In 1997, Paabo published a paper, describing that Neanderthals did not contribute other genes to modern humans according to mtDNA. Of course considering the way mtDNA is inherited, individual's mtDNA not exchanging bits with another's and mtDNA passing on only maternal lines, it may hell have disappeared until today even if some has passed from Neanderthals. Paabo faced a couple of hurdles to decode mtDNA of Neanderthals 1) scarcity of bones not damaged by acididation and bacteria contamination, 2) how easy modern human DNA contamination would happen, 3) shortness of degraded DNA, 4)when sequencing DNA, they would modify by nature. The bright side on Neanderthals' bones, because of their cannibalism, they had been butchered and their bones sucked free of any meat and marrow, thus limiting the chance for bacteria to multiply in them. The analysis of the nuclear genome was a decisive factor to see if Neanderthals contributed DNA to present-day European.The Neanderthal seemed to be equally distant from an African and a European individual, and the contribution was 2.5%. Because of the equality, the replacement crowd should've met with Neanderthals in Middle East, and the genes flowed from Neanderthals to modern humans(which means that the social status of modern humans should be lower than Neanderthals). *Also, Denisovans were founded along with the journey to explore Neanderthals.