Many biologists concur that the genome adds to a body of evidence showing that race is a product more of culture than of genetics.
Sure, there are very visible differences in things such as nose shape and skin color, and these are programmed by genes. The scientists don't deny this, but they argue that the lines we draw between "races" are not based on any biological reality.
"It's demonstrated that there's no scientific basis for assuming we are naturally, fundamentally divided into different groups," said University of Pennsylvania professor Pamela Sankar. Societies decide whether the world has four races or 40 or 400. Are Jews a race? Are Hispanics? No biological definition of race can answer that.
Our popular view of race hasn't changed much since it was put forth by biologist Carl Linnaeus in the 1700s. Linnaeus, who was famed for classifying the world's known plants and animals, also classified people into four groups - black, red, yellow, and white - "color-coded for convenience," as University of North Carolina anthropologist Jonathan Marks puts it.
The first problem with that, said Marks, is that the world is full of people who don't fit into any of those categories. What race are people from the Middle East? Siberia? Hawaii? New Guinea?
And while many people consider the term Hispanic to refer to a race, the category is based more on language. Hispanic people can have ancestors who are African, American Indian, or Spanish.
The ability to analyze DNA complicated Linnaeus' four-color picture even more. As early as the 1970s, geneticists found that there was a lot more variation within the so-called races than anyone thought.
As an example of diversity, Marks cites the common blood types - A, B, AB, and O. Some are more common in one population than another, but all populations have all blood groups.
In a similar way, most of humanity's genetic diversity is present within the designated "races." The genome project has reinforced this idea. There are some genetic variants that are more common in one group or another, but no distinctly black or white or Asian genes.
Even the sickle-cell gene, most commonly associated with Africans, also crops up in India, Saudi Arabia, and Sicily, but not in southern Africa.
To better grasp race and ethnicity, geneticists in the 1990s embarked on the Human Genome Diversity Project, which involved getting samples from 50 groups - Basques, Russians, Cambodians, Yorubans, Senegalese, Papuans, native Colombians, Palestinians, Bedouins, and others.
Those studies showed that we're much more mixed up than previously thought. People apparently have been moving around and interbreeding for thousands of years.
But that project didn't fully examine humanity's diversity, said Penn geneticist Sarah Tishkoff. She studies genetic patterns in Africa and says the project did not get a representative sample of that continent's people.
People in Africa are more genetically diverse than elsewhere, she said, because humanity originated there. All others started as some subset of Africans who migrated out over the last 60,000 years.
While anthropologists and geneticists often talk about populations rather than races, the concept of race is still used in medical research.
Studies have shown that African Americans have higher rates of hypertension and certain cancers. Maybe doctors could better diagnose and treat people using racial information. To fix those disparities, some companies are developing race-based drugs.
A decade ago, for example, a heart drug called BiDil was marketed just to African Americans.
And yet, there was never any direct evidence that the drug worked differently in people who identified themselves as white.
UNC's Marks points out that racial health differences seen in the United States often disappear when the same "races" are compared with people living in, say, France or Brazil.
Which suggests that many health disparities come down to environmental differences - poverty, poor diet, and stress, for example. In which case the cultural reality of race creates the biological and medical reality, and not the other way around.
Contact staff writer Faye Flam
at 215-854-4977 or email@example.com.