However, Pritchard said, "We do not exclude the possibility of modest levels of genome admixture."
Pritchard's team suggests that human and Neanderthal shared a common ancestor about 706,000 years ago, and that the human and the Neanderthal ancestral populations split around 370,000 years ago. (Researchers found some genetic variation between the two species, which the team attributes to the ancestral population.) Both lines co-existed in Europe and western Asia until about 30,000 years ago.
The team used DNA extracted from a 38,000-year-old Neanderthal specimen from Vindija, Croatia. They recovered 65,250 base pairs of the Neanderthal's 3 billion total base pairs and utilized traditional sequencing technologies used for the Human Genome Project as well as the new parallel pyrosequencing method to clone and insert missing fragmented DNA and create a library of Neanderthal DNA.
Unlike the libraries used to sequence the human genome, which contained only human DNA fragments, the Neanderthal DNA library is riddled with contamination from microbes that lived off the nutrients in the Neanderthal remains, as well as contamination from humans handling the specimens.
However, the scientists performed a variety of studies to confirm that the vast majority of the human-like sequence in the library was indeed Neanderthal and not just contamination from human bone collectors and laboratory workers.
The researchers then verified the authenticity of the Neanderthal sequence by comparing it to the human and chimpanzee genomes. This revealed multiple locations where the Neanderthal sequence matched more closely to that of chimpanzee and not human. Using the comparison of the Neanderthal to the human and chimp genomes enabled the investigators to estimate the human-Neanderthal divergence
Source:University of Chicago Medical Center