> Here is something that I keep thinking: you can't compare a living organism to, say, an airplane, because an airplane has fixed structural parts which are imp

> Here is something that I keep thinking: you can't compare a living organism to, say, an airplane, because an airplane has fixed structural parts which are impossible to replace, and those parts accumulate tear and wear. Not an airplane, but Alvin (the deep sea research vessel) has had all of its parts replaced over time. It’s a modern day ship of Theseus.