I think I have to back it up a little. I’ve jumped halfway into my argument about identity and not given a firm basis. So let us go back to the beginning, the origin of identity.
Where does it come from? It is not obvious. So let us ask our friends the sciences what they think of identity.
Particle Physics: I’ve no idea what you are talking about. There are no objects, no people. There are simply atoms, the things you describe might be made of atoms, but I just don’t care about them. They may as well not exist for all I care. I can predict everything without having to reference these things, ockhams razor suggests I get rid of these things.
Well not a good start. But we mere mortals cannot predict everything with particle physics, so we have to go up the scale.
Engineering : We we have bodies so that is a good start. However they aren’t really associated with people per se. We can cut them in half and get two bodies. And then predict Or join them two bodies together to get one, like the beast with two backs.
Beasts, eh. Maybe biology will be more helpful.
Biology : I know all about the self. One of my most important tenets is self-replication!
Finally! So how do you determine what is a self? Everything in a continuous body? Everything with the same genome?
Biology: Not so easy. You might have viruses in your body. They may even insert themselves in your genome and then preferentially self-replicate themselves. Cancer cells start off as normal cells part of your self, working towards normal goals then slowly get their genetic code subverted. Ants/Bees in a colony aren’t 100% identical DNA but all tend to work as one entity
So we have to do adopt something similar to the intentional stance, something is a self if it helps us to think of it as a self. By a self, I mean something with a coherent identity and goal. Including ourselves! Evolution will tend to produce things that are have an identity of self-hood, a thing that is replicated. It may even come to know itself and recognize what is itself vs what is other, so it can then protect itself.