The Xel'Naga created many failed races before they created the Protoss, and the Protoss are humanoid, so it could mean the Xel'Naga found humans, thought they could be pure of form, tinkered with them, called them failures, and moved on. Not that it would make any kind of difference. However, I doubt it. The Protoss watched over many races that the Xel'Naga had created, and when humanity arrived, they didn't think they were Xel'Naga creations. And on that note, the Xel'Naga never create races, they just steer their evolution. Not all races would be created by another race. I doubt the Xel'Naga were created by anyone. Until the Hybrids. It's been a long time, the Xel'Naga could start regrowing their population. No, they didn't want to assimilate humans, since they're an inferior species (which still manages to kick Protoss and Zerg butt). However, they had to assimilate Terran psionics to defeat the Protoss... or so the theory went. Kerrigan wasn't taken to Aiur when the Overmind went there, so one wonders if the Overmind suddenly forgot about his asset. They were Dark Templar, and not even close to pure of essence. Furthermore, we don't know if the Zerg need to do something special to infest the Protoss, since they haven't been able to do so. (The latter topic is very long on many StarCraft boards.) Only Protoss military units have shields. Of course, the best specimens to infest, High Templar, always have shields. She wouldn't make a good secret agent then, plus Kerrigan didn't seem interested in infesting the Protoss, and especially Dark Templar. It was supposed to be 10 years later, but things changed; now it happens at the same time as StarCraft. Yes, that does suck. Nihilistic, Blizzard's partner, quit the project. There's a new partner, but I can't recall it's name. PS it's extremely unlikely that Terrans are retrograde Xel'Naga; we're only 150,000 years old as a species and our genetic material is very similar to the stuff on Earth. We share 32% of our DNA with dandelions.