system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are viruses not considered living organisms and why do they exist?
gpt
There's disagreement on whether viruses are considered living organisms, but neither side has come out victorious yet. So people use the phrase "organisms on the edge of life" to describe it. The reason for the debate is viruses have some of the attributes of life, but not others.

It can reproduce, but it needs another organism to do so. They can evolve, they move on their own. They do not have a cell structure, which is normally considred necessary for life.

As for why they exist? We honestly don't know. All we know is they have existed as long as cells have, and maybe longer. Because viruses don't leave fossils, trying to get a clear picture on where they came from and why is incredibly difficult, and needs a lot of speculation.