Cells aren't the only things constantly being replaced - our souls/egos are always being replaced as well....or, rather, changed. Is there a real difference between dramatic change and replacement? Not really.

Our ego (soul) changes every second. Every new bit of information received, every new thought - changes us a little. Sometimes you can, in a matter of minutes, transform into a radically different person with different perspectives and behavior.

We are not really the same people we were 7 years ago, for example.
Let's see....the only things Odlov from today and Odlov from 7 years ago share is their origin, and some memories of past experiences which allow me to remember young Odlov as a previous state of myself. Some memories are all there is actually connecting us.

If i got hit over a head with a shovel and suffered total amnesia, that Odlov from 7 years ago would be gone forever from my memory. I would cease to associate myself with him.