Neanderthal groups more closely related

DNA coaxed from 120,000-year-old Neanderthal fossils suggests that early Neanderthals from Western Europe and later Neanderthals from Siberia were closely related.

Neanderthals were widespread across Western Eurasia prior to their demise around 40,000 years ago. Artefacts and fossils – including several near-complete skeletons – have been found scattered from Spain to the present-day middle east and southern Siberia.

Ancient DNA analysis has become an indispensable tool in understanding ancient human histories. Genetic information from several Neanderthal individuals – including entire genomes from fossils in Siberia and Croatia – has fleshed out what we know about our closest ancient relatives.

We know, for example, that Neanderthals interbred with the ancestors of modern humans some 50-60,000 years ago, as well as with the archaic humans known as the Denisovans.

But our knowledge of how different Neanderthal populations were related early on is limited, because ancient DNA older than about 100,000 years old is hard to come by.

In this latest study, published in the journal Science Advances, Stéphane Peyrégne from the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, and colleagues extracted ancient DNA from two Neanderthal fossils from Western Europe in an effort to fill in this gap.

A thigh bone found in the Hohlestein-Stadel Cave in Germany in 1937 and a child’s upper jawbone found in the Scladina cave in Belgium in 1993 both date to around 120,000 years ago. 

Previous analysis of the Hohlestein-Stadel individual’s mitochondrial DNA – tiny elements only inherited through the maternal line – suggested that early Neanderthal populations were quite different to later ones.

But the new analysis paints a more complicated picture. 

Peyrégne and colleagues cleaned and then drilled into the bone using a dental drill. They then extracted scraps of nuclear DNA from the powder.

But after decades of handling, the samples were peppered with genetic sequences from modern humans. So the team narrowed their focus on sequences with the clear signs of degradation that occurs with the ravages of time, and then compared these to known Neanderthal sequences to build a family tree.

Despite the odd-ball mitochondrial genome of the Hohlestein-Stadel Neanderthal, both turned out to be more closely related to a Croatian Neanderthal from the Vindija Cave that lived around 50,000 years ago, than to a Siberian Neanderthal that was their contemporary, living approximately 120,000 years ago.

This suggests that a single population of Neanderthals in Europe – which included the Hohlestein-Stadel and Scladina Neanderthals – gave rise to all later European Neanderthals.

This population also eventually replaced their Siberian contemporaries, according to comparisons with genes from a Neanderthal-Denisova hybrid that lived in the same cave in the Altai mountains of Siberia around 90,000 year ago.

“The mitochondrial genome suggested a very different story,” says Peyrégne.

To account for the seemingly distantly related mitochondrial sequences, Peyrégne and his colleagues put forward two possible scenarios.

The first sees two populations of European Neanderthals that become isolated during an ice age from 130-190,000 years ago. Once the ice melted, so to speak, the two populations could have reconnected, and the new population would have contained a mix of the two divergent mitochondrial DNA types.

The second scenario is that the bizarre mitochondrial genome could have its origins in a much earlier interbreeding event with modern humans.

“It’s difficult to resolve these questions,” says Peyrégne.

For that, older specimens – DNA intact – are required.

“It’s a really thoroughly done study,” says Bastien Llamas from the University of Adelaide, who was not involved in the work. “I’m certainly looking forward to some older Neanderthals if there are any out there,” he says.