Good point. Lots of people--some doctors included--still think there are some diseases that affect certain races more than others. Common examples are sickle cell anemia or Tay-Sachs, as well as high blood pressure (hypertension).

But the truth is more complicated than that.

Sickle cell anemia is an adaptation to resist malaria. So we see sickle cell trait in people who live in areas with high incidences of malaria, such as Central and West Africa, and around the Mediterranean. Depending on how you draw the arbitrary line between "black" and "white," it's clear that there are people we would now classify as white (Greeks, Sicilians, southern Italians, etc.) who have higher incidences of sickle cell trait. There are also people we would probably classify as black (southern Africans, for example) who don't have elevated incidences of sickle cell trait.

There is a clear statistical correlation between African-Americans and hypertension, or high blood pressure disease. But many studies in the last 10-15 years have pretty conclusively connected this correlation to social and cultural factors--i.e., racism--than to biological ones. For example, studies have compared hypertension rates of African-Americans with West Africans, who are genetically quite similar because most slaves were forcibly taken from this part of the world only 10 or 12 generations ago, which is an evolutionary blink of the eye. And these studies show that West Africans have very little incidence of hypertension. Other studies have sought to understand the biological effects of poverty, which disproportionately affect African-Americans. These studies suggest that poor diets, little access to fresh vegetables and fruit, poor health care, and other poverty factors have biological effects that lead to this correlation. Actually, some studies have found that poor whites as well as poor blacks are at higher risk for hypertension--further evidence that the health effects of poverty are what causes hypertension.

Evolutionary biologist Joseph L. Graves talked about malaria and Tay-Sachs when he was the featured "scientist on the spot":

"Tay Sachs results from a deficiency of the enzyme hexosaminidase A. It is found in all human populations at a carrier frequency of 1/250. This means that of 250 people, one person has the genotype +/ts, where + stands for a functional gene, and ts stands for the Tay Sachs allele. There are a variety of different mutations (changes in the genetic code) that can cause a functional HexA allele to become a Tay Sachs allele. These mutations differ around the world. The disease is in high frequency in a number of Mediterranean populations, including Arabs, as well as in non-Jewish French Canadians living near the St. Lawrence River and in the Cajun community of Louisiana."

"Due to genetic counseling, Tay-Sachs has been almost completely eradicated. For example, in 2003, ten babies were born in North America with Tay-Sachs, but not a single one was Jewish. The carrier frequency for Jews in the United States is 1/27. The frequency for Jews of Sephardic origin is about one in 250, which is equivalent to that of the general world population."

"The high frequency of Tay Sachs disease among Arab populations can be traced to the cultural practice of first cousin marriages. Persons who are related are more likely to share genes that are identical by descent (inherited from a common ancestor.) In such populations there is a higher frequency of all recessive deleterious genes, thus a higher frequency of a variety of genetically based diseases. The high frequency of Tay Sachs that was experienced in the Ashkenazim most likely results from the history of persecution of Jews in Europe. When a population is reduced by disaster (in this case, brought on my human prejudice), the frequency of genes in the survivors is random. These acts (programs against Jews throughout Western history, the last was the Jewish Holocaust of World War II) have left this community with 10 times greater frequency of a variety of genetic diseases (including early onset breast cancer), not just Tay Sachs."

"These examples illustrate how the social construction of race has biological impacts. Persons of the Jewish religion are not a biological race, but throughout European and Middle Eastern history they were treated as if they were, leading to an aberration in genetic disease frequencies."

The upshot is this: we do see racial differences in the incidence of many diseases. But Alan Goodman, physical anthropologist and featured "scientist on the spot" this month, has a few things to say on the subject:

"Genes may play a part [in causing disease]. But when we use race to explain illness, we miss the environmental factors that may also be in play and lose focus on the individual. You can’t determine a person’s genetic make-up by examining their skin color; genes don’t sort themselves according to the racial categories we’ve created."

"Focusing on genetics, when we know there is no white or black race, diverts attention from the sociopolitical origins of inequalities."

"Racism rests in part on the idea that race is biology. Then biology becomes an excuse for social differences—differences played out in forensics laboratories, law and housing offices, medical schools and dentists' offices. The social differences become naturalized in biology."