I'm Jim Al-Khalili, a professor of theoretical physics,
and I'm exploring how the most complex objects
we know of in the universe - our brains - evolved.
This is what your head looks like inside.
JIM LAUGHS
In the last episode, we went from the first neurons
to the early mammal brain.
Wow!
GIBBON SHRIEKS
In this episode, I learn how life in the forests shaped our brains...
..and how our primate ancestors solved problems to survive.
Look how quick! Oh, my word!
With my wife, I investigate how relationships made us intelligent...
You're not a show-off like me.
No, I'm not a show-off like you. Not many people are.
..and how our brains are wired to be social.
The single best predictor
of how long you're going to live into the future,
it's simply the number and quality of close friendships.
As we build artificial intelligence, vying to overtake our brains...
..I want to find out what makes the thing in our skulls so special.
This is my brain,
and this is its 600 million-year story.
66 million years ago, the Earth lay in desolation and darkness.
An asteroid smashed into the surface of the planet...
..soot and ash and vaporised bedrock dimming the sun.
Perhaps three-quarters of all life on Earth was wiped out...
..including the gigantic dinosaurs, which had ruled the world.
But as the Earth slowly recovered, forests returned
and spread across the land.
And with the dinosaurs gone,
small creatures colonised this new habitat.
Among them were our ancestors.
Now, here's the mystery, how did they survive this catastrophe?
Dr Ornella Bertrand studies the extremely limited evidence
that survives from this dark period in the Earth's history.
That is not an easy job.
You've drawn the short straw when it comes to palaeontology, right?
Definitely, because it's very difficult.
There's just not that many fossils.
We find teeth, we find, like, a bit of bone sometimes.
One group that I'm really interested in understanding
is a group called plesiadapiforms.
They were little, like, warm-blooded mammals.
Plesiadapiforms resembled modern shrews.
It's thought they used their sharp claws
to cling onto the branches of trees in the primeval forest.
They're the closest we've found to the predecessors
of all today's primates, including us.
Ornella studies their skulls, but she doesn't have many to work with.
We only have, like, six good specimens so far.
Six specimens in total... In total. ..of these creatures? Yeah, yeah.
So that's very little, but we can learn so much
just from those different skulls.
Ornella has a 3D print of the skull of a specimen
called Ignacius graybullianus, upscaled so we can see the details.
By scanning the cavity inside the skull,
she's been able to produce a cast of the missing brain.
Ta-dah! It's amazing, isn't it? That is incredible.
It gives us, like, so much information about
what actually those animals were able to do.
For example, these structures in front.
I was just going to ask you.
They're funny little knobbly bits at the front. Yes!
We still have that structure, the olfactory bulbs, in humans.
They're olfactory? OK. So that's for smell?
Yeah, yeah, exactly.
Plesiadapiforms had very large smell-processing systems.
Ornella believes they may have scavenged at dusk and at night,
when a strong sense of smell is very useful.
I imagine them being, like, quietly moving among the branches.
That's kind of, yeah, how I see them.
For this documentary, I've had my brain scanned.
I've been carrying around...
..a 3D-printed version of my brain. Wow!
Which is here, which I'm very proud of. I would be. That's amazing!
Which we can put alongside Ignacius.
Look, I'm not boasting - there's been some evolution.
Some... Just a little bit!
SHE CHUCKLES
I'm interested in a particular part of the brain -
the neocortex.
So, here we have the neocortex of Ignacius.
It's very small. It's actually just this part of the brain.
In Ignacius, it covers about 20% of the top of the brain.
That's very different in a human brain, isn't it?
Very, very different. You can see, like, the neocortex in humans
actually is covering the entire rest of the brain.
This is amazing, how big that it got in humans.
A rudimentary neocortex helped early mammals
analyse the world around them and respond to it.
For humans, it's become the seat of advanced thinking,
reasoning and perception.
But the mystery is, why did our neocortex grow so large
compared to any other mammal?
There's a compelling theory and it's to do with climate change.
About 56 million years ago,
greenhouse gases,
released by volcanic activity,
caused sudden global warming
of up to five degrees.
It was the beginning of the Eocene Era -
a time of astonishing changes.
In the hothouse environment of the Eocene,
dense rainforests spread around the world.
They even reached high enough latitudes
to be within what is today the Arctic Circle.
And, as with the rainforests of today, life proliferated.
Just look at these extraordinary fossils, found near Frankfurt
in Germany, dating nearly 50 million years ago.
They give us an incredible insight into the competition
which raged in the forests of the early Eocene.
There were birds and agile, tree-dwelling rodents.
There were highly-dangerous predators, too.
All of this meant fierce competition for food and resources
and, with all these new predators around,
it was much more dangerous, too.
Only those creatures able to adapt would survive.
