title: Early modern human dispersal from Africa: genomic evidence for multiple waves of migration.
abstract: BACKGROUND
  Anthropological and genetic data agree in indicating the African continent as the main place of origin for anatomically modern humans. However, it is unclear whether early modern humans left Africa through a single, major process, dispersing simultaneously over Asia and Europe, or in two main waves, first through the Arab Peninsula into southern Asia and Oceania, and later through a northern route crossing the Levant.
  
  
  RESULTS
  Here, we show that accurate genomic estimates of the divergence times between European and African populations are more recent than those between Australo-Melanesia and Africa and incompatible with the effects of a single dispersal. This difference cannot possibly be accounted for by the effects of either hybridization with archaic human forms in Australo-Melanesia or back migration from Europe into Africa. Furthermore, in several populations of Asia we found evidence for relatively recent genetic admixture events, which could have obscured the signatures of the earliest processes.
  
  
  CONCLUSIONS
  We conclude that the hypothesis of a single major human dispersal from Africa appears hardly compatible with the observed historical and geographical patterns of genome diversity and that Australo-Melanesian populations seem still to retain a genomic signature of a more ancient divergence from Africa.
authors.affiliation: Department of Life Sciences and Biotechnologies, University of Ferrara, Ferrara, Italy.
authors.forename: Francesca
authors.initials: F
authors.lastname: Tassi
authors.affiliation: Department of Life Sciences and Biotechnologies, University of Ferrara, Ferrara, Italy.
authors.forename: Silvia
authors.initials: S
authors.lastname: Ghirotto
authors.affiliation: Institute for Maternal and Child Health-IRCCS "BurloGarofolo", University of Trieste, Trieste, Italy.
authors.forename: Massimo
authors.initials: M
authors.lastname: Mezzavilla
authors.affiliation: Department of Life Sciences and Biotechnologies, University of Ferrara, Ferrara, Italy.|Present Address: Leibniz Institute for Zoo and Wildlife Research, Berlin, Germany.
authors.forename: Sibelle Torres
authors.initials: ST
authors.lastname: Vilaça
authors.affiliation: Department of Life Sciences and Biotechnologies, University of Ferrara, Ferrara, Italy.
authors.forename: Lisa
authors.initials: L
authors.lastname: De Santi
authors.affiliation: Department of Life Sciences and Biotechnologies, University of Ferrara, Ferrara, Italy.
authors.forename: Guido
authors.identifier: 0000-0001-7854-6669
authors.initials: G
authors.lastname: Barbujani
keywords: Admixture; Evolutionary divergence; Human demographic history; Linkage disequilibrium; Migration; Population structure