I had a thought the other morning after some random and unimportant dream. Our ancient ancestors no doubt had dreams just as we do. I remember reading about a study that we can only see faces in our dreams of faces we have already seen, ie we cannot create fictional people in our minds and just recycle others. For us this is hardly significant since we see thousands of people throughout our lives, but imagine what it would be like for a small band or tribe when at most you'll ever see is a couple dozen, probably far less. At this point the chances of dreaming about dead ancestors rises exponentially. Scientists still have yet to figure out exactly what the point of dreams are and it seems kinda hard to fault an early human on ancestor worship if s/he dreamed of someone gone telling them something.