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I'm Alice Roberts.

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I'm expecting my second
child in a few months

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and I'm having a day out
to visit some relatives.

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Hello, hello.

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Do you want this grape?

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This is Le Puri.

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She's a baby bonobo, or pygmy
chimpanzee.

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And of all animals alive today,
she's one of my closest relatives.

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Well, this is bringing out all
the maternal instincts in me.

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Oh, hello, Le Puri!

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Le Puri may be cute,
but having reached the grand old

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age of one, she's much more
developed than a one-year-old human.

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She and I share 99% of our DNA
and yet from the moment of birth,

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our lives are so very different.

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When my baby is born it will
take him a year to even walk,

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and yet with time, as a human,
his life will develop a richness

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far beyond that
of our hairy ape cousins.

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So what is it about our bodies,
our genes

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and ultimately our brains
that sets us apart?

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What is it that truly makes us
human?

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I've come somewhere I've long
been keen to visit,

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the great ape enclosure at the
Max Planck Institute at Leipzig Zoo,

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one of the biggest collections
of great apes on the planet.

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As well as humans,
the family of great apes is made

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up of gorillas, orangutans,
chimpanzees and bonobos.

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It's really lovely watching
the little ones with the adults

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because they're doing what you'd
expect a toddler to do.

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They're being annoying.

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They're kind of going up
and tickling the adults

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and they've got this mischievous
look in their eyes.

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These apes are our closest
living relatives.

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And I'm here to find out what makes
this particular ape,

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the human one, different
to all the others.

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Very difficult to sketch them,
really.

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They stay still for a minute
and then they're off again.

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For me, as an anatomist,

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the first thing to do is to look at
the differences between our bodies.

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Gorillas are the largest
of the great apes

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and looking at the massive
silverback right

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at the back of the enclosure there,
he really is enormous.

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He's magnificent.

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They're sitting quite nicely still
so you can get a real appreciation

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of the similarities and differences
between their anatomy and ours.

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There's an awful lot about them
which is very similar, in fact.

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So if you look at
the construction of the arms

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and the legs,
you've got all the same bones there.

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But they are different shapes
and different proportions,

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so you can see that the arms are
very long compared with the legs.

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They've got very short legs compared
with the rest of their bodies.

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We've got very long legs,
ridiculously long legs for an ape.

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These differences relate
to how we move around.

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Whereas gorillas and other apes
knuckle-walk on all fours,

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we humans, uniquely, habitually
walk around upright, on two legs.

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And there's another obvious
difference that becomes

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apparent
when you start drawing heads.

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It's quite difficult sketching them.

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I find the faces particularly
difficult because you've got

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such an idea in your head of what
a human face looks like, and you

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have to forget that entirely when
you're sketching these apes, because

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the proportions of their faces
are entirely different from ours.

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If you look at a human head,

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the eyes are quite low on the head,
perhaps about halfway down

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if we measure from the top
of the head to the chin.

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If you look at a gorilla head,
the eyes are right up on the top

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because their brain case
is so much smaller than ours.

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They don't have this massive
forehead

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and a massive brain inside it.

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We've long known that these two
features, big brains

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and upright walking,
really are hallmarks of humans.

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And somehow these big brains must
explain the vast gulf that we see

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between ourselves and our closest
ape relatives, the chimpanzees.

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Of all the great apes,

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these are the ones
to which we're most closely related.

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And the amazing thing
is that we now know from studies

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of DNA, our DNA, theirs, and that
of other apes, that, in fact, we are

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more closely related to chimpanzees
than either of us is to gorillas.

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It's extraordinary.

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There's this close-knit family of
us, common chimpanzees and bonobos.

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I think that says something really
important about our place

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in this primate family tree
and it makes it even more

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extraordinary that our lives
are so different to theirs.

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So what exactly has
changed in the six million years

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since we shared a common ancestor?

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We certainly have bigger brains

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and we think we're more intelligent,
but chimps are full of surprises.

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The Max Planck Institute is at the
forefront of some ground-breaking

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work, comparing intelligence
in humans and in chimps.

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For the past nine years,

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Michael Tomasello has been closely
studying this troop.

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So she did something which I think
in human society

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would be considered rather odd.

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She came along
and presented her bottom to you.

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So is that
a kind of friendly sign?

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It's a kind of a friendly greeting.
Right, OK.

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A little friendlier than we might
normally do in human society.

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You see,
there are these similarities,

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but there are some quite important
differences as well.

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Exactly so.

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'And his work on ape intelligence
is casting a fascinating new

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'light on what it means
to be human.'

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And when you first started
doing this work,

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were you surprised?

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Did you, did you find that they
were more or less intelligent

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than you expected them to be?

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Well, that's the great part,
is that they were, in some ways,

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more intelligent and in other ways
maybe a little less so.

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They will do some things that will
just absolutely surprise you

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and you just can't believe they're
so clever, and then they'll

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just turn around and do something
that's just kind of thick.

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We like to think we're the most
intelligent species on the planet,

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but we have to be careful about what
exactly we mean by intelligence.

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The first thing we have to get rid of
in thinking about animal intelligence

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is the idea that there's
this ladder of intelligence

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that goes from low to high,
and animals can just be placed on it.

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It's actually much more
complicated than that.

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Different animals have different
intelligences, as it were.

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So the best memorisers
in the world are squirrels

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and birds that hide their nuts in
different locations and can remember

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dozens and dozens and dozens
of locations, more than we can.

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Oh, I was going to say,
so when you say best memorisers
in the world, that includes us?

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That includes us. Absolutely.

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In the case of apes, what
we think is that they're especially

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good at cognising
things about the physical world

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and understanding space, and causal
relations like when using tools,

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what causes something to move
and whatever.

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They're very good at that
and basically they're not

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different from human children
in that kind of understanding.

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So here's this task.

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I put a little peanut,
this is for you, this is your reward

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and I just put it in here.

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'And to show me just how intelligent
chimps can be,

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'Michael's colleague, Daniel Hannus,
has invited me to try my hand

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'at solving a problem that they
regularly give to chimpanzees.'

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You just do whatever you want
to retrieve the peanut.

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'My task is to get the peanut
out of the tube

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'using anything that comes to hand.'

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I wonder if I could use the chain
somehow, and the teaspoon.

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That's going to be really difficult,
I think.

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Slightly worried I'm going to lose
the teaspoon as well.

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You'll never get it out again.

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I don't think that's
the right thing to do.

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It may take me
a while to figure it out,

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but the key to this puzzle
is something that you might

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think chimps don't have, the ability
to use a bit of lateral thinking.

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Am I allowed to use my water?

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Whatever you want.

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Any idea you have,
you could just try it out. OK.

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Yes! Here it comes.

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Yeah, wow!

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Excellent.

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It took me more than four
minutes to get my peanut,

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so now let's see how
a chimpanzee manages.

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Oh, here they come,
so Daniel's just trying to get them

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interested in the peanut and they're
going to have to do exactly

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the same test that I just did.

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Oh, look, he's doing it.

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It's just really clever,
it really is,

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watching this chimp doing that.

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And he doesn't have a
bottle of water like I had.

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He's got to think about how to get
the water in there.

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He takes some from his drinking
bottle into his mouth

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and then he spits it
out in the tube.

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He hasn't quite done enough.

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Can he reach it yet?

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There's another mouthful of water
gone in and, oh, it's just,

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it's almost there.

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It must be so frustrating.

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Oh!

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Yeah!
He's done it, he's done it.

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You clever chimpanzee.

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I think that was quicker than me.

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Twice as quick, in fact.

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But although this chimp has done
it before, even when presented with

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the task for the first time, many of
the apes here figured out that water

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could be used not only to drink, but
also as a tool to make peanuts move.

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At certain tasks, chimps
are cleverer than you might think.

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And what excites me is that Mike

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and his team are now homing
in on the specific aspects of human

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intelligence and behaviour that
set us apart from our hairy cousins.

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What makes us really different
is our ability to put our heads

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together and to do things that
neither one of us could do alone,

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to create new resources that neither
one of us could create alone.

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It's really all about communicating
and collaborating

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and working together.

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But you think there's some kind
of add-on effect then of teaching

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and of being in a society,

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in a culture which kind of builds
on those innate abilities?

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It makes all the difference.

