I'm Jim Al-Khalili, a professor of theoretical physics.
But today, my brain isn't pondering equations -
it's being scanned.
- You have about 160,000 kilometres of wiring
in about a kilo-and-a-half.
So, enough to wrap around the Earth four times,
or take you halfway to the moon. - Goodness me.
Like everybody else's, my brain contains about 100 billion neurons,
and over 100 trillion connections.
That's more than the stars in the Milky Way.
- This is what your head looks like inside.
- So, how did something so complex actually evolve?
Spanning hundreds of millions of years,
this story takes in the strangest of creatures.
So, there's a tiny brain?
- Yes, exactly.
- Now, thanks to the latest scientific breakthroughs,
we can tell the brain's extraordinary story
like never before.
- That's the first whisper of a revolution,
a cognitive revolution.
- MONKEY MAKES HIGH PITCHED CALL
It's an epic tale...
EXPLOSION
..with amazing twists and turns.
- Look how quick! - Oh, my word!
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.
To try to understand the beginning of my brain's story...
..I'm snorkelling off the west coast of Italy.
MUSIC: Concerto No.2 in G Minor by Vivaldi
This is home to some very strange-looking animals.
But go back some 560 million years,
and you'd encounter the common ancestor of us
and many of these creatures.
It had a rather special shape,
probably a bit like this worm with a head and tail,
and left-right symmetry.
This animal was, like us, bilateral,
but it had something else too.
Many scientists now believe that this was the first animal
to possess the basic building blocks of the brain.
It was in an epoch known as the Ediacaran
that these Bilateria first emerged.
ENGINE RUMBLES
To find out more about their early brains,
I've come to meet some scientists who are working in these waters.
- OK, pull up now and we will collect everything.
- They're pumping out the water from a depth of ten metres,
up through this filter, which lets through all the tiny organisms
that they don't want to catch,
and it captures all the ones they want to study.
They're looking for zooplankton -
animals like tiny worms that drift in water.
- So, this in here, it's hard to see,
but this is zooplankton.
We can analyse this under the microscope.
Small algae will go through, and the zooplankton will stay in the filter.
- Why is it studying this tiny worm helps us understand
the ancient early evolution of the brain?
- We have chosen to work on this worm, because we were convinced
that it has ancestral features, so that it would show us,
for example, characteristics of the brain
that are old, that have always been existing in animals.
- Like the first Bilateria, these zooplankton
have a tiny cluster of nerve cells in their heads
and a strand running down their bodies.
These cells co-ordinate muscle movement and other organ behaviour.
And, crucially, as well as coordinating,
early brains evolved ways of sensing
and responding to their environment.
- And so it was. So, the first thing we found about this worm
is that it uses light-sensitive cells, photoreceptor cells,
that it has in its brain.
And these cells are the same to the ones that we have in our retina,
the rods and cones.
And this was a big surprise, a big finding
that these are the same photoreceptor cells.
- So, these are cells that are activated,
that send signals to the brain, when light impacts on them?
- Exactly. We have these in our eyes.
So, whenever we see light, these cells are activated
and signal to the brain that there is light.
And the very same cells exist in this worm.
- Back on dry land, another member of the team shows me
what these worms can tell us about early brains.
Aha!
- Here it is.
So, this is a young juvenile.
- Right. So, how big is this?
Is it like, maybe, a millimetre or two?
- This is two millimetres. - OK.
- And it has, on the front, a nice head.
You can see the fangs of the animal,
where they take up food.
You can even see some movement
inside, these little dark dots, which are the eyes.
- So, it has four eyes?
- It has four eyes.
And you can see these dark speckles,
these are the pigments of the eye.
- Inside these simple eyes are molecules called opsins.
When light hits opsins,
they trigger an electrical signal,
which can make the worm move.
Can you show me how they react to light, then?
- Yes. So, here you see the larvae swimming.
And then we switch on a directional light stimulus
on this side of the chamber.
You see when the light comes on,
and they start to move to the light.
- Oh, I see. You're replacing sunlight with your artificial light,
and having the worm move towards it?
- Yes. We provide this directional light cue here, from the side.
