0:00:09 > 0:00:11I'm Alice Roberts.
0:00:11 > 0:00:14I'm expecting my second child in a few months
0:00:14 > 0:00:18and I'm having a day out to visit some relatives.
0:00:24 > 0:00:25Hello, hello.
0:00:26 > 0:00:27Do you want this grape?
0:00:29 > 0:00:31This is Le Puri.
0:00:33 > 0:00:36She's a baby bonobo, or pygmy chimpanzee.
0:00:38 > 0:00:43And of all animals alive today, she's one of my closest relatives.
0:00:45 > 0:00:47Well, this is bringing out all the maternal instincts in me.
0:00:49 > 0:00:50Oh, hello, Le Puri!
0:00:53 > 0:00:57Le Puri may be cute, but having reached the grand old
0:00:57 > 0:01:01age of one, she's much more developed than a one-year-old human.
0:01:02 > 0:01:08She and I share 99% of our DNA and yet from the moment of birth,
0:01:08 > 0:01:11our lives are so very different.
0:01:14 > 0:01:17When my baby is born it will take him a year to even walk,
0:01:17 > 0:01:23and yet with time, as a human, his life will develop a richness
0:01:23 > 0:01:26far beyond that of our hairy ape cousins.
0:01:28 > 0:01:31So what is it about our bodies, our genes
0:01:31 > 0:01:34and ultimately our brains that sets us apart?
0:01:36 > 0:01:38What is it that truly makes us human?
0:01:57 > 0:02:00I've come somewhere I've long been keen to visit,
0:02:00 > 0:02:05the great ape enclosure at the Max Planck Institute at Leipzig Zoo,
0:02:05 > 0:02:09one of the biggest collections of great apes on the planet.
0:02:22 > 0:02:25As well as humans, the family of great apes is made
0:02:25 > 0:02:30up of gorillas, orangutans, chimpanzees and bonobos.
0:02:35 > 0:02:38It's really lovely watching the little ones with the adults
0:02:38 > 0:02:41because they're doing what you'd expect a toddler to do.
0:02:43 > 0:02:45They're being annoying.
0:02:45 > 0:02:48They're kind of going up and tickling the adults
0:02:48 > 0:02:50and they've got this mischievous look in their eyes.
0:02:55 > 0:02:58These apes are our closest living relatives.
0:03:03 > 0:03:06And I'm here to find out what makes this particular ape,
0:03:06 > 0:03:10the human one, different to all the others.
0:03:13 > 0:03:16Very difficult to sketch them, really.
0:03:16 > 0:03:19They stay still for a minute and then they're off again.
0:03:22 > 0:03:24For me, as an anatomist,
0:03:24 > 0:03:28the first thing to do is to look at the differences between our bodies.
0:03:29 > 0:03:31Gorillas are the largest of the great apes
0:03:31 > 0:03:34and looking at the massive silverback right
0:03:34 > 0:03:37at the back of the enclosure there, he really is enormous.
0:03:37 > 0:03:38He's magnificent.
0:03:40 > 0:03:43They're sitting quite nicely still so you can get a real appreciation
0:03:43 > 0:03:48of the similarities and differences between their anatomy and ours.
0:03:48 > 0:03:52There's an awful lot about them which is very similar, in fact.
0:03:52 > 0:03:55So if you look at the construction of the arms
0:03:55 > 0:03:57and the legs, you've got all the same bones there.
0:03:59 > 0:04:02But they are different shapes and different proportions,
0:04:02 > 0:04:05so you can see that the arms are very long compared with the legs.
0:04:05 > 0:04:08They've got very short legs compared with the rest of their bodies.
0:04:08 > 0:04:11We've got very long legs, ridiculously long legs for an ape.
0:04:14 > 0:04:18These differences relate to how we move around.
0:04:18 > 0:04:22Whereas gorillas and other apes knuckle-walk on all fours,
0:04:22 > 0:04:28we humans, uniquely, habitually walk around upright, on two legs.
0:04:33 > 0:04:36And there's another obvious difference that becomes
0:04:36 > 0:04:39apparent when you start drawing heads.
0:04:39 > 0:04:41It's quite difficult sketching them.
0:04:41 > 0:04:44I find the faces particularly difficult because you've got
0:04:44 > 0:04:47such an idea in your head of what a human face looks like, and you
0:04:47 > 0:04:51have to forget that entirely when you're sketching these apes, because
0:04:51 > 0:04:55the proportions of their faces are entirely different from ours.
0:04:55 > 0:04:56If you look at a human head,
0:04:56 > 0:05:00the eyes are quite low on the head, perhaps about halfway down
0:05:00 > 0:05:02if we measure from the top of the head to the chin.
0:05:03 > 0:05:06If you look at a gorilla head, the eyes are right up on the top
0:05:06 > 0:05:09because their brain case is so much smaller than ours.
0:05:09 > 0:05:11They don't have this massive forehead
0:05:11 > 0:05:13and a massive brain inside it.
0:05:16 > 0:05:20We've long known that these two features, big brains
0:05:20 > 0:05:25and upright walking, really are hallmarks of humans.
0:05:28 > 0:05:34And somehow these big brains must explain the vast gulf that we see
0:05:34 > 0:05:39between ourselves and our closest ape relatives, the chimpanzees.
0:05:43 > 0:05:44Of all the great apes,
0:05:44 > 0:05:47these are the ones to which we're most closely related.
0:05:49 > 0:05:53And the amazing thing is that we now know from studies
0:05:53 > 0:05:59of DNA, our DNA, theirs, and that of other apes, that, in fact, we are
0:05:59 > 0:06:04more closely related to chimpanzees than either of us is to gorillas.
0:06:04 > 0:06:05It's extraordinary.
0:06:05 > 0:06:12There's this close-knit family of us, common chimpanzees and bonobos.
0:06:12 > 0:06:15I think that says something really important about our place
0:06:15 > 0:06:18in this primate family tree and it makes it even more
0:06:18 > 0:06:23extraordinary that our lives are so different to theirs.
0:06:27 > 0:06:31So what exactly has changed in the six million years
0:06:31 > 0:06:34since we shared a common ancestor?
0:06:35 > 0:06:38We certainly have bigger brains
0:06:38 > 0:06:44and we think we're more intelligent, but chimps are full of surprises.
0:06:49 > 0:06:53The Max Planck Institute is at the forefront of some ground-breaking
0:06:53 > 0:06:57work, comparing intelligence in humans and in chimps.
0:07:01 > 0:07:03For the past nine years,
0:07:03 > 0:07:07Michael Tomasello has been closely studying this troop.
0:07:07 > 0:07:10So she did something which I think in human society
0:07:10 > 0:07:11would be considered rather odd.
0:07:11 > 0:07:14She came along and presented her bottom to you.
0:07:14 > 0:07:16So is that a kind of friendly sign?
0:07:16 > 0:07:18- It's a kind of a friendly greeting. - Right, OK.
0:07:21 > 0:07:24A little friendlier than we might normally do in human society.
0:07:24 > 0:07:25You see, there are these similarities,
0:07:25 > 0:07:28but there are some quite important differences as well.
0:07:28 > 0:07:30Exactly so.
0:07:30 > 0:07:34'And his work on ape intelligence is casting a fascinating new
0:07:34 > 0:07:38'light on what it means to be human.'
0:07:38 > 0:07:40And when you first started doing this work,
0:07:40 > 0:07:42were you surprised?
0:07:42 > 0:07:45Did you, did you find that they were more or less intelligent
0:07:45 > 0:07:47than you expected them to be?
