Maybe these groups of humans were different genetically with different characteristics mentally from chimpanzees. Maybe you think. Need not to have genetically evolve but when the need arose the human genetics were there. No need from what I hear for chimpanzees to write experiences or warnings or dreams down, right? No need for chimps to build hospitals, invent planes, etc. they can get where they're going from tree to tree, so no need for air transport. They figure, ah who needs all that? We'll just stick with what we have...