I've heard the multi-phase sleep cycle has been practised by many prior to civilization. Take the American Indians out west. They would stay up telling stories and socialising till the midnight hour, drinking lots of water. The urge to relieve themselves coming around 4:00am, when hunters and gatherers could be safe from predators who've been up since dark. They would then catch the game coming to bed down at first light. Then doing the other work of camp in the light and morning cool. This would let them nap and save strength in the heat of the day till the cooler evening sets in for story and dinnertime.