A recent radiocarbon dating on an ancient male leg bone found on the bank of a Siberian river in 2008 reconstructed the oldest human genome ever at 45,000 years old.
But a subsequent DNA extraction from the same remains indicated that the pre-historic human actually interbred with Neanderthals, reported Newsmax.
Live Science describes Neanderthals as an extinct human species, popularly known today as the "original cave men." As the closest human relatives, they differ from modern humans in terms of DNA by only 0.12%
Neanderthals, who lived in Eurasia between 30,000 to 200,000 years ago, have appearance similar to modern humans but are shorter and stockier. They also have angled cheek bones and wide noses, noted Live Science.
International weekly journal of science Nature, published on Wednesday, the genome sequence of the 45,000-year-old modern human male found in Ust' Ishim in western Siberia.
"This individual carries a similar amount of Neanderthal ancestry as present-day Eurasians," Nature disclosed.
Prior to the latest discovery, the oldest modern human genome came from the remains of a 24,000-year-old boy buried at Mal'ta near Lake Baikal in eastern Siberia, The Guardian said.
The presence of Neanderthal DNA on the human genome strongly suggests that interbreeding between modern humans and the pre-historic Neanderthals must have taken place at least 45,000 years ago, The Guardian said.
A further study on the genome also gave scientists an accurate date range when the pre-historic mating between humans and Neanderthals began - between 50,000 to 60,000 years ago, cites The Washington Post.
"It's irreplaceable evidence of what once existed that we can't reconstruct from what people are now. It speaks to us with information about a time that's lost to us," says John Hawks to New York Times.
Hawk is a paleoanthropologist at the University of Wisconsin, but he was not involved in the study.
The New York Times reported that a team of scientists, led by Svante Paabo, a geneticist, and Janeth Kelso of the Max Planck Institute of Evolutionary Anthropology in Leipzig, Germany, made the discoveries on the oldest human genome.
Paabo, Kelso and their colleagues also compared the amount of Neanderthal DNA on a group of early humans coming from Europe and Asia to determine when specific ancestors interbred with Neanderthals, reported The Washington Post.
Based on their findings, the researchers estimate that mating began sometime between 37,000 to 86,000 years ago, the report added.
"We think that the ancestors of the Ust' Ishim man met and interbred with Neanderthals during the initial early admixture event that is shared by all non-Africans. We think it happened between 50,000 to 60,000 years ago and most likely somewhere in the Middle East," Kelso told The Guardian.