Recently I read Kim Stanley Robinson's Icehenge, the first of his Martian novels featuring humans who live hundreds of years but retain only about 80 years of memories. The concept raises important questions about future technology and personal identity.
In Robinson's world, many folks write autobiographies about themselves so that they'll retain the basic facts of their lives, if not vivid memories, as they grow older. Just as most of us know our birthplace thanks to our parents or good record-keeping, future humans who live hundreds or thousands of years may only know which jobs they've held or degrees earned because someone made a note of it.
In one of Robinson's Martian stories two ancient characters meet. Decades ago they shared a romance, but only one has any memory of their shared history; the other mistakenly thinks this is their first meeting. While not a major plot point, I found this detail at once fascinating and horrifying. If we don't remember our romances, can we really claim to be the same people we once were? Or do new personalities form as the centuries pass, rewriting our minds just as new data replaces the old on a computer hard drive?
Without wishing to become morbid, I've often wondered if my past self, the child I was, ceased to exist long ago. The being known as "Earl J. Woods" hasn't died yet; I'm still here, even if my cells have died and replicated themselves hundreds or thousands of times over the years.
Of course this is merely a reiteration of the old "grandfather's axe" problem: if you've replaced the handle and the head of an axe many times, is it in any sense still the same axe?All the physical components have changed, but it may nevertheless still feel like the same axe because of its associations in space and time.
I'm certain my parents consider me the same person I once was, for they've seen me grow up and I imagine certain character traits have remained relatively consistent over the years. I feel the same way about them, of course.
But without these associations, which would certainly fade over centuries given limited memory, could or should I really be considered the same person if Robinson's life-extension technology comes early enough for me to live to the age of 1000? Or might I be considered ten or fifteen different people over the course of a millennium? If I committed murder at age 500 but the crime remained undetected for 200 years, long after I've forgotten it happened, could or should I be charged?
A brain is not a hard drive, but perhaps humanity will address this problem by modifying minds in such a way to expand our capacity for memory to keep pace with our new longevity. Without persistence of identity, of what value is immortality anyway? It would almost be like slowly dying several times over the course of a lifetime, without even realizing it's happening. What a chilling fate!