When Johannes Krause was a graduate student working on the Neanderthal genome in the 2000s, so much of the DNA recovered from the ancient bone fragments came from everything else: the skin cells of excavators and scientists, the bacteria on those humans, the microbes in the soil. To get to Neanderthal DNA, you had to junk the rest. Once scientists figured out how, they rushed to sequence not just Neanderthal DNA but also ancient human DNA, which together have been rewriting the early history of our species.
Only later did scientists realize that there is gold in the “junk” too.
If you know exactly how and where to look, you can also find DNA from ancient pathogens in old bones. The “junk” might actually contain clues about long-ago pandemics. Over the past decade, scientists have used ancient DNA to study diseases including the plague, syphilis, hepatitis B, and a mysterious “cocoliztli” epidemic—all using techniques honed through decoding the Neanderthal genome. A boom in ancient pathogen DNA is uncovering hints of forgotten and even extinct diseases.
Krause, now the director of the archaeogenetics department at the Max Planck Institute for Evolutionary Anthropology, is a co-author of the recent book A Short History of Humanity, with the German journalist Thomas Trappe. I’ve written about Krause’s studies as they’ve come out over the years, but the book synthesizes two decades of work with ancient DNA, human and pathogen. This kind of research is difficult; it relies on a very small number of samples and requires the expertise of historians and archaeologists to interpret. And even then, some things about the past are unknowable. Amid our current pandemic, I spoke with Krause about some of the most intriguing yet puzzling genetic clues we now have about very old pandemics.