While I appreciate the biblical references for why we get old and die, science has a different explanation. At the end of our DNA we have telomere chains. As we age, the length of telomere chains becomes shorter. Eventually the telomeres become so short that cell replication produces lethal errors or missing pieces in the DNA sequence, ending the cell's ability to replace itself. This point, when the cell has lost vital DNA code and cannot reproduce, is called the Hayflick limit. It's the measure of how many times a cell can copy itself before it dies.
Some cells in our body have a very high hayflick limit. Cells that line the inside of your mouth and intestines, for example, are constantly being worn away and replaced. Indeed these cells appear to have the ability to regrow telomeres. Other cells do not do such a good job of replacing themselves. These have a low hay flick limit.
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How we spend our days is how we spend our lives. We make a living by what we get, but we make a life by what we give.
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