Report From Social to Genetic Structures in Central Asia

Laboratoire Ecologie Syste´matique et EvolutionCentre National de la Recherche Scientifique UMR 8079Universite´ Paris-SudOrsay 91405FranceSummaryPastoral and farmer populations, who have coexistedin Central Asia since the fourth millennium B.C. [1],present not only different lifestyles and means of sub-sistence but also various types of social organization.Pastoral populations are organized into so-calleddescent groups (tribes, clans, and lineages) and prac-tice exogamous marriages (a man chooses a bride ina different lineage or clan). In Central Asia, thesedescent groups are patrilineal: The children are sys-tematically affiliated with the descent groups of thefather. By contrast, farmer populations are organizedinto families (extended or nuclear) and often establishendogamous marriages with cousins [2–4]. This studyaims at better understanding the impact of thesedifferences in lifestyle and social organization on theshaping of genetic diversity. We show that pastoralpopulations exhibit a substantial loss of Y chromo-some diversity in comparison to farmers but that nosuch a difference is observed at the mitochondrial-DNA level. Our analyses indicate that the dynamics ofpatrilinealdescentgroups,whichimpliesdifferentmaleand female sociodemographic histories, is responsi-ble for these sexually-asymmetric genetic patterns.This molecular signature of the pastoral social organi-zation disappears over a few centuries only after con-version to an agricultural way of life.Results and DiscussionWe compared the genetic diversity of the HVS-1sequence from the maternally inherited mitochondrialDNA(mtDNA) in12pastoralandninefarmerpopulationsfrom Central Asia, as well as the diversity of six shorttandem repeats (STRs) from the nonrecombining regionof the paternally inherited Y chromosome (NRY) in 11pastoral and seven farmer populations. Uzbek popula-tions, who used to be pastoral nomads, were consid-ered in this study as farmers. Indeed, they settled inthe different parts of Uzbekistan from the 16