  If personhood isn't my essence, then what is? The most  plausible answer seems to be that I am a biological organism, a human animal.  And if this is my essence, it will also provide the conditions of my  persistence across time. From this move, then, we get the  Biological Criterion of Personal Identity: if X is  a person at t1, and Y exists at any  other time, then X=Y if and only if Y's  biological organism is continuous with X's biological  organism (Olson 1997b, DeGrazia 2005). Note that Y may or  may not be a person, which allows that X might be one and  the same as a fetus or someone in a PVS. This view is also sometimes  called animalism (e.g., Noonan 1998, Olson 2003, Blatti and Snowdon 2016).