When scientists first decoded the human genome in 2000, they were quick to portray it as proof of humankind's remarkable similarity. The DNA of any two people, they emphasized, is at least 99 percent identical.
But new research is increasingly exploring the remaining fraction to explain differences between people of different continental origins.
Scientists, for instance, have recently identified the small changes in DNA that account for the pale skin of Europeans, the tendency of Asians to sweat less and West Africans' resistance to certain diseases.
At the same time, genetic information is slipping out of the laboratory and into everyday life, carrying with it the inescapable message that people of different races have different DNA. Ancestry tests tell customers what percent of their genes are from Asia, Europe, Africa and the Americas. The heart-disease drug BiDil is marketed exclusively to African Americans, who seem genetically predisposed to respond to it. Jews are offered prenatal tests for genetic disorders rarely found in other ethnic groups.
Such developments are providing some of the first tangible benefits of the genetic revolution. Yet some social critics fear they may also be giving long-discredited racial prejudices a new potency. The notion that race is more than skin-deep, they fear, could undermine principles of equal treatment and opportunity that have relied on the presumption that we are all created equal.
"We are living through an era of the ascendance of biology, and we have to be very careful," said William Henry Gates Jr., director of the W.E.B. Du Bois Institute for African and African American Research at Harvard University. "We will all be walking a fine line between using biology and allowing it to be abused."
The assertion that there is a genetic basis for race is surfacing on mainstream blogs, in college classrooms, and among the growing community of ancestry test-takers. Because of the ubiquity of DNA, it seems, the idea is occurring to many who had previously rejected or never before considered the possibility. Non-scientists are already beginning to stitch together highly speculative conclusions about the historically charged subject of race and intelligence from the new biological data.
Last month, a blogger in Manhattan described a recently published study that linked several snippets of DNA to high IQ. An online genetic database used by medical researchers, he told readers, showed that two of the snippets were found more often in Europeans and Asians than in Africans.
No matter that the link between IQ and those particular bits of DNA was unconfirmed, or that other high IQ snippets are more common in Africans, or that hundreds or thousands of others may also affect intelligence, or that their combined influence might be dwarfed by environmental factors.
Just the existence of such genetic differences between races, proclaimed the author of the Half Sigma blog, a 40-year-old software developer, means "the egalitarian theory," that all races are created equal, "is proven false."
Although few of the bits of human genetic code that vary between individuals have yet been tied to physical or behavioral traits, scientists have found that roughly 10 percent of them are more common in certain continental groups, and can be used to distinguish people of different races. They say that studying the differences, which arose during the tens of thousands of years human populations evolved on separate continents following their ancestors' dispersal from humanity's birthplace in East Africa is crucial to mapping the genetic basis for disease.
Many geneticists are loath to discuss the social implications of their findings. Still, some acknowledge that as their data and methods are extended to non-medical traits, the field is at what one leading researcher recently called "a very delicate time and a dangerous time."
"There are clear differences between people of different continental ancestries," said Marcus Feldman, a professor of biological sciences at Stanford University. "It's not there yet for things like IQ, but I can see it coming. And it has the potential to spark a new era of racism if we do not start explaining it better." Feldman said any finding on intelligence was likely to be exceedingly hard to pin down. But given that some may emerge, he wants to create "ready response teams" of geneticists to put such socially fraught discoveries in perspective.
Some fear that the authority DNA has earned through its use in freeing wrongly convicted inmates, preventing disease and reconstructing family ties, scientists warn, leads people to wrongly elevate genetics over other explanations for differences between groups.
"I've spent the last 10 years of my life researching how much genetic variability there is between populations," said Dr. David Altshuler, director of the Program in Medical and Population Genetics at the Broad Institute in Cambridge, Massachusetts. "But living in America, it is so clear that the economic and social and educational differences have so much more influence than genes. People just somehow fixate on genetics, even if the influence is very small." But on Half Sigma and elsewhere, the conversation is already flashing forward to what might happen if genetically encoded racial differences in socially desirable - or undesirable - traits are identified.
"If I were to believe the 'facts' in this post, what should I do?" one reader responded. "Should I advocate discrimination against blacks because they are less smart? Should I not hire them to my company because odds are I could find a smarter white person? Stop trying to prove that one group of people are genetically inferior to your group. Just stop."
Renata McGriff, 52, an African American health care consultant who had been encouraging black clients to volunteer genetic information to scientists, said she and other African Americans have been discussing "opting out of genetic research until it's clear we're not going to use science to validate prejudices."
Such discussions are among thousands that followed the Nobel Prize-winning geneticist James Watson's assertion last month that Africans are innately less intelligent than other races. Watson subsequently apologized and quit his post at the Cold Spring Harbor Laboratory on Long Island.
But the incident has added to uneasiness about whether society is prepared to handle the consequences of science that may eventually reveal appreciable differences between races in the genes that influence socially important traits.
Yet even some self-described liberals argue that accepting that there may be genetic differences between races is important for preparing to address them politically. Others hope the genetic data might overturn preconceived notions of racial superiority by, for example, showing that Africans are innately more intelligent than other groups. But either way, the recent outpouring of conversation on the normally taboo subject of race and genetics has prompted some to suggest that innate differences should be accepted, but - at some level - ignored. "Regardless of any such genetic variation, it is our moral duty to treat all as equal before God and before the law," wrote Perry Clark, 44, on a New York Times blog. It is not necessary, argued Clark, a retired doctor in Kansas City, to maintain the pretense that inborn racial differences do not exist.
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