- The worm isn't seeing, thinking,
or responding like we do, though.
It has a simple nervous system,
that makes it move when light strikes its opsins.
What does that tell us about the early evolution
of vision?
- We think that the first eyes were just, in fact, very simple -
a few cells, able to tell the direction of light.
And this kind of mechanism was probably there already
in the common ancestor, last common ancestor of the Bilateria animals,
around 540 million years ago.
- At about the same time,
other senses developed too.
For instance, cells that could respond to nutrients -
the forerunners of smell and taste.
But these first bilateral animals
also needed a way of sending sensory signals
around their bodies to control muscles and organs.
For that, they used a special type of cell -
the animal world's fibreoptic cable, a nerve cell,
or neuron.
It's taken over 100 years for scientists to understand the neuron.
Much of that story happened just down the coast here in Italy,
at a true landmark in the history of science.
This is the Stazione Zoologica in Naples.
It was founded in the 1870s by zoologist Anton Dohrn.
Anton Dohrn was an early and passionate adopter
of Charles Darwin's theory of evolution by natural selection,
and that passion drove him to create a station for scientists
to study marine life.
For his location, he chose Naples, because...
Well, Naples.
Dohrn built this impressive laboratory right on the beach
with easy access to the Mediterranean,
and facilities to study all kinds of sea creatures.
To explore how neurons and nervous systems worked,
he had his team make some exquisitely detailed
and beautiful illustrations.
Dr Graziano Fiorito showed me some examples.
- There was a strong tradition
by...by Dohrn
of supporting the study
of various organisms.
- Wonderful. So, these are illustrations made for
this journal, which is...
..Fauna und Flora.
1896.
- They were interested not only in the shape of the animal, the organs,
but in the nervous system,
how the nervous system is organised.
- Then, in 1932, here at the Stazione,
a British scientist called John Zachary Young, or JZ,
made a breakthrough in understanding how the neuron works.
Scientists had previously suspected electricity was involved
in neuron signals,
but these cells were always too small and thin to really study.
Then JZ found an exception -
squid possesses neurons so long and thick,
they're actually visible to the naked eye.
- This is a classic video, where JZ was showing how to dissect a squid.
He's now removing some part of the organs, the gills,
in order to reveal this network.
You see? - Right.
JZ realised that because these neurons were so large,
he could isolate one with the correct dissection techniques.
So, these are all nerves, each one of those lines?
- Nerves. Yeah. And finally, this is the giant single nerve.
- Scientists used electrodes
to measure what was happening inside the neuron,
and this led to the discovery of precisely how electrical signals
travelled along it.
Would you say this was the beginning of
modern neuroscience? - Yes.
JZ Young published this paper in 1939.
And this was the emergence, I would say, of neuroscience.
- We now understand that nerve cells, or neurons,
are the building blocks of all brains.
Neurons take signals from molecules like light-sensitive opsins,
and transmit them through the body as electrical pulses.
But how exactly do they do that?
Most neurons consist of three basic parts.
Dendrites, these branching filaments that pick up the signals,
a cell body that processes the signal
and a long strand called an axon
that carries the signal to other cells.
But what's really incredible is just how fast the signal can move.
Let me show you the patella reflex,
or the knee jerk reaction.
My director, Tim, has kindly volunteered here.
So, look what happens when I do this.
Hitting the tendon triggers a nerve in the thigh,
and a signal travels to the spine and back,
and the thigh muscles jerks.
Watch how fast it is.
It takes about 18 milliseconds,
which means the signal is travelling at about 200km an hour.
Electricity doesn't flow along the whole length of an axon,
as it might do in a copper wire.
Instead, the signal starts when a tiny channel
at the beginning of the axon opens,
allowing electrically-charged particles to flow through it.
This then triggers other channels to open a little further along.
It's rather like a domino effect.
Each tile moves very little,
but the ripple effect travels rapidly.
Same in the axon - the charged particles themselves hardly move,
but the signal races down.
Ultimately, what we see is a pulse of electricity
passing from one end to the other,
and it all happens in the blink of an eye.
But what makes the brain and nervous system so flexible
is that neurons signal other neurons,
creating a complex network.
