In a new Science study, scientists read the family tree buried inside modern genomes and turned up “ghost ancestors” in every population on Earth that no fossil records can account for. These archaic lineages interbred with ancient human groups who had migrated out of Africa, which scientists can confirm by comparing rare preserved samples of their DNA with ours. Because we have never found any archaic hominin genomes in sub-Saharan Africa, scientists couldn’t tell. It found that 2 percent of the DNA in non-African genomes came from archaic lineages, consistent with prior research. If both have equally low similarity, Reilly argues, we could infer that these ghosts formed an equally distant sister group to Denisovans, Neanderthals and possibly modern humans.