[randcraw]

I can see an extended two stage sleep rhythm making more sense at times of year when daylight is short (9 hours of daylight at my latitude) than when it's long (15 hours). It's much harder to extend your night downtime to last 10-11 hours when it overlaps at one/both ends with sunshine.

With the increase in physical activity during Summer, two stage sleep seems more biologically useful in Winter anyway. In days of yore, what else was there to do during all that dark?