0:07:47 > 0:07:51Well, that's the great part, is that they were, in some ways,
0:07:51 > 0:07:55more intelligent and in other ways maybe a little less so.
0:07:55 > 0:07:58They will do some things that will just absolutely surprise you
0:07:58 > 0:08:01and you just can't believe they're so clever, and then they'll
0:08:01 > 0:08:05just turn around and do something that's just kind of thick.
0:08:08 > 0:08:12We like to think we're the most intelligent species on the planet,
0:08:12 > 0:08:16but we have to be careful about what exactly we mean by intelligence.
0:08:18 > 0:08:21The first thing we have to get rid of in thinking about animal intelligence
0:08:21 > 0:08:24is the idea that there's this ladder of intelligence
0:08:24 > 0:08:27that goes from low to high, and animals can just be placed on it.
0:08:27 > 0:08:29It's actually much more complicated than that.
0:08:29 > 0:08:33Different animals have different intelligences, as it were.
0:08:33 > 0:08:36So the best memorisers in the world are squirrels
0:08:36 > 0:08:41and birds that hide their nuts in different locations and can remember
0:08:41 > 0:08:44dozens and dozens and dozens of locations, more than we can.
0:08:44 > 0:08:48Oh, I was going to say, so when you say best memorisers in the world, that includes us?
0:08:48 > 0:08:50That includes us. Absolutely.
0:08:50 > 0:08:54In the case of apes, what we think is that they're especially
0:08:54 > 0:08:57good at cognising things about the physical world
0:08:57 > 0:09:02and understanding space, and causal relations like when using tools,
0:09:02 > 0:09:05what causes something to move and whatever.
0:09:05 > 0:09:07They're very good at that and basically they're not
0:09:07 > 0:09:10different from human children in that kind of understanding.
0:09:13 > 0:09:14So here's this task.
0:09:14 > 0:09:17I put a little peanut, this is for you, this is your reward
0:09:17 > 0:09:19and I just put it in here.
0:09:20 > 0:09:24'And to show me just how intelligent chimps can be,
0:09:24 > 0:09:27'Michael's colleague, Daniel Hannus, has invited me to try my hand
0:09:27 > 0:09:31'at solving a problem that they regularly give to chimpanzees.'
0:09:33 > 0:09:36You just do whatever you want to retrieve the peanut.
0:09:36 > 0:09:39'My task is to get the peanut out of the tube
0:09:39 > 0:09:41'using anything that comes to hand.'
0:09:43 > 0:09:49I wonder if I could use the chain somehow, and the teaspoon.
0:09:49 > 0:09:52That's going to be really difficult, I think.
0:10:01 > 0:10:04Slightly worried I'm going to lose the teaspoon as well.
0:10:05 > 0:10:07You'll never get it out again.
0:10:07 > 0:10:09I don't think that's the right thing to do.
0:10:14 > 0:10:16It may take me a while to figure it out,
0:10:16 > 0:10:19but the key to this puzzle is something that you might
0:10:19 > 0:10:25think chimps don't have, the ability to use a bit of lateral thinking.
0:10:25 > 0:10:26Am I allowed to use my water?
0:10:26 > 0:10:28Whatever you want.
0:10:28 > 0:10:31- Any idea you have, you could just try it out.- OK.
0:10:39 > 0:10:41Yes! Here it comes.
0:10:46 > 0:10:48Yeah, wow!
0:10:49 > 0:10:50Excellent.
0:10:53 > 0:10:57It took me more than four minutes to get my peanut,
0:10:57 > 0:11:01so now let's see how a chimpanzee manages.
0:11:03 > 0:11:06Oh, here they come, so Daniel's just trying to get them
0:11:06 > 0:11:10interested in the peanut and they're going to have to do exactly
0:11:10 > 0:11:11the same test that I just did.
0:11:18 > 0:11:20Oh, look, he's doing it.
0:11:20 > 0:11:23It's just really clever, it really is,
0:11:23 > 0:11:24watching this chimp doing that.
0:11:27 > 0:11:29And he doesn't have a bottle of water like I had.
0:11:29 > 0:11:32He's got to think about how to get the water in there.
0:11:34 > 0:11:37He takes some from his drinking bottle into his mouth
0:11:37 > 0:11:39and then he spits it out in the tube.
0:11:39 > 0:11:40He hasn't quite done enough.
0:11:42 > 0:11:44Can he reach it yet?
0:11:49 > 0:11:52There's another mouthful of water gone in and, oh, it's just,
0:11:52 > 0:11:53it's almost there.
0:11:53 > 0:11:54It must be so frustrating.
0:11:55 > 0:11:57Oh!
0:11:57 > 0:11:59- Yeah! - He's done it, he's done it.
0:12:02 > 0:12:03You clever chimpanzee.
0:12:04 > 0:12:06I think that was quicker than me.
0:12:07 > 0:12:09Twice as quick, in fact.
0:12:10 > 0:12:13But although this chimp has done it before, even when presented with
0:12:13 > 0:12:18the task for the first time, many of the apes here figured out that water
0:12:18 > 0:12:24could be used not only to drink, but also as a tool to make peanuts move.
0:12:24 > 0:12:28At certain tasks, chimps are cleverer than you might think.
0:12:30 > 0:12:32And what excites me is that Mike
0:12:32 > 0:12:36and his team are now homing in on the specific aspects of human
0:12:36 > 0:12:41intelligence and behaviour that set us apart from our hairy cousins.
0:12:43 > 0:12:46What makes us really different is our ability to put our heads
0:12:46 > 0:12:50together and to do things that neither one of us could do alone,
0:12:50 > 0:12:53to create new resources that neither one of us could create alone.
0:12:53 > 0:12:57It's really all about communicating and collaborating
0:12:57 > 0:12:58and working together.
0:12:58 > 0:13:02But you think there's some kind of add-on effect then of teaching
0:13:02 > 0:13:04and of being in a society,
0:13:04 > 0:13:08in a culture which kind of builds on those innate abilities?
0:13:08 > 0:13:09It makes all the difference.
0:13:09 > 0:13:13If you raised a child on a desert island with no social contact
0:13:13 > 0:13:19so no teaching, no contact with humans, their intelligence
0:13:19 > 0:13:22as an adult would be very similar to that of other apes.
0:13:22 > 0:13:23It would be a little bit different,
0:13:23 > 0:13:26but they're evolved to learn from others
0:13:26 > 0:13:28and to communicate with others and to collaborate with others,
0:13:28 > 0:13:32and if there was no-one there and no culture and no tools and no
0:13:32 > 0:13:36language, then that natural human intelligence just wouldn't develop.
0:13:36 > 0:13:39Fish are born expecting water, OK?
0:13:40 > 0:13:43They've got fins, they've got gills, they're born expecting water
0:13:43 > 0:13:45and humans are born expecting culture.
0:13:53 > 0:13:58At the heart of being a human then is our culture,
0:13:58 > 0:14:01and something that goes hand in hand with human culture
0:14:01 > 0:14:06is our ability to co-operate, and Michael has devised an experiment
0:14:06 > 0:14:11that he believes reveals a specific piece of behaviour that separates
0:14:11 > 0:14:16us from chimps, that defines us a species, and truly makes us human.
0:14:19 > 0:14:22So what's this test designed to look at then?
0:14:22 > 0:14:26OK, this is a test of being able to collaborate or co-operate
0:14:26 > 0:14:32by pulling in on a rope such that they each get their reward.
0:14:32 > 0:14:36The rope is strong through these hooks, so that
0:14:36 > 0:14:40if anyone individual pulls, it'll just pull the rope out loosely.
