Jessa Gamble is an award-winning science writer based in Yellowknife, Canada, just a few hundred miles south of the Arctic Circle. Because of Yellowknife's high latitude, the length  of daylight  varies widely during the year - from 5 hours in December to 20 hours in June.

The cultural adaptation of traditional subarctic cultures to that dramatic seasonal variation in day length is how she begins her discussion of natural human sleep cycles in her brief TED talk:

As Gamble notes, before artificial light became common in people's homes, most people did not sleep in an unbroken eight hour block. Instead they went to bed at dusk, slept four hours or so, had a couple hours of wakefulness (used for meditation, sex, study or work), and then returned to sleep until dawn.

As a night owl, I find it hard to imagine going to bed when the sun goes down. Even if I wanted to change my sleeping habits, unless my husband and friends also changed their schedules along with mine,  I would find it socially isolating to hit the sack at 8pm. And that doesn't even take into account the difficulty of finding a truly dark place to sleep so early in the evening. Living in a suburb laced with street lights, it doesn't ever get completely dark outside.

I doubt I'm alone in thinking that "natural" sleep patterns aren't easily compatible with modern life. What Gamble suggests is that we should consider the cost of that attitude to our mental well being.

Gamble's book about the daily rhythms of life in different cultures - The Siesta and the Midnight Sun - will be published by Viking Canada in March 2011.

For a primer on human sleep patterns, you check out "Everything You Always Wanted To Know About Sleep (But Were Too Afraid To Ask)" at the old Blog Around the Clock.