1. Department of Anthropology, University College London, 14 Taviton Street, London, UK
2. State Key Laboratory of Grassland and Agro-ecosystems, School of Life Sciences, Lanzhou University, 222 Tianshui South Rd, Lanzhou, Gansu Province 730000, People's Republic of China
3. Department of Epidemiology and Public Health, University College London, 1-19 Torrington Place, London, UK
4. Institute for Advanced Study in Toulouse, Université Toulouse 1 Capitole, 1 esplanade de l’Université, 31080 Toulouse Cedex 06, France