Uruks Appear - The first Uruk-hai of Middle Earth were not bred by Saruman, but by Sauron centuries earlier. Treebeard speculates that Uruks are a hybrid of Orcs and Men.
"He has taken up with foul folk, with the Orcs. Brm, hoom! Worse than that; he has been doing something to them; something dangerous. For those Isengarders are more like wicked Men. It is a mark of evil things that came in the Great Darkness that they cannot abide the Sun; but Saruman's Orcs can endure it, even if they hate it. I wonder what he has done? Are they Men he had ruined, or has he blended the races of Orcs and Men? That would be a black evil!" ~The Two Towers, Book III, chap. 4 (Treebeard)