"Why we grow old and die"... I remember seeing this article quite a lot, but maybe you could tell me if it still comes around?
Anyhow, I was watching a TV programme the other day about nature following the second law of thermodynamics and I realised that everything around us breaks down, everything wears, things that move generate friction, the tendancy for particles is to fall apart and "entropy" to increase, just as the universe itself will one day have no structure left as such, just randomness of elementary particles floating about and darkness.
Really, the question implies a bogus argument. The question should really be "why does everything die, or gradually break down and decay?" And the answer is, because the laws of science dictate it. The human body has evolved to repair and protect itself in many fascinating ways for as long as it takes to procreate and spread our gentic makeup, and then time takes it's toll, the body is no longer needed and we pass away... If there is any element of us left, it's certainly not in this universe or dimension, maybe as a part of god, that's the only place where memories of us can live on forever...