I'll give you an example -- if you take a horseshoe crab off the beach, and you fly it all the way across the continent, and you drop it into a sloped cage, it will scramble up the floor of the cage as the tide is rising on its home shores, and it'll skitter down again right as the water is receding thousands of miles away. It'll do this for weeks, until it kind of gradually loses the plot. And it's incredible to watch, but there's nothing psychic or paranormal going on; it's simply that these crabs have internal cycles that correspond, usually, with what's going on around it.

So, we have this ability as well. And in humans, we call it the "body clock." You can see this most clearly when you take away someone's watch and you shut them into a bunker, deep underground, for a couple of months. (Laughter) People actually volunteer for this, and they usually come out kind of raving about their productive time in the hole. So, no matter how atypical these subjects would have to be, they all show the same thing. They get up just a little bit later every day -- say 15 minutes or so -- and they kind of drift all the way around the clock like this over the course of the weeks. And so, in this way we know that they are working on their own internal clocks, rather than somehow sensing the day outside.

So fine, we have a body clock, and it turns out that it's incredibly important in our lives. It's a huge driver for culture and I think that it's the most underrated force on our behavior. We evolved as a species near the equator, and so we're very well-equipped to deal with 12 hours of daylight and 12 hours of darkness. But of course, we've spread to every corner of the globe and in Arctic Canada, where I live, we have perpetual daylight in summer and 24 hours of darkness in winter. So the culture, the northern aboriginal culture, traditionally has been highly seasonal. In winter, there's a lot of sleeping going on; you enjoy your family life inside. And in summer, it's almost manic hunting and working activity very long hours, very active.

So, what would our natural rhythm look like? What would our sleeping patterns be in the sort of ideal sense? Well, it turns out that when people are living without any sort of artificial light at all, they sleep twice every night. They go to bed around 8:00 p.m. until midnight and then again, they sleep from about 2:00 a.m. until sunrise. And in-between, they have a couple of hours of sort of meditative quiet in bed. And during this time, there's a surge of prolactin, the likes of which a modern day never sees. The people in these studies report feeling so awake during the daytime, that they realize they're experiencing true wakefulness for the first time in their lives.

So, cut to the modern day. We're living in a culture of jet lag, global travel, 24-hour business, shift work. And you know, our modern ways of doing things have their advantages, but I believe we should understand the costs.

Thank you.