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I saw in the YouTube video COVID-19 that bats carry so many viruses, yet never or almost never get a disease by any of them. I'm looking for an evolutionary reason as well as a reason based on how their bodies work. However, when you're giving the reason based on how the bodies work, I want you to find some clever way to summarize the reason in a way that I can understand because I hardly know anything about biology.

Could the evolutionary reason be something like this? Bats live in large groups all the time and keep switching around their groupings. Viruses that infect bats evolved by natural selection to do everything they can to spread between bats and survive and not have every last bit of it fought off. Bats in turn evolved by natural selection to not let viruses take over their body more than just a tiny bit. So it was to the evolutionary advantage of both bats and viruses that infect them to form a compromise where the virus gets to invade their bodies to a very small extent but not too much.

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Excellent review in the New Yorker, that discusses that very question, among other things. https://www.newyorker.com/science/elements/from-bats-to-human-lungs-the-evolution-of-a-coronavirus Here's what Carolyn Kormann writes: "As the coronavirus family grows, different strains simultaneously co-infect individual bats, turning their little bodies into virus blenders, creating new strains of every sort, some more powerful than others. This process happens without making bats sick—a phenomenon that scientists have linked to bats’ singular ability, among mammals, to fly. The feat takes a severe toll, such that their immune systems have evolved a better way to repair cell damage and to fight off viruses without provoking further inflammation. But when these viruses leap into a new species—whether a pangolin or a civet or a human—the result can be severe, sometimes deadly, sickness." Hope it helps…

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  • $\begingroup$ I got the answer to my question in the article you linked. It said bats and viruses have been coevolving for a long time. I also got curious to find out how large flocks of bats can get so I YouTube searched "flock of bats" and got the YouTube video youtube.com/watch?v=PNPioS_roRE. They go into caves in such large numbers in an inclosed space easy for viruses to spread. Maybe the bats didn't evolve to strongly fight the viruses and instead the viruses evolved to not try to take over the body to such a huge extent in order to not be fought back so hard. It's kind of interesting to $\endgroup$ – Timothy Apr 10 '20 at 2:43
  • $\begingroup$ think how they might have coevolved. They probably evolved a compromise where they're all like the common cold to bats. The different types of viruses are probably also in a mixed evolutionary stable strategy. Isn't it amazing that bats constantly live so close together in such large numbers in caves and carry so many viruses and are resistant to getting disease from any of them? $\endgroup$ – Timothy Apr 10 '20 at 2:49
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    $\begingroup$ When the video was saying it was something to do with the fact that bats evolved to fly, I couldn't understand what it was saying. After I saw it again in npr.org/sections/goatsandsoda/2020/02/05/802938289/… which was linked by npr.org/sections/goatsandsoda/2020/02/09/803543244/…, I quickly figured out what they were saying this time. Bats need to fly. They require a lot of energy to fly so the energy drain of viruses is less compared to the total amount $\endgroup$ – Timothy Apr 10 '20 at 3:08
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    $\begingroup$ of energy they burn so they had weaker natural selection to fight off the viruses almost completely. Really they tolerate a larger amount of viral infection in their bodies but not that large an amount. The virus tries really hard not to be fought off completely and the bat evolved to try really hard not to have the viruses invade to a really huge extent so they evolved a compromise where the viruses can invade to some extent but not too much. $\endgroup$ – Timothy Apr 10 '20 at 3:14

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