  There are a couple of replies here. DeGrazia, for one, admits that  the transplant intuition is a thorn in the side of the Biological  Criterion (DeGrazia 2005, 54). But when it comes to that criterion's  seemingly poor fit with our practical concerns generally, he suggests that, “in the world as we know it,” there's much less of  a problem than we might think (DeGrazia 2005, 60–61). After all, in  nearly all everyday cases, a necessary condition for the  psychological continuity grounding our practical concerns is  biological continuity. So if the grounding for our practical concerns requires psychological continuity, but psychological continuity  (ordinarily) presupposes biological continuity, then the grounding  for our practical concerns (ordinarily) requires biological  continuity as well.