Now here's something really fun from Mark Johnston's book Surviving Death: the Hibernators (chapter 4). This is a tribe of humans with an unusual brain chemistry. They stay awake for 9 months out of the year and sleep for the winter months, preparing for "the great awakening" by leaving themselves all sorts of provisions and instructions. They also have an unusual understanding of personal identity.
You see, they believe that the persons who wake up are not the same as the persons who fell asleep. They think sleep is akin to death, and waking up is birth. So in retrospect, the Sally who wakes up thinks of herself as Sally2, an entirely different person from Sally1, who fell asleep. Johnston argues that "there are no independent justifiers that settle the appropriate lineaments of personal identity" (p. 267) so it's impossible to say the Hibernators are mistaken.
Are the Hibernators mistaken? That's the $64,000 question, and I suspect they are, but a preliminary question occurs to me. How could a society sustain this odd view of personal identity--what else would they have to believe? I think we need the help of Hollywood here. So imagine: coming soon, to a theater near you, THE HIBERNATORS (with Tom Cruise and Cameron Diaz).
The exciting question of the movie is whether the Hibernators will go on like this forever. After much sleuthing around and of course a painstaking reading of the personal identity literature (cinematically exciting, to be sure--and this is where the good looks of our stars will come in handy), will Cameron (perhaps) say "Oh my God, that was me!" about her earlier zisters, and throw the concepts of zisterhood and zotherhood into the flames?
I suspect that the Hibernators' view of personal identity is not sustainable, and that this is (somehow or other) revealing.