An international research team led by Martin Petr and Janet Kelso of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, has determined Y chromosome sequences of three Neandertals and two Denisovans. These Y chromosomes provide new insights into the relationships and population histories of archaic and modern humans, including new evidence for ancient gene flow from early modern humans into Neandertals. The data show that Neandertals may have benefited from these interactions as the gene flow resulted in the complete replacement of the original Neandertal Y chromosomes by their early modern human counterparts.