Eight Hour Sleep May Be Unnatural

I've just read an interesting article on the BBC website saying that the eight hour sleep may be unnatural and that in the past, we used to sleep in two segments, often four hour stretches with a couple of hours in between

To quote 'We often worry about people who lie awake in the middle of the night - but it could be good for you. Scientists have been saying for 20 years that the eight-hour sleep may be unnatural, and historians increasingly are backing them up.'

Psychiatrist Thomas Wehr conducted an experiment in the early nineties, in which, for one month, a group of people were plunged into darkness for 14 hours every day.
Interestingly, by the fourth week, the subjects had settled into a pattern of sleeping for four hours, waking up for one or two hours and then going back to sleep for another four hours.
The theory that humans naturally slept in two distinct chunks has come up again, as historian Roger Ekirch at Virginia Tech undertook an intensive study into the human relationship with night, and found more than 500 references to a segmented sleeping pattern.

Sleep psychologist Gregg Jacobs says that waking up during the night is part of normal human physiology.
He says the idea that we must sleep in a consolidated block could be damaging, if it makes people who wake up at night anxious, as this anxiety can itself stop you from sleeping and is likely to trickle into your waking life too.

Source: BBC - Myth of the eight-hour sleep