0:14:40 > 0:14:41Ah, right.
0:14:41 > 0:14:45And so you have to pull together in order to get the food.
0:14:49 > 0:14:52- So now they each have their rope. - I see. So that's a moveable plank?
0:14:52 > 0:14:53It's a moveable plank.
0:14:53 > 0:14:56- With their pieces of banana, which is their reward.- Exactly.
0:14:56 > 0:14:58- So they have to pull together? - And they have to pull together.
0:14:58 > 0:15:01If any one of them pulls alone, they just pull it out.
0:15:03 > 0:15:06So now it's tightened up and they're ready to actually make it move,
0:15:06 > 0:15:09but they have to be sensitive to what the other one is doing.
0:15:09 > 0:15:12- Notice there was actually a look to the other?- Yeah, this is amazing.
0:15:12 > 0:15:15OK, and they both pull it in and get their rewards.
0:15:18 > 0:15:20These are two of our best at doing this.
0:15:20 > 0:15:22- That is stunning. - They are very good.
0:15:22 > 0:15:25Proper, proper co-operation. It's brilliant.
0:15:27 > 0:15:32But co-operation in the chimp world is a fragile thing.
0:15:32 > 0:15:37What happens if something goes wrong and one chimp gets her reward first?
0:15:37 > 0:15:39- This one has tangled her rope. - Oh!
0:15:41 > 0:15:42She can't quite reach it.
0:15:42 > 0:15:45And now she can't do it, as long as this one's let go.
0:15:45 > 0:15:47You can now see the rope coming out.
0:15:47 > 0:15:51- She's frustrated because they didn't pull exactly synchronously.- Yeah.
0:15:55 > 0:15:58So she's got her reward. She's happy now, she's gone.
0:15:58 > 0:16:01And then her poor partner is left without a reward.
0:16:03 > 0:16:08For our closest relatives, clever as they are, that's as far as it goes.
0:16:08 > 0:16:12Chimps will co-operate, but only for selfish ends.
0:16:27 > 0:16:30But the experiments get really interesting
0:16:30 > 0:16:33when you start testing humans.
0:16:33 > 0:16:38Michael has been comparing how young children perform in the same task.
0:16:41 > 0:16:44This is a very similar test to the test that the chimpanzees
0:16:44 > 0:16:46were doing with the bananas.
0:16:46 > 0:16:49Yes, it's the same basic idea, same basic idea.
0:16:50 > 0:16:54'Like the chimps, the kids have to collaborate by pulling
0:16:54 > 0:16:57'on a string at the same time to release the marbles.
0:17:04 > 0:17:07'And just like the chimps, they have no problem co-operating.'
0:17:11 > 0:17:14'Instead of a piece of banana, their reward is
0:17:14 > 0:17:19'the satisfaction of placing a marble in the plinck machine.'
0:17:19 > 0:17:23THEY SPEAK GERMAN
0:17:27 > 0:17:29'The experiment can be set up
0:17:29 > 0:17:34'so that the children receive either an equal or an unequal reward.'
0:17:34 > 0:17:38THEY SPEAK GERMAN
0:17:40 > 0:17:42So, Mike, what's the idea of this test?
0:17:42 > 0:17:45They have to work together to get the reward?
0:17:45 > 0:17:48Yeah, so the idea of this test is that kids are not that
0:17:48 > 0:17:53naturally generous with their own things, and so if they just
0:17:53 > 0:17:56have some things and you tell them they can share, maybe they will,
0:17:56 > 0:18:01maybe they won't, but when they work together and they generate together
0:18:01 > 0:18:05these rewards, they have a tendency to want them to be equally split.
0:18:12 > 0:18:13Here they come.
0:18:18 > 0:18:20So she's setting it up...
0:18:22 > 0:18:26..but this time making sure it's going to be an uneven distribution?
0:18:27 > 0:18:32Yes. One of them's going to get more than the other and we'll see
0:18:32 > 0:18:35if they need to even it out before they cash in their rewards.
0:18:43 > 0:18:44Pulling.
0:18:49 > 0:18:51Ah, so there's uneven rewards, no?
0:18:55 > 0:18:57This little girl's got one and that one's got three.
0:19:00 > 0:19:01Are they sharing?
0:19:03 > 0:19:04Let's see.
0:19:08 > 0:19:09They shared them out.
0:19:09 > 0:19:10Yes, they shared them out.
0:19:13 > 0:19:15So they ended up with two each, yep.
0:19:19 > 0:19:20Isn't that interesting?
0:19:22 > 0:19:23That was quite extraordinary,
0:19:23 > 0:19:26because I wouldn't have naturally thought that kids of this age,
0:19:26 > 0:19:29two-year-olds, three-year-olds, would be that into sharing.
0:19:29 > 0:19:32It's only when they work together for it.
0:19:34 > 0:19:35That's just fascinating.
0:19:39 > 0:19:44'In these experiments, Mike and his team have uncovered a seemingly
0:19:44 > 0:19:48'small but crucial difference between us and chimpanzees.'
0:19:48 > 0:19:49OK, here they come.
0:19:51 > 0:19:55'Human children do something that no other ape will do.'
0:20:01 > 0:20:03- He rolls one over to him. - He's rolled one over.- Yeah.
0:20:10 > 0:20:15'In that small act of sharing, they reveal something that really does
0:20:15 > 0:20:17'lie at the heart of what it is to be human.'
0:20:19 > 0:20:25'It's a tiny but profound difference between us and the other apes,
0:20:25 > 0:20:30'and it's a way of thinking that underpins our ability
0:20:30 > 0:20:33'to co-operate and create human culture.'
0:20:39 > 0:20:44Somehow these huge brains that we've got encapsulate the main differences
0:20:44 > 0:20:47between ourselves and our closest cousins,
0:20:47 > 0:20:49because look at these chimpanzees.
0:20:49 > 0:20:52They're naked and hairy, they're not wearing clothes,
0:20:52 > 0:20:56they're not talking about me, they're not sketching me.
0:20:56 > 0:20:59So there are some really massive differences between us and them
0:20:59 > 0:21:03which must come down, in some ways, to what is going on
0:21:03 > 0:21:06inside this huge organ in our heads.
0:21:21 > 0:21:25'With just a few months left until I'm due to give birth,
0:21:25 > 0:21:29'I'm off for a scan to see how my new baby is getting along.'
0:21:32 > 0:21:36- So shall I just lie back on here, then, Chrissie?- Yes.
0:21:38 > 0:21:40- Right, this is some cold jelly. - Yeah.
0:21:44 > 0:21:46So I'll just have a little look around first of all.
0:22:04 > 0:22:09'It is an emotional experience seeing my baby growing inside me.'
0:22:11 > 0:22:13- That's the head. - That's the head, yeah.
0:22:15 > 0:22:16There's the heart beating.
0:22:16 > 0:22:17Oh, that's wonderful.
0:22:21 > 0:22:22That is my baby.
0:22:27 > 0:22:28Look at that.
0:22:28 > 0:22:33That is my baby inside my womb.
0:22:36 > 0:22:38And looking at him, he's obviously small now.
0:22:38 > 0:22:42He's only six months of gestation,
0:22:42 > 0:22:44so he's got another few months to go,
0:22:44 > 0:22:49but he looks like a perfect but small little baby at this point,
0:22:49 > 0:22:50so everything is there.
0:22:50 > 0:22:53He's got his fingers in place, his toes in place, and it is just
0:22:53 > 0:22:58amazing that all of that has come from a single fertilised egg.
