And here, Bill, we get in at the problem of free will. We stressed on genetics in recent posts, but the main problem of orcs lies not with hroa, but with fea. The immortality of elves is a consequence of their souls being bound in the confines of the world. Hroa dies not, for fea is fated to be here.
Melkor is stated to be able to mock, not to create, twist, but not make. So whatever basical stuff he used to create orks, changes imposed were minor with regards of the whole thing. Acting on given starting material, he was working on strenghening characteristics useful for his purpose - say, twisting bravery to become violence, self preservation instinct to be cowardice etc. But he was unable to rob "given material" of it's main characeristic, given by Eru - free will. {In case he was, than he was much greater than we imagine, but JRRT states he was not). And elvish free will (btw, take a look at
this also) is bound to operate as long as Arda lasts. So, in case orks are elves, they are immortal within the bounds of time exactly as "normal" elves are. Those which are human, die as all humans do. Those which are beasts, are unable to act without direct control of Dark Lord's (Morgoth or Sauron) adn scatter when aforesaid is overthrown.
I'll be so bold to say I guess why Tolkien was so unhappy with elvish origin, though it was so polished and fitting. In case Orks came from elves, somewhere deep down inside they are still Eruhini, and doing what they do, ultimate sinners. Now imagine multitude of those, the condition in which they die, and you get that on every Child of Eru acting in harmony (more or less) with his/her Creator, there are 50 almost (mark - almost) iredeemable orks. It's not so horrible with beasts - well, they are kind of automata, it's a pity something beautiful can be so twisted, but, well, they are just fea-less after all.
well, hasty as I am, I'm unable to back myself up with quotes right away. I'll come back to this later
[ November 06, 2002: Message edited by: HerenIstarion ]