>It's an evolutionary thing. Having children, adolescents, adults and the elderly on different sleep schedules affords a family unit with nearly round the clock

>It's an evolutionary thing. Having children, adolescents, adults and the elderly on different sleep schedules affords a family unit with nearly round the clock protection Erm. No. If you look at modern primitive groups of people, you don't sleep all night. You wake up several times throughout the night and are, generally, considerably lighter sleepers. Some people in 'civilized' societies still do this. I wake up a handful of times a night, the vast majority of the time, and always have. It's not a medical issue, I'm getting quality sleep and I'm back asleep in a couple of minutes tops. Same goes for a lot of career soldiers/warriors throughout history including modern times, they can be out cold in a couple of minutes any time of the day with minimal effort and can be fully functional within seconds of being woken up.