0:22:58 > 0:22:59It never fails to amaze me.
0:22:59 > 0:23:03I mean, that's just extraordinary that the whole complexity
0:23:03 > 0:23:06of the human body comes from that,
0:23:06 > 0:23:11that single cell with genes from me and genes from my husband,
0:23:11 > 0:23:14and that somehow, at the end of it, you end up with a human.
0:23:16 > 0:23:20'But as well as being an expectant mother, I'm also an anatomist,
0:23:20 > 0:23:26'so looking at the scan I can't help but be fascinated by the structures
0:23:26 > 0:23:30'I can already see inside this brand new human of mine.'
0:23:30 > 0:23:34So if we come back to looking at the head now...
0:23:34 > 0:23:37You can almost see structures inside the brain, can't you? That's amazing.
0:23:37 > 0:23:39You can. This is the cerebellum.
0:23:41 > 0:23:44- Do you see this sort of dumbbell shape here?- Yeah, yeah.
0:23:44 > 0:23:47And this dark area here is the...
0:23:47 > 0:23:49Yeah, so that's the back of the lateral ventricle, isn't it?
0:23:49 > 0:23:54- That's right, that's the posterior ventricle there.- That's amazing.
0:23:54 > 0:23:58'After just six months, my baby's brain is already more than half
0:23:58 > 0:24:02'the size of an adult chimpanzee's and it's still growing fast.'
0:24:06 > 0:24:08How big is the head at the moment, Chrissie?
0:24:08 > 0:24:09Well, shall we measure it and see?
0:24:11 > 0:24:14So it says gestation just over 27 weeks,
0:24:14 > 0:24:20and the head circumference is 25.6 centimetres.
0:24:20 > 0:24:22What's the diameter?
0:24:22 > 0:24:24The diameter, BPD 7.2 centimetres.
0:24:24 > 0:24:277.2, so it's going to get a little bit bigger.
0:24:27 > 0:24:29Rather, yeah.
0:24:29 > 0:24:30Oh, dear.
0:24:30 > 0:24:32That's kind of big enough, I think.
0:24:36 > 0:24:39'That growing head can't fail to remind me
0:24:39 > 0:24:42'of something that's getting closer by the day.'
0:24:42 > 0:24:46'Something that's particularly tricky for us humans.'
0:24:46 > 0:24:47'Birth.'
0:24:50 > 0:24:52'The enormous size of our brains,
0:24:52 > 0:24:55'together with another uniquely human trait,
0:24:55 > 0:24:58'our strange way of walking around on two legs,
0:24:58 > 0:25:03'conspire to make human birth something of a squeeze,
0:25:03 > 0:25:05'as any mother with tell you.'
0:25:07 > 0:25:09WOMAN SCREAMS
0:25:09 > 0:25:10And again.
0:25:10 > 0:25:12Push, that's it, push.
0:25:12 > 0:25:15WOMAN SCREAMS
0:25:24 > 0:25:28It's quite strange being on a maternity ward and thinking that
0:25:28 > 0:25:33I'm going to be back in a place like this in just two months' time,
0:25:33 > 0:25:37ready for the appearance of my own little baby into the world.
0:25:37 > 0:25:42I think it brings it home that human childbirth is really something
0:25:42 > 0:25:47quite special, quite unique, even, amongst all other animals.
0:25:50 > 0:25:53'By way of comparison, take a look at this,
0:25:53 > 0:25:57'some rare film of a chimpanzee birth taken at Leipzig Zoo.'
0:26:02 > 0:26:06'What's remarkable is just how quick and easy it is,
0:26:06 > 0:26:10'certainly when compared with the rather more drawn-out
0:26:10 > 0:26:13'and painful business of a human birth.'
0:26:13 > 0:26:15WOMAN SCREAMS
0:26:15 > 0:26:16Push harder, come on.
0:26:27 > 0:26:30What I've drawn is essentially the anatomy of childbirth.
0:26:32 > 0:26:33This is a human, female pelvis.
0:26:33 > 0:26:36We're looking down on it from above, we're looking through
0:26:36 > 0:26:39the birth canal and this is the baby's head
0:26:39 > 0:26:41passing through that birth canal,
0:26:41 > 0:26:45and you can see why childbirth is such a difficult process.
0:26:45 > 0:26:48The birth canal is about ten centimetres in diameter,
0:26:48 > 0:26:52the baby's head is about nine centimetres in diameter.
0:26:52 > 0:26:55Now it's always been thought that there are constraints on the width
0:26:55 > 0:26:59of the pelvis, which are all about walking on two legs,
0:26:59 > 0:27:03that we can't actually push the hips any further apart
0:27:03 > 0:27:06because that would make walking inefficient, and so that means,
0:27:06 > 0:27:09for our big-brained babies,
0:27:09 > 0:27:11they couldn't actually stay in the womb any longer,
0:27:11 > 0:27:16because their heads would be too big to fit out through this birth canal.
0:27:16 > 0:27:19And so our babies are born
0:27:19 > 0:27:22at a relatively early stage of development.
0:27:22 > 0:27:24Our new born babies are helpless.
0:27:29 > 0:27:32'And that is one of the most puzzling paradoxes
0:27:32 > 0:27:34'about being human.'
0:27:34 > 0:27:38'For all our brilliance as a species, compared with other apes,
0:27:38 > 0:27:43'our babies come into the world a bit useless.'
0:27:46 > 0:27:50'For decades, we've assumed that our helpless babies are an unfortunate
0:27:50 > 0:27:55'consequence of walking upright and having big brains.'
0:27:55 > 0:27:58'It's called the obstetric dilemma.'
0:27:58 > 0:28:00'It's in all the textbooks.'
0:28:00 > 0:28:02'It's what I was taught at university
0:28:02 > 0:28:05'and it's what I've gone on to teach others.'
0:28:05 > 0:28:08'The female pelvis is struggling to do two different jobs,
0:28:08 > 0:28:11'and we're stuck with these helpless babies.'
0:28:22 > 0:28:26'If we could explain this dilemma, we'd start to open the door
0:28:26 > 0:28:29'to a treasure trove of insights about being human...'
0:28:31 > 0:28:34'..and there's some science emerging from the east coast of America
0:28:34 > 0:28:39'that's shaking up the traditional view of women's hips.'
0:28:42 > 0:28:45'Dr Holly Dunsworth decided that the female pelvis
0:28:45 > 0:28:48'deserved a closer examination.'
0:28:49 > 0:28:53It does seem peculiar, I mean, it really does mark us out amongst
0:28:53 > 0:28:58all the other apes that childbirth for humans is...is difficult.
0:28:58 > 0:29:01It's much more difficult than it is in chimpanzees and gorillas.
0:29:01 > 0:29:03I know this from personal experience,
0:29:03 > 0:29:08so what is it about our evolution that sets up this problem?
0:29:10 > 0:29:14It's a dilemma. We have a tight fit.
0:29:14 > 0:29:17We've got these two exceptional conditions.
0:29:17 > 0:29:20We've got this funny way of getting around that we're doing right now,
0:29:20 > 0:29:24and we've got these huge brains on top of our heads,
0:29:24 > 0:29:28and natural selection acting on those two things
0:29:28 > 0:29:33has come together and created this very difficult childbirth.
0:29:33 > 0:29:35So is it a compromise, then?
0:29:35 > 0:29:37The female pelvis is a compromise between something
0:29:37 > 0:29:43that needs to be wide to let a large-brained baby out,
0:29:43 > 0:29:48but needs to be narrow in order to make walking efficient?
0:29:48 > 0:29:49Right, right.
0:29:49 > 0:29:53And that's the obstetric dilemma, and it's unique to humans.
0:29:53 > 0:29:58So the idea is that ideally we'd kind of want to get our pelvis
0:29:58 > 0:30:01a bit wider, but actually, female pelves
0:30:01 > 0:30:03are already making us less efficient
0:30:03 > 0:30:08than men at walking and running, and we can't push it any further?
0:30:08 > 0:30:09Right.
0:30:09 > 0:30:14But as this hypothesis goes, they can't get any wider
0:30:14 > 0:30:18or else women would be even worse at walking and running
0:30:18 > 0:30:21than we already are, and everything would fall to pieces.
0:30:21 > 0:30:23Yeah, that you'd end up kind of waddling along,
0:30:23 > 0:30:25and it would be really inefficient.
0:30:25 > 0:30:27Right. You'd never escape a sabre-toothed cat, you know.
0:30:32 > 0:30:36'What's amazing is that in all these decades, no one has ever thought
0:30:36 > 0:30:41'to question the assumptions that underlie the obstetric dilemma,
0:30:41 > 0:30:44'or the suggestion that women are rubbish at running.'
0:30:46 > 0:30:47'Until now.'
0:30:52 > 0:30:56'Together with her colleagues, Herman Pontzer and Anna Warriner,
0:30:56 > 0:30:59'Holly set about exhaustively testing the assumptions
0:30:59 > 0:31:01'about the female pelvis...'
0:31:02 > 0:31:06'..and she's invited me to Herman's lab in New York to see the results.'
0:31:16 > 0:31:18Awesome, thank you.
0:31:19 > 0:31:21So, Holly, this was part of the original research that you did
0:31:21 > 0:31:24with Herman and Anna, looking at the efficiency
0:31:24 > 0:31:27of running and walking in women and men.
0:31:27 > 0:31:29I saw them starting to do this sort of research,
0:31:29 > 0:31:32and it fit really well with the doubts I was having about
0:31:32 > 0:31:35all of this obstetric dilemma business.
0:31:35 > 0:31:36Yeah, yeah.
0:31:36 > 0:31:41So I'd been thinking about how kind of strange this idea was
0:31:41 > 0:31:44that our pelvis was limiting our gestation length
0:31:44 > 0:31:47and it was sort of, like, you know, an epiphany.
0:31:56 > 0:31:59'The team set out to explore the assumption that women,
0:31:59 > 0:32:02'with our wide hips especially adapted for birth,
0:32:02 > 0:32:05'are less efficient at walking and running than men.'
0:32:07 > 0:32:11'Using a motion capture system and a force plate, Anna devised an
0:32:11 > 0:32:16'experiment to analyse the internal mechanics of hip and leg bones.'
0:32:18 > 0:32:21'Until now it had always been assumed that women's hip muscles,
0:32:21 > 0:32:24'being attached to a wider pelvis,
0:32:24 > 0:32:27'had to work harder than those of men.'
0:32:27 > 0:32:28Go ahead, Lesley.
0:32:29 > 0:32:30And there she comes.
0:32:32 > 0:32:34That's great, isn't it?
0:32:34 > 0:32:36A pair of legs walking about.
0:32:38 > 0:32:43'But what the experiments revealed was that throughout each step,
0:32:43 > 0:32:46'the angle of the pelvis is constantly adjusted
0:32:46 > 0:32:50'to minimise the necessary work.'
0:32:50 > 0:32:54'Women's hips may be wider, but the wobbling makes a key difference.
0:32:56 > 0:32:58As you sort of move through the course of the step,
0:32:58 > 0:33:01she's adjusting her balance and her weight.
0:33:03 > 0:33:05So from this wavering around,
0:33:05 > 0:33:09you start to suspect that it's not going to be so simple
0:33:09 > 0:33:12saying that women have wider pelves and therefore their muscles around
0:33:12 > 0:33:15their hips need to work harder when you're walking and running?
0:33:15 > 0:33:16Yeah, exactly. Exactly right.
0:33:19 > 0:33:21'The result of all these measurements
0:33:21 > 0:33:26'is to show that, for decades, we got it wrong.'
0:33:26 > 0:33:30This is really important because it means that there isn't a constraint
0:33:30 > 0:33:34on how wide the pelvis is in terms of being efficient at bipedalism.
0:33:34 > 0:33:38These data indicate that there is no effect
0:33:38 > 0:33:42of having a pelvis adapted for birth on your efficiency
0:33:42 > 0:33:44during walking or running.
0:33:46 > 0:33:51'The female pelvis is not, it seems, compromised at all,
0:33:51 > 0:33:52'and women, with our wide hips,
0:33:52 > 0:33:55'are just as efficient at walking and running as men.'
0:33:59 > 0:34:04'So why didn't the female pelvis evolve to be even wider, to allow
0:34:04 > 0:34:08'our babies to grow a bit bigger and to be a bit less helpless at birth?'
0:34:11 > 0:34:14'The answer was revealed to me through an experiment
0:34:14 > 0:34:17'that involved me drinking some specially-labelled water
0:34:17 > 0:34:21'and then sending Herman frozen samples of my urine.'
0:34:21 > 0:34:25So, Herman, I recognise these little plastic tubes.
0:34:25 > 0:34:27That's right.
0:34:27 > 0:34:29So we had you drink a small dose of what
0:34:29 > 0:34:31we call doubly-labelled water,
0:34:31 > 0:34:34and then we collected a bunch of urine samples as we have here,
0:34:34 > 0:34:38and we can actually calculate how much carbon dioxide you're producing
0:34:38 > 0:34:40every day, and therefore how many calories your body
0:34:40 > 0:34:41is burning every day.
0:34:41 > 0:34:43It's the gold standard for measuring energy
0:34:43 > 0:34:47expenditure in people during normal life.
0:34:47 > 0:34:50'The length of gestation, it turns out, has nothing to do
0:34:50 > 0:34:55'with the width of the birth canal, but everything to do with energy.'
0:34:55 > 0:34:58So here we have the energy that the foetus is using. This is
0:34:58 > 0:35:02based on data from other studies, and we see it goes up exponentially.
0:35:02 > 0:35:06As the kid gets bigger, it needs more and more and more energy,
0:35:06 > 0:35:08and we take a look at the energy
0:35:08 > 0:35:12that mums actually burn during pregnancy.
0:35:12 > 0:35:16We see it goes up quite quickly at first, but then it levels off.
0:35:16 > 0:35:18It hits a ceiling. You just can't do any more.
0:35:18 > 0:35:21Your body is limited in how much energy it can burn.
0:35:21 > 0:35:23Presumably then it doesn't matter if I were to eat more,
0:35:23 > 0:35:26so if I were to eat a few more hundred calories, it doesn't matter.
0:35:26 > 0:35:28I'm not going to be able to give that to the foetus
0:35:28 > 0:35:30because I can't actually metabolise any quicker.
0:35:30 > 0:35:33That's right. There's a limit to how much energy your body can put through.
0:35:33 > 0:35:35There's a hard limit on that.
0:35:35 > 0:35:37If gestation continued for another month,
0:35:37 > 0:35:38you'd shoot through that ceiling.
0:35:38 > 0:35:40It would be metabolically impossible to do.
0:35:40 > 0:35:43So instead, what you do is, as you approach nine months,
0:35:43 > 0:35:44you give birth.
0:35:44 > 0:35:45Right.
0:35:45 > 0:35:47So we take a look at your data, right?
