Type 2 diabetes affects some ethnic groups at significantly higher rates than others. Type 2 is the form of the disease that develops in adults, especially those who are overweight.

For decades, some scientists have held that early human groups that experienced cycles of feast and famine evolved so that in times of famine their bodies were able to conserve scarce calories. They believe that people from those populations no longer experience famine, but their bodies still store calories too efficiently, making them more susceptible to obesity and therefore, diabetes. This idea is known as the thrifty genotype hypothesis.

But some are starting to question that idea. Anthropologist Michael Montoya from the University of California at Irvine worked with a team of researchers to review the mass of literature surrounding the hypothesis. They found it was based on flimsy evidence. "It doesn't make evolutionary sense," he says, pointing out all human groups would have had this genotype because all human groups experienced feast and famine cycles equally. He adds, "Furthermore, the ethnic minority groups that currently have type 2 diabetes don't have a dissimilar long-term evolutionary history from those groups that currently do not have type 2 diabetes. So it must be something else."

Montoya says medical researchers have found that many factors can contribute to the development of type 2 diabetes, including activity level, stress and low birth weight, not only genetics. "When you add up the 250 or so genes that have been looked at as putatively responsible for type 2 diabetes, together they only account for one percent of the global prevalence of the disease."

Montoya says social science research shows groups that experience long-term social disadvantage consistently tend to have higher rates of type 2 diabetes. "The common sense is that of course behavioral factors are vitally important to who gets overweight and who can manage their disease, who can understand complicated medical directions and follow them." He says these socio-cultural factors are central.

Montoya says he's surprised that so many scientists have sought explanations for the worldwide increase in diabetes using a framework he considers to be faulty. He hopes his group's paper will prompt better debate about the thrifty genotype hypothesis. His paper appears in the spring issue of the journal .