In these changed circumstances,
simply staying alive would take brains as well as brawn.
As I'm very quickly finding out,
a tree is a tricky place to call home.
It's actually quite difficult, moving around up here.
It doesn't just take physical strength,
you need judgment, you need to decide whether a branch
is strong enough to hold your weight,
whether it's too wobbly, you need to plan a route through the trees.
On top of the physical and mental agility you need,
coping with the incredibly complex visual field
of a canopy of leaves poses yet more problems.
I'm finding it really difficult,
peering through the leaves and twigs and branches.
Keeping an eye out for predators, as well as foraging for food,
must have been a real challenge.
In the face of these evolutionary pressures,
a new kind of creature appears in the fossil record of the Eocene.
They're called crown primates - the forerunners
of all today's primates - including, of course, us.
Is this the way we sit?
Like this?
Early primates were well-adapted to life in the trees.
What's interesting is the way he's grasping the branch.
During the Eocene, primates evolved gripping hands and feet with nails.
They're much more dextrous.
They're able to hold on to this branch.
It also means they can use these hands to find food,
to forage, to manipulate objects much more easily.
The other thing to notice is that they have eyes
at the front of their heads, not on the side.
Animals with eyes on the side of their heads
have a wider field of view and can spot predators better.
But eyes at the front help with what's ahead of you,
judging the distance to the next branch or locating food.
The effect of millions of years of tree-dwelling is clear
when we look at the fossil record.
This is the brain cast of Ignacius, the plesiadapiform
we've already seen clambering around the forest
in the years after the dinosaur extinction.
And this is the brain cast of a primate called Rooneyia.
It evolved around 20 million years after Ignacius.
With Ignacius, the neocortex covered 20% of its brain.
With Rooneyia, it now covers half its brain.
The neocortex analyses visual data...
..and it has many other functions besides.
It works in extraordinarily complex ways,
which we take for granted in our everyday lives.
Take, for instance, what happens inside our brains
when we do something as deceptively simple
as reaching out and grabbing an apple.
It's actually far more complicated than you might think.
I'm getting an extraordinary insight into what's involved
when we reach out and grab something.
Dr David Pitcher at the University of York has carried out
a functional MRI, which measures the way the blood flows in my brain...
OK, Jim, this is going to be an eight-minute scan.
..while he plays me videos of reaching out and grasping an apple.
My colleague, Amelle, is going to put this... Hello. Right.
..on your head.
Then he uploads my results to this machine...
..which uses spatial recognition technology
to guide me around my own brain.
Now where she points to with that pointer... Ah!
This is what your head looks like inside.
JIM LAUGHS Lovely death mask well, isn't it?
Oh, I can rotate that for you as well, so we can see.
DAVID LAUGHS
My scan shows astonishing activity across my cerebral cortex
as I watch the video.
First, David shows me how my visual processing works -
a complex system which really started to develop
with those early primates.
Light hits your eyeball,
that's then converted into neural signalling.
That information is then sent down the optic nerve,
all the way to primary visual cortex,
which, in humans, is right at the back of your head.
As I was looking at the apple, my visual cortex connected
with another part of my brain which helps us recognise objects.
You see this pathway that lights up?
This is the ventral object recognition pathway.
And that pathway leads to the bit of the brain
where I'm storing information of what apples look like? Yeah.
The hard drive of my brain. It's where we store everything, yeah.
Then a second connection activates from the visual cortex
at the back of the brain to the parietal lobe.
The parietal lobe judges where things are in space around us
and where our body is positioned.
But to issue the orders to the body to move,
you need a third part of the neocortex -
the primary motor cortex.
This is your motor cortex,
and there's parts that control all the motor function in your body.
And if Amelle moves the pen down the side of your head,
we're sort of tracking through different parts of the motor cortex.
And where we come to...
..sort of roughly where Amelle is now,
that's roughly where the hand area is.
So that's the... So different parts of the motor cortex
physically relate to different parts of my body? Exactly.
The visual, parietal and motor cortex
all developed in our primate ancestors,
and a new area of the neocortex was also beginning to evolve.
It would become the most sophisticated
cognitive area of our brains.
The other thing you have to do
is be able to plan and control the motor action,
so if Amelle brings the pointer forward a little bit,
is the prefrontal cortex. It's where we do all our thinking,
it's where cognitive control happens - the voice inside your head.
So, just picking up an apple means the visual cortex,
the parietal lobe, the motor cortex, and the prefrontal cortex
all have to work together.
So four different parts of the brain
are all involved in the simple action
of reaching out and picking up an apple -
visual cortex, parietal lobe, motor cortex, frontal cortex.
From 40 million years ago,
the creatures we now call monkeys
were evolving.
Their neocortex was becoming bigger
and more complex in structure.
