Let's start with day and night.
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)