The Black Death may have transformed medieval societies in sub-Saharan Africa

In the 14th century, the Black Death swept across Europe, Asia, and North Africa, killing up to 50% of the population in some cities. But archaeologists and historians have assumed that the plague bacterium Yersinia pestis, carried by fleas infesting rodents, didn't make it across the Sahara Desert. Medieval sub-Saharan Africa's few written records make no mention of plague, and the region lacks mass graves resembling the "plague pits" of Europe. Nor did European explorers of the 15th and 16th centuries record any sign of the disease, even though outbreaks continued to beset Europe.

Now, some researchers point to new evidence from archaeology, history, and genetics to argue that the Black Death likely did sow devastation in medieval sub-Saharan Africa. "It's entirely possible that [plague] would have headed south," says Anne Stone, an anthropological geneticist who studies ancient pathogens at Arizona State University (ASU) in Tempe. If proved, the presence of plague would put renewed attention on the medieval trade routes that linked sub-Saharan Africa to other continents. But Stone and others caution that the evidence so far is circumstantial; researchers need ancient DNA from Africa to clinch their case. The new finds, to be presented this week at a conference at the University of Paris, may spur more scientists to search for it.

Plague is endemic in parts of Africa now; most historians have assumed it arrived in the 19th century from India or China. But Gérard Chouin, an archaeologist and historian at the College of William & Mary in Williamsburg, Virginia, and a team leader in the French National Research Agency's GLOBAFRICA research program, first started to wonder whether plague had a longer history in sub-Saharan Africa while excavating the site of Akrokrowa in Ghana. Founded around 700 C.E., Akrokrowa was a farming community surrounded by an elliptical ditch and high earthen banks, one of dozens of similar "earthwork" settlements in southern Ghana at the time. But sometime in the late 1300s, Akrokrowa and all the other earthwork settlements were abandoned. "There was a deep, structural change in settlement patterns," Chouin says, just as the Black Death ravaged Eurasia and North Africa. With GLOBAFRICA funding, he has since documented a similar 14th century abandonment of Ife, Nigeria, the homeland of the Yoruba people, although that site was later reoccupied.

Events in the 14th century also transformed the site of Kirikongo in Burkina Faso, where Daphne Gallagher and Stephen Dueppen, archaeologists at the University of Oregon in Eugene, recently excavated. Starting around 100 C.E., people there farmed, herded cattle, and worked iron. The settlement steadily grew for more than 1000 years. Then, sometime in the second half of the 14th century, it suddenly shrank by half. There's no evidence of food stress, conflict, or migration. "We don't see it coming," Gallagher says. Stone says the sudden changes at Kirikongo and Akrokrowa resemble those seen in the British Isles during the Justinian Plague in the sixth to the eighth centuries C.E.

New hints are also turning up in historical records. Historians have found previously unknown mentions of epidemics in Ethiopian texts from the 13th to the 15th centuries, including one that killed "such a large number of people that no one was left to bury the dead." It's not clear what the disease was, but historian Marie-Laure Derat of the French National Center for Scientific Research in Paris found that by the 15th century, Ethiopians had adopted two European saints associated with plague, St. Roch and St. Sebastian.

Some genetic evidence supports the idea, too. A 2016 study in Cell Host & Microbe revealed a distinct subgroup of Y. pestis now found only in East and Central Africa is a cousin of one of the strains that devastated Europe in the 14th century. "It's the closest living relative to the Black Death strain," says Monica Green, an ASU historian of plague who analyzed this and other previously published plague phylogenies in the journal Afriques. "We [historians] have no story that fits with this evidence that the genetics is screaming about." She thinks this Black Death relative likely arrived in East Africa in the 15th or 16th centuries—after another, now-extinct Y. pestis strain had already burned through West Africa and perhaps beyond.

"[Green's] analysis is very strong," says Javier Pizarro-Cerda, a microbiologist at the Pasteur Institute in Paris who studies Y. pestis. It's intriguing, agrees Benjamin Adisa Ogunfolakan, an archaeologist and director of the Museum of Natural History at Obafemi Awolowo University in Ife, but the evidence so far isn't strong enough to rewrite centuries of African history.

"The silver bullet I dream of," Chouin says, is ancient Y. pestis DNA from human remains in sub-Saharan Africa. Although the region's heat and humidity quickly degrade DNA, Stone hopes researchers will begin to look for DNA in human teeth, where Y. pestis DNA is most likely to be preserved.

Whatever calamity struck medieval sub-Saharan Africa, its impact was lasting. Akrokrowa was abandoned by about 1365, and Kirikongo was never the same. The settlement stayed small, the ceramics got much simpler, and the culture changed to more closely resemble that of the nearby Mali Empire. "It does seem to be a break," Dueppen says. He hopes more archaeologists will start to focus on the 14th century in Africa, looking for hints of plague—or evidence that rules it out. "This is just the beginning of the story," Dueppen says.