Three Is Not Enough

• Genes:

In 1972, population biologist Richard Lewontin of Harvard University laid out the genetic case against race. Analyzing 17 genetic markers in 168 populations such as Austrians, Thais and Apaches, he found that there is more genetic difference within one race than there is between that race and another. Only 6.3 percent of the genetic differences could be explained by the individuals' belonging to different races. That is, if you pick at random any two "blacks" walking along the street, and analyze their 23 pairs of chromosomes, you will probably find that their genes have less in common than do the genes of one of them with that of a random "white" person. Last year the Human Genome Diversity Project used 1990s genetics to extend Lewontin's analysis. Its conclusion: genetic variation from one individual to another of the same "race" swamps the average differences between racial groupings. The more we learn about humankind's genetic differences, says geneticist Luca Cavalli-Sforza of Stanford University, who chairs the committee that directs the biodiversity project, the more we see that they have almost nothing to do with what we call race.

• Traits:

As sickle-cell "races" and epicanthic-fold "races" show, there are as many ways to group people as there are traits. That is because "racial" traits are what statisticians call non-concordant. Lack of concordance means that sorting people according to these traits produces different groupings than you get in sorting them by those (equally valid) traits. When biologist Jared Diamond of UCLA surveyed half a dozen traits for a recent issue of Discover magazine, he found that, depending on which traits you pick, you can form very surprising "races." Take the scooped-out shape of the back of the front teeth, a standard "Asian" trait. Native Americans and Swedes have these shovel-shaped incisors, too, and so would fall in the same race. Is biochemistry better? Norwegians, Arabians, north Indians and the Fulani of northern Nigeria, notes Diamond, fall into the "lactase race" (the lactase enzyme digests milk sugar). Everyone else -- other Africans, Japanese, Native Americans -- forms the "lactase-deprived race" (their ancestors did not drink milk from cows or goats and hence never evolved the lactase gene). How about blood types, the familiar A, B and O groups? Then Germans and New Guineans, populations that have the same percentages of each type, are in one race; Estonians and Japanese comprise a separate one for the same reason, notes anthropologist Jonathan Marks of Yale University. Depending on which traits are chosen, "we could place Swedes in the same race as either Xhosas, Fulani, the Ainu of Japan or Italians," writes Diamond.