Ancient DNA from three humans buried 31,000 years ago at Dolni Vestonice in the Czech Republic has altered genetic history.

Ancient DNA from three humans buried 31,000 years ago at Dolni Vestonice in the Czech Republic has altered genetic history.

Our ancestors may have left Africa more recently than previously thought according to new research. Using ancient DNA for the first time from ancient Europeans such as Ötzi, the famous Iceman, a team of evolutionary geneticists has dated the start of the exodus to less than 95,000 years ago and, possibly, as recently as 62,000 years ago.

The findings fit with the evidence from fossils and stone tools, but they contradict a spate of recent genetic studies. Those studies determined the mutation rate for the entire genome from living humans by counting the number of new mutations that arise in the nuclear DNA of a newborn baby compared with its parents. The number of mutations per generation—the mutation rate—can be used to fine-tune a molecular clock that has long been used to date key events in human evolution. This supposedly better molecular clock has pushed back several important dates, such as when the ancestors of humans and chimps split and the exodus of modern humans out of Africa. Indeed, one team revised the date of the migration out of Africa from less than 80,000 years ago to at least 90,000 to 130,000 years ago.

Evolutionary geneticist Johannes Krause of the University of Tübingen in Germany, however, wasn’t so sure that a mutation rate calibrated for living humans could be applied so far back in time. He and his colleagues decided to test the idea by sequencing the DNA from the maternally inherited mitochondria (mtDNA), or powerhouses of the cell, from fossils of modern humans who lived in the past 40,000 years and whose age was reliably known from calibrated radiocarbon dating methods. If the age of the fossil was 40,000 years, for example, it would be missing 40,000 years of evolution that took place in the lineage of a living person—and, therefore, missing mutations that would have arisen during the time since the fossil human died.

The team analyzed 10 well-dated fossils, including a medieval man who lived in France 700 years ago; the 4550-year-old Iceman; two 14,000-year-old skeletons from the tombs of Oberkassel in Germany; three related, modern humans from 31,000 years ago in Dolni Vestonice in the Czech Republic; and an early modern human from 40,000 years ago in Tianyuan, China. When the researchers applied this ancient DNA-derived mutation rate to the out-of-Africa migration, they got a range of dates from 62,000 to 95,000 years ago for the start of the migration, which is almost half the age of the migration out of Africa that was calculated using the “de novo” mutation rate, the group reports online today in Current Biology. “The nice thing about this is it was similar to the archaeological evidence,” Krause says.

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