Human migrations and population structure: what we know and why it matters.

The increasingly obvious medical relevance of human genetic variation is fueling the development of a rich interface between medical genetics and the study of human genetic history. A key feature of this interface is a step increase in the size and diversity of genetic data sets, permitting a range of new questions to be addressed concerning our evolutionary history. Similarly, methodologies first developed to study genetic history are being tailored to address medical challenges, including mapping genes that influence diseases and variable drug reactions. In this paper we do not attempt a comprehensive review of human genetic history. Rather we briefly outline some of the complications and challenges in the study of human genetic history, drawing particular attention to new opportunities created by the explosive growth in genetic information and technologies. First we discuss the complexity of human migration and demographic history, taking both a genetic and archaeological perspective. Then we show how these apparently academic issues are becoming increasingly important in medical genetics, focusing on association studies, the common disease/common variant hypothesis, the evaluation of variable drug response, and inferences about gene function from patterns of genetic variation. Finally we describe some of the inferential approaches available for interpreting human genetic variation, focusing both on current limitations and future developments.