Historians have long speculated that Europeans introduced smallpox to the Americas, which then killed hundreds of millions of Indigenous peoples. Genetic evidence has recently proved they were onto something. In a newly published Science study, scientists revisited two mummies recovered from northern Chile in 1990 and performed an advanced DNA analysis of their genomes. The individuals, who presumably died between the late 15th and early 17th centuries, hosted a lost strain of variola viruses that cause smallpox—specifically the kind known to have affected Europeans around the same time period. “This discovery provides the first molecular confirmation that smallpox was carried to the Americas during the colonial period,” Shigeki Nakagome, the study’s co-author and a geneticist at Trinity College Dublin in Ireland, said in a statement. “But beyond tracing the disease’s arrival, our study also sheds new light on how smallpox evolved.” Unexpected discoveries As often happens with major discoveries, the team wasn’t looking for what it ended up finding, which in this case was traces of ancient smallpox DNA. Initially, the researchers wanted to study the ancestry and population history of people from northern Chile, Constanza de la Fuente Castro, the study’s co-author and an anthropologist at the University of Chile, told Scientific American. This was why the team revisited the mummies, which featured a woman in her 30s and a man around his 20s, both likely Inca and buried at an Indigenous site.