When the ancestors of modern humans left Africa 50,000 years ago they met the Neandertals. In this encounter, the Neandertal population contributed around two percent of the genome to present day non-African populations. A collaboration of scientists from Aarhus University in Denmark, deCODE Genetics in Iceland, and the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, have conducted the most comprehensive study to date using data obtained from 27,566 Icelanders, to figure out which parts of our genomes contain Neandertal DNA and what role it plays in modern humans.