1. Department of Human Genetics, University of Chicago, Chicago, IL 60637, USA.
2. Department of Ecology, Evolution and Behavior, Hebrew University of Jerusalem, Givat Ram, Jerusalem 91904, Israel.
3. Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford OX3 7BN, UK.
4. Department of Statistics, University of Oxford, Oxford OX1 3TG, UK.
5. Department of Ecology and Evolution, University of Chicago, Chicago, IL 60637, USA.
6. Howard Hughes Medical Institute, University of Chicago, Chicago, IL 60637, USA.