Diabetes, arthritis and multiple sclerosis can be traced back to the Black Death, research found.
It shaped human evolution by influencing responses against pathogens. And pandemics, such as Covid may do so in the future.
Natural selection occurred at pace in plague survivors, say scientists. Our immune systems have evolved to respond in different ways to pathogens.
Some variants increase the risk of autoimmune diseases such as rheumatoid arthritis.
It may not have mattered during the Black Death as the urgency made the trade-off inevitable.
So what had once been a protective gene against plague is today associated with increased susceptibility to illness.
Autoimmune disease happens when the body’s natural defence system can not tell the difference between your own and foreign cells – so the body mistakenly attacks itself.
There are more than 80 types that affect a wide range of organs.
Co-author Professor Hendrik Poinar, of McMaster University in Ontario, explained: “Even a slight advantage means the difference between surviving or passing.”
“Of course, those survivors who are of breeding age will pass on their genes.”
The findings are based on 516 DNA samples extracted from the teeth of individuals who died before, during or soon after outbreaks. Some were from a mass grave in East Smithfield, London.
The Black Death is the most deadly pandemic ever, claiming up to 200 million lives between 1346 and 1353. In the study, published in the journal Nature, Prof Luis Barreiro, of Chicago University, said: “A single pathogen can have such a strong impact to the evolution of the immune system.”