“What Makes You You?”, by Tim Urban (Wait But Why? Dec. 2014):
A few years ago, my late grandfather, in his 90s and suffering from dementia, pointed at a picture on the wall of himself as a six-year-old. “That’s me!” he explained.
He was right. But come on. It seems ridiculous that the six-year-old in the picture and the extremely old man standing next to me could be the same person. Those two people had nothing in common. Physically, they were vastly different—almost every cell in the six-year-old’s body died decades ago. As far as their personalities—we can agree that they wouldn’t have been friends. And they shared almost no common brain data at all. Any 90-year-old man on the street is much more similar to my grandfather than that six-year-old.
But remember — maybe it’s not about similarity, but about continuity. If similarity were enough to define you, Boston you and London you, who are identical, would be the same person. The thing that my grandfather shared with the six-year-old in the picture is something he shared with no one else on Earth — they were connected to each other by a long, unbroken string of continuous existence. As an old man, he may not know anything about that six-year-old boy, but he knows something about himself as an 89-year-old, and that 89-year-old might know a bunch about himself as an 85-year-old. As a 50-year-old, he knew a ton about him as a 43-year-old, and when he was seven, he was a pro on himself as a 6-year-old. It’s a long chain of overlapping memories, personality traits, and physical characteristics.