It's a commonly held belief that before artificial lighting, human sleep was 'naturally' divided into two distinct periods, but how true is that?

All human beings need sleep. We spend a third of our lives asleep, and it’s as important as food, water or air to our survival. While scientists are still working to understand the exact nature of ...

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 ...