Breeding for fear

[Nils]

The Elf origin theory was proposed in the Silmarillion, which as an account of Elvish myth, not history.

In Morgoth's Ring you can find where Tolkien was going away from the Elf origin theory and wanted to work to a Man origin. Here is something Chris Tolkien published in Morgoth's Ring:

This then, as it may appear, was my father's final view of the question: Orcs were bred from Men, and if 'the conception in mind of the Orcs may go far back into the night of Melkor's thought' it was Sauron who, during the ages of Melkor's captivity in Aman, brought into being the black armies that were available to his Master when he returned

Even if one is going to hold on to the Elvish origins theory, my theory would still work. Just replace men with elves.