Over a few million years, human genes gradually evolved, enabling us to survive frequent periods of famine. Our genes are still essentially the same; but we are currently exposed to lifestyles for which we are not programmed. We were programmed for frequent physical activity and a relatively low-energy diet. The collision between these ancestral genes and the effects of urbanization is resulting in a global epidemic of the metabolic syndrome. But it appears that not all ethnic groups, or indeed people within the same ethnic group, are affected in the same way. While the metabolic syndrome epidemic can largely be explained by environmental changes, Marju Orho-Melander describes the importance of genetic factors in contributing to the large variations in susceptibility to the different disorders of the metabolic syndrome and the way these come together.