They communicate across a tiny gap called a synapse.
Here, the electrical signal triggers the release of a chemical
called a neurotransmitter,
which crosses from one neuron to another.
In this way, signals can cascade through your brain and body.
And new technology means scientists can see and hear neurons at work.
In Boston Harbour, on the Eastern Seaboard of the United States,
a fresh haul of tasty crabs is just in.
But before they reach the plate of a hungry diner,
some of these crabs are being diverted for scientific research.
- So, what Kyra's doing now is,
she's putting out the stomatogastric nervous system.
- Professor Eve Marder runs this lab at Brandeis University near Boston.
- Once it's pinned down flat,
she'll place recording electrodes on the nerves that will allow her
to identify the neurons and record the motor patterns.
- Eve's team are measuring electrical activity in the neurons.
- These very fine white lines are the nerves themselves,
and you can see how delicate they are.
- LOW CHIRRUPING
And the technology here means those signals are converted into sound.
CHIRRUPING CONTINUES
- So, using the electrodes to record the activity of the nerves,
and you can hear that the rhythm is going pretty fast right now.
You're hearing that nice rhythm of bah-dub, bah-dub, bah-dub, bah-dub.
It's the circuit doing its thing.
- This is a real-time representation of the crab's nervous system
actually sending messages,
much like the ones that control our bodily functions.
But in an era of fear about climate change,
with temperatures set to rise,
the discovery also has a worrying aspect -
neurons are prone to fail as their surroundings warm up.
- Every human neurological disorder
is exacerbated by high temperature.
The fact that poor people and ill people
are less likely to be in environments where they can regulate
their room temperatures, and therefore their body temperatures,
means that we're potentially heading into a major health crisis.
- This fragility means we should never take neurons for granted.
After all, these cells carrying billions of pulses
around our brains and bodies every second
arguably make us who we are.
All the thoughts and all the dreams of the entire human race
are just made up of these tiny electric signals
racing along neurons.
It's mind-boggling.
For neurons to become really effective,
and lead to brains like ours,
they had to do more than simply carry signals.
They had to take context into account -
respond to stimuli in much more nuanced ways.
To do that, evolution picked a group of ancient proteins
and found a new use for them -
neuropeptides.
Let me give you a sense of the rather subtle ways these work.
You see, depending on circumstances,
the same thing could be either good or to be avoided.
Let me give you an example of how important this is, even now.
Think about how you might respond to a delicious-looking cake.
If I haven't eaten for a while, then I really just want to tuck in.
But if I've just had a big meal,
then it looks a whole lot less appetising.
And if I've just been sick from food poisoning,
then the same cake can look repulsive.
Our brains have a way of adapting our behaviour
by reprogramming what the neurons tell us to do.
These subtle alterations of when and why neurons fire
are controlled by neuropeptides.
For instance, they change our behaviour
when we're with friends rather than strangers,
or how a mother acts when she's with her new baby.
All these new behaviours happen slowly, over minutes or hours,
and are very different from the rapid response to, say,
touching something hot.
Professor Cori Bargmann, at Rockefeller University in New York,
has made it her life's work to study how neuropeptides alter behaviour,
and to understand how they evolved.
- The neuropeptides are very old.
This system is one of the first ways that the nervous system functioned,
even before there was sort of a centralised brain,
while it was still kind of fuzzy and distributed.
- To understand neuropeptides,
Cori studied a tiny worm known as C. elegans.
- This is a single adult C. elegans,
and here's a little adolescent next to her,
moving around in real-time.
Because she's transparent, under the right circumstances,
you can see every neuron in her nervous system.
- C. elegans has precisely 302 neurons,
and scientists have now mapped exactly how each one
connects to the others.
Cori's research examines how neuropeptides influence
this basic nervous system
and enable the worms to have complex behaviours,
like socialising or courting.
- Some of the worms were very interested in associating
with other worms, and we can actually see these behaviours
here in this movie.
And what you can see is that they're tending to hang out together
in these little groups, and this is an aggregation behaviour.
Aggregation behaviour is very common in animals.
Animals often associate with other animals in their same species.
