Ancient DNA traces the history of hepatitis B Hepatitis B virus (HBV) infections represent a worldwide human health concern. To study the history of this pathogen, Kocher et al . identified 137 human remains with detectable levels of virus dating between 400 and 10,000 years ago. Sequencing and analyses of these ancient viruses suggested a common ancestor between 12,000 and 20,000 years ago. There is no evidence indicating that HBV was present in the earliest humans as they spread out of Africa; however, HBV was likely present in human populations before farming. Furthermore, the virus was present in the Americas by about 9000 years ago, representing a lineage sister to the viral strains found in Eurasia that diverged about 20,000 years ago. —LMZ