if you can just replace parts of your body which are wearing out how come immortality is still impossible?

Question: if you can just replace parts of your body which are wearing out how come immortality is still impossible?
- Keywords:
  immortality,
  replace
Asked by ./hannah/. to Carolyn, Peter, Richard, Sara on 20 Nov 2015. This question was also asked by bongi.
- Richard Unwin answered on 20 Nov 2015:
  
  Hi Hannah,
  
  Great question. IF you could just replace parts of the body that are wearing out then maybe you could become immortal. Unfortunately we can’t replace things like the brain, for example, or all of our blood vessels – they are massively complicated connection and ‘plumbing in’ a replacement would be virtually impossible.
  
  There’s also the question of how much you would still be ‘you’. There’s an old joke about a thick road sweeper who once boasted he’d been “using the same brush to sweep up every day for the last 40 years”. “Wow, that’s amazing” said his friend, “How has it managed to last that long?”. He replied “I’ve looked after it. Its had 27 new heads and 12 new handles”.

Question: if you can just replace parts of your body which are wearing out how come immortality is still impossible?