That could be called herding behaviour in...in sheep,
or it could be called schooling behaviour in fish.
And we see exactly this, even in these very simple worms.
- Normally, when worms bump into things, they move away.
But Cori found that sometimes, something very different happened.
A neuropeptide you might have heard of, called oxytocin, was released,
which changed how the neurons work
and how the worms behave.
- Oxytocin is required for mating behaviours in C. elegans.
I'm showing you here a mating pair of a male C. elegans
and its female-like partner.
And in the male, there's a single neuron,
it's this bright spot here that looks almost like an eye,
that's the neuron that's making oxytocin when the animal was mating.
And so, this male is resending his behaviours,
so that in the presence of a mating partner,
he'll respond appropriately for this, for the next five minutes.
And then, once she disappears again, he'll go back to the other kinds
of exploratory behaviours that he's doing.
- But what really surprised Cori
was how neuropeptides like oxytocin changed behaviour
in almost all living things.
- We found that there was an oxytocin in ants,
which of course are a social species,
and it's involved in some of their social behaviours as well.
- And in mammals like us,
oxytocin has developed a crucial role.
- Oxytocin is released when a female mammal gives birth.
It helps to rewire the mother's brain,
to stimulate bonding between the mother and her offspring.
It's being able to flip from one state into another.
And we all know that experience in our own lives,
we all know how emotional states are changing our behaviours
on a moment-to-moment basis.
- In our brains, neuropeptides control our moods -
bonding, love, anger, sex.
In fact, modern drugs like Ozempic, which is set to revolutionise
obesity, is linked to the action of the neuropeptide GLP-1,
which controls appetite.
It's quite incredible that so much of our behaviour
is based on these proteins inside our brains
that evolved hundreds of millions of years ago.
The next huge leap in the brain's development
happened about 530 million years ago,
in what's known as the Cambrian Explosion.
Evolution went into overdrive.
There was a huge burst of new, strange-looking species,
big creatures with shells,
thorns, fierce claws and hooks.
And one particular adaptation that would have far-reaching consequences
for our brains.
I'm about to show you something really exciting.
Hi, Filomena. - Hi.
- Can I have a look at... - Yes. - ..what's in that dish?
Thank you. I'll put it on this dark background.
What's inside here is really rare.
These long creatures,
that's called amphioxus.
It's regarded to be very similar to the earliest common ancestor,
about 500 million years ago,
that marked the transition to the first vertebrates.
Maybe we can have a closer look... - Yes. - ..under the microscope?
- Here, we have the adult amphioxus.
Here, we can see the anterior part, the head.
Here, the posterior part, the tail.
- And from head to tail, the nerve cord has been supplemented
with a string of cartilage and bone -
a primitive spine.
This gave the ancient version of amphioxus an advantage
over earlier Bilateria -
it would allow brains to get bigger.
So, there's a tiny brain?
- Yes, exactly.
If we go more in...
..we can see.
Here, we have this enlargement.
And here, there is the brain of amphioxus.
- The rigidity of spinal cords and early skeletons
allowed vertebrates and their brains to grow.
Amphioxi have 20,000 neurons.
You can get a sense of the advantages of having a smarter brain
and internal spine and skeleton by watching this fish tank.
Right now, this looks like a perfectly peaceful habitat.
Fish gently moving about, calmly, harmoniously
but that's because they're not thinking about their lunch.
Let the feeding commence.
Vertebrates of all kinds
proliferated in the Cambrian Explosion.
Thanks to their speed and manoeuvrability,
the ones with spines and bigger brains
were great at both hunting and escaping.
- The main scan is basically ready.
- At the MRI scanner at University College London,
I'm being shown the debt my brain owes
to my early vertebrate ancestors.
- That's your spinal cord, coming up into your brain stem.
Brain stem is one of the sort of evolutionarily older parts
of the brain that keeps your heart beating, your lungs pumping,
moves your eyes around.
So, lots of important things.
- Another crucial component of vertebrate brains
is the hippocampus, which we use for memory formation.
- The hippocampus is a little C-like structure that shows up here.
I can see it because I'm used to looking at hippocampi,
but it may be a little bit challenging.
