That doesn't really ring true - after all, they're going to be passed to newborns too. "Gunk" collects in tissues that are never replaced, but why does that oc

That doesn't really ring true - after all, they're going to be passed to newborns too. "Gunk" collects in tissues that are never replaced, but why does that occur in the first place? Clearly, growing new tissue isn't a biologically hard problem - when there's evolutionary pressure to do so, several species evolved means to replace surprisingly large parts of their body. Some insect metamorphose; crustaceans rebuild complete skeletons - energetically, it's almost certainly hell of a lot cheaper to occasionally replace bad bits than it is to procreate and lose the previous generation. There's something else going on there.