“The original project wasn’t trying to find pathogens,” says study co-author Constanza de la Fuente Castro, an anthropologist at the University of Chile. Samples from an adult woman and a young man yielded fragments of variola virus, the pathogen that causes smallpox. “We didn’t know that there was evidence of smallpox here,” says de la Fuente Castro. The now extinct lineage branched off after medieval European strains but before those that gave rise to modern smallpox. “It was kind of like a perfect collaboration for us,” says de la Fuente Castro.