It's sitting just below your amygdala,
which is part of the brain that's sort of an emotional centre.
- This new, large vertebrate brain
was matched by an increase in body complexity and size too,
and this meant the brain and body needed more sophisticated
internal communication.
Brains not only had to get better and better at sensing
what was going on in the world outside,
but also what was going on inside the body.
And one very important way they do this is fascinating.
They use a molecule that works a bit like a telegraph key
sending Morse Code.
MACHINE BEEPS
A telegraph key is pretty simple.
A battery connects across a lever arm and a contact below.
So, when I press down on the arm,
I complete the circuit and a current flows through the wire,
enabling me to send a message.
BEEPING
In essence, a mechanical force,
in this case the pressure of my finger,
is triggering an electrical signal.
MACHINE BEEPS
For years, scientists suspected something similar was happening
in our nervous system.
Something was transforming mechanical force
into some sort of signal to the brain.
For instance, as a stomach fills, its walls stretch,
and somehow the animal knew it didn't need to eat for a while.
But how did this actually work?
The answer was finally discovered in 2010 by Professor Ardem Patapoutian,
at Scripps Research Institute in Southern California.
- We're used to thinking about taste and smell, sensing chemicals.
But this is actually sensing physics, right?
It's mechanical forces, pressure.
You have to turn this physical stimulus into an electrical
or chemical signal that neurons would understand,
and this transformation has been a big mystery.
- BEEPING
The challenge was to find a molecule that, like a telegraph key,
was triggered by mechanical pressure
to send an electrical signal.
So, Ardem's team built an ingenious probe that gently applied pressure
to cells just a few thousandths of a millimetre across.
- We have a video here of the cell poking assay
under high magnification.
And so, what we're doing here is, using that to deliver
sub-micron - so very, very small fractions of a millimetre -
indentations to this cell that's sitting on the dish right here.
- After nearly a year of poking and prodding...
..they finally found a single molecule on the cell's membrane,
which triggered a tiny electric current when pressed.
- So, when we poke very far into the cell, we see a very large current.
And when we only poke the cell a little bit,
we see a very small current or none at all, and this tells us
that the cells are really exquisite centres of mechanical force.
- They called this molecule Piezo.
This is a model of one of the molecules
that Ardem and his team discovered -
the biological world's telegraph key.
It's embedded in the surface membrane of cells like the neuron.
And it's tiny -
just a few millionths of a millimetre across.
But despite that, it's a really complicated molecule.
It's a single protein, made up of roughly 50,000 atoms
arranged in this intricate shape,
with three spiral arms and a cap in the middle.
The shape of the protein is crucial.
When the cell wall stretches, the whole structure flattens out,
and the centre opens up, creating a channel
through which charged particles can flow into the cell.
This is analogous to pressing the telegraph key,
allowing electric current to flow.
We now know there are hundreds of thousands of Piezo molecules
throughout our bodies,
signalling our brains.
They can monitor our blood pressure, appetite,
the need to wee, the timing of our heartbeat,
and even regulate our breathing.
And because hundreds of thousands of Piezos
are embedded in our skin too,
they enable the most exquisite and underrated of all senses -
the sense of touch.
Think about it - our ability to touch is amazing.
We can feel the tiniest breath on our fingertips,
or the feel of a single grain of sugar,
or the gentlest brush of a feather.
Scientists say we can sense something on our fingertips
that's just one 500th of the width of a human hair.
Having discovered Piezo molecules,
Ardem Patapoutian's team then looked at where evolution
had used them, and what they discovered was astonishing.
- They seem to be really conserved across evolution.
So, we don't see them in bacteria, but in anything that has a nucleus.
Even unicellular organisms have them.
We have seen them in flies, in worms.
Plants, of course, have to sense mechanosensation as well.
Roots, as they navigate through the soil and hit a harder surface,
they have to decide to go through it,
or, if it's too hard, go around it.
- The fact Piezo molecules can be found across such a wide variety
of life tells us they evolved a long time ago.
- Our sense of pressure sensing,
that we mainly think of as a sense of touch,
was present hundreds of millions of years ago in organisms
that were just maybe swimming in the ocean
and bumping into different things,
and needed to know what they were bumping against.
