Sciencing on MSN
Did the modern world kill this human sleep habit?
It's a commonly held belief that before artificial lighting, human sleep was 'naturally' divided into two distinct periods, but how true is that?
The amount of sleep a person needs recalibrates over time, and circadian rhythms change with age. The 16-year-old who stayed up until midnight may become a 36-year-old who gets drowsy by 10 p.m. At 70 ...
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