Originally Posted by
holytrousers
At some point in time, all the atoms of your body will be gone and replaced with new ones. Whether some cells die out faster than others is not the point.
Never mind the atoms and cells of of an individual organism. Does life itself still happen in the same way it originally did? Here's an article about the puzzle that biologists are working on regarding RNA, and the fact that its current structure must differ from how it first developed:
LINK. (It's pretty technical, but even non-scientists should be able to get a rough idea of the interesting concepts involved.)