The Black Death triggered 'a form of Darwinian evolution' that gave rise to modern immunity, suggests new study

The Black Death, also known as the bubonic plague, may have influenced the evolution of genes involved in immune responses, suggests a new study of ancient genomic data published in Nature today (Oct .19).

The findings indicate that past pandemics might have affected present-day disease susceptibility and may continue to do so in the future. Professor Luis Barreiro, one of the study's co-authors, provides additional insight in a conversation with Interesting Engineering (IE).

The Black Death, caused by Y. pestis, eliminated between 30% and 50% of the population

Between 1346 and 1350, Yersinia pestis (Y. pestis) bacteria swept throughout Europe, the Middle East, and Northern Africa, causing the Black Death. The virus killed between 30 and 50 percent of the population at the time. The significant mortality rate indicates there was little to no preexisting immune response to Y. pestis in these regions.

Mortality rates dropped during future plague outbreaks over the following 400 years, which may have been due to altered cultural customs or pathogen evolution. Still, this could also signify the genetic adaptation of humans to the bacterium (which this new study relates to).

Ancient DNA samples taken from people who passed away before, during, and after The Black Death were analyzed

Luis Barreiro and colleagues examined 516 ancient DNA samples taken from people who passed away before, during, or shortly after Black Death. The evolution of genetic variation in immune-related genes was investigated using outbreaks in London, UK (318 samples), and throughout Denmark (198 samples). For the primary analysis, 206 of these samples were used in total.

The samples were dated using historical records and radiocarbon dating. They included those of people buried in a plague cemetery in London who had passed away between 1348 and 1349.

'Yes, it is a form of Darwinian evolution (or positive selection)'

The researchers discovered evidence of positive selection of genetic variants in immune-related genes during and after the Black Death. They found 245 genetic variants significantly different in London's pre- and post-Black Death samples.

Four of these strongest candidates for positive selection were replicated in the Danish cohort (an establishment investigating the possibilities for disease prevention).

During this investigation, one of the four variants was linked to the control of Y. pestis in lab tests using blood cells (macrophages). The researchers believe this 'control' may have led to the development of Y. pestis resistance.

"Yes, it is a form of Darwinian evolution (or positive selection). The idea is that individuals that harbored genetic variants that protected them against Y. pestis were more likely to survive the pandemic and pass their genes to the next generation," Prof. Barreiro tells IE.

"We'd expect these variants to increase in frequency after the Black Death."

Protection from Y. pestis could also mean increased susceptibility to autoimmune diseases

The scientists point out that the same genes linked to protection from Y. pestis overlap with those that cause higher susceptibility to autoimmune disorders. They highlight that this overlapping suggests the potential influence of previous pandemics on present-day disease risk.

In other words, "We show that the same genetic variants that were protective against the Black Death are the same variants that today increase the risk for several autoimmune disorders," clarifies Barreiro.

Genome Wide Association Studies (GWAS) conducted by different researchers provided evidence for the link between specific variants and higher incidence of autoimmune illnesses.

Could a comparable natural selection have been triggered by the pandemic that dominated 2020?

The new research advances our understanding of how the evolutionary paths of these variants produce changes in allele frequency in modern populations.

With this in mind, does such a discovery prompt you to consider how COVID, which has claimed over six and half million lives to this date, may have induced similar changes? That is, a comparable form of natural selection. We suppose future generations will tell.