In today's primates,
the larger the brain,
the denser and more closely packed the neurons,
the more networks they develop, the cleverer they become.
So what were the driving factors
which caused some primates to evolve differently from others?
And why did humans evolve the most intelligence?
One theory has to do with the ability to find the best,
most calorific food, and is something we can study
by looking at two species of modern monkeys side-by-side.
So, this is the viewing deck, and here we can see both species -
the capuchins and the squirrel monkeys.
They're our relatives, but if we study enough
of our primate relatives, we can start to make inferences
about what our ancestors - our primate ancestors -
might have been like.
This is The Living Link Centre at Edinburgh Zoo.
Professor Amanda Seed studies these species side-by-side
to try to understand the story of our own brains.
The capuchin monkeys are our larger monkeys, they're more robust.
They have this characteristic dark colouring on their head
and a little tuft at the front. The squirrel monkeys,
on the other hand, they're smaller, they're more slender.
They look a little bit like they've been dipped in chocolate.
Capuchin monkeys and squirrel monkeys evolved together
in the same place - the forests of the new world,
and yet capuchins have a much larger neocortex
compared to their body size and exhibit greater intelligence.
The question is, why?
And what might that tell us about the evolution of our own brains?
Amanda and her staff have devised a challenge
these monkeys haven't encountered before.
They've hidden food in papier mache boxes.
The challenge is, which species will figure out
that there's food inside and manage to get it?
Straight in. "Thank you very much."
Straight away, the capuchins have come out.
They're very, very curious and their first thought is,
"Can I break it? Is there food inside?"
Meanwhile, the squirrel monkeys hang around on the sides,
and not one of them looks inside a box.
Instead, they wait for the capuchins to finish feasting
and they pick up scraps from their table.
Amanda believes today's test has helped confirm a theory
which links intelligence to diet.
The capuchins rely on fruit to a much greater extent
than the squirrel monkeys. The squirrel monkeys
eat fruit as well, but their diet is largely comprised of insects.
The squirrel monkeys just have to wait for an insect to come along
and grab it, and that happens a lot,
but fruit only appears a few months every year.
It's found around the forest in patches,
in often hard-to-find places.
So, in order to find it, you have to remember and plan ahead.
An ability to map your environment and space,
and even time, to be able to predict when those resources
are going to become available now becomes useful,
and so now we have more selective pressure
for areas of the brain that can deal with that.
The penny's starting to drop for me now, that it's not so much
that they have larger brains, they're smarter, therefore they're
able to figure out things like, you know, how to find food.
The need to look for food has stimulated the growth
of a larger brain over millions of years. Over millions of years.
So it may be that at some point in our evolution,
our ancestors were like the capuchins,
they concentrated more and more on fruit -
high-calorie fuel for growing brains -
but it takes more intelligence to find.
By 25 million years ago,
the first apes were evolving.
Ape brains are generally
larger than monkeys
and they have more complex
structures and networks.
It's now thought that around this time,
our ancestors took their first baby steps
towards one of our most important cognitive abilities -
complex spoken language.
I've come to see something very unexpected,
which might provide a vital clue.
These gorillas live at Port Lympne Safari Park in Kent.
I'm with Professor Gillian Forrester,
who's been studying the primates at this sanctuary for 20 years.
I really like working here at Port Lympne,
because it feels like more of a collaboration with the gorillas.
We work together, but they're in an environment that really suits them.
The enclosure was made for them, not for people to view them. Right.
It's lunchtime, and the gorillas have an unusual treat.
Nettles - which they find very tasty.
They've found a clever strategy to deal with their stinging leaves.
They strip the nettles off the stem in one direction -
a direction which doesn't trigger the spines,
so they don't get stung.
One gorilla decides to literally walk away with her spoils.
"These are mine." Look at her go! Fantastic!
We follow this gorilla to the inside area,
where we catch a glimpse of a more complex form of nettle preparation.
Rolling the leaves into a ball to crush the stinging spines.
This method of preparing nettles has been recorded
in many different gorilla groups.
And you want me to try this, don't you? Yeah.
OK, right, let's see how we go. Let's see.
Ah! Well, OK, there we go.
I was so careful not to get stung, which I think I've survived,
but I've dropped the leaves. Dropped the leaves, yeah.
Not as delicate as you. No, but... But nearly there. Yeah.
I think it's interesting because eating the nettles requires
the gorillas to take certain actions in order to not get stung. OK.
We could think of that as almost like
what we'd call a syntax in language.
When I speak, these are motor action sequences.
So my mouth has to make the right words at the right time
in order for you to understand what I'm saying.
This is a syntax in language,
and this is a syntax in its physical form.
Gillian has created some puzzle boards,
which require an understanding of more complicated syntax
than nettle-stripping.
The boards have a series of cogs.
