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wewbull t1_j95tpui wrote

Reply to comment by fack_yuo in Why are fevers cyclical? by Key-Marionberry-9854

Sounds like a classical control feedback loop in engineering.

However if it was just this there'd be no reason the body wouldn't have developed some kind of hysteresis to "debounce" the system, latching the fever on for a period after the viral load drops to ensure the complete eradication of the virus.

I suspect the fever is expensive or damaging in itself. So the best system is something less drastic, but that might take longer to kill the virus.

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Shadowfalx t1_j96254v wrote

There also isn't a reason to think the body would evolve a way to stay in fever after vital load drops. Remember, evolution is random and if this never randomly occurred we wouldn't evolve it.

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wewbull t1_j964efw wrote

It's random in the short term. In the long term, beneficial traits will improve survivability and be selected for. If staying in fever benefitted surviving it's reasonable to assume it would have arisen by chance and then been selected for by now.

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yaminokaabii t1_j96bbp2 wrote

Be careful saying that beneficial traits will necessarily become more prevalent. It's all probability. If getting the long-term better trait necessitates going through a worse trait in the short-term, it may never happen. As an example with arbitrary numbers, say staying in fever another 1 to 5 hours is actually disadvantageous, even if staying 5-10 hours is advantageous.

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wewbull t1_j96d4tw wrote

True. Local inflections like that can act as barriers to getting to a much more advantageous trait. I agree.

...but I also think it's wrong to say evolution is random. It's random experiments in a game of procreation. Those experiments which fail are discarded. As such the overall process is guided away from failure and not random.

Maybe I was asserting the positive case (towards success) too much, when the negative case (away from failure) is really the stronger aspect.

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yaminokaabii t1_j96lbr8 wrote

I had just wanted to add to your last comment, I think we are in violent agreement here! Saying evolution is "random" is simplified to the point of inaccuracy—I would say it is probabilistic.

There is definitely something to be said about going towards success. I'm thinking of the RNA world hypothesis about the origin of life wherein RNA molecules both held replicable genetic information (as DNA does) and catalyzed the chemical reactions to replicate itself. The self-sustaining molecules won out because... they sustained themselves. Life now is pretty damn good at "being successful", except when it's threatened by other life being more successful, which looks like moving away from failure.

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Shadowfalx t1_j9756f9 wrote

You are correct but are missing the forest for the trees as they say.

The original mutation is random, benefiting (or at least not harming) is selected for. So without the random mutation there isn't anything being selected for.

For example, say we need to change gene 1 from A to C for the fever to last 1 hour longer (this is very simplified of course) but throughout history no one has changed gene 1 to C then there will be no longer fever to select for.

We can't see evolution as something that moves creatures along with intent. Nothing is guaranteed since you must first have a random mutation to progress.

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