Our ancestors bred with other species in the Homo genus, according to a study published today in the Proceedings of the National Academy of Sciences1. The authors say that up to 2% of the genomes of some modern African populations may originally come from a closely related species. Palaeontologists have long wondered whether modern humans came from a single, genetically isolated population of hominins or whether we are a genetic mix of various hominin species. Last year, an analysis comparing the Neanderthal genome sequence to that of modern H. sapiens showed that some interbreeding did take place between the two...