I agree. In the (pre)stone age, it was very dangerous to wander around in the night. So humans (and other such animals) that could keep still at night were at

I agree. In the (pre)stone age, it was very dangerous to wander around in the night. So humans (and other such animals) that could keep still at night were at an competitive advantage. Sleeping is the ultimate keeping still. And evolution just improved on that, using the sleep for other stuff, which then became unskipable. It seems for me that many of those who accept evolution, still thinks in creationist terms: that however the human body works today, must have been the original purpose. And that we are not the result of an evolutionary history filled with random input and short-sighted adjustments, thus ending up with something that could never have been conceived in the beginning. Sometimes stuff "just came into existance" without an (initial) purpose. Purpose is not a pre-condition for existence.