1. Department of Statistics, Oxford University, 1 South Parks Road, Oxford OX1 3TG, UK.
2. Wellcome Trust Centre for Human Genetics, Oxford University, Roosevelt Drive, Oxford OX3 7BN, UK.
3. Department of Comparative Genetics and Refinement, Biomedical Primate Research Center, Lange Kleiweg 139 2288 GJ, Rijswijk, Netherlands.
4. Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK.