Short answer is entropy. The long answer is that to be alive we need to sustain a series of very complex processes going and failures and mistakes accumulate over time until that's not possible. Reproduction is the only mechanism that allows resetting all those processes.
But in the end even planets, stars and even atoms will "die".
Jellyfishes are much simpler than mammals. And modern medicine can effectively bring people back from the dead in some cases when the damage is not too extensive and doctors can act fast enough. But even if you could repair severe damage to any dead human being to make them alive again, the lost information in the brain caused by dying would mean they wouldn't effectively be the same person - we already have some cases like that when people survive significant brain trauma.
Short answer is entropy. The long answer is that to be alive we need to sustain a series of very complex processes going and failures and mistakes accumulate over time until that's not possible. Reproduction is the only mechanism that allows resetting all those processes.
But in the end even planets, stars and even atoms will "die".
We sure can live longer than a meager 80 years though.
Check out sens.org.
Isn't there a type of medusa that can "rebirth" itself and essentially live forever? Why can't we?
Jellyfishes are much simpler than mammals. And modern medicine can effectively bring people back from the dead in some cases when the damage is not too extensive and doctors can act fast enough. But even if you could repair severe damage to any dead human being to make them alive again, the lost information in the brain caused by dying would mean they wouldn't effectively be the same person - we already have some cases like that when people survive significant brain trauma.