The investigators extracted mitochondrial DNA (mtDNA) from the bones of a Neanderthal sequenced it and compared it to mtDNA from modern humans from 994 mitochondrial lineages on different continents. Modern human mtDNA types only differ from each other by an everage of 8 substitutions; they differed from the Neanderthal sequence by an average of 27.2 substitutions. They conclude that Neanderthals did not pass any of their DNA on to modern populations, not even those of Europeans, presumably because they could not, indicating that they were a separate species.