0:35:47 > 0:35:50We've got you plotted on here. You're right there.
0:35:50 > 0:35:52Ah, right, so...
0:35:52 > 0:35:54So you're about five months in.
0:35:54 > 0:35:58That's exactly... So you could tell how many months pregnant I was
0:35:58 > 0:36:01by looking at this without actually...without me telling you?
0:36:01 > 0:36:03Without you telling me,
0:36:03 > 0:36:05- I could know that you've approached that ceiling.- Yeah.
0:36:05 > 0:36:08You were just about at the maximum energy expenditure
0:36:08 > 0:36:11- that we could expect your body to be able to do.- Yeah.
0:36:11 > 0:36:14It'll get to be unsustainable at just about nine months in,
0:36:14 > 0:36:15and you'll give birth.
0:36:15 > 0:36:16This is fascinating.
0:36:16 > 0:36:21It means that the baby comes out at a moment in time
0:36:21 > 0:36:24when it is just about to start demanding more energy
0:36:24 > 0:36:27from the mother than the mother can possibly give it via the placenta.
0:36:27 > 0:36:28That's right.
0:36:34 > 0:36:39'This research is, I think, really revolutionary.'
0:36:39 > 0:36:43'What it reveals is that however wide our hips became,
0:36:43 > 0:36:49'our babies couldn't stay inside the womb a moment longer than they do.'
0:36:51 > 0:36:54It makes me look at the female pelvis in a new light
0:36:54 > 0:36:57and say, "Well, actually this isn't a design compromise."
0:36:57 > 0:36:59"It works very well."
0:36:59 > 0:37:01But also, it makes me look at those helpless babies
0:37:01 > 0:37:04in a new light as well, because they work well, too.
0:37:04 > 0:37:08- Right.- You know, on the one hand, we say they're coming into the world
0:37:08 > 0:37:12too early, but it works. It works within the context of human society
0:37:12 > 0:37:16because otherwise we wouldn't be here in the numbers that we are.
0:37:16 > 0:37:18We gestate as long as we should for primates of our body size,
0:37:18 > 0:37:20and maybe a little longer.
0:37:20 > 0:37:25We give birth to babies at the right size for primates of our body size,
0:37:25 > 0:37:26or maybe a little larger.
0:37:28 > 0:37:32It's just that once they're born, they have so much more growth
0:37:32 > 0:37:36to experience, particularly in the brain,
0:37:36 > 0:37:38and while we are achieving that growth,
0:37:38 > 0:37:42we also have much more to learn about how to be a human
0:37:42 > 0:37:45than a chimp has to learn about how to be a chimp.
0:38:05 > 0:38:09'It turns out, then, that the very nature of human birth,
0:38:09 > 0:38:13'the fact that I will deliver a seemingly underdeveloped baby,
0:38:13 > 0:38:18'is in fact a key ingredient in my son's path to becoming human.'
0:38:23 > 0:38:28'Our babies may be born helpless, but far from being a dumb idea,
0:38:28 > 0:38:32'it turns out to be one of the smartest moves we ever made...
0:38:34 > 0:38:37'..because in order to develop their full human potential,
0:38:37 > 0:38:43'the brains of our human babies need the stimulation of other humans.'
0:38:54 > 0:39:00'Somehow, the secrets of being human are locked away inside the brain,
0:39:00 > 0:39:05'the most complicated, mysterious object in the universe.'
0:39:07 > 0:39:11'But it's an organ that keeps its secrets wrapped up tight.'
0:39:11 > 0:39:15So this is a brain which has been removed from a skull and you can
0:39:15 > 0:39:18see that it's still got its coverings on it, its meninges,
0:39:18 > 0:39:21so there are several layers of membrane
0:39:21 > 0:39:23around the outside of the brain.
0:39:28 > 0:39:32In order to see the brain, we're going to have to peel this back.
0:39:32 > 0:39:35There we go, it's just going to come away actually.
0:39:41 > 0:39:45I just need to get an edge and then when you've got an edge,
0:39:45 > 0:39:47it peels off quite nicely.
0:39:48 > 0:39:51It's rather like peeling the pith off an orange.
0:39:53 > 0:39:56And once I've cleared this layer away,
0:39:56 > 0:40:00we're starting to see really nicely the texture of the surface
0:40:00 > 0:40:03of the brain, so this is the cerebral cortex that we're starting
0:40:03 > 0:40:07to see here, and you can see how heavily folded it is.
0:40:07 > 0:40:11This is one of the characteristics of a human brain,
0:40:11 > 0:40:13that the cortex is incredibly heavily folded.
0:40:13 > 0:40:16You get the impression that there's a lot of information
0:40:16 > 0:40:18being packed into a small area.
0:40:22 > 0:40:25So that's it, this is the brain, nicely cleaned up.
0:40:27 > 0:40:31And I think that however many times I do this,
0:40:31 > 0:40:36it is utterly extraordinary to be holding in my hands
0:40:36 > 0:40:42the organ that, more than any other part of our body, is us.
0:40:42 > 0:40:47It seems utterly extraordinary that this actually quite
0:40:47 > 0:40:53unprepossessing physical object contains somebody's personality,
0:40:53 > 0:40:58the seat of their emotions, and it was where they experienced the world
0:40:58 > 0:41:01and where they held their memories.
0:41:02 > 0:41:05It is just quite remarkable.
0:41:10 > 0:41:15'Despite several hundred years of probing, exactly how the
0:41:15 > 0:41:20'human brain achieves all that remains shrouded in mystery.'
0:41:20 > 0:41:24'What little we do know only makes it seem all the more extraordinary.'
0:41:26 > 0:41:30'We know that a human brain contains a staggering one hundred billion
0:41:30 > 0:41:36'neurons, but it's not just the number of brain cells that matters.'
0:41:36 > 0:41:40'What makes the human brain so incredible is the huge number
0:41:40 > 0:41:46'of connections between those cells, the vastly complex internal wiring.'
0:41:47 > 0:41:51So, I'm going to start slicing it
0:41:51 > 0:41:53with this incredibly sharp brain knife.
0:41:55 > 0:42:00'Human brains have about 40% more connections between cortical neurons
0:42:00 > 0:42:03'than the brains of other primates.'
0:42:03 > 0:42:09'That's around a hundred trillion connections in every brain.'
0:42:09 > 0:42:11'We know the basic anatomy quite well
0:42:11 > 0:42:15'but if we want to begin to understand this extraordinary level
0:42:15 > 0:42:20'of complexity, we need to look at the brain with a whole new toolkit.'
0:42:47 > 0:42:51'To discover exactly how our human brains came to be
0:42:51 > 0:42:57'so highly connected, I've come to America to find out about the latest
0:42:57 > 0:43:02'research into the human genome, the recipe for making a human.'
0:43:13 > 0:43:16'There are three billion letters in the human genome,
0:43:16 > 0:43:20'stored in the 23 chromosomes that hold this recipe
0:43:20 > 0:43:23'in every cell of our bodies.'
0:43:23 > 0:43:28'Each letter, A, G, C and T, represents one of the four bases,
0:43:28 > 0:43:33'the chemical building blocks, which make up the long strands of DNA.'
0:43:35 > 0:43:38'And for geneticists, like Franck Palleux, these letters hold
0:43:38 > 0:43:43'the clues that could unlock the secrets of the human brain.'
0:43:44 > 0:43:46So this is chromosome one written out?
0:43:46 > 0:43:47Uh-huh.
0:43:51 > 0:43:55- And how much of chromosome one is it?- Just one fiftieth.
