New research reveals how the black rat colonized Europe in Roman and medieval times
A new analysis of ancient DNA has shed light on how the black rat, blamed for spreading the Black Death, spread across Europe – revealing the rodent colonized the continent twice in Roman and medieval times. The study, conducted by the University of York with the University of Oxford and the Max Planck Institutes for the Science of Human History (Jena) and Evolutionary Anthropology (Leipzig), is the first ancient genetic study of the species, also known as the ship rat.
The black rat (Rattus rattus) is one of the three species of rodents, along with the house mouse (Mus musculus) and the brown rat (Rattus norvegicus), to have distributed worldwide due to its ability to live around dwellings humans by taking advantage of food and transport. Roof rats were widespread throughout Europe until at least the 18th century, before their population declined massively, most likely due to competition with the newly arrived brown rat, the now dominant rat species in temperate Europe .
By analyzing the DNA of ancient black rat remains found at archaeological sites spanning from the first to the 17th century in Europe and North Africa, researchers have pieced together a new understanding of how rat populations dispersed following to the ebb and flow of human commerce, urban planning, and empires.
The study shows that the black rat colonized Europe at least twice, once with Roman expansion and then again in medieval times, consistent with archaeological evidence of a decline or even a disappearance of rats at the beginning of the medieval period. According to the authors, this was probably linked to the break-up of the Roman economic system, although climate change and the 6th-century Justinian plague also played a role. When towns and long-distance trade reappeared in medieval times, a new wave of black rats also appeared.
Repeated colonization of Europe
“We have long known that the spread of rats is linked to human events, and we suspected that Roman expansion brought them to northern Europe,” said David Orton of the Department of Archeology at the University of York. . “But a remarkable result of our study is how unique this appears to have been: all of our Roman rat bones, from England to Serbia, form one group in genetic terms.” He adds: “When the rats reappear in medieval times, we see a completely different genetic signature – but again, all of our samples from England to Hungary to Finland all cluster together. We wouldn’t have could not have hoped for clearer evidence of the repeated colonization of Europe.
Greger Larson and Alex Jamieson, co-authors from Oxford University, said: “The modern dominance of brown rats has obscured the fascinating history of roof rats in Europe. Generating genetic signatures from these ancient roof rats reveals how closely the population dynamics of roof rats and humans mirror each other.
According to the authors, the study could also provide information on human movements across continents. “This study is an excellent showcase of how the genetic makeup of human commensal species like the roof rat, animals that thrive around human settlements, can reflect human historical or economic events. We can learn a lot from these small animals. often overlooked,” said lead author He Yu, a researcher at the Max Planck Institute for Evolutionary Anthropology.