What makes me "me"? What makes a person who they are? If you cause a truly significant change in someone, have you in some sense killed one person to create another?
Lately I've been remembering the works of one Jack L. Chalker, an author from a couple decades back who wrote a great deal of science fiction and fantasy that tended to involve people being transformed. Sometimes physically, such that they weren't even the same species anymore. Sometimes mentally, from some extreme brainwashing. And it has me wondering what it is that makes someone who they are.
Let me give you an example. In Chalker's Dancing Gods series, one of the main characters is a man named Joe. Joe was a truck driver whisked away to a fantasy world by a powerful wizard who needed a hero (wow, it sounds utterly ridiculous when I put it that way-- I swear it's a good series. Not great, but good.). Once in this fantasy world, the first thing that happens to Joe is the wizard calls in a favor from a demon to give Joe his dream body, which apparently was 6'6", with incredible muscles. He became the epitome of the barbarian warrior image.
Throughout the series (though I haven't been able to track down the last book), Joe gets temporarily turned into a cow (but retains his consciousness), then temporarily into a wood nymph (where he gradually loses his consciousness), then regains his original body, but at the age of 20, and eventually back to the wood nymph, but retaining his consciousness this time. He wasn't too happy about that.
And Chalker is hardly the only person to write such things (though he wrote about transformation a lot!). The popular Doctor Who series on the BBC is another example that deals with the issue of transformation, and identity. If you're not familiar with that series, the main character is an alien called The Doctor. He travels through time and space having adventures and saving people, and picking up strays along the way. When he is about to die, he can instead choose to regenerate, which completely changes his appearance, and his personality. That latter part is key. Is the Doctor who walks away from these regenerations the same as the one who went into them? Is he still the same person?
Many personality traits are still there, and seem to be key components to the Doctor's personality. Curiosity, a sense of adventure, a desire to help. One version said that there were two words he could never ignore: "help me." That trait seems common throughout, at least in the modern version of the series (which is a continuation of a series from a few decades back). But some versions have been more fun loving, or dorky, or angry, or dark. In other words, different in mind as well as body. As a result, when number 10 (David Tennant was the actor) knew that his time was coming to an end, he stated to a friend of his "I can still die. If I'm killed before regeneration, then I'm dead. Even then, even if I change, it feels like dying. Everything I am dies. Some new man goes sauntering away... and I'm dead."
So what makes a person. . . them? How much change can we undergo before we are no longer the same, and could say that the previous person is dead? In the past, when I was what? 12? I don't recall exactly, but I was young, and I realized that the person I was then, at that moment, would someday not exist. He would change, into I didn't know what, and had no way of accurately predicting or controlling. This terrified me on an existential level. I think, trying to look back at it, that I felt like I would die in some way so that someone new could live. Kinda like the Doctor, now that I think about it.
And yet, I don't feel that way now. I look back on very significant changes that I've undergone in my life, but I can still find certain consistent threads running through my life. A love of logic or reason, an interest in right and wrong, a love of reading, an interest in science. There's also been the depression as a persistent thread, at least since puberty, shaping my experience of life, even as I've come to see my depression not as me, but rather just as an illness. Are these consistent threads enough to claim a persistent identity of "Nathan"? Enough to say that all previous versions of me are still me, fundamentally?
I'm not entirely sure. I think so. But I haven't worked out why, and could be wrong.
There is an idea (which I first encountered in a post by Dan Fincke, but can't find the link now) that we are the complete, sum-total of all of our experiences, minor or major, and including our unique biological circumstances as well. So we aren't just memories, but also bodies, and everything involved in that. Under such a view, it really doesn't make sense to consider who we would have been had something different happened, because that person would then not be us at all. Similar, but not us. One consequence of this would seem to be that maybe we are constantly dying, only to be reborn in the same instant.
At this stage, I have no firm conclusions. Right now, I don't see these questions as having a great deal of immediate impact to our lives. But who knows? Maybe the technology to fundamentally alter personality or body is right around the corner, in which case these questions will have an impact.