Europe was as prone through the Middle Ages and Renaissance to periodic famines as any place, Diamond points out. European countries just happened to develop stable food sources earlier than other parts of the globe. He contends that a diabetes epidemic swept through Europe following the region's last famines, beginning in the late 1600s.
"Europe's new reliability of adequate food supplies eliminated most European diabetes-prone bearers of the thrifty gene," Diamond said.
Groups with the highest diabetes rates today, meanwhile, were until fairly recently at periodic risk for starvation, so natural selection favored those who retained the "thrifty gene." These groups often experienced an "extra bout" of natural selection when an especially brutal famine in historic times further concentrated the gene's carriers in the population, Diamond found.
For instance, Arizona's Pima Indians experienced crop failures, widespread starvation, and the likely enrichment of the surviving population with thrifty genes after white settlers blocked access in the late 19th century to a traditional source of irrigation water. With 50 percent of the tribe now diagnosed as diabetic, the Pimas today lay claim to the world's highest diabetes rates.
Diamond's theory would also explain another disparity in diabetes rates that have puzzled researchers: why white Americans and Australians of European extraction are three to four times more likely than Europeans still living in Europe to be diagnosed with the disease.
"The Europeans who stayed at home tended to be richer that those who emigrated, and the genotype that predisposed the stay-at-homes to diabetes may already have been selected out by centuries of abundant food," Diamond said. "Those who emigrated may have been the starvation-prone poor such as the Irish who flocked to America during the Potato Famine of the 1840s. These immigrants may carry the thrifty gene in larger proportion be
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Contact: Meg Sullivan
megs@college.ucla.edu
310-825-1046
University of California - Los Angeles
4-Jun-2003