Not who I used to be
Scientists tell us that our cells are constantly dying and being replaced by new ones. Some do this fairly quickly, wearing out in only a year or two. Some take longer, but within seven years all the old cells have disappeared and, in essence, a whole new me exists.
Yet memories continue, seemingly without interruption - except I know they become corrupted with time. I've had the good fortune to have written some journals when younger, and looking at them recently I was surprised at how different my memory of events today is from how I described them at the time. Maybe the memory cells make inexact copies in this aging process. Maybe memories disappear altogether.
I am not who I used to be in so many ways. As a teen I was deeply depressed - to the point of having suicidal ideation. I was miserable and could not imagine ever being happy, so why live? I've changed every cell in my body about seven times since that dark period. I'm grateful for having left the cells with those morose thoughts far behind.
So, physically, I am not the same person. That teenager disappeared long ago. And so did the child, and the young man. A new being "reborn" every seven years, and yet with a modicum of continuity for I still identify as me, myself, and I. Certainly, I have different desires, a different outlook on life, different hopes and dreams for the future, and yet whatever it is that defines me as "me" has not disappeared.
Perhaps the magic of this continual cell replication is our "shape-shifting" ability for which so many yearn. Maybe we can't magically change into wolves or butterflies, but we change nonetheless, which is better than disappearing completely (we'll save that final act of cell alteration for after we depart this life).