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If you raised a child on a desert
island with no social contact

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so no teaching, no contact
with humans, their intelligence

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as an adult would be very similar
to that of other apes.

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It would be a little bit different,

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but they're evolved
to learn from others

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and to communicate with others
and to collaborate with others,

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and if there was no-one there
and no culture and no tools and no

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language, then that natural human
intelligence just wouldn't develop.

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Fish are born expecting water, OK?

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They've got fins, they've got gills,
they're born expecting water

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and humans are born
expecting culture.

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At the heart of being a human
then is our culture,

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and something that goes
hand in hand with human culture

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is our ability to co-operate, and
Michael has devised an experiment

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that he believes reveals a specific
piece of behaviour that separates

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us from chimps, that defines us
a species, and truly makes us human.

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So what's this test designed
to look at then?

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OK, this is a test of being able
to collaborate or co-operate

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by pulling in on a rope such
that they each get their reward.

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The rope is strong through
these hooks, so that

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if anyone individual pulls, it'll
just pull the rope out loosely.

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Ah, right.

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And so you have to pull
together in order to get the food.

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So now they each have their rope.
I see. So that's a moveable plank?

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It's a moveable plank.

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With their pieces of banana,
which is their reward. Exactly.

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So they have to pull together?
And they have to pull together.

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If any one of them pulls alone,
they just pull it out.

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So now it's tightened up and they're
ready to actually make it move,

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but they have to be sensitive
to what the other one is doing.

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Notice there was actually a look to
the other? Yeah, this is amazing.

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OK, and they both pull it in
and get their rewards.

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These are two of our best
at doing this.

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That is stunning.
They are very good.

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Proper, proper co-operation.
It's brilliant.

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But co-operation in the chimp world
is a fragile thing.

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What happens if something goes wrong
and one chimp gets her reward first?

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This one has tangled her rope.
Oh!

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She can't quite reach it.

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And now she can't do it, as long as
this one's let go.

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You can now see the rope coming out.

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She's frustrated because they didn't
pull exactly synchronously. Yeah.

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So she's got her reward.
She's happy now, she's gone.

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And then her poor partner is left
without a reward.

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For our closest relatives, clever as
they are, that's as far as it goes.

234
00:16:09,040 --> 00:16:12,720
Chimps will co-operate,
but only for selfish ends.

235
00:16:28,200 --> 00:16:30,920
But the experiments get really
interesting

236
00:16:30,920 --> 00:16:33,880
when you start testing humans.

237
00:16:33,880 --> 00:16:38,520
Michael has been comparing how young
children perform in the same task.

238
00:16:42,040 --> 00:16:45,120
This is a very similar test to the
test that the chimpanzees

239
00:16:45,120 --> 00:16:46,840
were doing with the bananas.

240
00:16:46,840 --> 00:16:49,520
Yes, it's the same basic idea,
same basic idea.

241
00:16:51,080 --> 00:16:54,600
'Like the chimps, the kids have to
collaborate by pulling

242
00:16:54,600 --> 00:16:58,240
'on a string at the same time
to release the marbles.

243
00:17:04,440 --> 00:17:08,000
'And just like the chimps,
they have no problem co-operating.'

244
00:17:11,880 --> 00:17:14,920
'Instead of a piece of banana,
their reward is

245
00:17:14,920 --> 00:17:19,600
'the satisfaction of placing
a marble in the plinck machine.'

246
00:17:19,600 --> 00:17:23,640
THEY SPEAK GERMAN

247
00:17:28,320 --> 00:17:29,960
'The experiment can be set up

248
00:17:29,960 --> 00:17:35,360
'so that the children receive either
an equal or an unequal reward.'

249
00:17:35,360 --> 00:17:38,320
THEY SPEAK GERMAN

250
00:17:41,320 --> 00:17:43,160
So, Mike,
what's the idea of this test?

251
00:17:43,160 --> 00:17:45,640
They have to work together to
get the reward?

252
00:17:45,640 --> 00:17:49,240
Yeah, so the idea of this test
is that kids are not that

253
00:17:49,240 --> 00:17:53,520
naturally generous with their own
things, and so if they just

254
00:17:53,520 --> 00:17:57,120
have some things and you tell them
they can share, maybe they will,

255
00:17:57,120 --> 00:18:02,240
maybe they won't, but when they work
together and they generate together

256
00:18:02,240 --> 00:18:06,080
these rewards, they have a tendency
to want them to be equally split.

257
00:18:12,360 --> 00:18:13,400
Here they come.

258
00:18:19,080 --> 00:18:20,640
So she's setting it up...

259
00:18:23,080 --> 00:18:26,720
..but this time making sure it's
going to be an uneven distribution?

260
00:18:27,880 --> 00:18:32,760
Yes. One of them's going to get more
than the other and we'll see

261
00:18:32,760 --> 00:18:36,320
if they need to even it out before
they cash in their rewards.

262
00:18:44,080 --> 00:18:45,280
Pulling.

263
00:18:49,920 --> 00:18:51,840
Ah, so there's uneven rewards, no?

264
00:18:55,800 --> 00:18:58,080
This little girl's got one
and that one's got three.

265
00:19:01,280 --> 00:19:02,280
Are they sharing?

266
00:19:04,040 --> 00:19:05,200
Let's see.

267
00:19:08,440 --> 00:19:09,600
They shared them out.

268
00:19:09,600 --> 00:19:11,080
Yes, they shared them out.

269
00:19:13,920 --> 00:19:15,560
So they ended up with two each, yep.

270
00:19:19,800 --> 00:19:21,160
Isn't that interesting?

271
00:19:22,680 --> 00:19:24,120
That was quite extraordinary,

272
00:19:24,120 --> 00:19:27,360
because I wouldn't have naturally
thought that kids of this age,

273
00:19:27,360 --> 00:19:30,200
two-year-olds, three-year-olds,
would be that into sharing.

274
00:19:30,200 --> 00:19:32,400
It's only
when they work together for it.

275
00:19:34,640 --> 00:19:36,160
That's just fascinating.

276
00:19:40,120 --> 00:19:44,600
'In these experiments, Mike and his
team have uncovered a seemingly

277
00:19:44,600 --> 00:19:48,800
'small but crucial difference
between us and chimpanzees.'

278
00:19:48,800 --> 00:19:49,760
OK, here they come.

279
00:19:52,200 --> 00:19:56,160
'Human children do something
that no other ape will do.'

280
00:20:01,400 --> 00:20:03,560
He rolls one over to him.
He's rolled one over. Yeah.

281
00:20:10,840 --> 00:20:15,720
'In that small act of sharing, they
reveal something that really does

282
00:20:15,720 --> 00:20:18,120
'lie at the heart of what it is
to be human.'

283
00:20:19,560 --> 00:20:26,080
'It's a tiny but profound difference
between us and the other apes,

284
00:20:26,080 --> 00:20:31,160
'and it's a way of thinking
that underpins our ability

285
00:20:31,160 --> 00:20:34,160
'to co-operate and create
human culture.'

286
00:20:39,520 --> 00:20:45,160
Somehow these huge brains that we've
got encapsulate the main differences

287
00:20:45,160 --> 00:20:48,160
between ourselves
and our closest cousins,

288
00:20:48,160 --> 00:20:50,040
because look at these chimpanzees.

289
00:20:50,040 --> 00:20:53,400
They're naked and hairy,
they're not wearing clothes,

290
00:20:53,400 --> 00:20:56,520
they're not talking about me,
they're not sketching me.

291
00:20:56,520 --> 00:21:00,280
So there are some really massive
differences between us and them

292
00:21:00,280 --> 00:21:04,040
which must come down, in some ways,
to what is going on

293
00:21:04,040 --> 00:21:06,880
inside this huge organ in our heads.

294
00:21:22,320 --> 00:21:26,160
'With just a few months left
until I'm due to give birth,

295
00:21:26,160 --> 00:21:30,000
'I'm off for a scan to see how
my new baby is getting along.'

296
00:21:33,080 --> 00:21:36,720
So shall I just lie back on here,
then, Chrissie? Yes.

297
00:21:39,000 --> 00:21:41,000
Right, this is some cold jelly.
Yeah.

298
00:21:44,680 --> 00:21:47,080
So I'll just have a little
look around first of all.

299
00:22:05,400 --> 00:22:09,640
'It is an emotional experience
seeing my baby growing inside me.'