0:43:55 > 0:43:57And there's a thousand pages here.
0:43:59 > 0:44:03A thousand pages, 45,000 base pairs per page.
0:44:06 > 0:44:11'The whole genome would fill 670,000 sheets of paper
0:44:11 > 0:44:15'and at this rate, it would take me and Franck more than a week,
0:44:15 > 0:44:20'working 24 hours a day to lay out the entire human code.'
0:44:27 > 0:44:32It's amazing to think that our entire life, you know,
0:44:32 > 0:44:33lies in this code.
0:44:44 > 0:44:47'And if we want to find out what makes the human code unique,
0:44:47 > 0:44:52'we need to compare our own recipe with others.'
0:44:52 > 0:44:56'The breakthrough that lets us do this is that as well as the
0:44:56 > 0:45:01'human genome, we now have sequenced the genomes of many other animals.'
0:45:04 > 0:45:07'But finding the crucial sections of code
0:45:07 > 0:45:10'that make us human is a monster puzzle.'
0:45:14 > 0:45:18One of the important steps in this process to try to identify
0:45:18 > 0:45:22what, in our genome, in the human genome, could underly what makes
0:45:22 > 0:45:26us human, is to try to find differences at the base pair level,
0:45:26 > 0:45:31in the coding sequences between us, basically our genome,
0:45:31 > 0:45:35and the genome of our closest living relative at least, the chimpanzee.
0:45:44 > 0:45:48'Franck has homed in on one particular change that is specific
0:45:48 > 0:45:52'to humans which he believes could be fundamental.'
0:45:52 > 0:45:57'It involves a gene called SRGAP2 that is found in all animals
0:45:57 > 0:46:01'and mainly affects the developing brain,
0:46:01 > 0:46:07'but in humans, and only in humans, this gene is duplicated four times.'
0:46:09 > 0:46:16This gene starts at page 814 and the very beginning of the sequence
0:46:16 > 0:46:22is this sequence, CACAGGAA, and so the gene starts here.
0:46:22 > 0:46:24I can't believe you can recognise that.
0:46:27 > 0:46:32The gene is about 125,000 base pairs long,
0:46:32 > 0:46:36so it goes from page 814 to 840.
0:46:36 > 0:46:38So that is a single gene, all of that?
0:46:38 > 0:46:40That's a single gene. Exactly.
0:46:41 > 0:46:48And the sequence basically ends right here, TGCTGCGT.
0:46:48 > 0:46:54So this is a gene that we have in common with the other apes,
0:46:54 > 0:46:57but we've got three more copies of it?
0:46:57 > 0:47:00Correct. We've got three more copies of this gene.
0:47:00 > 0:47:03That would be in volume 30.
0:47:03 > 0:47:07Remember, this is only one volume for chromosome one.
0:47:07 > 0:47:10The full sequence of chromosome one would take about 50 volumes, right?
0:47:10 > 0:47:13So the copies would be in volume 30, 31, 32.
0:47:18 > 0:47:21'What Franck discovered was that the human duplication of SRGAP2
0:47:21 > 0:47:26'has a dramatic effect on the connectivity of neurons.'
0:47:27 > 0:47:31'By splicing the human duplicate into mouse DNA, he showed that
0:47:31 > 0:47:36'the mouse neurons increased their ability to form connections.'
0:47:39 > 0:47:41So this is a normal mouse brain, and that's what happens
0:47:41 > 0:47:46- if you put that duplicated bit of SRGAP2?- Exactly.
0:47:46 > 0:47:49You form many, many more spines, basically and we have other evidence
0:47:49 > 0:47:54to show that those neurons are actually hyper-connected there.
0:47:54 > 0:47:57You increase by about 40% the total number of connections
0:47:57 > 0:47:58made onto these neurons.
0:47:58 > 0:48:00Why is it so exciting?
0:48:00 > 0:48:03Basically, humans stand apart completely.
0:48:03 > 0:48:07Human neurons have about 40% to 50% increase in the total number
0:48:07 > 0:48:11of connections made onto those neurons, which we know is a feature
0:48:11 > 0:48:15that sort of distinguishes human neurons, basically.
0:48:15 > 0:48:18For me, this is when genetics gets really exciting, because we've got
0:48:18 > 0:48:22an actual observable difference in the brains of chimpanzees
0:48:22 > 0:48:27versus the brains of humans, and now we've got something in the genome
0:48:27 > 0:48:30which could explain that actual physical difference in our brains.
0:48:30 > 0:48:31Exactly.
0:48:43 > 0:48:49'Every nuance of human behaviour somehow springs from this massive,
0:48:49 > 0:48:52'branching network of hyper-connected neurons
0:48:52 > 0:48:55'in our huge brains.'
0:48:55 > 0:48:58'It's what makes the human brain so brilliant,
0:48:58 > 0:49:04'this complex wiring diagram of connections that holds our memories,
0:49:04 > 0:49:09'our emotions, our ability to row a boat or to draw.'
0:49:11 > 0:49:12'It's what makes us human.'
0:49:15 > 0:49:18'But to even contemplate drawing this diagram,
0:49:18 > 0:49:21'we need a whole new way of looking.'
0:49:34 > 0:49:36'I've come to Harvard University to meet
0:49:36 > 0:49:39'one of the world's foremost neuroscientists,
0:49:39 > 0:49:42'who has set himself a task of overwhelming ambition.'
0:49:46 > 0:49:50'Jeff Lichtman is planning to create the ultimate map,
0:49:50 > 0:49:55'a wiring diagram of the human brain, one connection at a time.'
0:50:00 > 0:50:04'If he can ever complete it, this monumental map could finally
0:50:04 > 0:50:07'reveal the mystifying workings of the human brain.'
0:50:11 > 0:50:14'But before he can begin, Jeff is first attempting to map
0:50:14 > 0:50:18'the connections in the more modestly-sized mouse brain.'
0:50:20 > 0:50:24This is a little plastic block where the brain is embedded.
0:50:24 > 0:50:25That's not a whole mouse brain in there?
0:50:25 > 0:50:27No, it's probably about a quarter of a mouse brain
0:50:27 > 0:50:31so in order to see what's going on, we have to slice it extremely thin,
0:50:31 > 0:50:35so we're slicing these brains with a diamond knife.
0:50:35 > 0:50:39That diamond knife cuts off a section that's about 30 nanometres
0:50:39 > 0:50:43thick, so that's 300 hydrogen atoms.
0:50:43 > 0:50:47You know, it's just very small, it's about a thousandth the thickness
0:50:47 > 0:50:52of a human hair, so that you end up with a very, very, very long tape
0:50:52 > 0:50:57that has many, many, many thousands and thousands of sections on it.
0:50:57 > 0:50:59I can just about see the sections on there actually,
0:50:59 > 0:51:01those little rectangles.
0:51:01 > 0:51:04Yes, and those sections are like frames of a movie.
0:51:05 > 0:51:09'Every one of those thousands of wafer-thin sections
0:51:09 > 0:51:12'must then be individually scanned.'
0:51:12 > 0:51:15So this is actually real time, this is the images actually
0:51:15 > 0:51:19coming in from the electron microscope here?
0:51:19 > 0:51:22At 20 million pixels per second.
0:51:22 > 0:51:25This will take 15 minutes, and then we do the next one,
0:51:25 > 0:51:27and we have 10,000 to do in this data set.
0:51:28 > 0:51:29That's three months.
0:51:29 > 0:51:32The numbers are just astronomical, aren't they?
0:51:32 > 0:51:36It is like looking at galaxies and counting stars.