The question is, can great apes turn them in the right direction,
in the right order, to solve the puzzles?
Sorry, Jim, but you've got that the wrong way 'round.
Argh!
GILLIAN LAUGHS
We're trying out her puzzle boards on two orangutan brothers -
Malu and Haddy.
Oh, here they are.
Oh, look at that. Oh, they're right in there. Straight away.
They've spotted the nuts, which Gillian has put
at the top of the puzzle boards.
But, to get them out,
they'll have to manoeuvre the nuts to the bottom of the board.
On his board, Haddy tries using a twig as a tool,
but that's not going to work.
Over on the other board, Malu lands on the correct solution.
Oh, look at that. OK, that's Malu. Wow. Malu's worked that out.
Well done. Here we go.
Malu's got into the second set of cogs, and now he...
Oh, look how quick! Oh, my word!
I can't believe how fluid his movements are.
He's getting to the last stage now.
This is the double cog, the exciting bit.
Will he think about...? Yes, he's thought about which way to turn it.
Ah! He's gone to the access point.
This could be the solution.
OK, he's been... I mean, the last...
Oh, look, at the last stage... No! ..and big brother has taken over.
Big brother's taken over and Haddy is going to get the reward.
But between them, they've solved it. Yes, it was a collaboration!
GILLIAN LAUGHS
Gillian is convinced that our ape ancestors
developed the ability to solve ever more complicated
physical syntax problems and were unknowingly building
the foundations of what would one day become language.
Our ancestors split from orangutans
around 17 million years ago
and from gorillas
about ten million years ago.
Again, climate change was bringing new threats.
Millions of years of slow global cooling
meant that rainforests were retreating,
to be replaced by open grasslands and woodland.
Competition for the most nutritious and calorific foods
in the rainforest was becoming ever more intense.
Life for our primate ancestors was getting harder and harder.
Survival would now depend on making finely-balanced judgments
based on limited information about where to find food.
To find out what mark climate change made on our brains,
I'm visiting the chimpanzees
who live at Budongo Research Unit at Edinburgh Zoo.
Along with bonobos, they're our closest primate relatives.
I've been told I can play a game with them
to test their cognitive powers...
Not one of you has said thank you yet.
..so I head to the indoor part of their living quarters.
When the chimps start making their noises, it is really loud in here.
CHIMPANZEES SCREECH
The chimpanzees have complete freedom to do as they like here,
so I have to wait to see if one of them wants to join me.
CHIMPANZEE GRUNTS
Eventually, four-year-old Masindi decides she wants to play.
Masindi, look.
To get the game started, I show her two empty cups.
Nothing.
Then I cover them with a screen...
..and put a grape under one of them.
Do you feel lucky?
I'll put it under this one, pretend to put it under this one.
She doesn't know which cup has the grape,
so she guesses the cup on the left.
That one? OK.
But now I complicate things.
I move this cup back? Yeah.
I remove the cup she doesn't want and offer her an alternative -
a half-grape.
Now what do you want?
So now she has a choice -
pick up a cup which may or may not have a grape under it,
or settle for a guaranteed half-grape.
This one?
That one, you want?
OK, well, look... Look what you could have won.
But, unfortunately, you have a half.
She's chosen the half-grape.
It's a safe decision,
but she's missed the chance of winning a full one.
And that's the choice they have to make - whether they want
half a grape for sure or a whole grape half of the time.
We play the game again, and this time, she sticks with the cup.
You're going for it, are you? Are you confident?
Clever!
Of course, Masindi's having to guess if the cup has a grape under it.
But now, what happens if I give her more information to act on?
I offer her two cups with one grape, as usual,
but this time I show her that one of them is empty.
Let's see. This is... This is going to be the clincher.
What are you going to...?
Good girl! You... Yes!
You've got it. Well done!
She immediately realises that the other cup must be hiding the grape.
She knew there was definitely a grape under this one,
so a choice between that and the half-grape,
she's sticking with the cup because she knows there's a grape under it.
The chimps also play video games...
..which simulate complicated foraging tasks...
..looking for hidden fruit scattered around a complex landscape.
The game is helping investigate the theory
that as the rainforests retreated, the need to find scarcer food
required greater brain power, memory and planning ahead.
These games are posing a vital question -
are the chimps able to keep track of their own awareness of the world?
What they know and what they don't know.
The ability to keep track of what you know and don't know
is a vital and mysterious part of human intelligence
known as metacognition.
It's something which particularly interests
the head of the research unit, Professor Josep Call.
Metacognition is the ability
to monitor and control your own thought processes,
your own mental content.
There is a thing called - in metacognition -
that is called the tip-of-the-tongue phenomenon.
When somebody asks you a question, and you say,
"I cannot give you the answer, but I know that I know this answer"...
It happens all the time. Yes, there you go.
