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Interesting finding: COVID-19 populations show high convergent evolution


A paper on SARS-CoV-2 sequencing around the globe reports:

We find that two particular mutation rates, G →U and C →U, are similarly elevated and considerably higher than all other mutation rates, causing the majority of mutations in the SARS-CoV-2 genome, and are possibly the result of APOBEC and ROS activity. These mutations also tend to occur many times at the same genome positions along the global SARS-CoV-2 phylogeny (i.e., they are very homoplasic). We observe an effect of genomic context on mutation rates, but the effect of the context is overall limited. While previous studies have suggested selection acting to decrease U content at synonymous sites, we bring forward evidence suggesting the opposite.

Nicola De Maio, Conor R Walker, Yatish Turakhia, Robert Lanfear, Russell Corbett-Detig, Nick Goldman, Mutation rates and selection on synonymous mutations in SARS-CoV-2, Genome Biology and Evolution, 2021;, evab087, https://doi.org/10.1093/gbe/evab087

The paper is open access.

Evolution appears to converge on goals—but in Darwinian terms, is that possible?

This is fairly easy to understand, and yes, it is a perfect example of what Darwinian "evolution" can do, while yet underscoring its severe limitations. The original virus came from some non-human animal. In jumping to humans, the external proteins were an imperfect fit to human cell receptors - good enough to become viral, yet still imperfect. If one simple amino acid change is enough to improve the receptor fit, then in the quadrillions of viruses infecting the billion or so humans, that one substitution is a sure thing, and should arise quickly. The result is a slightly modified virus that infects humans more readily and hence spreads more often or more rapidly. In Darwin speak, it is more fit than the initial virus, and so becomes selected naturally in the human population. A clear example of Darwinism in action! But note that quadrillions of copies are needed for a single codon change. As Michael Behe has shown, if two amino acids would need to change before a benefit resulted, then it would take much longer for that to occur, even in a population of quadrillions. (He demonstrated this with the malaria disease vs. drug treatments.) And if more than two were needed, the virus might never get there unless each change was somehow sequentially beneficial to it. This he called the Edge of Evolution: natural selection can only tweak things a tiny bit, and sometimes that helps, so the changes become dominant in the population. Once the function has been optimized (i.e. best possible fit to the human receptors), no further "evolution" of that function can occur. And no new function ever arises! Of course, in animals and humans, with populations in the millions instead of quadrillions, along with reproductive cycles in years instead of days, such "evolution" proceeds far more slowly, taking eons for even the simplest tweaks. This greatly limits even the possibility of significant Darwinian evolution towards new species in higher animals, even over millions of years. Darwinism works for tiny changes, but not for the big ones. Fasteddious

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