Why am I me?

[Anomalocaris]

A very complex question. One that isn't so easily answered.

I can speak of death and help give an idea of what being dead is like but on the how and why we are here and in this unique body and mind is beyond me.

We have all been dead. We each have been dead for billions of years. When dead, not only will vision and sound be gone but everything we once could perceive. Our very consciousness will be gone.
Time and space will no longer have any meaning to you. Billions of years would pass and you'll never be aware of it. Fear, hate, lust and love will no longer have any meaning to you. The world from it's point of view is rid of you, but from your POV, you are rid of the world.
I see our existence as nothing more than a taster, a taste of what it is to exist, to look around and wonder. We will have to give it up whether we like it or not. I find the idea interesting that everything we see and understand will one day have no meaning to us. Whether we do good or bad, death is equal to all.

I will be less poetic and say you are you simply because your brain has been wired to perceive a collection of stimuli that corresponds to your physical body, you feelings and your thoughts as a discrete, highly preferred entity; and this wiring was in place long before evolution added to your brain the additional features that enable you to wonder why this is so, what alternatives are there for you other than being you, what happened before you began, and what will happen after you end.

The longer story might be that once matter has been organized by evolution into system potentially capable of thinking, it was likely advantageous for that system to be able to conceptualize itself as something distinct from everything else. This is because harm to any part of the system harms that system's overall ability to reproduce itself, so a thinking system that includes circuitry which separately conceptualize "self" and "not self" when planning its own actions would enjoy advantages in dealing with the world compared to another thinking system which treats its own left foot just like another rock its right foot could tread on. Hence progress towards circuits that give you your concept of self would be preferred and over time this preference would steer the ancestor of your genes towards organizing circuitry that give you yours sense of self.

Why don't we have circuits that allow ourselves to perceive ourselves as someone else? Well, we do. There is evidence that when you put yourself in someone else's shoes, you are not just using general purpose thinking circuits to rationally deduce what the other must think and feel. Cringing when seeing someone else hit in the gonads does not appear to involve much thinking. Instead, you seem to be invoking a dedicated set of circuitry that enables you to rapidly simulate someone else's mental predicament in your own head ahead of any thinking. Empathy doesn't come wholly from thought. Evolution probably did this because social creatures that can empathize probably does better in building social bonds than those who don't, hence gene pools with the empathy gene would be at an advantage to those that lack this gene.

But you can also imagine if you live in someone else's shoes full time that would be harmful to your own survival. Starving yourself to death because you are empathizing with another's need for food is in most cases not good for keeping your empathy gene in the gene pool. An exception might be if the other happens to be your own brood. This may be why we tend to reflexively empathize more with our children's feelings than anyone else.

So while we have circuits to perceive self, and we have circuits to put ourselves in another's shoes, we also seem to have genetic determinates that adjust the weight of the self-circuit relative to the weight of the empathy circuit depending on how important the one we empathize with is to the survival not only of ourselves, but our genes. Any one whose circuit for putting him or herselves in someone else's shoes is too strong or too weak relative to the other person's importance to the survival of one's own gene is less likely to survive to pass this trait onto his descendants. This system was firmly in place long before we acquired additional brian power for idle extrapolation, and for escapist fantasies when confronted with the observation that the highly prefered self is likely to end inspite of our best effort. Hence our evolutionarily derived mental equipment conditioned the basic properties of religion we invented. A stronger case can hardly be made for material evolution by natural selection of heritable trait, rather than intelligent design, as the cause not only of our physical bodies, but also what we perceive to be our soul.

Hence you are you and not someone else, but you feel empathy for someone else, because evolution found these circuits, and their relative strengths in different conditions, good for the survival of your line of ancestry.