The problem of material origins

Saul Kripke has convinced many of us that material things have their material origins essentially. Plutarch, through his Ship of Theseus story, has convinced many of us that material things can sometimes survive gradual replacements of their material parts, that they are materially nonrigid. By way of a series of counterexamples, I will argue that any attempt to specify what in particular is essential about material origins will founder on the phenomenon of material non-rigidity.