Even if geneticists can see a difference between races at the level of DNA, what practical difference does that make at the level of the physical person? Biologists make a useful distinction between the genotype and phenotype of an organism. The genotype is simply the genome or hereditary information; phenotype is the physical creature that is generated from the genotype.
Because so much of the genome is nonworking DNA that does not code for genes, it is possible for genotype to vary without causing much change in phenotype. The Icelanders whose genotype can be matched to the island's 11 regions probably don't look any different from each other (although a survey is under way to see if they have a slightly different pattern of disease).
The work of Risch and Feldman showing that people can be genetically assigned to their continent of origin—that is, race—is based on genotype, and does not in itself indicate how much people of different racial genotypes might differ in phenotype. However, the sites on the genome that they examined move around during recombination (the shuffling of blocks of DNA that occurs between generations) in the same way that genes do. So some of these sites, especially those that lie close to genes, will be proxies for the genes themselves. Thus the fact that people can be assigned to racial groups based on sampling just a few hundred sites in their genome suggests that quite a large number of genes may also vary between races and that so may the phenotype influenced by such genes. Races certainly vary in physical appearance. Nor are the differences just skin deep; there are also variations in susceptibility to disease and in the response to drugs. The overarching similarity of all races is just what would be expected, given that the ancestral human population existed only 50,000 years ago, and given that human nature must to a great extent have been molded before the ancestral dispersal, since all its principal features are found universally. Proof of the continuing unity of the human family is that people of different races have no difficulty in interbreeding, and that the members of any one culture can, absent discrimination, function in any other.
But the existence of considerable variation between races should not be any surprise either, given that the human family has long been split into separate branches, each of which has evolved independently for up to 50,000 years or more, buffeted in different directions by the random forces of genetic drift and the selective pressures of different climates, diseases and societies. Study of racial variation is not yet a scholarly pursuit, except in the area of medicine, and even there is not without controversy. Physicians who study racial disparities in medicine are well aware that many social attributes, such as poverty or lesser access to health care, track along with race. These factors, just as often as genetics, may be the explanation why African Americans, say, suffer a greater burden of certain diseases than white patients. But to ignore race altogether, as some argue should be done, would blind researchers to many findings of value, both social and genetic. A physician cannot tell if his black patients receive worse health care than whites unless he has first noted which race they belong to. As for genetic contributions, BiDil would never have been discovered if Jay Cohn had not analyzed the response of African American patients to the drug. The discovery of an important drug for an underserved community might seem unalloyed good news. Nonetheless, some African Americans greeted BiDil with a distinct lack of enthusiasm because of a wider concern. These spokesmen fear that if African Americans are defined genetically, even for the benign purpose of medicine, the public may associate them with less reputable attributes, such as propensity to crime. "If you think in terms of taxonomies of race, you will make the dangerous conclusion that race will explain violence," Troy Duster, a sociologist at New York
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