"Dr. Darwin’s Rx" by Beth Saulnier, in Cornell Magazine (Mar.–Apr. 2001), Cornell Alumni Federation, 55 Brown Rd., Ithaca, N.Y. 14850–1247.

There seems no end to the frontiers of medicine. The latest: "Darwinian medicine," an emerging field that takes an evolutionary perspective on human health. Advocates, notes Saulnier, an associate editor of Cornell Magazine, look at the symptoms of illnesses or injuries that physicians traditionally treat, and ask whether some symptoms are not beneficial.

Consider fever, for instance. "A moderate fever, below about 103 degrees, actually can speed the healing process," says Paul Sherman, an evolutionary biologist at Cornell University. "It makes the body’s environment less able to be invaded by the pathogen, and it enables its immune system to work faster."

Morning sickness, in the Darwinian perspective, is another misunderstood protective response, writes Saulnier. Sherman and a student, Sam Flaxman, found that women "who experience moderate morning sickness are less likely to miscarry." Meat, eggs, and certain other foods are likely to contain chemicals or pathogens that could harm the developing fetus, so the mother’s nausea and vomiting protect the baby. Thus, women genetically disposed to morning sickness are "more likely to reproduce and pass on the trait."

"Human biology is designed for Stone Age conditions," wrote researchers Randolph Nesse and George Williams in a 1991 article that gave the nascent field of "Darwinian medicine" its name. That design lag can help explain information age maladies.

The craving for fat, for instance, once was "a distinct evolutionary advantage," Saulnier says, since fat has more calories than other types of food. But "in an age of abundance... that same craving can be a one-way ticket to obesity and heart disease."

Modern conditions also have altered the worth of some evolutionary tradeoffs, Saulnier points out. The gene that causes sickle-cell anemia once gave people who had only one copy of the gene (rather than the deadly two copies) valuable protection against malaria. Similarly, the gene that causes Tay-Sachs disease warded off tuberculosis. But with the threats posed by malaria and TB so much diminished today, the genes’ benefits are minimal, while their dangers remain.

Only a few dozen American researchers are now at work in the field of Darwinian medicine, and the field is not well known. But that may change, says Saulnier. One big contribution Darwinian medicine could make lies in the allocation of medical resources. Why develop costly drugs to relieve morning sickness, for example, if it protects the baby?