The deadliest event in humans’ recorded history, the Black Death, killed an estimated 75 million to 200 million people before its peak in the mid-1300s.

Now, researchers have used DNA from those who died during the bubonic plague era to better understand the connections between natural selection during past pandemics and disease susceptibility today.

Led by scientists from Canada’s McMaster University and the University of Chicago, an international team analyzed centuries-old data, including more than 500 DNA samples taken from those who lived during a 100-year window in the Black Death era.

The samples were taken from those who lived in London and Denmark and died before the plague, those killed by the plague and those who made it through the plague that swept through Europe, Asia and Africa.

The researchers were on the hunt for clues to genetic adaptation related to the plague, caused by the bacterium Yersinia [yer-sin-ee-uh] pestis.

The team zeroed in on versions of four genes, called alleles [ul-leelz], that either protected or made one more susceptible to the plague.

Those with two identical copies of a particular gene, called ERAP2 [E-R-A-P 2], likely as much as 40 to 50%, were able to survive at much higher rates than those who had the opposing — and let’s be honest, not so helpful —  set of genes.

In a curious evolutionary turn, however, those genes that helped some mount a spirited defense against the plague are today associated with increased susceptibility to autoimmune diseases, such as Crohn’s, rheumatoid arthritis and lupus.

The question does spring to mind: What changes might Mother Nature now be imposing on our DNA as we’re in the midst of another pandemic?