45,000-Year-Old Bone Connects Modern Humans to Neanderthals

Through studying a 45,000-year-old specimen, evolutionary geneticists have determined that the ancestors of modern humans and present-day people of Eurasian descent have similar levels of Neanderthal DNA.

The findings, which come from genome sequencing performed at the Max Planck Institute for Evolutionary Anthropology in Germany and which were published on Oct. 22 in the journal “Nature,” may shed new light on the human mutation rate over time.

The 45,000-year-old modern human femur that prompted these results was found in 2008 by artist and amateur paleontologist Nikolai Peristov in a West Siberian river bank.

“Peristov was travelling in the region, collecting mammoth ivory for his carvings,” Janet Kelso, a professor specializing in evolutionary genetics at the Max Planck Institute, said in an email. “He recognized that the bone might be important and brought it to scientists in Omsk for further work.”

When the scientists applied initial radiocarbon dating techniques to the sample, they were surprised by the results.

“This [sample] is almost older than the early modern humans [previously found in] Africa and the Middle East,” said Qiaomei Fu, a research fellow studying genetics at Harvard Medical School who worked on the specimen. In fact, scientists at the Planck Institute performed the radiocarbon test twice to verify the sample’s age, Kelso said.

When both tests confirmed that the sample was from Siberia and dated to 45,000 years ago, the scientists also concluded that early modern human migrations into Eurasia were not solely via the route that had been suggested by previous models. Since this genetic makeup also indicated that the specimen’s ancestors interbred with Neanderthals close to the time of the major expansion of modern humans out of Africa and the Middle East, the original settling patterns may have to be reassessed, Kelso said.

“There might be more than one possibility for the humans’ movement,” Fu said.

During the DNA testing process, the scientists said that they continued to make unexpected discoveries.

“Ancient DNA analysis, which once was a dream, has now become a possibility,” said Priya Moorjani, a postdoctoral student in biology at Columbia University who worked on the techniques for the specimen’s DNA analysis while obtaining her Ph.D. from Harvard. “That really gives you an opportunity to study the past in a way that was not possible before.”

While scientists found that the specimen’s genome was broadly similar to that of present-day humans, they noted that it contained longer segments of Neanderthal DNA, suggesting that the ancestors of the specimen mixed with Neanderthals approximately 7,000-13,000 years before the man lived.

“[The sample] is really close to present-day humans but is much, much more close to the Neanderthal,” Fu said.

Analyzing the specimen’s genome also allowed the Planck team to gain new insight into human evolution. “Ancient DNA has been able to provide an independent estimate of the human mutation rate…and suggests that between one and two mutations per year have accumulated in the genomes of populations in Europe and Asia since [the specimen] lived,” Kelso said.

The scientists said that they are excited to see what these results will mean for the field in the coming years.

“[These specimens] help us tease apart where humans come from and how long they have inhabited different parts of the world,” Moorjani said.