This is metacognition, where even though you cannot
produce the answer, you know that you know the answer.
One theory states that our ancestors developed metacognition
as they solved problems posed by the environment,
such as finding fruit in changing landscapes.
It's thought this led to what's known as the Theory of Mind -
the awareness not just of your own mind, but others' minds, too.
It's about knowing about your own processes
but also inputting processes to others.
What others can see, what others want,
what others intend, what others believe.
Thinking about others is a crucial step towards becoming
the socially-connected creatures which human beings are today.
Our ancestors split from the lineage of chimpanzees
around six to eight million years ago.
After that came a huge change in lifestyle -
a change with astonishing consequences.
No-one knows exactly how, why or when it happened,
but at some point during the millions of years
after our own lineage split from that of chimpanzees and bonobos,
our ancestors left the forests
to make a new life out on the open plains.
They become bipedal, walking up on two legs,
so better able to adapt to different terrains and environments.
Between two and three million
years ago,
homo habilis was evolving -
the first human species.
They were developing areas of the neocortex involved in planning,
thinking, problem-solving,
and we start to see some astonishing results of improved brainpower.
Dr Nada Khreisheh is an experimental archaeologist.
She works at the Ancient Technology Centre in Dorset.
I'm meeting up again with Gillian Forrester.
She and Nada have both investigated the fascinating links between tools
and the story of our brain.
So, Jim, I'm really excited to introduce you to Nada.
She works in this beautiful place,
and she actually teaches people how to make these ancient toolsets. Wow.
OK, teach me.
So, we'll just start with a brief history
of some of the ancient types of stone tool
that were made by our hominid ancestors.
This is a core, a thin core, where sharp pieces,
as you can see down on the floor here, have been knocked off,
and these sharp pieces were used as tools for cutting.
I want to know how much brainpower it takes
to create the kind of tools which our ancestors made,
so Nada sets me a task to make this half-finished hand axe thinner.
So, yeah, you can see that that's... NADA LAUGHS
..not coming off.
It's not brute force. It's not just brute force, unfortunately.
Ooh. You're breaking the hammer stone.
So he's actually broken the hammer stone and not the actual flint.
Which is quite an achievement, really.
LAUGHTER
So, as you can see, just hitting it as hard as you can
directly on the spot which you want to remove... Isn't working.
..isn't the right approach, really. NADA CHUCKLES
Making the flint break in the direction you want it to
turns out to be extremely complicated.
It might seem counterintuitive, but you actually have to hit it
from this side to be able to thin it effectively. Ah.
And before we do that even, we need to prepare a place for us to hit,
to take a piece, which should travel down there
and thin the flint, if I do it right.
I just need to do a few more preparatory flakes.
Only after a few minutes of careful preparation can she do this.
I'm going to hit on the top, and that's taken a piece... Ooh.
..which hasn't travelled as far as I want, but it's kind of isolated
this spot a bit more, so made it stick out a bit more. Mmm.
A lot of times, when people think of stone tools, they're thinking
of cavemen, they're thinking of mighty muscles - big, hard hit -
but it's also about planning and thinking ahead.
Gillian believes this supports the theory that our ancestors
were using cognitive abilities
which had developed millions of years beforehand.
As we've seen, our shared primate ancestors
had likely already developed an ability
to master syntactical problems.
We've looked at nettle processing... Yeah. ..with the gorillas,
we've looked at puzzle-solving with orangutans,
and now we're looking here at stone toolmaking.
They might seem like very, very different kinds of behaviours
on the surface, but they have a commonality.
And that common point is that they require us
to put actions in the right order, and that's not different from
how we put words in the right order to make meaning out of a sentence.
Gillian believes that during our evolution,
carrying out problem-solving actions with our hands
led to our ability to produce spoken language.
She has intriguing evidence from brain scans,
which she explains to me using the 3D model of my own brain.
This is your brain, as you well know.
We've got the back of it here and the front of it here,
and running right down the middle, here, is your motor cortex.
This is telling your body to move, effectively.
The hand area and the mouth area,
they're really quite close to one another,
and just in front of that area here
is a region that we call Broca's area, or Broca's region.
It's always been thought to be a language-specific region.
It is activated when we speak.
But, interestingly, it is also activated
when a deaf signer signs their language.
It doesn't seem to matter if you're vocalising or gesturing.
It likes syntax.
Broca's region is also activated when we carry out
any sequential syntactic tasks with our hands.
As part of an investigation into the evolution of our brains,
Nada co-authored a huge study of volunteers,
who did 100 hours of training in stone knapping.
So one before they'd done any flint knapping
and one after almost 100 hours of flint knapping,
and we could see activations in Broca's area and changes -
so, development in that area as well.
It's fascinating, isn't it?
