Effective artificial light hasn't been around long enough for any evolutionary adaptations to it. Normally, people were awake when it was light and slept when

Effective artificial light hasn't been around long enough for any evolutionary adaptations to it. Normally, people were awake when it was light and slept when it was dark. When camping, I normally wake at the crack of dawn and go to sleep pretty early after sunset. At home, when not working (which means without a fixed schedule) I tend to sleep from 4 AM to noon. When working I can adapt fairly easily to any working shift, but without the external focus I always drift back to the 4 AM to noon. I have tried to maintain other schedules (as I have mentioned previously on HN posts on sleeping), but they never work out for very long. As for the point of the article, sleeping the 4 AM to noon shift seems to be stable for me because I never seem to "crash" on that schedule as I sometimes do on others. I can stay up much longer than 4 AM, even completely miss a sleep period, and still be back to 4 AM to noon the next day; I cannot do that with other sleep schedules.