IN 2009, WHEN the most recent major monograph was published on life in an Italian city of the mid-fourteenth century, its author deferred judgment on whether the disease that struck Italy in 1348—“an infinite mortality the likes of which ha[ve] never been seen on earth”—was in fact plague as defined by modern science (Wray 2009: 1). The authors contributing to this, the inaugural issue of The Medieval Globe, no longer feel that such caution is necessary. Since 1998, several international teams of microbiologists have tested and contested the possibilities for establishing the presence of plague's causative organism, Yersinia pestis, in the physical remains of Europeans who died at various moments in premodern history when major epidemics were raging. The reason that there is scientific consensus now, when there was not before, is a function of two developments, both of them having to do with trajectories in genetics research in the past thirty years that have come together quite recently.

On the one hand, researchers have been exploring methods to capture and analyze “ancient” DNA (aDNA), by which they mean any genetic material from older remains. Because Y. pestis would be circulating throughout the bloodstream by the time it kills a person, and because the hard enamel of intact teeth could potentially preserve small amounts of blood found within the dental pulp, teeth became the focal point of attempts to retrieve Y. pestis from human remains. But the challenges of developing viable methods of extraction and analysis were significant. DNA, like every other part of the body, begins to decay immediately after death, so degradation of the genetic material was the first of the challenges encountered by researchers. For example, the full genome of Yersinia pestis is about 5.6 million base pairs long. The fragments that researchers have had to deal with are rarely even fifty to seventy-five base pairs long. Add to this issue the problems of the material's possible contamination (which could occur when collecting it in the field, or in the lab, or at any point in between), and it is quite understandable, looking back on them now, why the “aDNA debates” of the late 1990s and 2000s were so intense.