Reich is an associate professor of genetics at Harvard University who also serves as a population geneticist at the Broad Institute of MIT and Harvard.
He and his colleagues analyzed over one billion DNA fragments taken from Neanderthal bones -- dating to approximately 38,000 years ago -- found in Croatia, Germany, Russia and Spain.
Although 95 percent of the fragments consisted of bacteria and microorganisms that colonized the Neanderthal remains, special DNA isolation and anti-contamination measures enabled the scientists to piece together over 60 percent of the entire Neanderthal genome.
The researchers next compared the Neanderthal DNA to samples taken from present-day humans in southern Africa, western Africa, China, France and Papua New Guinea.
One of the first determinations concerned the point at which humans diverged from their common ancestor with Neanderthals, who lived in much of Europe and western Asia before they went extinct.
"According to our results, the ancestors of Neanderthals and modern humans went their separate ways about 400,000 years ago," said co-author Jim Mullikin, a computational geneticist at the National Human Genome Research Institute.