[ThomasMore]

I always thought that orcs were once elves and goblins were once men. And a cross between the two were the Uruk Hai.

I guess I was wrong!

[HairOfTheDog]

You are not alone!

Tolkien was vague on that.... intentionally or not. It was in fact somehow crossing them with men that allowed them to move in daylight, was it not? - I don't remember that.