We thank all DNA donors, and we thank Santos Alonso, Jaume Bertranpetit, Helena Côrte-Real, Adolfo López de Munain and Carlos Polanco for provision of samples. We also thank Dolors Bramon (University of Barcelona) for historical advice and two anonymous reviewers for helpful comments. M.A.J. was supported by a Wellcome Trust Senior Fellowship in Basic Biomedical Science (grant no. 057559), and S.M.A., E.B., P.L.B., S.J.B., and A.C.L. were supported by the Wellcome Trust.