From Frederico Henning
The virus adapts to us through natural selection and initially follows predictable steps
“Mutations” and “variants” have become common words in the press and pose some important questions about society: Will vaccines continue to work? Can people get infected again? Is the Virus More Dangerous? A specialist recently stated in an interview that “mutations are occurring and some are becoming more common variants”. Well, this process has a first and last name: evolution by natural selection. We often hear that the new variants are responsible for the uncontrolled pandemic. But is evolution really unpredictable?
Humans often associate the evolution of species with the great changes that have taken place in life forms over a long period of time. It is widely believed that evolution leads to the “progress” of organisms towards perfection or complexity. In reality, evolution works continuously in short steps and “progress” or “adaptation” must be viewed as “the solution of immediate problems”. With a coronavirus, the advance is to increase the transmission rate. In the long term, there is no direction for evolution, as the course of life changes due to drastic changes in the environment, such as the fall of meteors. However, on the timescale in which we live, developments are surprisingly predictable.
Adaptive evolution always takes place when there are two things: mutation and natural selection. The first part, the mutation, happens randomly and alone does not make organisms more adaptable. Every time a virus multiplies, one in a hundred thousand nucleotides – represented by the letters A, C, U, and G that make up the genetic sequence of RNA – is copied incorrectly, resulting in random mutations. But there is a certain regularity in chaos. We cannot predict which letter will be exchanged for another in one mutation event, but how many mutations will occur in each generation. Since the virus genome is made up of 30,000 letters, there is a 30% chance of any new virus being mutated.
Because of this regularity, we can compare the genetic sequences of current organisms and, based on the number of differences between them, infer how much time has passed in evolution. This “mutation timer” is the main tool in scientific research to find out where the virus came from, how it arrived and spread in Brazil, and to monitor the appearance and spread of new variants.
The second part of the equation, natural selection, explains why some of these mutants dominate the population and “become more common variants.” It’s not a random process, so much so that food production has benefited from geneticists’ prediction for more than a century. An example of the predictability of natural selection is that the different coronavirus strains, even isolated from one another, evolve in a similar way. A virus can change in more than 150,000 different ways, but the variants accumulate the same mutations that increase immune transmission and bypassing. This “convergent” evolution – starting from different points and achieving the same answer – shows the genetic pathways in which the virus evolves, the variants that should be the focus of surveillance, and the next steps in viral evolution. We know how to neutralize adaptive evolution. When we interrupt transmission, especially of strains that contain common mutations, we prevent natural selection from working. Although mutations will continue to occur, there will be no accumulation of mutations that are good for the virus.
Anticipating evolution is important so that vaccines against new variants can remain effective and even make the diagnosis, as the RT-PCR test only detects the presence of the virus if we know part of its genetic sequence. Therefore, scientists need to predict the genetic changes that will occur in order to interpret and develop tests that will continue to work as the virus evolves.
“There is greatness in this worldview,” wrote Darwin at the end of his most famous book. There is great use as well, but controlling the process starts with naming the ox and this is called evolution.
Frederico Henning is a biologist and professor at UFRJ, where he coordinates research, teaching and expansion projects in the fields of genetics, genomics and evolution.
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