- Up to this point, all life on Earth had lived and died in one place...
..in the oceans.
The land was sterile and empty.
But then, things changed.
Towards the end of the Cambrian Explosion,
about 500 million years ago,
we think the first complex life began to creep out of the sea
and onto the land.
Those first things that colonised the land
were algae, mosses, basic bacteria.
But then, larger, more structured organisms began to emerge.
Plants evolved root systems that went underground.
Tall grasses emerged, and eventually trees.
Following them out of the water were early insects too,
crawling and burrowing and wriggling things.
For sea creatures that lived close to the shoreline,
the land now represented a new
and potentially resource-rich environment.
But, of course, these animals would have to evolve considerably
if they were going to survive above water.
The process took millions of years.
You have to jump forward to 375 million years ago,
to see the first vertebrates
starting to venture onto terra firma.
This is a mud skipper.
It's similar to the kind of animals that were beginning to evolve
at this time.
Their eyes have moved upwards on their heads,
instead of on each side with most fish.
Many scientists now believe that the way eyes worked out of the water
led to one of the most significant turning points
in the evolution of the brain.
Professors Malcolm MacIver and Dan Dombeck, at Northwestern University
in the States, have been studying this critical moment in evolution.
- With just their rising of the eyeball out of the water,
you go from a medium which absorbs light so intensely
that you only see a body length in front of you
to essentially a perfectly transparent medium.
That gives you a huge multiplication in your visual range.
- Now, the key reason for that is to do with physics,
or more specifically, the physics of light.
You see, light travels far better through air
than it does through water.
That might sound rather obvious, but let me show you.
Safety goggles on.
What I have here is a tank full of sea water
and a laser pointer that shines light through the water,
to be picked up by a detector on the other side, which I can read here.
When I turn on the laser, the light metre reading doubles
from 25,000 to 50,000 lux.
That's how much light is getting through the sea water
to the other side. Guys, give me a hand here.
OK, thanks, guys.
Right, now we do this again.
We'll repeat the test, but with an empty tank.
And the reading has jumped to over 100,000 lux.
Air is at least 20 times more transparent than sea water.
You can clearly see this, when you swim in the sea.
You just can't see very far underwater.
That's because water is denser than air and often murkier too,
because of mud or sea life.
And this had huge implications.
As animals moved out of the sea and onto the land,
the amount of raw visual information they could receive
increased enormously,
and their brains had to evolve to keep up.
- How are you going to process all of that visual input
to survive threats that are coming at you,
or to find food that might be trying to escape from you
some distance away? So, you need to have...
You're going to have to up your computational brain,
in order to process all that information.
- Malcolm and Dan believe that moving from sea to land
led to a massive growth in size and power of the brain.
- I want to demonstrate with these two skeletons
just how big a change it was in relative brain size
between ancestral fish and mammals.
And so, here is a fish
that's in real life about this big
and its body mass, a bit larger,
but it's approximately similar to what a cat is.
And yet the total volume of this animal's brain
is about two teaspoons,
and it's a factor of ten larger brain
in mammals, compared to fish.
- The consequences of the move to land are stamped all over our brains.
Significant regions of the brain have evolved to make sense
of the mass of visual data pouring in via optic nerves
connected to our retinas.
Regions like the primary and secondary visual cortex,
the posterior parietal lobe,
and the fusiform gyrus.
But though the move to land put down the foundations
of these parts of my brain,
it very nearly never got going.
Because around 250 million years ago,
catastrophe struck.
LOUD BOOM
A massive series of volcanoes erupted in Siberia.
The cataclysm exposed a huge geological fault,
stretching for hundreds of miles.
And from this gash poured billions of tonnes of hot lava.
Some suggest this flooded the plains below
and came into contact with one the largest exposed coal deposits
in the world.
Picture the scene - 252 million years ago,
billions of tonnes of red hot lava,
billions of tonnes of thick, black, dirty coal deposits.
The result was a toxic gas release on a catastrophic scale.
Poisons like sulphur dioxide,
nitrogen sulphide and methanes filled the atmosphere.
