I don't recall the last time I had straight 8 hours of sleep. For a young child or toddler, it is alright to sleep for that long. I average at least 5 to 6 hours daily. Talking of Einstein, 2 hours is really not healthy at all. It could be that his mind was always innovative and alert.I read somewhere that it isn't really necessary to sleep for a full 8 hours every day. Some of the greatest minds in human history have attested to this fact, one of them in particular Einstein is reported to have only slept for 2 hours each night.