Also, you suggest that people deprived of artificial light snap into a "exactly" 24-hour schedule. This is actually not correct. Many studies have been done sho

Also, you suggest that people deprived of artificial light snap into a "exactly" 24-hour schedule. This is actually not correct. Many studies have been done showing that the default schedule ends up being about 25 hours when you deprive people of clocks and light sources. According to the book, the 25h result was a result of previous studies not controlling the presence of lights carefully enough (just a single light bulb in a room is bright enough to make a difference), and when this was recognized, the natural circadian period was ~ 24h 10m. This was a study by Chuck Czeisler at Stanford and has apparently been confirmed by other studies.