RACIAL DIVISIONS IN HUMAN BEINGS ARE AS DEEP AS DNA

Saturday, May 10,2003

The Human Genome Project is forcing a re-evaluation of conventional thinking about race. The sequencing of the genome has demonstrated that human beings anywhere in the world are remarkably alike at the genetic level. Yet the division into the continental sub-populations traditionally called "races" is observable in human DNA, putting paid to the fashionable notion that the connection between race and biology is merely skin-deep.

In 1998, the American Anthropological Association issued a "statement on 'race' " saying that "physical variations in the human species have no meaning except the social ones that humans put on them." The complete statement, which is more subtle than that (available at www.aaanet.org/stmts/racepp.htm on the Web), also gives a capsule summary of the historical reasons why scientists today are so skittish about anything that might link them to the discredited racist views of the past. It's worth reading. But as a statement about biology it is wrong.

Statistically significant differences in susceptibility to a wide range of diseases, in response to treatments, and in sensitivity to environmental contamination are "physical variations" meaningful indeed to the people who get sick. The claim that these differences "have no meaning" except the social one is akin to the equally untenable claim that differences between men and women have nothing to do with biology but are "socially constructed." Of course culture and society have a great deal to do with what kind of differences are observed, but the underlying biology shapes what societies construct.

At its annual convention, the American Association for the Advancement of Science addressed these issues in a panel titled "Ethical, social and policy implications of studies of human genetic variation."

Mildred Cho, co-director of the Stanford Center for Biomedical Ethics, organized the panel. She has written about the need for an acceptable vocabulary for discussing population-based genetic diversity. "Rejecting race as genetic hierarchy is not tantamount to rejecting the idea that human populations differ genetically," she and a co-author wrote last year.

David Altshuler, a geneticist and endocrinologist who does research into diabetes at Massachusetts General Hospital, led off the panel.

The question of how similar or different people are has been around a long time. For example, Altshuler said, around the time of the Civil War the celebrated American naturalist Louis Agassiz argued vigorously that groups from different parts of the world might be considered different species.

The genetic answer is clear, however. We're all one species, and in fact surprisingly alike at the level of the genes. How alike? We each have two copies of the human genome in each of our cells. "If we took one copy of my genome," Altshuler said, "and one from anybody else in the room, or one from anywhere on earth, it turns out the answer is the same. How many letters among the 3 billion in the genome would vary? One in a thousand or less."

Moreover, about 90 percent of the variation that does exist is very old, tracing back on average about 400,000 years. "So 99.99 percent of your genome is either exactly the same as everyone's, or if it varies it varies in a way that wherever you went on earth you'd find the same variants," Altshuler said.

Altshuler was followed by Noah Rosenberg from the University of Southern California, who discussed his research using a computer algorithm to identify genetic clusters in the human population structure.

Rosenberg and his colleagues used what are called "microsatellite markers," a particular spot on the genome where a tiny fragment of DNA, for example "GATA," using letters from the genetic code, is repeated a number of times. The number of repetitions varies because copies tend to be added or lost by mutation. Each different type is called an allele. They typically have no effect on anything that could be called a genetic trait because they are from the part of the genome that doesn't code for any genes.

The project used information from 377 marker sites for 1,056 people from 52 fairly distinct populations. Nearly half of all the possible alleles are found everywhere in the world. But for most of the 377 different markers the frequencies are different in different regions. Given enough people and enough computer time you can pretty well sort them into regions without telling the computer ahead of time what the regions ought to be.

When the algorithm separated them into five clusters, the clusters were populations from Africa, three regions together including Europe, the Middle East and Central/South Asia, then East Asia, Oceania and the Americas.

That might be what you'd expect. However, the important thing to understand is that the computation isn't influenced by what you expected because it doesn't use information about the sampling location. If there were a more plausible way to separate people into clusters the algorithm would find it.

But does clustering matter? As Altshuler noted, the information you get from the algorithm is pretty much what people will tell you about their ancestry. And neither his work nor Rosenberg's deals with observable genetic traits, or with the potentially problematic question of whether there might exist genetic traits that are culturally or socially important.

The reason research of this kind is threatening is that it unequivocally demolishes the claim that racial categories have no support from biology, as the anthropologists' statement claimed -- a claim that, as Altshuler pointed out, is itself political.

So it's not surprising that the panelists sounded more than a little uneasy. I mentioned this to someone after the panel concluded and he said, "Of course. You have to understand that being misquoted on this topic can mean the end of your career."

Actually, I do understand that. I just think it's unfortunate and I'm encouraged that the discussion is at least beginning.