Are you the you you were when you first began to wonder who you were?
It has been claimed that every cell in the body is replaced each seven years. Like most dramatic claims, this one is false (or, at best, only partly true). While some cells of the body have a fast turn around (colon cells for example last about four days before they are replaced by new ones), others pretty much stay with you from birth to death. For example, you get to keep most of your brain cells – although your personal mileage may very on that one.
However, even the brain does get partly replaced. There is good evidence to suggest that new neurons are generated in the hippocampus, especially when you are under pressure to learn new things. These new cells—generated from the body’s stem cells—start out fairly undifferentiated as they move out of the hippocampus to where they are needed, usually the frontal cortex. Then, hopefully, they turn into the specific type of cell needed for the task.
Of course, even if most of your cells are replaced, you are still you, right? Each new cell (these produced by cell division rather than stem cell differentiation) has the same DNA and general structure as the parent cell that they replace. Up to a point, this is true. But cell replication errors do occur as well as cellular degradation over time. Skin cells produced later in life do not have the elasticity of those when you are young (hence wrinkles) and mutations can lead to discoloration and deformation (brown spots, moles, skin tags are all the result).
But aren’t we more than a cluster of cells working cooperatively (and not only with other of our own cells but with the multitudes of bacteria that live in happy symbiosis inside of us)? Presumably what we really mean when we talk about our identity is the accumulation of memories, thoughts, emotions that we are in the continuous process of adding.
But there’s the rub. The net loss of brain cells, which goes on from childhood, does impact how and with what degree of clarity we remember things. Moreover, whenever we learn a new skill, we reprogram existing neurons and neural connections (in addition to those new cells mentioned above) often at the price of old pathways. Take, for example, the typical way many people learn tennis. Most simply pick up a racket and start to play—or, at most, have a few lessons before thinking they know enough. In the process they learn lots of bad ways to serve, back hand, etc. The day comes when they want to get better. Now, lessons are not enough—they need coaching and supervised practice because only then do the old pathways get destroyed and new ones constructed. They literally become a different tennis player.
Then there is brain damage. Sometimes those travelling neurons wind up in the wrong place or don’t get properly integrated. Some scientists suggest that this is the root cause of Parkinson’s disease or, even schizophrenia. There is a well documented case of a brain tumour that caused a man to become a pedophile. When it was removed in prison, he lost the urge. When the urge came back, the doctor’s checked – a new tumour had grown.
All of this is more than idle scientific speculation. Our entire legal and social system is predicated on the idea of the continuity of human existence. Long-term contracts (like mortgages) are based on it, as are presumptions about people’s past behavior being something they have to be held to account for. If some made a racist (or xyz) remark, thirty years ago they need to be held to account today. While an actual crime remains a crime, is a thought or opinion or nasty remark also immutable? And if so, can no-one ever truly be rehabilitated or reformed? Because the possibility of moral redemption is also central to our social order. Just a few thoughts on a weekend dedicated to death and resurrection.
And that’s a little more than ten minutes.