I read this in The Economic Times a few days ago and found it to be an intriguing question.
Assume that you have a knife. An ordinary knife with two parts to it: a wooden handle and the steel blade. Now, after a few years of use, you find out that the blade is in a bad condition, has lost its edge and must be replaced. So you go ahead and replace the blade with another piece of steel blade.
Considering that the blade is the more 'essential' part of the knife, would you say that it is the same knife or a new/different knife?
Ok.. let's go ahead.
After another few years, you realise that the wooden handle of the knife too needs to be replaced as it has weathered considerably. You remove the wooden handle too and replace it with a new handle.
What now? Is it still the same knife?
Interesting, isn't it?
Now, let's consider the human body.
Considering that after every few years, almost all our body cells die and are replaced with new cells, are we then the same person or have we finally found an answer why man 'changes over time' ??