Allons-y!* Yes, it's high time I out myself as a huge nerd. Last night I attended a screening of the two-part Doctor Who adventure, "Rise of the Cybermen" and "The Age of Steel," seamlessly combined to make a feature film. It was glorious. Now, I know that science fiction is not what the "cool kids" watch, but it really does offer a great medium for exploring philosophical questions, especially in areas like personal identity and the philosophy of mind. Even many analogies surrounding the abortion issue are science fiction scenario (e.g. Thomson's violinist and Warren's captured astronaut).
This episode is one that should seem familiar to veterans of science fiction: The Doctor and his two companions, Rose and Mickey, find themselves trapped in a parallel universe, on an Earth that is very much like their own but with minor variations. On this parallel earth, a man by the name of John Lumic and his staff have created a race of cybernetic creatures as a way to transplant his own brain (and the brains of everyone on Earth) into an immortal body. Of course this makes the President of England (parallel Earth, remember?) uncomfortable, and he denies allowing the project to go forward. In a fit of rage, Lumic unleashes the Cybermen on the people of London, forcing them to surrender for "upgrade" or be exterminated.
Personal identity and personhood tend to be a favorite subject for science fiction franchises. Like the Borg of Star Trek fame, human beings are turned into cybernetic beings. But unlike the Borg, in which the organic parts of the person assimilated remain largely intact, to upload someone's brain into a Cyberman, the organic body must be destroyed and the brain is transplanted into the cybernetic body. Supposedly their identity remains intact, though there is a chip that suppresses their emotions so that they can kill without remorse and not be troubled by the new body they find themselves in.
The question of personal identity is an important one, because it has far-reaching implications. If a person commits a crime and becomes literally a different person later, we can't justly hold the new person responsible for the crime. Thankfully, we have very strong intuitions that we retain our identity throughout our entire lives -- when I think back to when I was a kid, I can be confident that those really were my parents and it really was my school that I attended, not a similar person whose memories I now have and thinks myself to be the original. So it seems that whatever view of personal identity we hold, it has to account for the fact that we retain our identity throughout our entire lives.
Many people (including philosophers) tend to believe that a person is the sum total of all of one's memories and personal experiences. But this doesn't seem correct, since it doesn't account for who, exactly, is the subject of our experiences. Plus, I was still "me" even at the points in my life that I can't remember, or before I was able to form memories. As philosopher Peter Kreeft wrote in his book Heaven: The Heart's Deepest Longing, Expanded Edition (Ignatius Press, San Francisco, CA, 1989, p. 176), "The only thing whose presence can make an all-encompassing difference, a difference to everything in my life, to something not contained by but containing my life. That's me. I am the constant amid millions of variables that make up my life. All my experiences are not X or Y or Z, but all my experiences are mine. Each experience is 'I experiencing X and Y in way Z'. X, Y, and Z are the variables: I am the constant."
There are many drastic changes we go through from the time that we are conceived until now, but all of these changes are identity-preserving changes. My five-year-old self and my present-day self are drastically different: I am several feet taller, I have gone through puberty, I have gained many more and new experiences, my skin cells have died and been replaced, I am now able to engage in higher thought, etc. Yet that was still "me."
But the problem with science fiction scenarios is that we can only speculate regarding them -- we cannot test them, empirically. There may come a time when it becomes scientifically possible to transfer someone's brain into a machine and have them continue to live, or it may never happen because it's simply not possible to do. You could transplant the brain but the person may not survive the transplant. In fact, if all we are is a sum total of our memories and experiences, then if our brain is transplanted, how do we know the original person hasn't died? What we may be left with is a similar (but different) entity, with all of the original person's thoughts, experiences, and memories, believing himself to be the original.
As a Christian, I believe that what accounts for my continuity of existence through all points in my life is the soul, and I believe that our continuity of existence is evidence for the soul. I think that trying to adopt an alternate view regarding personal identity and personhood leads to many absurdities. I can't remember what it was like to be an embryo, but that was certainly "me" in my mother's womb. I can look back and say there was a time in which my mother was pregnant with me, and "I" was born.
*Allons-y is a French phrase which means "let's go!" It's a phrase that the Tenth Doctor repeated often.