Remember my post "Everything is a Part of You"? I heard an NPR story about how in one year from now, 98% of the atoms in your body won't be there. They will have been replaced by new atoms. You lose atoms through not only excrement (including sweat), but by cutting your hair or fingernails and by shedding your skin. As I was listening to the report, I thought that the atoms in your DNA should stay put so that they could instruct the new atoms how to form the proper structures. Near the end of the piece, my suspicions were confirmed.
I'm not sure what the figure is on the rate of replacement of atoms in other living things. I wonder if it's lower for trees. Or tortoises (or anything with a slow metabolism).
It's nice when you hear somebody else clarify your idea. Now I have a quantitative figure behind me too (which is good for those science types).