Late last year, three distinct and fast-spreading coronavirus variants were observed in the UK, South Africa and Brazil. More recently, variants in India, the US and elsewhere are causing alarm. Does the emergence of these variants portend a protracted battle with the pandemic, or will the virus soon run out of evolutionary room to manoeuvre and settle down as a more benign, endemic pathogen?

Predictions about the evolutionary course of the virus, and specifically changes in virulence, will always be riddled with uncertainty. The vagaries of randomly mutating RNA, chaotic patterns of transmission and expansion, and partially understood forces of natural selection, present challenges to even the most insightful evolutionary soothsayer. Nevertheless, established evolutionary concepts, combined with a wealth of data from the virus itself, can at least provide some pointers.

SARS-CoV-2, the virus that causes COVID-19, jumped into humans from an unidentified animal host, and in doing so entered a new evolutionary space full of obstacles, threats, dead ends, and – very occasionally – opportunity. This space is difficult to imagine and measure. It is annoyingly multidimensional and its boundaries and topographies can be viewed from many esoteric vantages.

An unsophisticated entry point is to consider the upper limits to genome sequence diversity, or the boundaries of mutational space. Assume the SARS-CoV-2 genome is 30,000 sites long, each of which can be occupied by one of four bases (adenine, cytosine, guanine and uracil). It follows there are over a quintillion (four to the power 30) possible genome sequences, roughly equivalent to the width of the Milky Way in metres.

But this mathematical limit takes no account of biology and as such is completely unhelpful. Hardly any of these hypothetical genomes would encode a virus that is able to infect and replicate. This basic requirement to maintain the viral machinery in top working order is good news. Evolutionary constraints to maintain viral function will limit how quickly and how well the virus will adapt.

Read:

https://theconversation.com/can-scientists-predict-all-of-the-ways-the-coronavirus-will-evolve-156673