Matt Ridley

Stresses and strains: the evolution of Covid is not random

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Matt Ridley has narrated this article for you to listen to.

In the genetic diaspora of an epidemic, there is ferocious competition between strains of virus to get to the next victim first. That leads to apparently purposeful outcomes, as if the virus had a mind. One of the things people find hardest to grasp about evolution is that it appears purposeful but the mutations on which it feeds are random. How come dolphins evolved to swim if all they had to work with were random changes in genes? Viruses also mutate at random — but most people talk as though the rise and fall of these mutant versions is mainly down to chance or luck. It’s not.

Mutations occur all the time in RNA viruses; what matters is which ones find favour in natural selection. The champions of ‘Darwinian medicine’ have been calling for their colleagues to take evolution and adaptation more into account for years, and one of them, Paul Ewald of the University of Louisville, has something very relevant to say about this pandemic. Years ago, Ewald came up with a theory of why some diseases are lethal and others are mild. He argues it is all about the mode of transmission. Infections that you catch from coughs and sneezes are mostly mild; we get more than 200 different kinds of common cold virus and on the whole none of them puts you in bed, let alone kills you. Yet insect-borne diseases such as malaria, plague and yellow fever, and water-borne diseases such as cholera and typhoid, seem quite content to kill you.

The reason, says Ewald, is that in direct-contact diseases such as colds, mild strains will do better than nasty ones, because they send you out to work and to parties, coughing and sneezing.

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Written by
Matt Ridley
Matt Ridley is the author of How Innovation Works: And Why It Flourishes in Freedom (2020), and co-author of Viral: The Search for the Origin of Covid-19 (2021)

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