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Incendas1 t1_jdjouzu wrote

I don't know about specific viruses, but regarding evolution:

Nothing really "wants" to do anything or "knows how to" do anything in this way. It's a simple way of explaining it, that's all.

Before this trait evolved in rabies, let's say, it didn't compel hosts to bite other animals.

Eventually one strain of rabies had a random mutation that made the host more aggressive, or maybe salivate more - something that would cause it to bite or attack.

This particular strain spread really well, because that's a good advantage. This "biting" strain is now the dominant strain - most rabies strains make hosts bite other animals...

So, the virus doesn't want to do anything. It's just the most successful "breed" of virus, so it survived.

A lot of mutations are negative - they usually die out.

This is just an example, not how rabies evolved exactly.

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A1sauc3d t1_jdkbgkz wrote

Exactly. And I think it’s important for the OP to note that rabies doesn’t “make the host want to bite others to spread the virus”. It simply causes the host to lose fear and become agitated, confused and agressive, which leads to biting incidents. But it’s not like there’s a voice in the animal’s head telling it to go find something to bite so they can spread the infection, like you might imagine with zombies who are hungry for brains or whatever. It’s just a consequence of the behavioral changes. Which as you said, happened to help it spread, yada yada.

This article gets into the details of what’s causing the behavioral changes and such if you’re interested OP:

https://www.medicalnewstoday.com/articles/319735#Virus-interacts-with-muscle-receptors

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