300
00:22:11,760 --> 00:22:13,440
That's the head.
That's the head, yeah.

301
00:22:15,440 --> 00:22:17,120
There's the heart beating.

302
00:22:17,120 --> 00:22:18,280
Oh, that's wonderful.

303
00:22:21,400 --> 00:22:22,640
That is my baby.

304
00:22:27,920 --> 00:22:29,240
Look at that.

305
00:22:29,240 --> 00:22:33,800
That is my baby inside my womb.

306
00:22:36,480 --> 00:22:39,040
And looking at him,
he's obviously small now.

307
00:22:39,040 --> 00:22:43,080
He's only six months of gestation,

308
00:22:43,080 --> 00:22:45,360
so he's got another
few months to go,

309
00:22:45,360 --> 00:22:49,640
but he looks like a perfect but
small little baby at this point,

310
00:22:49,640 --> 00:22:50,880
so everything is there.

311
00:22:50,880 --> 00:22:54,360
He's got his fingers in place,
his toes in place, and it is just

312
00:22:54,360 --> 00:22:58,560
amazing that all of that has
come from a single fertilised egg.

313
00:22:58,560 --> 00:23:00,240
It never fails to amaze me.

314
00:23:00,240 --> 00:23:04,240
I mean, that's just extraordinary
that the whole complexity

315
00:23:04,240 --> 00:23:07,160
of the human body comes from that,

316
00:23:07,160 --> 00:23:11,720
that single cell with genes from me
and genes from my husband,

317
00:23:11,720 --> 00:23:14,800
and that somehow, at the end of it,
you end up with a human.

318
00:23:16,720 --> 00:23:21,040
'But as well as being an expectant
mother, I'm also an anatomist,

319
00:23:21,040 --> 00:23:26,640
'so looking at the scan I can't help
but be fascinated by the structures

320
00:23:26,640 --> 00:23:30,720
'I can already see inside this
brand new human of mine.'

321
00:23:30,720 --> 00:23:34,440
So if we come back to
looking at the head now...

322
00:23:34,440 --> 00:23:38,200
You can almost see structures
inside the brain, can't you?
That's amazing.

323
00:23:38,200 --> 00:23:40,240
You can. This is the cerebellum.

324
00:23:41,880 --> 00:23:44,880
Do you see this sort of dumbbell
shape here? Yeah, yeah.

325
00:23:44,880 --> 00:23:47,360
And this dark area here is the...

326
00:23:47,360 --> 00:23:50,000
Yeah, so that's the back of the
lateral ventricle, isn't it?

327
00:23:50,000 --> 00:23:54,880
That's right, that's the posterior
ventricle there. That's amazing.

328
00:23:54,880 --> 00:23:58,440
'After just six months, my baby's
brain is already more than half

329
00:23:58,440 --> 00:24:03,200
'the size of an adult chimpanzee's
and it's still growing fast.'

330
00:24:06,800 --> 00:24:08,720
How big is the head at the moment,
Chrissie?

331
00:24:08,720 --> 00:24:10,160
Well, shall we measure it and see?

332
00:24:11,760 --> 00:24:15,200
So it says gestation
just over 27 weeks,

333
00:24:15,200 --> 00:24:21,040
and the head circumference
is 25.6 centimetres.

334
00:24:21,040 --> 00:24:22,680
What's the diameter?

335
00:24:22,680 --> 00:24:24,960
The diameter, BPD 7.2 centimetres.

336
00:24:24,960 --> 00:24:27,760
7.2, so it's going to get
a little bit bigger.

337
00:24:27,760 --> 00:24:29,560
Rather, yeah.

338
00:24:29,560 --> 00:24:31,000
Oh, dear.

339
00:24:31,000 --> 00:24:32,960
That's kind of big enough, I think.

340
00:24:36,720 --> 00:24:39,560
'That growing head can't
fail to remind me

341
00:24:39,560 --> 00:24:42,960
'of something that's getting
closer by the day.'

342
00:24:42,960 --> 00:24:46,400
'Something that's particularly
tricky for us humans.'

343
00:24:46,400 --> 00:24:47,560
'Birth.'

344
00:24:50,920 --> 00:24:52,960
'The enormous size of our brains,

345
00:24:52,960 --> 00:24:55,840
'together with another
uniquely human trait,

346
00:24:55,840 --> 00:24:59,280
'our strange way of walking
around on two legs,

347
00:24:59,280 --> 00:25:03,920
'conspire to make human birth
something of a squeeze,

348
00:25:03,920 --> 00:25:05,520
'as any mother with tell you.'

349
00:25:07,560 --> 00:25:09,600
WOMAN SCREAMS

350
00:25:09,600 --> 00:25:11,240
And again.

351
00:25:11,240 --> 00:25:13,240
Push, that's it, push.

352
00:25:13,240 --> 00:25:15,400
WOMAN SCREAMS

353
00:25:25,280 --> 00:25:28,720
It's quite strange being on a
maternity ward and thinking that

354
00:25:28,720 --> 00:25:34,200
I'm going to be back in a place
like this in just two months' time,

355
00:25:34,200 --> 00:25:38,280
ready for the appearance of my own
little baby into the world.

356
00:25:38,280 --> 00:25:43,160
I think it brings it home that human
childbirth is really something

357
00:25:43,160 --> 00:25:47,600
quite special, quite unique, even,
amongst all other animals.

358
00:25:50,640 --> 00:25:53,920
'By way of comparison,
take a look at this,

359
00:25:53,920 --> 00:25:58,160
'some rare film of a chimpanzee
birth taken at Leipzig Zoo.'

360
00:26:03,040 --> 00:26:07,320
'What's remarkable is just how
quick and easy it is,

361
00:26:07,320 --> 00:26:10,560
'certainly when compared with
the rather more drawn-out

362
00:26:10,560 --> 00:26:13,960
'and painful business
of a human birth.'

363
00:26:13,960 --> 00:26:15,840
WOMAN SCREAMS

364
00:26:15,840 --> 00:26:17,040
Push harder, come on.

365
00:26:27,640 --> 00:26:31,240
What I've drawn is essentially
the anatomy of childbirth.

366
00:26:32,680 --> 00:26:34,320
This is a human, female pelvis.

367
00:26:34,320 --> 00:26:36,960
We're looking down on it from above,
we're looking through

368
00:26:36,960 --> 00:26:39,560
the birth canal and this
is the baby's head

369
00:26:39,560 --> 00:26:42,040
passing through that birth canal,

370
00:26:42,040 --> 00:26:45,520
and you can see why childbirth
is such a difficult process.

371
00:26:45,520 --> 00:26:48,600
The birth canal is about ten
centimetres in diameter,

372
00:26:48,600 --> 00:26:52,920
the baby's head is about nine
centimetres in diameter.

373
00:26:52,920 --> 00:26:56,280
Now it's always been thought that
there are constraints on the width

374
00:26:56,280 --> 00:26:59,880
of the pelvis, which are all about
walking on two legs,

375
00:26:59,880 --> 00:27:03,400
that we can't actually push
the hips any further apart

376
00:27:03,400 --> 00:27:07,200
because that would make walking
inefficient, and so that means,

377
00:27:07,200 --> 00:27:09,880
for our big-brained babies,

378
00:27:09,880 --> 00:27:12,320
they couldn't actually stay
in the womb any longer,

379
00:27:12,320 --> 00:27:17,360
because their heads would be too big
to fit out through this birth canal.

380
00:27:17,360 --> 00:27:20,000
And so our babies are born

381
00:27:20,000 --> 00:27:22,680
at a relatively early stage
of development.

382
00:27:22,680 --> 00:27:25,080
Our new born babies are helpless.

383
00:27:29,600 --> 00:27:32,600
'And that is one of the most
puzzling paradoxes

384
00:27:32,600 --> 00:27:34,640
'about being human.'

385
00:27:34,640 --> 00:27:39,320
'For all our brilliance as a
species, compared with other apes,

386
00:27:39,320 --> 00:27:44,120
'our babies come into the world
a bit useless.'

387
00:27:47,240 --> 00:27:51,320
'For decades, we've assumed that our
helpless babies are an unfortunate

388
00:27:51,320 --> 00:27:55,960
'consequence of walking upright
and having big brains.'

389
00:27:55,960 --> 00:27:59,000
'It's called the obstetric dilemma.'

390
00:27:59,000 --> 00:28:00,840
'It's in all the textbooks.'

391
00:28:00,840 --> 00:28:02,880
'It's what I was taught
at university

392
00:28:02,880 --> 00:28:05,920
'and it's what I've gone on
to teach others.'

393
00:28:05,920 --> 00:28:09,240
'The female pelvis is struggling
to do two different jobs,

394
00:28:09,240 --> 00:28:11,880
'and we're stuck with these
helpless babies.'

395
00:28:23,000 --> 00:28:26,680
'If we could explain this dilemma,
we'd start to open the door

396
00:28:26,680 --> 00:28:29,880
'to a treasure trove of insights
about being human...'

397
00:28:31,720 --> 00:28:35,400
'..and there's some science emerging
from the east coast of America

398
00:28:35,400 --> 00:28:39,520
'that's shaking up the traditional
view of women's hips.'

399
00:28:42,920 --> 00:28:46,040
'Dr Holly Dunsworth decided
that the female pelvis

400
00:28:46,040 --> 00:28:48,840
'deserved a closer examination.'

401
00:28:50,400 --> 00:28:53,560
It does seem peculiar, I mean, it
really does mark us out amongst

402
00:28:53,560 --> 00:28:58,480
all the other apes that childbirth
for humans is...is difficult.

403
00:28:58,480 --> 00:29:01,440
It's much more difficult than it is
in chimpanzees and gorillas.

404
00:29:01,440 --> 00:29:04,440
I know this from personal
experience,

405
00:29:04,440 --> 00:29:09,080
so what is it about our evolution
that sets up this problem?

406
00:29:10,640 --> 00:29:14,600
It's a dilemma. We have a tight fit.

407
00:29:14,600 --> 00:29:17,480
We've got these two
exceptional conditions.

408
00:29:17,480 --> 00:29:21,080
We've got this funny way of getting
around that we're doing right now,

409
00:29:21,080 --> 00:29:24,600
and we've got these huge brains
on top of our heads,

410
00:29:24,600 --> 00:29:29,440
and natural selection
acting on those two things

411
00:29:29,440 --> 00:29:34,000
has come together and created this
very difficult childbirth.

412
00:29:34,000 --> 00:29:35,720
So is it a compromise, then?

413
00:29:35,720 --> 00:29:38,240
The female pelvis is a compromise
between something

414
00:29:38,240 --> 00:29:44,240
that needs to be wide to let
a large-brained baby out,

415
00:29:44,240 --> 00:29:48,320
but needs to be narrow in order
to make walking efficient?

416
00:29:48,320 --> 00:29:49,600
Right, right.

417
00:29:49,600 --> 00:29:54,240
And that's the obstetric dilemma,
and it's unique to humans.

418
00:29:54,240 --> 00:29:59,200
So the idea is that ideally we'd
kind of want to get our pelvis

419
00:29:59,200 --> 00:30:02,160
a bit wider, but actually,
female pelves

420
00:30:02,160 --> 00:30:04,360
are already making us less efficient

421
00:30:04,360 --> 00:30:09,040
than men at walking and running,
and we can't push it any further?

422
00:30:09,040 --> 00:30:10,360
Right.

423
00:30:10,360 --> 00:30:14,520
But as this hypothesis goes,
they can't get any wider

424
00:30:14,520 --> 00:30:18,800
or else women would be even worse
at walking and running

425
00:30:18,800 --> 00:30:21,640
than we already are,
and everything would fall to pieces.

426
00:30:21,640 --> 00:30:23,840
Yeah, that you'd end up
kind of waddling along,

427
00:30:23,840 --> 00:30:25,600
and it would be really inefficient.

428
00:30:25,600 --> 00:30:28,320
Right. You'd never escape
a sabre-toothed cat, you know.

429
00:30:33,200 --> 00:30:37,280
'What's amazing is that in all these
decades, no one has ever thought

430
00:30:37,280 --> 00:30:41,560
'to question the assumptions that
underlie the obstetric dilemma,

431
00:30:41,560 --> 00:30:45,160
'or the suggestion that women
are rubbish at running.'

432
00:30:47,040 --> 00:30:48,320
'Until now.'

433
00:30:52,520 --> 00:30:56,720
'Together with her colleagues,
Herman Pontzer and Anna Warriner,

434
00:30:56,720 --> 00:30:59,960
'Holly set about exhaustively
testing the assumptions

435
00:30:59,960 --> 00:31:01,480
'about the female pelvis...'

436
00:31:03,120 --> 00:31:07,120
'..and she's invited me to Herman's
lab in New York to see the results.'

437
00:31:17,040 --> 00:31:18,360
Awesome, thank you.

438
00:31:19,640 --> 00:31:22,280
So, Holly, this was part of the
original research that you did

439
00:31:22,280 --> 00:31:24,760
with Herman and Anna,
looking at the efficiency

440
00:31:24,760 --> 00:31:28,000
of running and walking
in women and men.

441
00:31:28,000 --> 00:31:30,360
I saw them starting to do this sort
of research,

442
00:31:30,360 --> 00:31:33,080
and it fit really well with
the doubts I was having about

443
00:31:33,080 --> 00:31:35,640
all of this obstetric
dilemma business.

444
00:31:35,640 --> 00:31:37,200
Yeah, yeah.

445
00:31:37,200 --> 00:31:41,440
So I'd been thinking about how
kind of strange this idea was

446
00:31:41,440 --> 00:31:44,520
that our pelvis was
limiting our gestation length

447
00:31:44,520 --> 00:31:47,920
and it was sort of, like, you know,
an epiphany.

448
00:31:57,040 --> 00:32:00,160
'The team set out to explore
the assumption that women,

449
00:32:00,160 --> 00:32:03,200
'with our wide hips especially
adapted for birth,

450
00:32:03,200 --> 00:32:06,240
'are less efficient at walking
and running than men.'

451
00:32:07,840 --> 00:32:11,920
'Using a motion capture system
and a force plate, Anna devised an

452
00:32:11,920 --> 00:32:16,760
'experiment to analyse the internal
mechanics of hip and leg bones.'

453
00:32:18,840 --> 00:32:22,240
'Until now it had always been
assumed that women's hip muscles,

454
00:32:22,240 --> 00:32:24,920
'being attached to a wider pelvis,

455
00:32:24,920 --> 00:32:27,480
'had to work harder
than those of men.'

456
00:32:27,480 --> 00:32:28,440
Go ahead, Lesley.

457
00:32:29,520 --> 00:32:30,560
And there she comes.

458
00:32:32,600 --> 00:32:34,720
That's great, isn't it?

459
00:32:34,720 --> 00:32:36,440
A pair of legs walking about.

460
00:32:39,280 --> 00:32:43,520
'But what the experiments revealed
was that throughout each step,

461
00:32:43,520 --> 00:32:47,320
'the angle of the pelvis
is constantly adjusted

462
00:32:47,320 --> 00:32:50,640
'to minimise the necessary work.'

463
00:32:50,640 --> 00:32:55,160
'Women's hips may be wider, but the
wobbling makes a key difference.

464
00:32:56,600 --> 00:32:59,280
As you sort of move through
the course of the step,

465
00:32:59,280 --> 00:33:01,520
she's adjusting her balance
and her weight.

466
00:33:04,120 --> 00:33:05,760
So from this wavering around,

467
00:33:05,760 --> 00:33:09,840
you start to suspect that it's not
going to be so simple

468
00:33:09,840 --> 00:33:12,960
saying that women have wider pelves
and therefore their muscles around

469
00:33:12,960 --> 00:33:15,680
their hips need to work harder
when you're walking and running?

470
00:33:15,680 --> 00:33:16,880
Yeah, exactly. Exactly right.

471
00:33:20,200 --> 00:33:22,360
'The result of all these
measurements

472
00:33:22,360 --> 00:33:26,880
'is to show that, for decades,
we got it wrong.'

473
00:33:26,880 --> 00:33:30,920
This is really important because it
means that there isn't a constraint

474
00:33:30,920 --> 00:33:35,200
on how wide the pelvis is in terms
of being efficient at bipedalism.

475
00:33:35,200 --> 00:33:38,760
These data indicate
that there is no effect

476
00:33:38,760 --> 00:33:43,200
of having a pelvis adapted for
birth on your efficiency

477
00:33:43,200 --> 00:33:44,720
during walking or running.

478
00:33:47,160 --> 00:33:51,360
'The female pelvis is not, it seems,
compromised at all,

479
00:33:51,360 --> 00:33:53,280
'and women, with our wide hips,

480
00:33:53,280 --> 00:33:56,200
'are just as efficient at walking
and running as men.'

481
00:33:59,880 --> 00:34:05,040
'So why didn't the female pelvis
evolve to be even wider, to allow

482
00:34:05,040 --> 00:34:09,200
'our babies to grow a bit bigger and
to be a bit less helpless at birth?'

483
00:34:11,680 --> 00:34:14,600
'The answer was revealed to me
through an experiment

484
00:34:14,600 --> 00:34:17,880
'that involved me drinking
some specially-labelled water

485
00:34:17,880 --> 00:34:21,880
'and then sending Herman
frozen samples of my urine.'

486
00:34:21,880 --> 00:34:26,160
So, Herman, I recognise these
little plastic tubes.

487
00:34:26,160 --> 00:34:27,720
That's right.

488
00:34:27,720 --> 00:34:30,000
So we had you drink
a small dose of what

489
00:34:30,000 --> 00:34:31,480
we call doubly-labelled water,

490
00:34:31,480 --> 00:34:35,320
and then we collected a bunch of
urine samples as we have here,

491
00:34:35,320 --> 00:34:38,600
and we can actually calculate how
much carbon dioxide you're producing

492
00:34:38,600 --> 00:34:40,840
every day, and therefore
how many calories your body

493
00:34:40,840 --> 00:34:42,040
is burning every day.

494
00:34:42,040 --> 00:34:44,280
It's the gold standard
for measuring energy

495
00:34:44,280 --> 00:34:47,720
expenditure in people
during normal life.

496
00:34:47,720 --> 00:34:51,160
'The length of gestation, it turns
out, has nothing to do

497
00:34:51,160 --> 00:34:56,280
'with the width of the birth canal,
but everything to do with energy.'

498
00:34:56,280 --> 00:34:59,280
So here we have the energy that the
foetus is using. This is

499
00:34:59,280 --> 00:35:03,240
based on data from other studies,
and we see it goes up exponentially.

500
00:35:03,240 --> 00:35:06,720
As the kid gets bigger, it needs
more and more and more energy,

501
00:35:06,720 --> 00:35:09,240
and we take a look at the energy

502
00:35:09,240 --> 00:35:12,800
that mums actually burn
during pregnancy.

503
00:35:12,800 --> 00:35:16,680
We see it goes up quite quickly
at first, but then it levels off.

504
00:35:16,680 --> 00:35:19,200
It hits a ceiling.
You just can't do any more.

505
00:35:19,200 --> 00:35:21,440
Your body is limited in
how much energy it can burn.

506
00:35:21,440 --> 00:35:24,120
Presumably then it doesn't matter
if I were to eat more,

507
00:35:24,120 --> 00:35:26,920
so if I were to eat a few more
hundred calories, it doesn't matter.

508
00:35:26,920 --> 00:35:29,000
I'm not going to be able to give
that to the foetus

509
00:35:29,000 --> 00:35:31,160
because I can't actually
metabolise any quicker.

510
00:35:31,160 --> 00:35:34,320
That's right. There's a limit
to how much energy your body
can put through.

511
00:35:34,320 --> 00:35:35,640
There's a hard limit on that.

512
00:35:35,640 --> 00:35:37,440
If gestation continued
for another month,

513
00:35:37,440 --> 00:35:39,400
you'd shoot through that ceiling.

514
00:35:39,400 --> 00:35:41,440
It would be metabolically
impossible to do.

515
00:35:41,440 --> 00:35:43,640
So instead, what you do is,
as you approach nine months,

516
00:35:43,640 --> 00:35:44,680
you give birth.

517
00:35:44,680 --> 00:35:45,800
Right.

518
00:35:45,800 --> 00:35:47,800
So we take a look at your data,
right?

519
00:35:47,800 --> 00:35:51,320
We've got you plotted on here.
You're right there.

520
00:35:51,320 --> 00:35:52,880
Ah, right, so...

521
00:35:52,880 --> 00:35:54,960
So you're about five months in.

522
00:35:54,960 --> 00:35:58,720
That's exactly... So you could tell
how many months pregnant I was

523
00:35:58,720 --> 00:36:02,240
by looking at this without
actually...without me telling you?

524
00:36:02,240 --> 00:36:03,480
Without you telling me,

525
00:36:03,480 --> 00:36:06,320
I could know that you've
approached that ceiling. Yeah.

526
00:36:06,320 --> 00:36:09,200
You were just about at the
maximum energy expenditure

527
00:36:09,200 --> 00:36:11,840
that we could expect your body
to be able to do. Yeah.

528
00:36:11,840 --> 00:36:15,240
It'll get to be unsustainable
at just about nine months in,

529
00:36:15,240 --> 00:36:16,240
and you'll give birth.

530
00:36:16,240 --> 00:36:17,320
This is fascinating.

531
00:36:17,320 --> 00:36:21,560
It means that the baby comes
out at a moment in time

532
00:36:21,560 --> 00:36:24,760
when it is just about to start
demanding more energy

533
00:36:24,760 --> 00:36:27,640
from the mother than the mother can
possibly give it via the placenta.

534
00:36:27,640 --> 00:36:28,640
That's right.

535
00:36:34,840 --> 00:36:39,960
'This research is, I think,
really revolutionary.'

536
00:36:39,960 --> 00:36:43,920
'What it reveals is that however
wide our hips became,

537
00:36:43,920 --> 00:36:49,360
'our babies couldn't stay inside the
womb a moment longer than they do.'

538
00:36:52,120 --> 00:36:54,480
It makes me look at the female
pelvis in a new light

539
00:36:54,480 --> 00:36:57,680
and say, "Well, actually this
isn't a design compromise."

540
00:36:57,680 --> 00:36:59,480
"It works very well."

541
00:36:59,480 --> 00:37:01,600
But also, it makes me look at those
helpless babies

542
00:37:01,600 --> 00:37:04,840
in a new light as well,
because they work well, too.

543
00:37:04,840 --> 00:37:08,680
Right. You know, on the one hand, we
say they're coming into the world

544
00:37:08,680 --> 00:37:13,160
too early, but it works. It works
within the context of human society

545
00:37:13,160 --> 00:37:16,560
because otherwise we wouldn't be
here in the numbers that we are.

546
00:37:16,560 --> 00:37:19,080
We gestate as long as we should
for primates of our body size,

547
00:37:19,080 --> 00:37:20,840
and maybe a little longer.

548
00:37:20,840 --> 00:37:25,400
We give birth to babies at the right
size for primates of our body size,

549
00:37:25,400 --> 00:37:26,720
or maybe a little larger.

550
00:37:28,760 --> 00:37:33,400
It's just that once they're born,
they have so much more growth

551
00:37:33,400 --> 00:37:36,520
to experience,
particularly in the brain,

552
00:37:36,520 --> 00:37:38,760
and while we are achieving
that growth,

553
00:37:38,760 --> 00:37:42,600
we also have much more to learn
about how to be a human

554
00:37:42,600 --> 00:37:46,040
than a chimp has to learn
about how to be a chimp.

555
00:38:05,360 --> 00:38:10,200
'It turns out, then, that the
very nature of human birth,

556
00:38:10,200 --> 00:38:14,280
'the fact that I will deliver
a seemingly underdeveloped baby,

557
00:38:14,280 --> 00:38:18,920
'is in fact a key ingredient in my
son's path to becoming human.'

558
00:38:23,720 --> 00:38:28,520
'Our babies may be born helpless,
but far from being a dumb idea,

559
00:38:28,520 --> 00:38:32,360
'it turns out to be one of the
smartest moves we ever made...

560
00:38:34,400 --> 00:38:38,200
'..because in order to develop
their full human potential,

561
00:38:38,200 --> 00:38:43,960
'the brains of our human babies need
the stimulation of other humans.'

562
00:38:55,200 --> 00:39:01,000
'Somehow, the secrets of being human
are locked away inside the brain,

563
00:39:01,000 --> 00:39:06,000
'the most complicated, mysterious
object in the universe.'

