New DNA analysis puts date of human migration as early as 62,000 years ago

Our ancestors migrated out of Africa more recently than thought, leaving the cradle of humanity as recently as 62,000 years ago, new research has claimed.

The new findings from a genetic analysis of fossil skeletons contradict recent gene studies which date our first footsteps out of Africa to 90,000 to 120,000 years ago.

That dating was problematic for researchers because it seemed to contradict the evidence given by the archaeological record.

This way chaps! A human hunting party imagined for the BBC series Planet of the Apeman. New genetic analysis has once again changed the date of our ancestors initial journey from the fertile plains of Africa

But the most recent research, reported in the journal Current Biology, used a novel method to get results which, in the words of one co-author, 'agree with what we know from archaeology.
Even though the mass migration is one of the most important events in human evolution, exactly when it began has been the subject of fierce scientific debate.

Recent studies have used the rate of mutation in the modern human genome over generations like ticks in a molecular clock to date key events in human evolution.

In so doing, they pushed back several important dates including the evolutionary split between humans and chimpanzees and the exodus of modern humans out of Africa.

One team revised the date of the migration out of Africa from less than 80,000 years ago (based on archaeological evidence) to at least 90,000 to 130,000 years ago.

Another study put the date as far back as 200,000 years ago.

However, evolutionary geneticist Johannes Krause of the University of Tübingen, Germany, was doubtful that the mutation rate calibrated from living humans could be applied so far back in our species' history.

To test the idea, he and his colleagues sequenced mitochondrial DNA found in 10 fossilised skeletons of humans whose age was reliably known from radiocarbon dating methods.

The oldest was estimated to be 40,000 years old, while the most recent came from Medieval times.
In so doing they hoped to more reliably calibrate the molecular clock used to date important events in human history by seeing how quickly mutations had occurred in the periods each individual was born.

When the researchers applied this ancient DNA-derived mutation rate to the out-of-Africa migration, they got a new estimate of 62,000 to 95,000 years ago for the start of the migration - almost half the age given by other methods.

'The nice thing about this is it was similar to the archaeological evidence,' Dr Krause told ScienceNOW.

Of course, the wide variation in date the research found still leaves many questions to be answered. The researchers said that in their effort to avoid false positive their method may have missed a lot of real mutations.

As LiveScience reports, that would have led them to underestimate the mutation rate, resulting in a longer estimate for when humans left Africa.

Quantitative geneticist Peter Visscher, of the University of Queensland, who was not involved in the study, told LiveScience that it is not yet clear which method is most reliable.

'This debate will continue a bit longer, but soon there is likely to be a consensus on what mutation rates are in the present, because there is so much sequencing being done around the world,' he said.

By Damien Gayle