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Sunday, March 6, 2016

High Neanderthal Ancestry in Ust’-Ishim Man

A large team of genetic scientists led by Dr Qiaomei Fu of Harvard Medical 
School has recovered and sequenced the DNA from a thighbone of a male 
hunter-gatherer who lived in what is now Siberia 45,000 years ago. 
... 
The sequence revealed that the bone came from an anatomically modern human, 
a man whose remains are the oldest ever found and carbon-dated outside of 
Africa and the Middle East. 

Comparison to diverse humans around the world today showed that the 
Ust’-Ishim man was a member of one of the most ancient non-African 
populations. 

“The ancient Siberian was related equally to West European hunter-gatherers, 
North Asian hunter-gatherers, East Asians, and the indigenous people of the 
Andaman Islands off South Asia,” said Dr Fu, who is the first author of a 
paper published in the journal Nature. 

“The fact that this population separated so early indicates that theories 
of an early split of people who followed a coastal route to Australia, New 
Guinea, and coastal Asia are not strongly supported by this data.” 
... 
The scientists also obtained a high-resolution estimate of the mutation 
rate in humans. 

Previous studies had given scientists evidence of two possible rates, one 
twice as fast as the other. Because of this large range, dates obtained 
from genetic research have tended to be quite uncertain. 

By measuring the number of mutations missing in the Ust’-Ishim man and 
comparing with people now, the scientists obtained an accurate estimate 
of the rate that mutations accumulated over time. They revealed a slower 
mutation rate, corresponding to between one to two mutations per genome 
per year. 
... 
“Instead of humans and Neanderthals becoming distinct offshoots sometime 
between 270,000 and 380,000 years ago, for example, the slower rate would 
put that shift much further back in time, between 550,000 and 770,000 
years ago.” 

“Similarly, the slower rate pushes back estimates for the date of the 
separation of African and non-African populations.” 

The slow mutation rates indicate that the present-day subdivisions among 
human populations date back to almost 200,000 years ago, well before the 
period around 50,000 years ago when the archaeological record documents 
art and new styles of tool-making. 
... 
The researchers also found that about 2.3 percent of the Ust’-Ishim man’s 
genome came from Neanderthals. 

The genomic segments of Neanderthal ancestry are substantially longer than 
those observed in present-day individuals, indicating that Neanderthal gene 
flow into the ancestors of this individual occurred 7,000-13,000 years 
before he lived (i.e. 58,000-52,000 years ago – a much tighter window than 
the previous range of between 37,000 and 86,000 years ago). 
... http://www.nature.com/nature/journal/v514/n7523/full/nature13810.html http://www.sci-news.com/genetics/science-genome-45000-year-old-siberian-man-02227.html
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