564
00:39:08,120 --> 00:39:12,400
'But it's an organ that keeps
its secrets wrapped up tight.'

565
00:39:12,400 --> 00:39:15,880
So this is a brain which has been
removed from a skull and you can

566
00:39:15,880 --> 00:39:19,280
see that it's still got its
coverings on it, its meninges,

567
00:39:19,280 --> 00:39:22,120
so there are several layers
of membrane

568
00:39:22,120 --> 00:39:23,760
around the outside of the brain.

569
00:39:28,440 --> 00:39:32,800
In order to see the brain, we're
going to have to peel this back.

570
00:39:32,800 --> 00:39:35,640
There we go, it's just
going to come away actually.

571
00:39:42,440 --> 00:39:45,680
I just need to get an edge and then
when you've got an edge,

572
00:39:45,680 --> 00:39:47,520
it peels off quite nicely.

573
00:39:48,880 --> 00:39:51,360
It's rather like peeling
the pith off an orange.

574
00:39:54,280 --> 00:39:56,440
And once I've cleared
this layer away,

575
00:39:56,440 --> 00:40:00,480
we're starting to see really nicely
the texture of the surface

576
00:40:00,480 --> 00:40:04,040
of the brain, so this is the
cerebral cortex that we're starting

577
00:40:04,040 --> 00:40:07,960
to see here, and you can see
how heavily folded it is.

578
00:40:07,960 --> 00:40:11,680
This is one of the characteristics
of a human brain,

579
00:40:11,680 --> 00:40:14,000
that the cortex is
incredibly heavily folded.

580
00:40:14,000 --> 00:40:16,640
You get the impression that
there's a lot of information

581
00:40:16,640 --> 00:40:18,880
being packed into a small area.

582
00:40:22,480 --> 00:40:25,480
So that's it, this is the brain,
nicely cleaned up.

583
00:40:27,920 --> 00:40:31,440
And I think that however
many times I do this,

584
00:40:31,440 --> 00:40:37,080
it is utterly extraordinary
to be holding in my hands

585
00:40:37,080 --> 00:40:42,480
the organ that, more than any other
part of our body, is us.

586
00:40:42,480 --> 00:40:47,720
It seems utterly extraordinary
that this actually quite

587
00:40:47,720 --> 00:40:53,640
unprepossessing physical object
contains somebody's personality,

588
00:40:53,640 --> 00:40:59,400
the seat of their emotions, and it
was where they experienced the world

589
00:40:59,400 --> 00:41:01,440
and where they held their memories.

590
00:41:02,960 --> 00:41:06,280
It is just quite remarkable.

591
00:41:11,240 --> 00:41:15,680
'Despite several hundred years
of probing, exactly how the

592
00:41:15,680 --> 00:41:20,960
'human brain achieves all that
remains shrouded in mystery.'

593
00:41:20,960 --> 00:41:25,200
'What little we do know only makes
it seem all the more extraordinary.'

594
00:41:27,040 --> 00:41:31,320
'We know that a human brain contains
a staggering one hundred billion

595
00:41:31,320 --> 00:41:36,760
'neurons, but it's not just the
number of brain cells that matters.'

596
00:41:36,760 --> 00:41:40,920
'What makes the human brain so
incredible is the huge number

597
00:41:40,920 --> 00:41:47,120
'of connections between those cells,
the vastly complex internal wiring.'

598
00:41:48,120 --> 00:41:51,560
So, I'm going to start slicing it

599
00:41:51,560 --> 00:41:53,680
with this incredibly sharp
brain knife.

600
00:41:55,600 --> 00:42:01,000
'Human brains have about 40% more
connections between cortical neurons

601
00:42:01,000 --> 00:42:04,400
'than the brains of other primates.'

602
00:42:04,400 --> 00:42:10,080
'That's around a hundred trillion
connections in every brain.'

603
00:42:10,080 --> 00:42:12,160
'We know the basic anatomy
quite well

604
00:42:12,160 --> 00:42:15,880
'but if we want to begin to
understand this extraordinary level

605
00:42:15,880 --> 00:42:20,640
'of complexity, we need to look at
the brain with a whole new toolkit.'

606
00:42:48,360 --> 00:42:52,360
'To discover exactly how our human
brains came to be

607
00:42:52,360 --> 00:42:57,840
'so highly connected, I've come to
America to find out about the latest

608
00:42:57,840 --> 00:43:02,440
'research into the human genome,
the recipe for making a human.'

609
00:43:13,800 --> 00:43:16,840
'There are three billion
letters in the human genome,

610
00:43:16,840 --> 00:43:21,040
'stored in the 23 chromosomes
that hold this recipe

611
00:43:21,040 --> 00:43:24,160
'in every cell of our bodies.'

612
00:43:24,160 --> 00:43:29,320
'Each letter, A, G, C and T,
represents one of the four bases,

613
00:43:29,320 --> 00:43:33,360
'the chemical building blocks, which
make up the long strands of DNA.'

614
00:43:35,640 --> 00:43:39,280
'And for geneticists, like Franck
Palleux, these letters hold

615
00:43:39,280 --> 00:43:43,440
'the clues that could unlock
the secrets of the human brain.'

616
00:43:44,560 --> 00:43:46,960
So this is chromosome one
written out?

617
00:43:46,960 --> 00:43:48,000
Uh-huh.

618
00:43:51,600 --> 00:43:56,280
And how much of chromosome
one is it? Just one fiftieth.

619
00:43:56,280 --> 00:43:58,160
And there's a thousand pages here.

620
00:43:59,560 --> 00:44:04,280
A thousand pages, 45,000
base pairs per page.

621
00:44:06,520 --> 00:44:12,200
'The whole genome would
fill 670,000 sheets of paper

622
00:44:12,200 --> 00:44:15,840
'and at this rate, it would take me
and Franck more than a week,

623
00:44:15,840 --> 00:44:20,880
'working 24 hours a day to lay out
the entire human code.'

624
00:44:28,240 --> 00:44:32,320
It's amazing to think that
our entire life, you know,

625
00:44:32,320 --> 00:44:34,200
lies in this code.

626
00:44:44,520 --> 00:44:48,360
'And if we want to find out what
makes the human code unique,

627
00:44:48,360 --> 00:44:53,080
'we need to compare our
own recipe with others.'

628
00:44:53,080 --> 00:44:56,880
'The breakthrough that lets us
do this is that as well as the

629
00:44:56,880 --> 00:45:01,520
'human genome, we now have sequenced
the genomes of many other animals.'

630
00:45:05,280 --> 00:45:07,640
'But finding the crucial sections
of code

631
00:45:07,640 --> 00:45:10,440
'that make us human
is a monster puzzle.'

632
00:45:14,600 --> 00:45:18,640
One of the important steps in this
process to try to identify

633
00:45:18,640 --> 00:45:22,680
what, in our genome, in the human
genome, could underly what makes

634
00:45:22,680 --> 00:45:27,160
us human, is to try to find
differences at the base pair level,

635
00:45:27,160 --> 00:45:32,040
in the coding sequences between us,
basically our genome,

636
00:45:32,040 --> 00:45:35,760
and the genome of our closest living
relative at least, the chimpanzee.

637
00:45:44,600 --> 00:45:49,160
'Franck has homed in on one
particular change that is specific

638
00:45:49,160 --> 00:45:53,320
'to humans which he believes
could be fundamental.'

639
00:45:53,320 --> 00:45:58,240
'It involves a gene called SRGAP2
that is found in all animals

640
00:45:58,240 --> 00:46:01,800
'and mainly affects
the developing brain,

641
00:46:01,800 --> 00:46:08,160
'but in humans, and only in humans,
this gene is duplicated four times.'

642
00:46:10,200 --> 00:46:17,320
This gene starts at page 814 and the
very beginning of the sequence

643
00:46:17,320 --> 00:46:22,960
is this sequence, CACAGGAA,
and so the gene starts here.

644
00:46:22,960 --> 00:46:25,120
I can't believe you can
recognise that.

645
00:46:28,040 --> 00:46:32,520
The gene is about 125,000
base pairs long,

646
00:46:32,520 --> 00:46:36,840
so it goes from page 814 to 840.

647
00:46:36,840 --> 00:46:39,320
So that is a single gene,
all of that?

