Until a few decades ago, certain 'new-world' populations that kept to traditional dietary habits were virtually free from diabetes; then, after they began eating some foods that are common in Europe, the disease reached epidemic proportions. Europeans, by contrast, have a low rate of diabetes. To account for this paradox, it has been suggested that those new-world populations have a thrifty genotype, which would have conferred a selective advantage during the frequent famines of the past, while today it would be detrimental because the recently adopted foods are constantly available. Here it is proposed that thrifty genes are unlikely to exist. Both the diabetes epidemics that occur in newly westernized populations and the low rate of diabetes in Europeans can be explained by the hypothesis that Europeans, through millenary natural selection, have become adapted, albeit incompletely, to some diabetogenic foods for which humankind is genetically unequipped.