0:51:39 > 0:51:44So in three months, you will have imaged a cube,
0:51:44 > 0:51:46a three-dimensional cube,
0:51:46 > 0:51:51which actually measures a quarter of a millimetre in each direction?
0:51:51 > 0:51:52That's right, roughly.
0:51:52 > 0:51:56In order to image a millimetre cubed, then,
0:51:56 > 0:51:58that would be 16 times.
0:51:58 > 0:52:01Yeah, so about four years.
0:52:01 > 0:52:03Then how long to image a whole mouse brain?
0:52:03 > 0:52:06You'd have to do that about a thousand times,
0:52:06 > 0:52:08so that's about, what, 4,000 years.
0:52:08 > 0:52:11OK, and how long to image a human brain?
0:52:11 > 0:52:14That would be a thousand times longer, so about...
0:52:14 > 0:52:16Four million years!
0:52:16 > 0:52:20So not in my lifetime, at this speed.
0:52:20 > 0:52:22Jeff, you've got to hope it gets quicker.
0:52:25 > 0:52:28'A multi-million year timescale may sound daunting,
0:52:28 > 0:52:32'but technology advances, and already Jeff and his team
0:52:32 > 0:52:35'are giving us an incredible glimpse
0:52:35 > 0:52:37'into the inner workings of the brain.'
0:52:37 > 0:52:40I've asked one of my colleagues, Bobby Kestheri,
0:52:40 > 0:52:44to hold one of these wafers that is being imaged really still
0:52:44 > 0:52:48so that we can zoom up on here, and he's very courageous.
0:52:48 > 0:52:51He's going to jump into the electron microscope in a second.
0:52:51 > 0:52:53And this is one of those sections.
0:52:53 > 0:52:56So that's just like one of the sections that we saw
0:52:56 > 0:52:57- coming off the...- That's right.
0:52:58 > 0:53:02'The images are so detailed they allow Jeff to zoom in right down
0:53:02 > 0:53:05'to the scale of individual neurons...'
0:53:05 > 0:53:08Those big white circles are nerve cells.
0:53:08 > 0:53:11'..revealing, at the smaller scale, the cross-section
0:53:11 > 0:53:15'of the maze of wires at the heart of the brain.'
0:53:15 > 0:53:17As we zoom up more,
0:53:17 > 0:53:22we see, finally, an axon making a synapse onto a dendrite of a cell.
0:53:29 > 0:53:35'Jeff can then reassemble the tiny cube of brain inside a computer,
0:53:35 > 0:53:38'piling up the brain slices, tracking the complex path
0:53:38 > 0:53:43'of each neuron with a different colour and creating a 3-D model
0:53:43 > 0:53:46'of the individual wires that connect the brain.'
0:53:48 > 0:53:51'The wires are packed incredibly densely.'
0:53:51 > 0:53:55'This shows the wiring in just one five-millionth
0:53:55 > 0:53:58'of a cubic millimetre of brain.'
0:53:58 > 0:54:02So that's the circuitry, that's your three-dimensional wiring diagram?
0:54:02 > 0:54:06It's quite beautiful to look at the brain this way and to realise
0:54:06 > 0:54:11this is an infinitesimally small piece of a very large brain.
0:54:16 > 0:54:19I think for humans trying to contemplate this,
0:54:19 > 0:54:24the difficulty is that it's very hard for a human brain
0:54:24 > 0:54:28to understand the extraordinary complexity of a human brain.
0:54:28 > 0:54:31We think we're really smart and that we can understand everything,
0:54:31 > 0:54:35but, in fact, the machine we're using to allow us
0:54:35 > 0:54:37to understand things is way more complicated
0:54:37 > 0:54:42than the rather simple thoughts that come out of our minds.
0:54:44 > 0:54:48'Our brains are not only large, they have many more connections
0:54:48 > 0:54:50'than the brains of any other animal.'
0:54:51 > 0:54:55'Ultimately, by reaching down to these individual neurons,
0:54:55 > 0:54:58'by mapping the trillions of connections,
0:54:58 > 0:55:03'we may be able to pinpoint exactly how these hyper-connections
0:55:03 > 0:55:08'translate into the psychology and behaviour of human beings.'
0:55:09 > 0:55:14For most animals, their brains are largely encoded by their genes.
0:55:14 > 0:55:18A fruit fly does not have to go to school to fly
0:55:18 > 0:55:21and doesn't even have to learn how to fly.
0:55:21 > 0:55:23It knows how to fly from the get-go.
0:55:23 > 0:55:25In humans, it's very hard to know
0:55:25 > 0:55:27what kinds of behaviours we have intrinsically.
0:55:27 > 0:55:31Probably coughing, pooping, peeing and a few other things
0:55:31 > 0:55:33we definitely can do, breathing,
0:55:33 > 0:55:37but learning how to button your shirt or read or use the language
0:55:37 > 0:55:41you think with, all of that requires learning.
0:55:41 > 0:55:43You're an obligate learner.
0:55:43 > 0:55:48It's not an extra, it's an essential ingredient of being a human being.
0:55:48 > 0:55:52So humans have essentially got more behaviour which is learned
0:55:52 > 0:55:55and less behaviour which is programmed right from the beginning?
0:55:55 > 0:56:01Yes, we end up with brains that are capable of all these amazing things,
0:56:01 > 0:56:05but we come into the world seemingly knowing much less about the world
0:56:05 > 0:56:07than almost any other animal.
0:56:07 > 0:56:11It takes us a year to walk, 18 years to leave the nest,
0:56:11 > 0:56:15and during all that time, humans are building up information
0:56:15 > 0:56:19about how to behave, and the neural circuits for behaviour
0:56:19 > 0:56:24based on experience, rather than based on genetic information.
0:56:24 > 0:56:30A human today, as an adult, is doing an entirely different set of things
0:56:30 > 0:56:32than humans were doing thousands of years ago,
0:56:32 > 0:56:35and any young person will tell you that their parents seem
0:56:35 > 0:56:40old-fashioned and their grandparents seem positively ancient,
0:56:40 > 0:56:42but imagine, you know, what people were doing
0:56:42 > 0:56:45thousands or tens of thousands of years ago.
0:56:45 > 0:56:48It's because humans constantly evolve in a cultural way,
0:56:48 > 0:56:52even though our genetic heritage has not changed very rapidly.
0:56:52 > 0:56:54That's the genius of being a human being.
0:57:14 > 0:57:18I really love the beauty in Jeff's work,
0:57:18 > 0:57:23those fantastic rainbow-coloured neurons all connected together
0:57:23 > 0:57:27in incredibly complex and dense networks.
0:57:27 > 0:57:31And, of course, all those connections are being made
0:57:31 > 0:57:36at the moment inside the brain of my baby inside my womb...
0:57:37 > 0:57:43..and that's an extraordinary thought in itself, but I think the
0:57:43 > 0:57:48point at which he will really start to become human is the point where
0:57:48 > 0:57:52we get that interplay between nature and nurture,
0:57:52 > 0:57:56the process that really carves out a human mind,
0:57:56 > 0:57:59and that starts at birth.
0:58:05 > 0:58:09'And here he is, my beautiful baby boy.'
0:58:09 > 0:58:14'He's very, very new, and he's certainly very helpless.'
0:58:15 > 0:58:17'He's also got a big head.'
0:58:20 > 0:58:25'He is full of potential, having emerged into the world,
0:58:25 > 0:58:28'and he's ready to learn to become a human being.'
0:58:59 > 0:59:02Subtitles by Red Bee Media