| 2 November 2014
Earliest human genome ever analysed
Scientists have reconstructed the genome of a man who lived 45,000 years ago - by far the oldest ever obtained from modern humans. The research provides new clues to the expansion of modern humans from Africa into Europe and Asia, adding support to a provocative hypothesis: Early humans interbred with Neanderthals.
The discoveries were made by a team of scientists led by Svante Paabo, a geneticist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. Comparing Neanderthal to human genomes, Dr Paabo and his colleagues found that we share a common ancestor, which they estimate lived about 600,000 years ago.
In 2008, a fossil collector searching for mammoth tusks along the Irtysh River in Siberia found a thighbone near a settlement called Ust'-Ishim, and brought it to scientists at the Russian Academy of Sciences. Researchers identified the bone as a modern human, and determined it to be about 45,000 years old - the oldest modern human fossil found outside of Africa and the Near East.
Dr Paabo and his colleagues used a number of genetic fragments to create a high-resolution copy of the man's complete genome, which they compared to those of ancient and living people. They found his DNA was more like that of non-Africans, but no more closely related to ancient Europeans than to East Asians. He was part of an earlier lineage - a group that eventually gave rise to all non-African humans.
Homo sapiens, our own species, appeared in Africa around 200,000 years ago. Previous studies, both on genes and on fossils, suggest they then expanded through the Near East.
Ust'-Ishim man's genome suggests he belonged to a group of people who lived after the African exodus, but before the split between Europeans and Asians. Dr Paabo and his colleagues also found pieces of Neanderthal DNA in his genome.
Fossils indicate that Neanderthals spread across Europe and Asia before becoming extinct an estimated 40,000 years ago. By comparing the Ust'-Ishim man's long stretches of Neanderthal DNA with shorter stretches in living humans, Dr Paabo and his colleagues estimated how long ago Neanderthals and humans interbred. Previous studies based only on living humans had yielded an estimate of 37,000 to 86,000 years. Dr Paabo and his colleagues narrowed that down: Humans and Neanderthals interbred 50,000 to 60,000 years ago.
The findings question research suggesting that humans in India and the Near East date back as far as 100,000 years ago. Some scientists believe that humans expanded out of Africa in a series of waves.
Christopher Stringer, a palaeo-anthropologist at the Natural History Museum, says the new study offers compelling evidence that living non-Africans descended from a group of people who moved out of Africa about 60,000 years ago. Any humans that expanded out of Africa before then probably died out.
Edited from The Washington Post, Examiner.com, The New York Times (22 October 2014)
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