No trace of race Genome Sequencing Project proves nothing biological separates peoples By Tina Hesman ST. LOUIS POST-DISPATCH June 4, 2003 Human races are a myth, biologically speaking. The recently completed Human Genome Sequencing Project confirmed what many scientists knew all along – that humans don't fit the biological criteria that defines race. The revelation strikes at the heart of some of the most deeply entrenched social, cultural and political divisions among Americans. But some experts say our conception of race is not likely to be swayed by the DNA evidence. Breaking down racial barriers could have implications for medicine. Public health officials are keen to remind people of certain ethnic or racial backgrounds of increased risks of certain diseases. But those risks may be due more to geography than genetics. And classifying people into arbitrary racial groups could impair individualized care, experts fear. "Race is real in a political, social sense, but it's not biological," said Alan R. Templeton, a population biologist at Washington University in St. Louis. Other species, including chimpanzees and wolves, divide into subspecies – known in human circles as races – but people are too good at mingling to create a subspecies. A subspecies arises when geographical boundaries cut off a group of organisms from the rest of the species. The isolated group begins to breed and adapt to the environment, causing changes in DNA over time. The longer a group is isolated, the more changes it accumulates in its collective DNA. If the split from the rest of the species lasts long enough, the separation becomes genetically, and sometimes physically, apparent. Eventually the isolated group may form a different species. That would mean that the new species could not reproduce when mating with the original species. Members of different subspecies can breed, but don't. Measuring differences Geographical constraints are the key to creating races. For example, collared lizards living on Ozark mountaintops can form subspecies, while human inhabitants of the same mountains don't. Templeton can hike the distance between Taum Sauk Mountain and Bell Mountain in less than a day, but the blue-green collared lizards he studies are mostly confined to their respective peaks. While the lizards are members of the same subspecies, they look slightly different. Some turn yellow or sport splashes of orange on their noses and toes instead of their throats. Those are cosmetic changes obvious only to biologists and other lizards. But the lizards also have specific changes in their DNA that clearly distinguish a Bell Mountain lizard from his cousin from Taum Sauk. Humans have proved that there ain't no mountain high enough, no ocean wide enough and no environment harsh enough to keep them confined. Roving feet also carry genes to different parts of the globe, ensuring that people never display sharp distinctions in their DNA. In fact, humans are one of the most homogenous species on the planet, Templeton said. His Ozark mountain collared lizards are three times more variable than humans. Biologists use a measurement called Wright's F statistic, or Fst, to quantify the amount of genetic difference, or heterozygosity, between two groups. The scale runs from zero – no difference – to a theoretical maximum of one – distinct populations. A heterozygote is an individual who inherits one version of a gene, called an allele, from the mother and a different variant of the gene from the father. Homozygotes inherit the same mom and pop alleles. Alleles arise naturally. Sometimes one allele causes disease, but most of the time the variations are harmless, just different. Some scientists who study insect races say that in order to be considered different races or subspecies, two groups must have an Fst score of at least 0.25 to 0.30. That means that at least 25 percent of their genes must be heterozygous. But those cutoff points are arbitrary, and many scientists refuse to pinpoint a number that would signify when a group qualifies as a subspecies. Many don't even recognize subspecies, saying that the distinction has no real meaning beyond qualifying groups of organisms for protection under endangered species laws. Zero for humans Regardless of where scientists draw the subspecies line, they agree on one thing – humans don't come close to crossing the racial divide. Gray wolves split into subspecies, scoring 0.7 on Wright's scale. Even Ozark mountain lizards living on ridges less than a mile apart differ from each other by an Fst score of 0.4. But human groups score only about 0.15 on the statistical scale. That's a worldwide total measuring all human variation. When scientists try to measure differences between only two groups of people, they usually find a lower score, on average about 0.08 – only 8 percent of the genes examined have more than one allele. The most disparate human groups barely make the 0.25 mark, far below the diversity seen in lizards. And even though they make the arbitrary cutoff, those human groups are not geographically isolated and qualify as races. Any way you measure it, the amount of divergence between people is essentially zero, said Joseph L. Graves Jr., an evolutionary biologist and author of books on biology and race. It's certainly not enough to qualify human groups as different races. "The scientific case for the nonexistence of human race is overwhelming," Graves said. Skin deep Humans traditionally divide people into races according to skin color. But the association really is only skin-deep and reveals nothing about genetic relationships. For instance, the Pygmy people living in Zaire and the Central African Republic, and people from Melanesia, such as people from the island of Fiji, are among the darkest-skinned populations in the world. A racial classification based on skin color would likely group them as members of the same race quite distinct from fair-skinned Europeans. But genetic analysis reveals that both African Pygmies and people from Fiji are more closely related to Europeans than to each other. What the differences in skin tone really reveal is geographic origins of a person's ancestors, Graves said. People from Fiji may look like African Pygmies because the two groups live in places where UV radiation from the sun is intense. "All traits are genetically determined. All traits are environmentally determined," Graves said. "Nature-nurture is a red herring. It's always nature and nurture." Nowhere is that more apparent than in medicine. Public health officials warn that diseases such as diabetes and heart disease are more prevalent in African- Americans than in white Americans. But the discrepancy is more likely due to diet, exercise and other social and environmental factors than to race, Graves said. Western Africans don't suffer from heart disease and Type 2 diabetes, but African-Americans and Afro-Caribbeans do, he said. If race determined disease risk, those groups would fall ill at the same rate. Other diseases appear at first glance to be linked to race. Sickle-cell anemia is often branded as a disease that primarily strikes blacks. That's true to some extent, but again the racial link crumbles under further scrutiny. People from Saudi Arabia, Greece and India also have high rates of the disease and other related blood disorders. Up to 50 percent of Saudi Arabians carry a gene for alpha thalassemia, and 35 percent of Indians from certain tribes carry sickle-cell alleles. Sickle-cell anemia is caused by a defect in one of the protein chains that compose hemoglobin molecules in red blood cells. In people who have two copies of the sickle cell gene, the hemoglobin molecules don't function properly, and red blood cells collapse into a half-moon shape. The disease can cause spleen damage, strokes and severe joint pain. People with only one copy of the sickle cell allele don't get sickle cell anemia. They are also protected from contracting a particularly deadly form of malaria caused by the mosquito-borne parasite Plasmodium falciparum. When researchers laid a map of malaria over a map showing the distribution of sickle cell disease, they saw that the two diseases often occur together. Researchers concluded that the sickle cell anemia allele must be an adaptation against malaria and is found in populations with high rates of malaria infection, regardless of race. Getting past the pseudo-scientific distinctions of race and ethnicity is likely to lead to more individualized medicine, many experts predict. People want to be treated for their own diseases, not those of their ethnic group, Templeton said. "If you're an individual and you're sick, you don't really care about the averages," he said. Copyright 2003 Union-Tribune Publishing Co.