[narfforc]

Since Melkor could not 'create' an independent species, but had immense powers of corruption and distortion of those that came into his power, it is probable that these Orks had a mixed origin. Most of them plainly (and biologically) were corruptions of Elves (and probably later Men).................... The Elves would have classed the creatures called 'trolls (in The Hobbit and The Lord of the Rings) as Orcs - in character and origin - but they were larger and slower. It would seem they were corruptions of primitive human types. (Morgoth's Ring).

In a letter dated September 1954, tolkien wrote the following:-


I am not sure about Trolls. I think they are mere 'counterfeits' and hence (though here I am of course only using elements old barbarous mythmaking that had no 'aware' metaphysic) they return to mere stone images when not in the dark. But there other sorts of Trolls beside these rather ridiculous, if brutal, Stone-trolls, for which other origins are suggested. Of course.....when you make Trolls speak you are giving them a power, which in our world (probably) connotes the possession of a 'soul'. (Morgoth's Ring).

I don't think we came seperate the Orcs and the Trolls when we discuss The Origins of Species, they were either both created or pre-existing corrupted forms. As Boromir88 says though, Tolkien kept changing his mind. If you take The Early Silmarillion view then 'Melkor made the orcs out of stone with hearts of hatred'. Later in The Earliest Annals of Beleriand 'He devised the (Balrogs and) Orcs'. These are the problems you encounter within HoME, and at the end Tolkien was comfortable enough to have the words of Treebeard published, even then he still kept thinking of the problem.