Neanderthal gene in humans traced back 50,000 years as DNA evidence uncovers new timeline

Study pinpoints when homo sapiens migrated out of Africa and reveals how species lived side-by-side for longer than previously thought

Research shows Neanderthals coexisted with humans for about 7,000 years until the group eventually died off. AFP

Neanderthals interbred with modern humans for longer than previously thought, with the two species now believed to have coexisted for about 7,000 years, analysis shows.

Genomics research has uncovered a new time frame for the species' relationship which is dated to about 50,000 years ago when Homo sapiens migrated from Africa into Europe and Asia.

Due to this interbreeding, about 1 to 2 per cent of people from Eurasia have some Neanderthal DNA, with those living in East Asia typically having a higher proportion than elsewhere. The study provides clues as to why some regions seem to have higher Neanderthal DNA than others.

The research was carried out by academics from the University of Rochester and from the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, who analysed present-day human genomes as well as 58 ancient genomes sequenced from DNA found in modern human bones and teeth from Eurasia.

They found an average date for Neanderthal-homo sapiens interbreeding of about 47,000 years ago. Previous estimates for the time of interbreeding ranged from 54,000 to 41,000 years ago.

The analysis was led by Benjamin Peter, an assistant professor at the University of Rochester and MPI-EVA. He believes humans would have encountered Neanderthals in the Levant as they migrated out of Africa due to the many Neanderthal settlements found in the region by archaeologists.

However, he says Neanderthal DNA may be lower in the Gulf due to relatively recent migration out of sub-Saharan Africa.

“We do think that the Levant is a likely region where Neanderthals and humans met”, adding there were many Neanderthal sites throughout present-day Israel, Iran, Iraq and other countries.

“We don't know for sure, but I think there is little direct spatial connection between the people that lived there 40,000 years ago to the people that lived there today,” he told The National. “I'd guess that Neanderthal ancestry in the Middle East is mainly impacted by relatively recent connections between the Arab world and Africa.”

“The extensive connections through the Arab world led to some degree of African ancestry in many Arab populations, and since Africans have less Neanderthal ancestry than Europeans/Asians, many of these people today have correspondingly lower Neanderthal ancestry.”

The new dates also suggest that the initial migration of modern humans from Africa into Eurasia was over 43,500 years ago.

Archaeologists had previously presented evidence that Neanderthals and early modern humans had lived together for about 6,000 to 7,000 years. The new genomics shows interbreeding began at the earliest end of that scale

The longer duration of gene flow, or the transfer of genes to other populations, may help explain why East Asians have about 20 per cent more Neanderthal genes than Europeans and West Asians. Modern humans are believed to have moved east 47,000 years ago, and would already have had intermixed Neanderthal genes.

“We show that the period of mixing was quite complex and may have taken a long time. Different groups could have separated during the 6,000 to 7,000-year period and some groups may have continued mixing for a longer period,” Dr Peter said. “But a single shared period of gene flow fits the data best.”

The study also provided fascinating insight as to why some regions have little to no Neanderthal admixture. These areas, known as Neanderthal deserts, may indicate that some Neanderthal gene variants were fatal to humans.

“We find that very early modern humans from 40,000 years ago don't have any ancestry in the deserts, so these deserts may have formed very rapidly after the gene flow,” said Leonardo Iasi, a graduate student at MPI-EVA.

However, other Neanderthal genes may have been useful to the early humans as they moved out of Africa. Most of the high-frequency Neanderthal genes are related to immune function, skin pigmentation and metabolism. Some of the Neanderthal genes involved in the immune system and skin pigmentation actually increased in frequency in homo sapiens over time, implying that they may have been advantageous to human survival.

“Neanderthals were living outside Africa in harsh, Ice Age climates and were adapted to the climate and to the pathogens in these environments. When modern humans left Africa and interbred with Neanderthals, some individuals inherited Neanderthal genes that presumably allowed them to adapt and thrive better in the environment,” Mr Iasi said.