To extract ancient human chromosomal DNA from caves, Vernot and colleagues identified regions in chromosomes rich in mutations specific to hominids to help the team filter out nonhuman DNA. This helped the researchers successfully analyze Neandertal chromosomal DNA from more than 150 samples of sediment roughly 50,000 to 200,000 years old from a cave in Spain and two caves in Siberia.After the team compared its data with DNA previously collected from Neandertal fossils of about the same age, the findings suggested that all these Neandertals were split into two genetically distinct waves that both dispersed across Eurasia. One emerged about...