They then mixed with moisture in the air to create powerful acids,
which then rained down,
wiping out nearly all life from the face of the Earth.
As well as this, the volcanoes belched carbon dioxide
from deep inside the Earth.
Trillions of tonnes suffocating almost all plants and animals.
Today, we consider the world to be on the brink
of a carbon dioxide catastrophe.
There are 420 parts per million of carbon dioxide in the atmosphere,
and rising.
But 250 million years ago, the Siberian volcanoes
released 5,000 parts per million -
over ten times more.
There was total devastation.
95% of all species were wiped out.
In the whole history of life on Earth,
it's the closest we've come to total extinction.
But, of course, it wasn't the end.
Some things did make it through.
The survivors were smaller animals that could hide away.
They could burrow underground, they could crawl into crevices
or slither into the mud.
They could survive on less oxygen,
they could cope with the heat, the darkness
and the toxic chemical mix.
The scene was now set for one of life's most incredible comebacks,
and one of the most profound moments in the story of our brains.
This is the Vale of Glamorgan in Wales.
After the massive extinction event,
this whole area was an archipelago of small, low-lying, linked islands,
which makes it particularly interesting to palaeontologist
Dr Elis Newham.
What was this place like back then?
- It's 50 million years after the end-Permian mass extinction,
the Great Dying.
So, life is bouncing back by then.
- We're now firmly in the era of the first dinosaurs,
the gigantic creatures that were coming to dominate the world.
But Elis is more interested in a much, much tinier creature -
one whose remains literally fell through the cracks.
- Within these islands, there were cracks and fissures
that naturally developed. And so, any animal that died,
their remains would have got washed in.
And so, this gives us an amazing snapshot onto what life
would have been like on those islands 200 million years ago.
- And what Elis and his colleagues found deep in these rocks
were new clues to how our brains were actually formed.
Bones from a tiny, rat-like creature called Morganucodon,
or Morgie.
- We found thousands of isolated teeth, jaws and bones.
And I've brought one here with me to show you.
- I mean, it's tiny.
This ain't no T. Rex.
So, what did this creature look like?
- It was about the size of a shrew.
It might have been furry, it probably had whiskers,
and it was kind of scrabbling around the undergrowth
in what is now South Wales. - Right.
- So, it was definitely insectivorous.
It fed on beetles, and kind of gnat wings and things like that,
that were living with it at the time.
- But what no-one expected is what they saw
when they started looking inside Morgie's skull.
- Colleagues CT scanned one of these skulls,
and what they found was pretty amazing.
So, this is a cast, a 3D print, of a model
that they created of the brain of Morganucodon. - Wow!
Very tiny. - Absolutely tiny.
Maybe I'll get a scaled version for you.
- Right. - So, here we go.
- On top of Morgie's brain,
they noticed an intriguing new development.
- We started noticing with this thing.
You can see this lumpy bit here?
- And so, the brains of other creatures
that lived around that time didn't have this bump?
- As far as we know.
So, Morgie shows a kind of, a jump-step
in the development of the brain.
The brain size, and also the brain complexity.
- This bump is a new part of the brain called the neocortex,
and it's what sets creatures like Morgie apart
from other animals of the time.
It's a small bump with huge implications,
because it's the bump that makes our brains so unique.
So, where did it come from?
To find out more about the neocortex,
I've come to meet Professor Steve Brusatte,
an expert in palaeontology and evolution.
- This is Morgie's brain.
This is a digital model from a CAT scan.
And just to orient ourselves, this bit here at the front,
that's the olfactory bulb,
that's the part that controls our sense of smell.
Back here is the cerebrum, one of the main components of the brain.
And up there, on the top, is that curious little bump.
- And that's what I'm interested in.
So, where did that come from?
- We have a few clues that we think helps tell that story.
And the first one of those is if we look at the bones of Morgie.
- Unlike any animals before this time, the microscope reveals
Morgie's bones are honeycombed by tiny holes -
evidence of a massive step-change in blood flow.
- Those are just digital renderings of the channels for blood vessels.
And the key thing is that their bones, their skeletons
were becoming much more full of blood and blood vessels,
and that means that they could have higher metabolic rates.
