Genes don't "become" something new, all the information is there already and selection processes act on that. But I think we press the analogy too far there.
Please keep in mind that I'm not campaigning for "only" using previous jokes. I'm campaigning for us to grow up a bit, and acknowledge the reality that what makes memes funny is the situational humour, and not primarily new informational content. As I said before, what goes into most popular memes are phrases, jokes, and concepts that are already existing (T-shirts, bumper stickers, family jokes, internet phrases, life situations etc).
You're the one saying your ideal would be 0%. This is what makes me say that I am opposed to you as far as I could possibly be. Maybe we are using terms differently (ie, maybe we have a different definition of what a "repost" actually is), but when you say you want 0% reposts it makes me think you're not taking the discussion seriously at all.
This is a meme site. Even if for some reason I were to change my mind and agree with you about (what I think is) a completely arbitrary standard that "memes can only be original," we both know it would never happen.
The only difference is I'm saying it shouldn't happen. An old joke you know well can be pleasant to hear. And an old joke can be new and fresh, if you quote it in a different context, with a different purpose than the original, which is one of the ways to creatively use reposts. Also, memes can be improved.
It's true that some memes "die out" - probably a very high percentage. But the true memes catch on and are repeated, or have elements of them that are repeated (and this is more than just "templates," it's templates and concepts together).
But I'm not sure what else I can say to you. I'm not going to honour your opinion that memes should ONLY be original. It's a bad opinion.