Genetic twist: Medieval plague may have molded our immunity

Our Medieval ancestors left us with a biological legacy: Genes that may have helped them survive the Black Death make us more susceptible to certain diseases today.

It's a prime example of the way germs shape us over time, scientists say in a new study published Wednesday in the journal Nature.

“Our genome today is a reflection of our whole evolutionary history" as we adapt to different germs, said Luis Barreiro, a senior author of the research. Some, like those behind the bubonic plague, have had a big impact on our immune systems.

The Black Death in the 14th century was the single deadliest event in recorded history, spreading throughout Europe, the Middle East and northern Africa and wiping out up to 30% to 50% of the population.

Barreiro and his colleagues at the University of Chicago, McMaster University in Ontario and the Pasteur Institute in Paris examined ancient DNA samples from the bones of more than 200 people from London and Denmark who died over about 100 years that stretched before, during, and after the Black Death swept through that region.

They identified four genes that, depending on the variant, either protected against or increased susceptibility to the bacteria that causes bubonic plague, which is most often transmitted by the bite of an infected flea.

They found that what helped people in Medieval times led to problems generations later — raising the frequency of mutations detrimental in modern times. Some of the same genetic variants identified as protective against the plague are associated with certain autoimmune disorders, such as Crohn’s disease, rheumatoid arthritis and lupus. In these sorts of diseases, the immune system that defends the body against disease and infection attacks the body's own healthy tissues.

“A hyperactive immune...