: : I think the philosphical and theological reasons that Tolkien gives for rejecting the Elvish origin of Orcs is sound. He also considers and rejects the alternatives of (1) Orcs being seperately created by Morgoth (like Aulė with the Dwarves), and (2) Orcs being just intelligent animals, and not moral beings. He eventually decides on a Mannish origin for Orcs.

: : We also have an apparent contradiction on the question of Orkish lifespans. If they were of Elvish origin then they would be expected to be immortal. But Tolkien concludes that actually Orcs were shortlived compared even to the Edain.

: : However Tolkien avoids this last problem beautifully: "This last point [Orkish mortality] was not well understood in the Elder Days. For Morgoth had many servants, the oldest and most potent of whom were immortal ... the Maia; and these evil spirits like their Master could take on visible form. Those whose business it was to direct the Orcs often took Orkish shapes, though they were greater and more terrible. Thus it was that the histories speak of Great Orcs or Orc-captains who were not slain, and who reappeared in battle through years far longer than the span of the lives of Men."

: There are other aspects of orcs which fit badly with a human origin including no evidence that they suffered from disease. I think that there are enough pitfalls in the human origin view - the greatest of course being the timing problem in the Silmarillion you have mentioned - as to give it no particular superiority over the elvish.

One thing I think should be considered is the nature of Tolkien's opinion of his elves. I think we can all assume that he truly loved Middle Earth and the tales he had made of the elves. Maybe later in life he just found the idea of something as foul as the orcs coming from the elves just distasteful enough to want to change it.

It has been established that the nature of Morgoth's evil would not allow him to create anything truly alive of orginal so the orcs had to come from somewhere. The only living thing that was truly sentient from those days were the elves and the dwarves. There is no evidence or even hints for the fact but dwarves would make as much sense as humans for orcish origins. But even that would create complications in the evidence. No, I think it must be assumed that orcs were created from elves even if later in life Dr. Tolkien recanted of that view.

Morgoth's lack of true creativity still leaves the issue of from where the dragons and trolls came. I do think the idea that the dragons first came into being as maia that manifested is valid. Much like Melian took on to herself the ability to reproduce maybe those Maia that formed themselves into dragons also took this route. But one thing to remember is that in the first versions of the Fall of Gondolin in the Lost Tales the dragons were constructs of Morgoth inhabited by evil spirits. Maybe the dragons were not maia or even orginally alive but trapped spirits of orcs, warped elves or evil men, much like the barrow wights from the Fellowship of the Rings?