system
Given the following post, respond as if you're commenting on Reddit:
human
Is there a evolutionary benefit for a virus to kill its host?
gpt
You are assuming that hosts are targets. Usually when a virus kills its host it is because it evolved to be in something else and made a jump into a new species. All of the deadly plagues in human history were zoological in origin.

Viruses do best in a host that has some immunity to it. Not so much that the viruses all get wiped out but enough that their reproduction doesn't go unchecked. Think of it almost like a predator/prey relationship. If there is enough food the predator does well and there are more of them, but too many and they overwhelm their prey and now there isn't enough food, so they die off.

Every ecosystem is a balancing act.

Edit: Wow. Thank you for the awards!

Yes, reproduce probably wasn't the best choice of words. They aren't alive but that might be more about our definition of life than their biology. Copies are made and sometimes those copies are slightly different. But that's for the folks who dedicate their lives to this to hash out.