This connection between language, vocalisation and hand movements,
I'm doing it now as I talk, there is a connection,
and it's the same part of the brain that's controlling different actions
that I do with my hands and the words that come out of my mouth.
A lot of people's mouths will mimic what their fingers are doing.
For example, if you were sewing and you had to thread a needle...
Exactly.
LAUGHTER
You're going to purse your lips when you've got a tight space
and you're going to maybe open your lips more
when you're grabbing larger objects.
This could possibly date all the way back to just feeding behaviour.
If you're going to pick up something small and put it in.
If you're picking up something big, you need to open your mouth wider.
We also have this evolutionary theory that we might have been first
speaking with our hands, before language moved to our mouths.
Only a small portion of the way we communicate
is actually through our vocalisations.
We're still communicating a huge amount about what we think
and feel and intend through our facial expressions,
our body postures and the way we move.
So the theory is that carrying out complex tasks like toolmaking
helped put in place the final bit of the brain
which would be needed for language.
Over the past two million years,
our ancestors' brains tripled in size.
Particularly in the advanced cognitive areas,
such as the prefrontal cortex.
So, why did this happen?
One compelling theory lies in the large groups
which hunter-gatherer societies formed
and which we've inherited today.
It's known as the Social Brain Theory,
and it's something I'm about to explore in a very personal way.
I've been working on these documentaries now
for nearly 20 years.
I've worked with all sorts of people.
This is the first time I'm working with someone I know very well -
my wife Julie. We've been together for over 40 years.
I was asked to bring along either a good friend or my wife,
and I don't have any good friends. JIM LAUGHS
Yeah, not really. You weren't completely happy to come along.
It's not my kind of thing. You're not a show-off like me.
No, I'm not a show-off like you. Not many people are a show-off like you.
Anyway, I hope you know what you're letting yourself in for this time.
Not really, but I might finally get to find out
what you do on these shoots.
Let's stay friendly and see what happens. OK.
Julie and I have been offered an unusual opportunity.
We've been invited to drop in on a major five-year exploration
of a unique aspect of the evolution of the human brain.
Researchers from Nottingham Trent University
have taken over an entire house.
Cameras have been placed everywhere.
And, while we're here, every move will be filmed from different angles
and the footage will be analysed by researchers
hidden away in a different room.
Are you ready to play a game together? Yeah.
For months now, psychological and behavioural tests
have been carried out here, with 120 pairs of best friends or couples.
The game that you're going to play is called Lost on the Moon.
Lost on the Moon is a puzzle game.
Do we need this? Well...
We've been asked to put these items in order of importance
to help us survive on the Moon.
Why would we need a box of matches?
There's no atmosphere on the Moon, so you can't...
You can't... Light a fire.
I'm going to be hungry.
I'm saying I'm going to feel peckish and thirsty.
Yeah, but it's not just about you, Jim.
Well, you'll probably want a snack.
Yeah... What have you got? I've got the pistols. Pistols!
What are we going to shoot? You. LAUGHTER
Apparently we're going to need the pistol because if we run out
of food, Julie's going to get hungry and she's going to want to shoot me.
I'm not going to want to shoot you because I might get hungry.
Just because I'm getting on your nerves. Yeah. Fine.
As far as we're concerned, this is all about, you know,
whether we can survive on the Moon until we're rescued,
but it's clearly about, actually, whether we're cooperating.
We're quite good at that. It might not seem like it all the time,
but we actually do manage to compromise and cooperate.
What do you mean, doesn't seem like that?
JULIE LAUGHS
Sorry, dear.
While all this is happening,
our facial expressions are being recorded
and a team of evolutionary psychologists
are analysing our results.
Then they call us for a meeting.
So we've been videoing you while you've been doing all these tasks
and we've been measuring your facial movement.
Whether you furrow your brow, whether you raise your brow,
whether you smile, whether you wrinkle your nose.
Funny look, isn't it?
Eyebrow raises. Eyebrow raises.
So this gives a huge amount of very detailed information,
behavioural information, that's happening
during a normal conversation.
Jim has a rate of approximately 127 muscle movements per minute.
Woohoo! Is that good?
That's very high. Quite high, yeah.
The average is about 100.
Julie had slightly less facial movements than me,
but it might be because she tends to play her cards close to her chest.
I might just be one of those really deadpan people.
LAUGHTER
The poker face.
This project is investigating how much we use our facial expressions
to bond with others, especially our nearest and dearest,
and comparing it with other primates.
Many primates have facial expressions that are
similar to ours, but our faces are the most expressive,
and we think this sort of complexity is probably really important
to humans as a species
and how we manage these really... Mmm. ..complex, intense
social interactions we have with other people.
That's helped the evolution of our brains,
the fact that we are able to communicate with facial expressions?
That's the basic idea behind the Social Brain Theory -
that what is difficult is the social stuff.
