When the Elf Lords were in their power, they naturally vied amongs themselves for primacy. One among them took the gemmules of elves, humans and several other creatures, even plants, and created a new breed of warrior superior to any that had been seen before. He despatched armies of these growling, hulking berserkers and gained much power, until several of the others banded together and made common cause to defeat him. Regrettably for him he fell into their eager hands alive and eventually. under torture, revealed the secrets to the creation of his supermen.
Soon, there were many different breeds of these 'orks' , all carefully controlled with well-crafted enslavement spells. Eventually, some elf lord had the luminous idea of creating women for them, so they could reproduce after their own kind, sparing much effort in creating them. Of course, over time this resulted in inevitable mutation, but these could be bred out, or, if they were desirable, bred for.
The upshot of this was that the original, rigid artificial genotype grew, over time, into a much more varied and more natural gene pool.