They say that our cells die and regenerate at a pace such that every seven years they are completely replaced. Seven years from today there will be nothing of us that is here today, but everything that is there then will look and function like what is here now. So we will be like a replicants of ourselves, with implanted memories from our former selves.
You're crossing the ocean on a wooden ship. One of the boards rots, so you replace it with another that you've stored on your hold. It is still the same ship? Most people will agree that it is. But what if, bit by bit, as you make your journey, your ships sustains more and more damage, so that by the time you reach your destination, you have substituted each piece with its counterpart and not a single piece remains unreplaced. Now is it the same ship? Why or why not? How much of a thing is its pattern and how much its physical material? *
If each of us has a soul that resides within us somewhere, lubricating the space between the quarks perhaps, does it simply remain through this changing of the guard? Does the soul differentiate between the old and the new material? Does it remember and perhaps mourn the distinct identity of cells that once were? Does it feel abandoned? Does it tire of greeting endless parade of new cells, each believing it is authentic and that knows more than it does?
(*Quoted from Kevin Brockmeier in the anthology, My Mother She Killed Me, My Father He Ate Me.)