Why not design self-healing bodies?
Well, our bodies do heal themselves. If we're healthy. If they didn't we'd break down as fast as cars.
But I think the question can apply on a larger scale of death. Why do we have to die?
The way the world works, death is necessary for life. The living die to make room for the new born. Much of life feeds on dead matter. The rest of life eats life to live.
It's all part of a whole. A pretty incredible whole that has to work, and it works to grow life - where conditions are favorable. Any improvement we can imagine has to avoid unintended consequences.
If we discovered a means to live forever tomorrow, imagine the consequences.
I appreciate your reply and discussion very much.
Well, our bodies do heal themselves. If we're healthy. If they didn't we'd break down as fast as cars.
They do. Ancients didn't live very long. Besides, when you say heal, those are band-aid first-aid repairs. No internal organs can be regrown except the liver and when it heals the new tissue is nonfunctional with the rest of the liver. Hardly a work of perfection.
Why do we have to die?
We don't. There is no reason whatsoever for a cell to die other than an enzyme. Aging and death is really a genetic "disease" which is potentially treatable. One can envision a day in the near future (not in my lifetime) when an injection of telomerase will prolong human life manifold if not indefinitely.
I am sure many will find this a verification of the "Fall" in the Garden of Eden. Sin brought a genetic change in our makeup and made us mortal, essentially changing us (and the whole planet) ontologically. Very possible that some external factors favored a (short-time) survival instead, or that, as you noted, lacking in natural enemies, we would have overpopulated the earth, so inactivation of telomerase was an adaptive change.
It is interesting that the OT speaks of earliest man living much longer than we do today, which is not supported by archeology or historical accounts. But it could be an atavistic memory in ancient peoples who "remember" that their ancestors may have lived longer.
We see evidence of adaptive change in areas where genetic mutation favors resistance to malaria, but also gives rise to a blood disorder common to blacks (sickle cell anemia) as an unwanted side effect. Kind of like natural curing addiction with addiction.
The way the world works, death is necessary for life
Procreation problems could have been naturally adjusted by adjusting reproductive periods and estrus duration, sharply reducing offspring numbers. Instead, nature favored killing to control population numbers (much more efficient).
Much of life feeds on dead matter. The rest of life eats life to live.
That doesn't strike me as an intelligent design but a reactive design. Our history on earth was pretty violent and death resulted from climactic changes and volcanic eruptions, and probably from lack of ability to adapt to geological and climactic changes.
For a changing world, many generations favor genetic adaptation. At some point radiation and other factors damage our cells leading to breakdown. So, all this seems to be adaptive. When longevity becomes an essential survival tool the body will turn on telomerase and prolong cell-life.
If we play God and do it, we will have an overpopulation problem sooner than we anticipated. And don't forget that the consumers are producing faster than producers. None of this points to divine design or even intellect at work. We have the means to live forever, but the conditions favor higher turnover.