Nature: Worldwide human diversity in the genomic era
A genomic study published in Nature online on 21st of September this year, suggests Papuans harbour traces of an additional early dispersal out of Africa, highlights genetic gradients in Eurasia and reveals new genetic candidates underlying the local adaptation to the various diets and environments.
Unprecedented level of detail in the genomic diversity of modern humans is shown in 483 (379 new) high-resolution whole genome sequences. The samples from 125 human populations across the world were collected and analysed by an international collaboration led by Dr. Mait Metspalu from the Estonian Biocentre, Estonia and Dr. Toomas Kivisild from the University of Cambridge, UK. “This unique endeavour was made possible by the anonymous sample donors and the collaboration effort of nearly one hundred researchers from 74 different research groups from all over the World,” says Dr. Metspalu.
The suggested earlier dispersal of modern humans from Africa adds to the long-lasting scientific debate about the Out-of-Africa (OoA) expansion, peopling of Eurasia, Oceania and the New World by modern humans. In the same issue of Nature there are two other independent studies led by Dr. Reich and Dr. Willerslev, respectively, also addressing these questions. All three studies agree, that for the most part, the genomes of contemporary non-Africans show signs of only one expansion of modern humans out-of-Africa (OoA) that took place after 75.000 years ago. The other studies both conclude that if there were indeed earlier expansions of modern humans OoA, they have left little or no genetic trace. “And it is precisely this “little” - mounting to at least 2% of genetic ancestry of modern Papuans - that we found to derive from that earlier dispersal from Africa,” says Dr Luca Pagani who led this research direction together with Daniel Lawson and Mait Metspalu.
The high geographic coverage of the samples permitted many aspects of genetic and phenotypic differences between individuals and populations to be studied. Using a common spatial framework Drs. Anders Eriksson and Andrea Manica from the University of Cambridge found that the sharpest genetic gradient in Eurasia separates East and West Eurasians. This barrier runs roughly along the Ural Mountains in the north, opens in the Steppe belt connecting Central Asia to South Siberia and becomes strong again on the Tibetan plateau, elongating south toward the Indian Ocean while separating South and Southeast Asia.
Analyses of selection, led by Evelyn Jagoda, Alexander Mörseburg and Dr. Toomas Kivisild from the Cambridge team, showed environment dependent cases of purifying selection in pigmentation and immunity genes. Dr. Toomas Kivisild: “We revealed a number of metabolism- and immunity-related genes as new candidates for local adaptation to the various diets and environments in which human populations are living today.”
“Overall this work provides an invaluable contribution to the understanding of our evolutionary past and to the challenges that humans faced when settling down in ever-changing environments”, Dr. Richard Villems from the Estonian Biocentre says. In addition, the deluge of freely available data will serve as future starting point to further studies on the genetic history of modern and ancient human populations.
Proposed model of human expansions described as a Subway plot.
Toomas Kivisild (University of Cambridge, Cambridge, UK / Estonian Biocentre)
tk331 [ät] cam.ac.uk Tel: +44 (0)1223 764703
Mait Metspalu (Estonian Biocentre, Tartu, Estonia)
mait [ät] ebc.ee Tel: +372 737 5052; +372 5283315
Luca Pagani (Estonian Biocentre, Tartu, Estonia / University of Cambridge, Cambridge, UK)
lp336 [ät] cam.ac.uk
lp.lucapagani [ät] gmail.com Tel: +372 7374026 (+39 3407862518)