648
00:46:39,320 --> 00:46:41,280
That's a single gene. Exactly.

649
00:46:42,320 --> 00:46:49,000
And the sequence basically ends
right here, TGCTGCGT.

650
00:46:49,000 --> 00:46:55,320
So this is a gene that we
have in common with the other apes,

651
00:46:55,320 --> 00:46:57,960
but we've got three more
copies of it?

652
00:46:57,960 --> 00:47:00,960
Correct. We've got
three more copies of this gene.

653
00:47:00,960 --> 00:47:03,440
That would be in volume 30.

654
00:47:03,440 --> 00:47:07,800
Remember, this is only one
volume for chromosome one.

655
00:47:07,800 --> 00:47:11,400
The full sequence of chromosome one
would take about 50 volumes, right?

656
00:47:11,400 --> 00:47:14,160
So the copies would be
in volume 30, 31, 32.

657
00:47:18,480 --> 00:47:22,000
'What Franck discovered was that the
human duplication of SRGAP2

658
00:47:22,000 --> 00:47:26,360
'has a dramatic effect on the
connectivity of neurons.'

659
00:47:28,000 --> 00:47:32,280
'By splicing the human duplicate
into mouse DNA, he showed that

660
00:47:32,280 --> 00:47:36,480
'the mouse neurons increased their
ability to form connections.'

661
00:47:39,560 --> 00:47:42,240
So this is a normal mouse brain,
and that's what happens

662
00:47:42,240 --> 00:47:46,720
if you put that duplicated
bit of SRGAP2? Exactly.

663
00:47:46,720 --> 00:47:50,280
You form many, many more spines,
basically and we have other evidence

664
00:47:50,280 --> 00:47:54,400
to show that those neurons are
actually hyper-connected there.

665
00:47:54,400 --> 00:47:57,640
You increase by about 40% the
total number of connections

666
00:47:57,640 --> 00:47:59,240
made onto these neurons.

667
00:47:59,240 --> 00:48:01,320
Why is it so exciting?

668
00:48:01,320 --> 00:48:03,800
Basically, humans stand
apart completely.

669
00:48:03,800 --> 00:48:08,240
Human neurons have about 40% to 50%
increase in the total number

670
00:48:08,240 --> 00:48:12,280
of connections made onto those
neurons, which we know is a feature

671
00:48:12,280 --> 00:48:15,760
that sort of distinguishes
human neurons, basically.

672
00:48:15,760 --> 00:48:19,200
For me, this is when genetics gets
really exciting, because we've got

673
00:48:19,200 --> 00:48:22,440
an actual observable difference
in the brains of chimpanzees

674
00:48:22,440 --> 00:48:28,320
versus the brains of humans, and now
we've got something in the genome

675
00:48:28,320 --> 00:48:31,160
which could explain that actual
physical difference in our brains.

676
00:48:31,160 --> 00:48:32,360
Exactly.

677
00:48:44,200 --> 00:48:49,520
'Every nuance of human behaviour
somehow springs from this massive,

678
00:48:49,520 --> 00:48:53,200
'branching network of
hyper-connected neurons

679
00:48:53,200 --> 00:48:55,560
'in our huge brains.'

680
00:48:55,560 --> 00:48:59,040
'It's what makes the human brain
so brilliant,

681
00:48:59,040 --> 00:49:04,880
'this complex wiring diagram of
connections that holds our memories,

682
00:49:04,880 --> 00:49:09,400
'our emotions, our ability
to row a boat or to draw.'

683
00:49:11,760 --> 00:49:13,200
'It's what makes us human.'

684
00:49:16,080 --> 00:49:18,920
'But to even contemplate
drawing this diagram,

685
00:49:18,920 --> 00:49:22,240
'we need a whole new way
of looking.'

686
00:49:34,960 --> 00:49:37,200
'I've come to Harvard University
to meet

687
00:49:37,200 --> 00:49:39,640
'one of the world's foremost
neuroscientists,

688
00:49:39,640 --> 00:49:43,200
'who has set himself a task of
overwhelming ambition.'

689
00:49:47,360 --> 00:49:51,000
'Jeff Lichtman is planning
to create the ultimate map,

690
00:49:51,000 --> 00:49:55,680
'a wiring diagram of the human
brain, one connection at a time.'

691
00:50:01,160 --> 00:50:05,080
'If he can ever complete it,
this monumental map could finally

692
00:50:05,080 --> 00:50:08,200
'reveal the mystifying
workings of the human brain.'

693
00:50:12,120 --> 00:50:15,400
'But before he can begin,
Jeff is first attempting to map

694
00:50:15,400 --> 00:50:18,600
'the connections in the more
modestly-sized mouse brain.'

695
00:50:20,880 --> 00:50:24,600
This is a little plastic block
where the brain is embedded.

696
00:50:24,600 --> 00:50:26,160
That's not a whole mouse
brain in there?

697
00:50:26,160 --> 00:50:28,360
No, it's probably about a quarter
of a mouse brain

698
00:50:28,360 --> 00:50:32,320
so in order to see what's going on,
we have to slice it extremely thin,

699
00:50:32,320 --> 00:50:36,320
so we're slicing these brains
with a diamond knife.

700
00:50:36,320 --> 00:50:39,960
That diamond knife cuts off a
section that's about 30 nanometres

701
00:50:39,960 --> 00:50:44,000
thick, so that's 300 hydrogen atoms.

702
00:50:44,000 --> 00:50:47,640
You know, it's just very small, it's
about a thousandth the thickness

703
00:50:47,640 --> 00:50:52,920
of a human hair, so that you end up
with a very, very, very long tape

704
00:50:52,920 --> 00:50:57,440
that has many, many, many thousands
and thousands of sections on it.

705
00:50:57,440 --> 00:50:59,880
I can just about see the sections
on there actually,

706
00:50:59,880 --> 00:51:01,600
those little rectangles.

707
00:51:01,600 --> 00:51:04,720
Yes, and those sections
are like frames of a movie.

708
00:51:06,240 --> 00:51:10,360
'Every one of those thousands
of wafer-thin sections

709
00:51:10,360 --> 00:51:12,960
'must then be individually scanned.'

710
00:51:12,960 --> 00:51:16,120
So this is actually real time,
this is the images actually

711
00:51:16,120 --> 00:51:19,360
coming in from the electron
microscope here?

712
00:51:19,360 --> 00:51:22,400
At 20 million pixels per second.

713
00:51:22,400 --> 00:51:25,760
This will take 15 minutes,
and then we do the next one,

714
00:51:25,760 --> 00:51:27,680
and we have 10,000 to do
in this data set.

715
00:51:28,680 --> 00:51:29,960
That's three months.

716
00:51:29,960 --> 00:51:32,920
The numbers are just
astronomical, aren't they?

717
00:51:32,920 --> 00:51:36,480
It is like looking at galaxies
and counting stars.

718
00:51:40,280 --> 00:51:45,120
So in three months,
you will have imaged a cube,

719
00:51:45,120 --> 00:51:46,600
a three-dimensional cube,

720
00:51:46,600 --> 00:51:51,840
which actually measures a quarter
of a millimetre in each direction?

721
00:51:51,840 --> 00:51:53,080
That's right, roughly.

722
00:51:53,080 --> 00:51:56,400
In order to image a
millimetre cubed, then,

723
00:51:56,400 --> 00:51:59,120
that would be 16 times.

724
00:51:59,120 --> 00:52:01,520
Yeah, so about four years.

725
00:52:01,520 --> 00:52:04,000
Then how long to image
a whole mouse brain?

726
00:52:04,000 --> 00:52:06,440
You'd have to do
that about a thousand times,

727
00:52:06,440 --> 00:52:09,120
so that's about, what, 4,000 years.

728
00:52:09,120 --> 00:52:12,240
OK, and how long to image
a human brain?

729
00:52:12,240 --> 00:52:14,600
That would be a thousand times
longer, so about...

730
00:52:14,600 --> 00:52:17,080
Four million years!

731
00:52:17,080 --> 00:52:21,160
So not in my lifetime,
at this speed.

732
00:52:21,160 --> 00:52:23,200
Jeff,
you've got to hope it gets quicker.

