Life evolved under conditions

of light and darkness,

light and then darkness.

And so plants and animals

developed their own internal clocks

so that they would be ready for these changes in light.

These are chemical clocks,

and they're found in every known being that has two or more cells

and in some that only have one cell.

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.

(Applause)