. . . The discoveries were made by a team of scientists led by Svante Paabo, a geneticist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. Dr. Paabo and his colleagues have developed tools for plucking out fragments of DNA from fossils and reading their sequences.
Early on, the scientists were able only to retrieve tiny snippets of ancient genes. But gradually, they invented methods for joining the overlapping fragments of the ancient genes together, and assembled larger pieces of ancient genomes of humans and their relatives. In December, they published the entirety of a Neanderthal genome extracted from one toe bone. Comparing Neanderthal to human genomes, Dr. Paabo and his colleagues found that we share a common ancestor, which they estimated lived about 600,000 years ago. Recently, Dr. Paabo and his colleagues got an opportunity to test their new methods on an exceptional human bone.
In 2008, a fossil collector named Nikolai V. Peristov was in Siberia, searching for mammoth tusks in the muddy banks of a river. Near a settlement called Ust'-Ishim, he noticed a thighbone in the water and brought it to scientists at the Russian Academy of Sciences where researchers identified the bone as a modern human, not a Neanderthal. To determine its age, they sent samples to the University of Oxford where scientists measured the breakdown of radioactive carbon and determined the bone was about 45,000 years old — making it the oldest modern human fossil ever found outside of Africa and the Near East.
In 2012, Dr. Paabo and his colleagues took samples from the bone to search for DNA. It held a number of genetic fragments. The researchers used the DNA fragments to create a high-resolution copy of the man’s complete genome. A Y-chromosome revealed that the thigh bone belonged to a man . . . whose DNA was more like that of non-Africans than that of Africans. . . He was part of an early lineage — a group that gave rise to all non-African humans. . . . it had pieces of Neanderthal DNA in his genome, just as living non-Africans do but his Neanderthal DNA had important differences.
Fossils indicate that Neanderthals spread across Europe and Asia before becoming extinct an estimated 40,000 years ago. Today, the Neanderthal DNA in each living non-African human is broken into short segments sprinkled throughout the genome . . . During the development of eggs and sperm, each pair of chromosomes swaps pieces of DNA. Over the generations, long stretches of DNA get broken into smaller ones, like a deck of cards repeatedly shuffled.
Over thousands of generations, the Neanderthal DNA became more fragmented. . . . By comparing the Siberian Neanderthal DNA with shorter stretches in living humans, Dr. Paabo and his colleagues estimated the rate at which they had fragmented. They used that information to determine how long ago Neanderthals and humans interbred. . . . The answer is that humans and Neanderthals interbred 50,000 to 60,000 years ago. [Summarised from the New York Times]