733
00:52:25,800 --> 00:52:28,840
'A multi-million year timescale
may sound daunting,

734
00:52:28,840 --> 00:52:33,480
'but technology advances,
and already Jeff and his team

735
00:52:33,480 --> 00:52:35,720
'are giving us an incredible glimpse

736
00:52:35,720 --> 00:52:38,200
'into the inner workings
of the brain.'

737
00:52:38,200 --> 00:52:40,680
I've asked one of my colleagues,
Bobby Kestheri,

738
00:52:40,680 --> 00:52:45,280
to hold one of these wafers that
is being imaged really still

739
00:52:45,280 --> 00:52:48,800
so that we can zoom up on here,
and he's very courageous.

740
00:52:48,800 --> 00:52:52,200
He's going to jump into the electron
microscope in a second.

741
00:52:52,200 --> 00:52:54,360
And this is one of those sections.

742
00:52:54,360 --> 00:52:56,440
So that's just like one
of the sections that we saw

743
00:52:56,440 --> 00:52:57,840
coming off the... That's right.

744
00:52:58,960 --> 00:53:03,360
'The images are so detailed they
allow Jeff to zoom in right down

745
00:53:03,360 --> 00:53:06,000
'to the scale of individual
neurons...'

746
00:53:06,000 --> 00:53:09,000
Those big white
circles are nerve cells.

747
00:53:09,000 --> 00:53:12,080
'..revealing, at the smaller scale,
the cross-section

748
00:53:12,080 --> 00:53:16,000
'of the maze of wires
at the heart of the brain.'

749
00:53:16,000 --> 00:53:18,200
As we zoom up more,

750
00:53:18,200 --> 00:53:22,480
we see, finally, an axon making
a synapse onto a dendrite of a cell.

751
00:53:30,200 --> 00:53:35,880
'Jeff can then reassemble the tiny
cube of brain inside a computer,

752
00:53:35,880 --> 00:53:39,120
'piling up the brain slices,
tracking the complex path

753
00:53:39,120 --> 00:53:43,800
'of each neuron with a different
colour and creating a 3-D model

754
00:53:43,800 --> 00:53:46,800
'of the individual wires
that connect the brain.'

755
00:53:48,680 --> 00:53:51,720
'The wires are packed
incredibly densely.'

756
00:53:51,720 --> 00:53:55,800
'This shows the wiring in just
one five-millionth

757
00:53:55,800 --> 00:53:58,600
'of a cubic millimetre of brain.'

758
00:53:58,600 --> 00:54:03,280
So that's the circuitry, that's your
three-dimensional wiring diagram?

759
00:54:03,280 --> 00:54:07,240
It's quite beautiful to look at the
brain this way and to realise

760
00:54:07,240 --> 00:54:11,400
this is an infinitesimally small
piece of a very large brain.

761
00:54:16,640 --> 00:54:19,520
I think for humans trying to
contemplate this,

762
00:54:19,520 --> 00:54:24,400
the difficulty is that it's very
hard for a human brain

763
00:54:24,400 --> 00:54:28,800
to understand the extraordinary
complexity of a human brain.

764
00:54:28,800 --> 00:54:32,320
We think we're really smart and that
we can understand everything,

765
00:54:32,320 --> 00:54:35,680
but, in fact, the machine
we're using to allow us

766
00:54:35,680 --> 00:54:38,360
to understand things
is way more complicated

767
00:54:38,360 --> 00:54:42,400
than the rather simple thoughts
that come out of our minds.

768
00:54:44,760 --> 00:54:49,000
'Our brains are not only large,
they have many more connections

769
00:54:49,000 --> 00:54:50,960
'than the brains of
any other animal.'

770
00:54:52,240 --> 00:54:55,680
'Ultimately, by reaching down
to these individual neurons,

771
00:54:55,680 --> 00:54:58,400
'by mapping the trillions
of connections,

772
00:54:58,400 --> 00:55:03,680
'we may be able to pinpoint exactly
how these hyper-connections

773
00:55:03,680 --> 00:55:08,480
'translate into the psychology
and behaviour of human beings.'

774
00:55:09,760 --> 00:55:15,200
For most animals, their brains
are largely encoded by their genes.

775
00:55:15,200 --> 00:55:18,920
A fruit fly does not have to go
to school to fly

776
00:55:18,920 --> 00:55:21,480
and doesn't even have
to learn how to fly.

777
00:55:21,480 --> 00:55:23,960
It knows how to fly from the get-go.

778
00:55:23,960 --> 00:55:25,960
In humans, it's very hard to know

779
00:55:25,960 --> 00:55:28,120
what kinds of behaviours
we have intrinsically.

780
00:55:28,120 --> 00:55:32,160
Probably coughing, pooping, peeing
and a few other things

781
00:55:32,160 --> 00:55:33,960
we definitely can do, breathing,

782
00:55:33,960 --> 00:55:38,400
but learning how to button your
shirt or read or use the language

783
00:55:38,400 --> 00:55:41,640
you think with, all of that
requires learning.

784
00:55:41,640 --> 00:55:43,440
You're an obligate learner.

785
00:55:43,440 --> 00:55:48,880
It's not an extra, it's an essential
ingredient of being a human being.

786
00:55:48,880 --> 00:55:52,400
So humans have essentially got more
behaviour which is learned

787
00:55:52,400 --> 00:55:56,000
and less behaviour which is
programmed right from the beginning?

788
00:55:56,000 --> 00:56:01,600
Yes, we end up with brains that are
capable of all these amazing things,

789
00:56:01,600 --> 00:56:06,080
but we come into the world seemingly
knowing much less about the world

790
00:56:06,080 --> 00:56:08,200
than almost any other animal.

791
00:56:08,200 --> 00:56:12,280
It takes us a year to walk,
18 years to leave the nest,

792
00:56:12,280 --> 00:56:15,920
and during all that time, humans are
building up information

793
00:56:15,920 --> 00:56:20,080
about how to behave, and the neural
circuits for behaviour

794
00:56:20,080 --> 00:56:24,480
based on experience, rather than
based on genetic information.

795
00:56:24,480 --> 00:56:30,760
A human today, as an adult, is doing
an entirely different set of things

796
00:56:30,760 --> 00:56:33,200
than humans were doing thousands
of years ago,

797
00:56:33,200 --> 00:56:36,240
and any young person will tell
you that their parents seem

798
00:56:36,240 --> 00:56:40,520
old-fashioned and their grandparents
seem positively ancient,

799
00:56:40,520 --> 00:56:42,560
but imagine, you know,
what people were doing

800
00:56:42,560 --> 00:56:45,400
thousands or tens of
thousands of years ago.

801
00:56:45,400 --> 00:56:48,840
It's because humans constantly
evolve in a cultural way,

802
00:56:48,840 --> 00:56:52,480
even though our genetic heritage
has not changed very rapidly.

803
00:56:52,480 --> 00:56:54,680
That's the genius of being
a human being.

804
00:57:15,120 --> 00:57:18,720
I really love
the beauty in Jeff's work,

805
00:57:18,720 --> 00:57:23,840
those fantastic rainbow-coloured
neurons all connected together

806
00:57:23,840 --> 00:57:28,040
in incredibly complex
and dense networks.

807
00:57:28,040 --> 00:57:31,480
And, of course, all those
connections are being made

808
00:57:31,480 --> 00:57:36,520
at the moment inside the brain
of my baby inside my womb...

809
00:57:38,400 --> 00:57:43,640
..and that's an extraordinary
thought in itself, but I think the

810
00:57:43,640 --> 00:57:48,960
point at which he will really start
to become human is the point where

811
00:57:48,960 --> 00:57:52,600
we get that interplay between nature
and nurture,

812
00:57:52,600 --> 00:57:57,040
the process that really carves out
a human mind,

813
00:57:57,040 --> 00:57:59,440
and that starts at birth.

814
00:58:06,080 --> 00:58:10,080
'And here he is,
my beautiful baby boy.'

815
00:58:10,080 --> 00:58:14,520
'He's very, very new,
and he's certainly very helpless.'

816
00:58:16,000 --> 00:58:17,520
'He's also got a big head.'

817
00:58:20,520 --> 00:58:25,520
'He is full of potential,
having emerged into the world,

818
00:58:25,520 --> 00:58:29,120
'and he's ready to
learn to become a human being.'

819
00:58:59,960 --> 00:59:02,880
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