Does a "genetic component" cause a higher rate of premature births among black mothers? Do black people carry certain gene variants that give them weaker hearts? Do Asians have special genes that enable the drug Iressa to fight non-small cell cancer better in their lungs?

Yes, indeed, authors of several recent medical studies claim. More and more, researchers are holding out the hope that genetic differences may finally explain a good part of the troubling health disparities among races. Perhaps then, the reasoning goes, the powerful tools of molecular biology may help solve them.

This research is worth pursuing if it holds the promise to improve medical care. Still, whenever these claims arise, they deserve a tough second look. Race paired with genetics has a sordid history - not just in Nazi Germany but also today, in the form of weakly documented evolutionary claims implying one group's superiority over another.

So far, the claims about race and medical genetics remain disturbingly fuzzy. What's meant by a "genetic component," for instance? The team at Washington University in St. Louis that studied early births accounted for other known variables, such as lack of prenatal care, and found that the higher rate among black women persisted. Based on the trends they saw, the group concluded there were racial differences at the genetic level - despite lack of any data on genes.

The Johns Hopkins School of Medicine researchers studying heart function had used magnetic resonance imaging to compare heart muscle contractions in Chinese-Americans, whites, Hispanics, and African-Americans. They also pointed to genetic differences as a likely cause. But they hadn't yet looked at any genes, either.

In the original Iressa studies, Japanese patients did respond better to the drug. Once the researchers controlled for other factors, though, the statistical significance of the finding disappeared. Yet groups around the world remain hard at work searching for a race-related genetic cause.

Perhaps it's not surprising that these studies poorly describe genetics as it applies to race. When one team of philosophers asked 500 geneticists to point out what part of a DNA sample constituted a gene, the experts didn't concur.

Race may be an even trickier concept. Are the researchers referring to skin color? Eye shape? Does nationality factor in?

Even if we think we can agree on various groupings called races, we should understand the limits of how well they can help define health differences. "Asians" with ancestry in Vietnam or Laos, for instance, have very different health risks than those from China.

As science begins to intertwine genetics, medicine, and race, the results already are affecting our lives in important ways. We may be offered different tests, drugs, even vitamins, depending on our skin color. In 2005, U.S. regulators approved the first race-based drug, BiDil, for treating heart failure in black patients. Some pharmacologists have wondered whether race should affect prescription dosage, based on possible differences in drug metabolism.

It's hard to talk about race, but with a new medical enterprise focused on biological difference, we are forced to confront it. Lay people don't have to become experts. But we do need to understand the nature of the conversation.

Fortunately, we do have powerful weapons against poorly developed claims about biology and race. They are education, skepticism, and awareness. There are two simple questions that we should ask when we see these linked with genetics: What do the researchers mean by race? How did they come to the conclusion that it was important? While we many not know how to make observations in the lab or calculate the necessary statistics, we certainly can and should ask for clarity.

Sally Lehrman reports on health and science for Scientific American. This article first appeared in The Boston Globe.

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