The Genetic Archaeology of Race

DNA analysis is explaining where "racial difference" comes from—and what it does and doesn't mean. The study of human genetic variation has become the most contentious area in modern science

Over the past decade or so genetics researchers have been undermining the widespread belief that groups of people differ genetically in character, temperament, or intelligence. They have shown that all human beings are incredibly similar genetically—much more so than other species of large mammals. They have revealed the folly of attributing group behavioral differences to biology rather than culture.

But that's not how many of the news stories have read. On the contrary, here are the kinds of headlines you might have seen: "RESEARCHERS FIND GENETIC MARKER UNIQUE TO AFRICANS." "ASIANS BIOLOGICALLY LESS SUSCEPTIBLE TO ALCOHOLISM." "ALL NATIVE AMERICANS DESCENDED FROM A SMALL NUMBER OF FOUNDERS." In other words, given how journalists, pundits, and bigots have interpreted genetics research, people are probably more convinced than ever that group differences are significant.

We will continue to be inundated with DNA-sequence information—and with interpretations of that information—for many years to come. These genetic data have immense medical potential (though that potential will probably take much longer to realize than most people suspect). By studying the genetic differences among individuals, researchers will eventually find many DNA variants that contribute to health or disease.

But genetics research is also producing results of an entirely different kind. Differences in DNA sequences from person to person reflect the cumulative effects of human history. The patterns of genetic variation in the world today therefore carry a record of that history. They document the evolution of an African ape that began walking on two legs about four million years ago. They record the existence, sometime between 100,000 and 200,000 years ago, of a small group of people who are the ancestors of every person alive today. They chronicle the origins of "races" and "ethnic groups" and describe how those groups have both blended and separated over time.

Most genetics researchers are well aware of the historical dimensions of their work. But because these considerations raise uncomfortable issues, particularly issues of race, they tend to be downplayed. The White House news conference held on June 26 of last year to celebrate the sequencing of the human genome was filled with stirring but vague homages to human unity. "The human genome is our shared inheritance," said Francis Collins, the head of the publicly funded Human Genome Project, at the National Institutes of Health. "Race has no genetic or scientific basis," said Craig Venter, whose company, Celera Genomics, has been sequencing and analyzing human DNA.

The reality is considerably more complex. Genetics research is demonstrating that the differences in appearance among groups are profoundly incidental, but these differences do have a genetic basis. And although it's true that all people have inherited the same genetic legacy, the genetic differences among groups have important implications for our understanding of history and for biomedical research. These complications in an otherwise reassuring story have thoroughly spooked the leaders of the public and private genome efforts. The NIH has been collecting information about genetic variants from different ethnic groups in the United States, but it has refused to link specific variants with ethnicity. Celera has been sequencing DNA from an Asian, a Hispanic, a Caucasian, and an African-American, but it, too, declines to say which DNA is which.

This strategy of avoiding the issue is almost sure to backfire. It seems to imply that geneticists have something to hide. But the message emerging from laboratories around the world should be hailed, not muzzled. It is one of great hope and promise for our species.

One reason for the caution displayed by the genome sequencers is a largely overlooked drama that has been playing out on the fringes of the Human Genome Project for the past ten years. Unlike most scientific dramas, this one has a clear protagonist: Luigi Luca Cavalli-Sforza, a genial but sharp-tongued professor of genetics at Stanford University. Now seventy-nine, with thick silver hair and a perpetually inquisitive expression, Cavalli-Sforza combines the demeanor of a man accustomed to respect with a natural openness that has won him many friends. Born and educated in Italy, he went to Stanford University in 1971. There he quickly became a leader in the fledgling field of anthropological genetics, which draws inferences about the past based on the patterns observed in human DNA. His former students are now scattered around the world, carrying on the work he began. Yet he still rides his bike to campus each morning to write, read, and analyze the latest results from the lab. "He'll work until he drops," an associate says. "He's curious about the science."

In 1991 Cavalli-Sforza and a group of colleagues proposed a comprehensive study of human genetic differences, which they called the Human Genome Diversity Project. The study would involve gathering cells from several thousand people around the world, "immortalizing" the cells by converting them into laboratory cell lines, and using the cells' DNA to reconstruct human evolution and history. For Cavalli-Sforza, the Human Genome Diversity Project was to be the culmination of a lifetime of work.

The proposal loosed a flood of controversy. Aboriginal groups in the United States, New Guinea, and other countries accused the HGDP of stealing their genes, destroying their culture, and even contributing to genocide. Academic critics claimed that the project could encourage racist thinking, by oversimplifying issues of great complexity. "The idea of studying human genetic diversity is a good one," says one outspoken critic, Jonathan Marks, an anthropologist at the University of North Carolina at Charlotte. "But the way that Cavalli-Sforza has conceptualized it has problems at all levels."

Cavalli-Sforza has been baffled by the reaction to his proposal. He has always believed that the HGDP will help to end racism, not inflame it. In the 1970s he participated in public debates with the Stanford physicist William Shockley to dispute Shockley's racist ideas. He has worked closely with various African groups and cares deeply about their well-being. He protests that his intentions have always been purely scientific.

For almost a decade Cavalli-Sforza has been trapped in the paradox at the heart of human genetics: The only way to understand how similar we are is to learn how we differ. Yet any study of human differences seems to play into the hands of those who would accentuate those differences. Researchers might claim that the genetic differences they identify among groups have no biological significance. Yet simply by dividing human beings into categories—whether sub-Saharan Africans, Jews, Germans, or Australian aborigines—they reinforce the distinctions they would seek to minimize. How to resolve this dilemma is quickly becoming one of the most difficult problems facing the study of human genetics.

A Theory of Mutation

More than 10,000 years ago, on the frigid, wind-swept plains of northeastern Siberia, a genetic accident occurred in a testicle of a particular man. As one of the man's sperm cells divided, the Y chromosome in the cell underwent a copying error. One of the chemical units making up his DNA changed from a molecule called cytosine to one called thymine. An elaborate biochemical proofreading apparatus is supposed to correct such copying errors, which geneticists call mutations. But there are so many individual chemical units, or nucleotides, in human DNA—about 60 million in the Y chromosome, and about three billion in the other chromosomes in a human sperm or egg cell—that a few mutations inevitably creep in every time a cell divides.

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