http://www.ft.com/intl/cms/s/0/1d63a148-031d-11e2-a484-00144feabdc0.html#axzz27xIwG7gs

September 21, 2012 6:42 pm

                       

By Ling Ge


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http://www.ft.com/intl/cms/s/0/1d63a148-031d-11e2-a484-00144feabdc0.html#axzz27xIwG7gs

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3.New genetic light shed on human evolution 


September 21, 2012 6:42 pm

                                    New genetic light shed on human evolution

By Ling Ge

Getty

   A new genetic study of a group of sub-Saharan peoples has challenged the prevailing view that modern humans 
emerged from one location in Africa before spreading out across the world.
   An international research team found that the Khoe and San groups from southern Africa are descendants of the 
earliest diversification event in the history of modern humans  100,000 years ago. 
   Instead of localising the origin of modern humans to a single geographic region in Africa, the researchers 
discovered a complex record of interbreeding and genetic stratification, challenging the view of evolution in 
one place. Details appear in the journal Science. 
   There are two main theories concerning the spread of humans out of Africa. The dominant view holds that modern 
humans began to leave Africa and colonise Europe and Asia about 60,000 years ago. The alternative multiregional 
model suggests there were several movements out of Africa with parallel lines of evolution around the world. 
   It is possible that modern humans emerged from a non-homogeneous group, said Mattias Jakobsson from Uppsala 
University, one of the authors. 

   The scientists examined 2.3m DNA variants of 220 individuals representing 11 populations across southern Africa, 
the largest genomic study ever conducted among the click-speaking Khoe and San groups. 

   According to the study, the Khoe-San diverged from other populations more than 100,000 years ago but the genetic 
structure within the populations dated back to about 35,000 years ago, when it split into a northern and a 
southern group. 
   There is astonishing ethnic diversity among the Khoe-San group and we were able to see many aspects of the 
colourful history that gave rise to this diversity in their DNA, said lead author Carina Schlebusch.
   For example, genetic data showed that the Khoe pastoralists originated from a southern San group that adopted 
pastoralism with genetic contributions from people in east Africa. This is an indication of how agriculture first 
spread to southern Africa in combination with the Khoe culture. 
   The researchers also saw evidence of natural selection as the ancestors of Khoe-San adapted to the harsh 
conditions of their new environment, in genes involved in muscle function, immune system and UV-light protection. 
   They also looked for signals of ancient adaptations before the historical separation of the Khoe-San lineage 
from other humans. Although all humans today carry similar variants in these genes, the early divergence between 
Khoe-San and other human groups allowed us to zoom in on genes that have been fast evolving in the ancestors of 
all of us, said co-author Pontus Skoglund. 
   The genes of particular interest are those involved in skeletal development such as bone and cartilage growth 
that may have been crucial in determining the origin of anatomically modern humans. 
   The findings are a phenomenal tribute to the indigenous Khoe and San people of southern Africa, said 
co-author Professor Himla Soodyall. The genome data in this study will be made freely available and used in 
future disease-related studies. 

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