So, forming relationships, understanding the signals of others,
understanding relationships between other individuals,
maintaining your own relationships,
that's the stuff that's difficult to do and that requires big brains.
Proponents of the Social Brain Theory believe there's a direct link
between the relative intelligence of primates
and the social groups they can sustain.
As our ancestors spread out across the lands,
they formed bigger social groups.
This helped keep them safe from predators,
but took more brain power.
Living in groups has costs, but it also has lots of advantages
in terms of access to mates, you can monopolise resources,
and primates are very good at living in groups.
I think it's important to think about humans and what we're good at,
and what we're good at is intense social interaction.
For this programme, we decided to conduct a little test
on the Social Brain Theory.
And what could be more appropriate
than a good old traditional British pub quiz?
I've invited Professor Robin Dunbar to take part.
What are we having? A whisky, Jim, I think. Whisky?
It's a long evening.
JIM LAUGHS
He's the person who came up with the Social Brain Theory
after years studying primates.
I start with some easy questions.
The greatest science communicator of all time
is widely acknowledged to be, A, Carl Sagan,
B, Neil deGrasse Tyson, C, Brian Cox,
or, D, Jim Al-Khalili?
LAUGHTER
I set the questions, by the way. LAUGHTER
According to the Social Brain Theory,
what is the number of meaningful friendships
which the average human being is capable of maintaining?
It's 150.
In fact, that's a very famous number - the Dunbar Number.
CHEERING AND APPLAUSE
The Dunbar Number sets limits to the number of friends
and family we're cognitively capable of having proper relationships with.
The Dunbar Number you have
reflects the cognitive demands of managing relationships.
In fact, it's a concentric circle of numbers,
starting with your closest circle of five people -
the people you think about most, and feel most empathy for.
The single best predictor...
..of your mental health and wellbeing,
your physical health and wellbeing,
even how long you're going to live into the future from today,
it's simply the number and quality of close friendships.
An average of 50 people are good friends
and 150 is the average limit for meaningful friendships.
Beyond the 150, there's a layer that goes out to about 500,
of acquaintances.
You may spend quite a lot of time chatting to them
but you're probably not going to invite them home.
Robin says many studies show this.
From the average size of a medieval village - 150 -
to a huge study about the number of people
we communicate with properly on social media.
The average is 149.
I'm going to set our audience a cognitive test,
which Robin believes helps prove the Social Brain Theory.
See if you can solve it yourself.
Each card has a number on one side and a colour on the other.
If a card has an even number on one side,
then on the other side it has to be blue.
Which card, or cards, do you have to turn over
to find out if that statement is true or not?
Now, if you find this difficult, don't worry at all.
Up to 90% of people can't work it out.
I got it wrong.
THEY LAUGH
It's because it's deliberately phrased in a complicated
and abstract way.
Here's the answer.
To find out if that statement is true,
you'd have to turn over two cards.
They are the number eight card
and the red card.
How many people got that right? Can I have a show of hands?
Our audience tonight did pretty well,
but the majority didn't get it.
Now a second test.
Jane's going to put up on one side the age of the person,
and on the other side what they're drinking.
Beer...
..and lemonade.
Which card, or cards, do you have to turn over
to see if there are any underage drinkers in your pub?
This one just feels so much easier.
To check if anyone is an underage drinker,
you just need to check the 16-year-old
to see what they're drinking
and the beer drinker to see how old they are.
How many people got that right?
Oh, there you go!
Just about everyone.
How many people found the first test easier than the second test?
No-one.
And that's the real point,
because, amazingly, these two tests are actually the same test of logic.
The beer is equivalent to the red
and the underage card, the 16,
is equivalent to the even card, the number eight.
But we humans nearly always find one much harder than the other.
Somehow, phrasing it in that way, in terms of social activities
that we're familiar with in everyday life,
makes that logic test seem so much easier,
and yet it's exactly the same.
The argument is that's because the brain is attuned
to constantly checking for people who infringe on social rules.
So we didn't evolve as abstract, logical calculators.
We evolved to work out each other and to solve social problems
and police social rules such as spotting underage drinkers.
A rapidly-developing field of neuroscience
is now making some intriguing breakthroughs, revealing where
in our brains much of our social processing takes place.
Professor Nancy Kanwisher runs a laboratory at MIT in Massachusetts.
This is a slice through the middle of the brain, here.
So, you see, this is the front of the head,
that's the nose, that's the back.
She made a name for herself when she tried to detect brain activity
when we look at each other.
Faces are one of the most important kinds of visual stimuli.
They are the first stimulus that an infant wants to look at.
And for social primates like us, it's absolutely critical
to be able to perceive faces and all the rich information
they tell us about another person.
We popped people in the scanner - me, to start -
and I looked at pictures of faces and pictures of objects.
