Genetic isolates: Separate but equal?

The tiny volcanic island of Tristan da Cunha is the most remote inhabited place on Earth. It lies in the South Atlantic, 1,700 miles and a week’s journey by boat from Cape Town, South Africa. The island’s population of 300 is descended from a handful of founders, mostly shipwreck survivors, who settled there in the 19th century. The small number of founders is reflected in the fact that only seven surnames and five mitochondrial lineages (1) are found among the inhabitants. At first glance, this population couldn’t be more different from that of Europe, inhabited for tens of thousands of years and home to more than half a billion people and dozens of ethnic groups. So it may come as a surprise that a study in this issue of the Proceedings (2) reports that these two populations, along with a wide range of others, are remarkably similar in one important respect—the level of linkage disequilibrium between nearby genetic loci. Taken at face value, this study has significant implications for human geneticists who seek to use increased linkage disequilibrium in isolated populations as a tool for unraveling the genetics of common diseases.