The actual problem began when humans invented candles and lightbulbs and started staying up past 8pm, and going to bed at inconsistent hours, therefore waking up tired the next mornings.
Our optimal sleeping time is based on the rotation of earth around the sun. We have removed our brain's natural sleep trigger (lack of light) so our sleep habits have been getting out of whack for the last couple of hundred years.
What is really interesting is that human's natural sleep cycle is not to sleep continuously for 8 hours. Our natural sleep cycle is to go to bed when it gets dark and then to wake up for a few hours in the middle of the night and get up and do things (apparently this is also the time when most sex happened since other family members in the same room were still asleep) and then go back to sleep and get back up at dawn.
I live at 60 degrees Northern latitude, and I sleep a lot more in the winter. And it's really difficult in the summer too, because it never gets dark and you need to go to bed to get up in the morning.
For some reason it's not difficult for me to sleep past sunrise, but very hard to go to bed before sunset or wake before sunrise. And some people are the opposite.
This just applies to adults. Children and teenagers naturally sleep longer than adults and probably slept throughout the night. Plus, apparently people didn't all get up at the same time during the night. Some would be up from midnight-2am, others from 2am-4am, etc.
For the most part i agree, but how about summer times in the northern regions in US or the world when sun doesnt set until beyond 9pm or say Norway where it can be until midnight or more than 60 days in some areas?
Our optimal sleeping time is based on the rotation of earth around the sun. We have removed our brain's natural sleep trigger (lack of light) so our sleep habits have been getting out of whack for the last couple of hundred years.