Evolution: side effects of defense mechanisms: (Evolution)

by David Turell @, Saturday, July 27, 2019, 18:54 (377 days ago) @ David Turell

Many of our infections come from self-defense mechanisms of various agents:

https://aeon.co/essays/when-bacteria-kill-us-it-s-more-accident-than-assassination?utm_...

"Many of the bacteria and fungi that afflict us with severe diseases are not aiming at us at all. Instead, they have evolved to thrive in harsh environments or to fend off other microbes. It just so happens that these same adaptations allow them to thrive in our bodies or to fend off our immune systems.

***

"the thickly armoured strains of S.pneumoniae are impervious to white blood cells, and can stand their ground. Their armour would normally be a liability – they take so much energy to make that their owners get outcompeted by strains that make lighter and less costly coats. But with H.influenzae mobilising an immune army, a thick coat suddenly becomes worthwhile. And by coincidence, those coats make these strains better at invading deeper parts of the respiratory system, and causing serious disease. In defending itself from a competitor, S.pneumoniae inadvertently becomes an armoured killer.

"Its virulence – its ability to cause disease – is not an adaptation against its host. It is a side effect, a fluke. It kills through coincidence.

***

"The adaptations that allow bacteria, fungi and other pathogens to cause us harm can easily evolve outside the context of human disease. They are part of a microbial narrative that affects us, and can even kill us, but that isn’t about us. This concept is known as the coincidental evolution hypothesis or, as the Emory University microbiologist Bruce Levin described it in 2008, the ‘shit happens’ hypothesis.

***


"The coincidental evolution hypothesis explains a number of other recent discoveries about microbes. Scientists have found antibiotic resistance genes in bacteria that have been frozen for 30,000 years, or isolated in million-year-old caves. We might think of antibiotics as modern inventions, but they’re actually weapons that bacteria have been using against each other for aeons, or at least well before Alexander Fleming noticed a funky mould in a Petri dish in 1928. Antibiotic resistance genes evolved as part of this ancient war, but they also help today’s microbes to deal with the medicines that we mass-produce.

"Likewise, many of the ‘virulence genes’ that help pathogens to cause disease have counterparts in marine microbes with no track record of infecting humans. And some supposedly pathogenic bacteria were often common parts of the environment. ‘These organisms become accidental pathogens,’ says the microbiologist Arturo Casadevall.

***

"There are so many microbes out there that some of them will end up with a hand that lets them muscle their way into our game. ‘If you take all the microbial species in the world and imagine that they have these traits randomly, you can find pathogenic microbes for practically anything,’ says Casadevall.

***

"...if virulence is coincidental to begin with, there might not be much of an evolutionary pressure for the inadvertent pathogen to change its ways.

"There is something unsatisfying, almost nihilistic, about this idea. It deprives us of answers. As Casadevall wrote in a review, it says that virulence can arise by chance, ‘in a process that has no explanation, except for that it happened’. According to this outlook, we’re not central actors in the dramas that affect our lives. We’re not even bit players. We are just passers-by, walking outside the theatre and getting hit by flying props.

"The most important parts of a microbe’s world are, after all, other microbes. They’ve been dealing with each other for billions of years before we came along. When we step into the crossfire of this ancient war, we risk becoming collateral damage."

Comment: Part of evolutionary relationships may simply be unintended consequences, which brings us back to God as an impersonal being, not actually caring about humans welfare. Adler thought God answering prayers was a 50/50 proposition.


Complete thread:

 RSS Feed of thread

powered by my little forum