Friday, May 27, 2005

Race as a collection of genes that travel together

The New York Times > Opinion > Op-Ed Contributor: A Family Tree in Every Gene

The thesis of the article is that genes tend to travel together and that it's possible to assign a human being to a geographically isolated population in which that the gene set was very common. That assignment group can be called a "race" (actually, from the article, it might even be a "tribe" or "extended family") and this theory is a statistical (rather than cultural) model of "race".

This makes sense to me. I've been skeptical of passionate statements that "race does not exist" -- they reminded me of the earnest statements that "intelligence is not genetically determined". Well intentioned, but unpersuasive.
The New York Times
March 14, 2005
A Family Tree in Every Gene

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

... The dominance of the social construct theory [jf: of race, vs. the genetic 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...

...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 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...
A statistical model of "race" implies a (pardon the language) sort of n-dimensional "bell curve". Imagine a 'gene-space' consisting of (say) 100 or so marker gene values. If we treat this a 100-dimension space then an individual human should appear as a point in this space. If we add a dimension for frequency then we may "see" (humans aren't good at visualizing 100 dimensions -- pending our upgrades) "mountains" in the space. Those are "races". Most of us are somewhere on the flank of a mountain, but there ought to be (how can one resist the word) "pure" folk at the peaks.

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