, the unusually slight frames of some Filipinos. But the unique 
combination of genes that makes the Negritos so distinctive, and that took tens 
of thousands of years to evolve, will have disappeared. A human race will have 
gone extinct, and the human species will be the poorer for it.

Armand Marie Leroi, an evolutionary developmental biologist at Imperial College 
in London, is the author of "Mutants: On Genetic Variety and the Human Body."


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