Humans and viruses have been evolving together for millennia. Infectious diseases are one of the strongest forces steering human evolution. Pandemics such as the black death and the more recent Covid-19 have radically altered millions of human lives- sociologically and genetically.

 

To understand evolutionary changes brought on by the bubonic plague (caused by the bacteria Yersinia pestis), a team of scientists led by geneticists Jennifer Klun and Tauras Vilgalys studied the remains of over five hundred individuals who died in London and Denmark between 1346–1353. The remains represented three groups: people who died during the plague, before the plague, and the individuals who survived and died sometime after.

 

On comparing the genomes from the remains, the researchers found several genes which were selected for at an astonishing rate- these genes were responsible for producing proteins which aided in fighting against invading pathogens. For example, people having both copies of the ERAP2 gene were 40- 50% more likely to survive the plague.

 

However, some of those gene variants which were identified as a protection against the plague have subsequently been associated with the risk of autoimmune disorders such as Crohn’s and rheumatoid arthritis. The plague had much larger evolutionary pressure compared to a mere autoimmune risk, hence this outcome was inescapable.

 

Evolutionary pressure forces all infectious agents to alter host physiology and behaviour in ways that improve their survival and transfer to the succeeding host. It is physiologically apparent that SARS-CoV-2 affects the human body in ways that support the virus's evolutionary progress by seizing cells and using them to produce new replicas of itself.

 

It is also possible that its effects on host behaviour and psychology are merely collateral damage from the viral infection or immune response. The second approach SARS-CoV-2 can influence host behaviour is by causing mood disorders like mania, which could, at least briefly, boost activity levels and lessen feelings of sickness during periods of high transmissibility.

 

Additionally, regular exposure to novel infections that is typical of human social interaction would be put on hold due to quarantine. This alteration may have the greatest effects on children and teenagers, whose immune systems and brains are hugely shaped by microbial exposures.

 

Covid-19 and the subsequent lockdowns that followed in its wake have brought about a host of sociological changes which reflect the greater impact of such a pandemic on the evolution of human society.

 

The social nature of human beings is one the major contributing factors of the human dominance over other species. Hence, in light of the restrictions and lifestyle changes due to covid, one can expect severe changes in the sociological evolution of the species. It is indeed observed that the strain of lockdown on interpersonal relationships have caused them to evolve in unpredictable ways.

 

Scouring through multiple sources of data, it can be concluded that other than the black death, none of the pandemics over the course of human history have had a profound genetic effect on human evolution. To put into perspective, the fatality of the black death averaged out to 17-54% of the global population, whereas the Spanish flu, inspite of being the second deadliest pandemic, only had a fatality of 1-5.4% of the population.

 

It is only in the recent Covid-19 pandemic that there has been active research into the evolution of humanity as a society rather than a species in response to such an adversity.