And so the first time we did this, I remember coming out of the scanner
and finding this little blob in my brain,
and you could just see in the time course of response
in the experiment, a big peak during the times I was looking at faces,
and these little teeny bumps when I was looking at objects.
And I just thought, "That's amazing."
What Nancy had found is called the fusiform face area -
a highly specialised location in the brain.
So the fusiform face area seems to be involved
both in detecting a face -
like, "That thing I'm looking at, that's a face" -
and in figuring out which face that is -
"Is that Joe or Bob or Mary or Jay?"
This is the scan of my own brain and this is my fusiform face area,
activated when I looked at videos of faces.
Nancy and her colleagues have discovered
other specialised social areas of the brain.
This network has recently been discovered.
It's called the dynamic social pathway.
It helps us analyse and identify moving people and faces,
expressions, other people's intentions and moods.
This area is activated when we look at people's bodies.
We even have a spot of our brain called the theory of mind area,
activated when we think about what other people are thinking.
You can think of all of this apparatus
as part of our social mind.
This is how we function in society.
It's a very temping hypothesis to say, "Look, it makes total sense
"for evolution to have built this structure in us."
We are social primates, we care about each other,
we need to detect and recognise each other to survive,
and so it would make sense for evolution to have crafted
a specialised face-processing machine
and built it into a brain.
But we have to be careful.
This is still a fast-developing field of science.
These social networks could have developed in our infancy
as we became exposed to faces.
Or they may be part of our evolutionary inheritance.
What's known for sure is that our ability to bond together
as social creatures starts very early.
I'm convinced he's already saying, "Mama".
Dr Georgina Donati collaborates with Gillian Forrester
in studying brain evolution and development.
Recently, she's brought into the world her own test subject -
four month-old Elio.
Raspberry is a new skill, isn't it?
Ah.
Elio's social brain is already starting to kick in.
He's become very vocal recently. He's talking a lot,
although when other people are talking, he likes to listen.
But, I mean, there are all of these incredible mechanisms
that we've developed.
You know, they come out screaming their heads off, which makes us all
kind of run to them immediately, and then they develop smiles and giggles
and these things which keep us there and keep us interacting with them.
It creates this interaction, which the babies need to learn.
And humans have evolved that? This is something that
I think we're continuing to find out and explore.
How does this compare, humans babies, with other primates,
for example, or indeed other animals?
One of the special characteristics of us humans
is that we're born relatively early and underdeveloped
in comparison to other great apes.
Gorillas, when they're born, they can grip onto their mums better.
They're not independent yet, but they're not quite as vulnerable
as our human babies.
We've got a longer developmental period and it's made us able
to learn things more socially from a very young age.
Who's this?
JIM LAUGHS
Who's that? Of all the toys that he's been introduced to,
this gorilla is definitely the one that makes him happiest.
CONTENTED MOANS
A long childhood gives us what's known as high plasticity -
our brains can adapt according to the different environments we're in.
But it means our ancestors had to look after
a helpless infant for years in the wild.
It poses a huge question.
How did we survive?
Well... So, as you'll know, being a parent,
it's a massive parental investment.
With modern humans, we've often got two parents,
and we also have extended families that help raise these babies,
not just to be fed, but to be socially engaged
and to keep giving the stimulus and the stimulation to the brain.
Our brains carry on developing through adolescence
and we think now that this is carrying on
until we're sort of in our mid-20s.
Potentially, providing these very nurturing environments
really just allows this plasticity, this learning,
this flexibility, to continue for longer and longer.
So the lesson is, without loving, self-sacrificing parents
and supportive social communities,
we'd never have survived the rigours of the wild
and evolved the brains we have today.
The human brain has now started to build machines
which can surpass it in so many ways.
We humans have used our cognitive powers to astonishing effect,
from those very early stone tools to devices like this.
A smartphone is basically a pocket-sized super computer,
capable of processing vast amounts of information,
carrying out operations much more quickly
than our brains could ever do.
And today we're on the brink of a new technological revolution.
Artificial intelligence is already performing complex mental tasks,
from essay writing to composing music.
The future of AI - our most extraordinary creation -
is still unknown, but what I've learnt on my journey
has given me hope that being in a community with others
was the crucial final step in the evolution of our brains.
What has fundamentally shaped our brains
is our relationships with each other.
It's the family and friendship groups we form,
it's our shared histories, our shared cultures,
our beliefs, our memories.
Ultimately, it's our capacity for empathy,
for love, for self-sacrifice,
for thinking about each other, that has made us who we are.
Curious about how MRI technology can reveal the secrets of your brain?
To watch the Open University's new animation
exploring how an MRI works and what it reveals,
scan the QR code or go to bbc.co.uk/secretsofthebrain
and follow the links to the Open University.