I've heard many theories that aliens created us, or at least sped up our evolution. I don't really give any of these any credit. I think most people who believe these are not able to grasp how evolution and development of technologies could very easily have happened just fine without any outside interference.

I did hear an idea recently that once our ancestors left the tress and started venturing out that they may have started ingesting psychedelic mushrooms, and the mind altering reactions can help explain how the brain doubled in size in only a 2 million year period.