Evolutionary “Out of Africa” Theory Gets DNA Jolt

The evolutionary “out of Africa” theory—which holds that humans evolved in Africa and split off on different evolutionary paths as they migrated away from that continent—has been given yet another jolt by new DNA studies which have called the dating behind the belief into question.
The new development involves measurements of the rate at which children show DNA changes not seen in their parents—the so-called “mutation rate”—which have challenged the established view about major dates in the human evolutionary theory.

These changes have forced geneticists to “think again about key dates in human evolution,” according to a new study issued by researchers at the University of Tübingen and the Max Planck Institute for Evolutionary Anthropology in Leipzig, published in the latest edition of Current Biology.

The team, led by Johannes Krause from Tübingen University, was able to reconstruct more than ten mitochondrial genomes (mtDNAs) from modern humans from Eurasia that span 40,000 years of prehistory.

The samples include some of the oldest modern human fossils from Europe such as the triple burial from Dolni Vestonice in the Czech Republic, as well as the oldest modern human skeletons found in Germany from the site of Oberkassel close to Bonn.

The researchers show that pre-ice age hunter-gatherers from Europe carry mtDNA that is related to that seen in post-ice age modern humans such as the Oberkassel fossils.

This suggests that there was population continuity throughout the last major glaciation event in Europe around 20,000 years ago.

Two of the Dolni Vestonice hunter-gatherers also carry identical mtDNAs, suggesting a close maternal relationship among these individuals who were buried together.

The researchers also used the radiocarbon age of the fossils to estimate human mutation rates over tens of thousands of year back in time. This was done by calculating the number of mutations in modern groups that are absent in the ancient groups, since they had not yet existed in the ancient population.

The mutation rate was estimated by counting the number of mutations accumulated along descendent lineages since the radiocarbon dated fossils.

Using those novel mutation rates—capitalizing on information from ancient DNA—the authors calculate the last common ancestor for human mitochondrial lineages to around 160,000 years ago.

This means that, according to the “out of Africa” theory, the most recent common ancestor of Africans and non-Africans was between 62,000 and 95,000 years ago—the maximum date for mass migration out of Africa, if that theory is correct.

What it means is that the widely divergent racial types found on earth would have had far less time to speciate than previously believed. This in turn might very well underpin the rival multi-origin evolutionary theory, even though the new study did not say that.

"The results from modern family studies and our ancient human DNA studies are in conflict," says Krause. "One possibility is that mutations were missed in the modern family studies, which could lead to underestimated mutation rates.”