Choongwon Jeong1, Gorka Alkorta-Aranburu1, Buddha Basnyat2, Maniraj Neupane3, David B. Witonsky1, Jonathan K. Pritchard1,4,†, Cynthia M. Beall5 & Anna Di Rienzo1
1 Department of Human Genetics, University of Chicago, Chicago, Illinois 60637, USA. 2 Oxford University Clinical Research Unit, Patan Hospital, Lal Durbar marg, GPO Box 3596, Kathmandu, Nepal. 3 Mountain Medicine Society of Nepal, Maharajgunj, Kathmandu, Nepal. 4 Howard Hughes Medical Institute, Chevy Chase, Maryland 20815, USA. 5 Department of Anthropology, CaseWestern Reserve University, Cleveland, Ohio 44106-7125, USA. †Present address: Departments of Genetics and Biology, Stanford University, Stanford, California 94305-5020, USA.
Correspondence to: Anna Di Rienzo
Admixture is recognized as a widespread feature of human populations, renewing interest in the possibility that genetic exchange can facilitate adaptations to new environments. Studies of Tibetans revealed candidates for high-altitude adaptations in the EGLN1 and EPAS1 genes, associated with lower haemoglobin concentration. However, the history of these variants or that of Tibetans remains poorly understood. Here we analyse genotype data for the Nepalese Sherpa, and find that Tibetans are a mixture of ancestral populations related to the Sherpa and Han Chinese. EGLN1 and EPAS1 genes show a striking enrichment of high-altitude ancestry in the Tibetan genome, indicating that migrants from low altitude acquired adaptive alleles from the highlanders. Accordingly, the Sherpa and Tibetans share adaptive haemoglobin traits. This admixture-mediated adaptation shares important features with adaptive introgression. Therefore, we identify a novel mechanism, beyond selection on new mutations or on standing variation, through which populations can adapt to local environments.