COPENHAGEN, DENMARK—According to a Nature News report, an international team of researchers suggests that the virus that causes smallpox has been in the human population for about 1,700 years, or about 1,000 years longer than previously thought. The scientists screened DNA from the remains of 1,867 people who lived in Eurasia and the Americas between 32,000 and 150 years ago, and detected strands of DNA resembling the genetic makeup of the modern virus that causes smallpox in 26 of them. The researchers then extracted additional genetic material from the remains of 13 of these individuals for further study. Eleven of these individuals came from Scandinavia, Russia, and the United Kingdom, and their remains dated from between A.D. 600 and 1050. Evolutionary geneticist Martin Sikora said that four of these individuals carried a previously unknown strain of the virus. “It’s a separate evolutionary trajectory that died out at some point and, as far as we know, is not present any more today,” Sikora said. The scientists then used the differences between the ancient lineages of the virus and the modern one to determine that they split from a common ancestor about 1,700 years ago, he explained. To read about how ancient microbial DNA can be used to study health in the past and present, go to "Worlds Within Us."