Africans and Australian aborigines have similar skin color, but otherwise they're not closely related to one another.
Skin color and other physical traits often used to define race are based on a small number of genes and sometimes, but not always, reveal information about an individual's genetic makeup, according to Ï㽶ÊÓƵ of Utah physician Michael J. Bamshad, M.D., and science writer Steve E. Olson.
In the December cover story of Scientific American, Bamshad, associate professor of pediatrics at the U School of Medicine, and Olson write that common definitions of race often are inadequate, or even misleading, from a biological standpoint. As researchers look beyond physical differences or similarities into genetic relationships of people worldwide, their work may yield important clues about human disease, according to the article, "Does Race Exist?"
Defining race is not easy.
People of sub-Saharan Africa, southern India, and Australia, for example, can be described as "black." But it isn't because they are closely related that their skin color is similar. Natural selection is the reason: they developed dark skin as protection against the sun in the warm climates where they live.
"Using skin color is a pretty crude way to assign people to the same group," Bamshad said. "Common labels aren't particularly useful."
To determine biological relationships between groups geneticists look at variations in genetic makeup—polymorphisms. Differences between groups reflect, in part, the history of our species over the past 100,000 years or so as the first modern humans spread from Africa to the rest of the world. The ideal polymorphism to distinguish between groups, the authors write, would be present in all members of one group but absent in members of all others. But no such polymorphisms exist, particularly between racial groups. However, the frequencies of polymorphisms often vary among groups and differences in the frequency of polymorphisms can affect the health of people in one group differently from another group, the authors write.
It's well documented, for example, that people from Africa and the Mediterranean are susceptible to sickle cell disease, while Europeans are more likely to get cystic fibrosis. The genetic mutations responsible for sickle cell disease, and in some cases of cystic fibrosis, appear to be the result of environmental conditions and may have occurred to protect people against other diseases in Africa and Europe, according to the authors.
People with one copy of the sickle cell polymorphism show resistance to malaria, while those with one copy of the cystic fibrosis trait may be less prone to dehydration from cholera. Those who inherit both copies of the sickle cell and cystic fibrosis genes, and who get those diseases, also are more likely to show symptoms of malaria and cholera, write Bamshad and Olson.
When researchers better understand the genetic causes of disease, they may discover ways to treat or prevent them. But that opens a sticky question: Should people be given specific medical tests and therapies based on race?
Last January, the U.S. Food and Drug Administration issued guidelines advocating the collection of race and ethnicity information in all clinical trials, according to the authors. But the medical community is divided on this issue. Some physicians argue that accounting for racial membership, including skin color, can shed light on genetic and environmental factors in disease. Others say that historical abuses associated with categorizing people by race are so extreme that grouping people by racial membership should not have a role in genetic and medical studies.
That debate is likely to continue.
"The result of the debate will be a much deeper understanding of both our biological nature and our human interconnectedness," Bamshad and Olson write.