Interspecies Breeding: Ancient DNA Proves Early Europeans More Closely Related to Neanderthal Ancestors

Early Europeans were more closely related to their Neanderthal ancestors say geneticists after analyzing ancient DNA from a 40,000 year old human jawbone. The jawbone found in Romania in 2002 has provided the first genetic evidence of modern humans interbreeding with Neanderthals in Europe.

Homo sapiens and our Neanderthal Ancestors, Homo neanderthalensis

About 45,000 years ago and before then, Europe’s only human population was Homo neanderthalensis. But within only 10,000 years, the Neanderthal population had become extinct, replaced by Homo sapiens, or modern humans who had started to spread across the continent. Before being completely wiped out, our Neanderthal ancestors contributed to our genome. With the exception of sub-Saharan descendants, on average at least one to three percent of the modern human genome comes from Neanderthals.

The transition between species happened rather quickly in evolutionary terms. But what caused the dramatic shift?

Researchers have long known the two species interacted with each other as archaeological evidence has been found. During the time period that modern humans and Neanderthals were neighbors in Europe, there were cultural exchanges between the two groups as seen in subtle changes in tool-making, burial rituals and even in body decoration habits. However, those studies have lacked one important clue in the evolutionary game during that period: skeletons.

The Discovery of the Jawbone, the Link Between Modern Humans and Neanderthals

When archaeologists unearthed a jawbone in a Romanian cave in 2002, they were puzzled as to its origins. Besides a second skull found near the jawbone in Oase Cave, there was no evidence of other artifacts to indicate who the individuals were or to what culture they belonged. The physical features also presented a challenge to the anthropologists. Many of the features were clearly those of modern humans, but some definitively Neanderthal traits were also present. The anthropologists theorized that the two individuals must have been descendants of both groups.

An international group of geneticists, led by Harvard Medical School’s David Reich of Howard Hughes Medical Institute investigator and Svante Pääbo at the Max Planck Institute in Germany, conducted a new study to determine the jawbone’s human origins.

How a Single Jawbone Gave Away Our Neanderthal Ancestors’ Biggest Secret

Pääbo and Reich’s team set about a difficult quest to obtain the jawbone’s ancient DNA. Not only had it been sitting in soil filled with microbes for over 40,000 years, but since being found in 2002, it had over a decade of handling to be contaminated with several sets of modern human DNA.

Qiaomei Fu, then a graduate student, applied modern methods Pääbo’s lab had pioneered to retrieve the DNA via genetic probes. These methods spanned the DNA against 3.7 million human genome positions to evaluate the variations between human populations. Fu was able to separate the ancient DNA from its contaminants by restricting her analysis to DNA with a specific type of damage which resulted from deterioration that had occurred over thousands of years.

The DNA analysis revealed rather than the normal Neanderthal contribution of one to three percent in the genome, an astonishing six to nine percent of the jawbone’s genome came from Neanderthals.

Interbreeding with Our Neanderthal Ancestors

The new study suggests that the jawbone is evidence of modern humans interbreeding with Neanderthals more recently than previously postulated. As DNA passes from each generation, each segment is broken and recombined. With each generation, the DNA of all the other ancestors is interspersed. Reich’s team found segments of intact Neanderthal DNA that was large enough to indicate that the DNA hadn’t been passed down for more than four to six generations.

“In the last few years, we’ve documented interbreeding between Neanderthals and modern humans,” Reich says, “but we never thought we’d be so lucky to find someone so close to that event.”

Amazingly, the study has also proven the Oase cave individuals don’t have any living relatives in Romania or anywhere else for that matter. The team believes instead of passing on his ancestry, the individuals were part of a group that had, like the Neanderthals, disappeared after the modern humans took over.


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