Beginning anthropology undergrad here. Someone has yet to explain to me why we assume the paleo-indians migrated to the Americas and weren't always here to begin with. Even then, there's conflicting evidence that doesn't support a singular migration (rather multiple). However, I can't help but feel that if the first complex civilizations in the Americas arose the same time as the rest of the world, independently from each other mind you, then why not assume that there have always people here? Maybe, sorry I don't know a lot of Paleolithic/Neolithic archaeology yet, there are no material remains that have been found to support this. However this very crucial topic in anthropology seems underdeveloped. Sorry if this is more /his/, I might ask there after this, hoping for some earth science frens to help.