- So, their bodies were just working harder?
- Their bodies were working harder, they could grow faster,
their metabolism was increasing.
That's part of the story, but there's a second clue
to this as well, which we'll have to take a look over here. - OK.
- And this is a little fossil...
..discovered about a decade ago by teams from here
at the National Museum of Scotland, out on the Isle of Skye.
And if we put it under the scope,
you can see what it is.
The bit sticking up from the top, that tells us what this fossil is.
And those things are teeth.
So, this is a jawbone.
But when you blow it up in size, you 3D print it,
you can see all of these teeth here and it's in these teeth
that tell us the importance of these fossils,
and they tell us a few things.
These teeth, they're really sharp, there's lots of little points.
And when the teeth came together, all those points would interlock,
and they would bite really strongly, be able to chew the food.
But the other thing is, the babies did something different.
We can tell that these animals had one set of baby teeth,
one set of adult teeth,
and that means that the babies were drinking milk.
- OK.
What does that tell us?
- So, these, of course, are mammals, just like us.
These are early ancestors of ours.
What we see with these fossils at this time,
these mammals were entering an age of gluttony.
- So, these mammals ate more,
their offspring drank milk,
and they had more blood flow in their bones.
This wasn't just the start of mammals,
it was a new way of being.
- That tells us the big reveal here,
and that is that we think that these mammals were becoming warm-blooded.
And that means you have a constant body temperature,
a high body temperature,
and your body temperature is high and constant
regardless of the season, regardless of the time of day,
regardless of where you live.
And that's a very special superpower, that's what we have.
- Warm-bloodedness enabled animals to exploit new niches -
hunting at night and in the cold.
So, it takes resources to be warm-blooded.
If you think about the cost of heating our homes, it's expensive.
- A mammal needs to eat about eight times, give or take,
as much food as a cold-blooded animal of a similar size.
- So, brining this back to the beginning, how do all these changes
affect the brain of Morganucodon?
- That's where that bump on the brain comes in - that's the neocortex.
It's clearly getting larger.
That's the expansion of the brain
that's happening at the exact same time in evolution
as these changes to the teeth, changes to the diet,
changes to the metabolism.
- So, you have the evidence, the bones, the teeth,
suggesting they are eating more, they're metabolising more,
er, they have to find food more...
..often, and to do that, they need bigger brains.
- That's it, that's the story.
And it's a huge story and it's one of the biggest changes
that we see in the evolution of animals.
- So, what did these new parts of the brain allow animals to do?
It seems to have led to the development of a remarkable
new ability, a true superpower.
That superpower is what we might loosely call imagination -
our remarkable ability to remember scenes from our past,
or to conjure up ones in our future.
Cast your mind back to when you were a young child.
Try to remember what it was like.
Now, conjure up your next Christmas or family gathering.
Can you see in your mind's eye what it will be like?
What's amazing is how effective this internal visualisation can be,
our ability to see the past or imagine the future.
We can link it to smell and even to our emotions.
To investigate the mammalian origins of imagination,
Malcolm MacIver and Dan Dombeck built this -
an open maze with food at several reward ports.
And because genuine early mammals no longer exist,
his team use mice to see how they visualise the world around them.
And to help motivate the mouse, an unusual predator.
- We came up with a large arena,
where we could essentially run a predator-prey scenario,
but with the predator being an autonomous robot
that we have designed and developed.
The robot doesn't physically attack the rodent in the space,
it simply puffs it an intense blast of air
and rodents really dislike that, so they avoid the robot.
- The team then attached probes into the mouse's hippocampus,
which processes location information from the mammalian neocortex.
- And we asked, "What exactly is going through the mind of the mouse?
"Is it imagining a future position of the robot?
"Is it imagining a future position of itself?"
- They put the mice through the maze thousands of times,
an environment specially designed to make them think ahead.
They then took data from the probes
to get a sense of what was happening inside their brains.
- So, here's the experiment that you saw earlier.
We've also included neural data.
- The blue dot represents where the mouse actually is,
and the red dot is where the robot is.
But incredibly, by reading the signals from the mouse's neurons,
the team could tell where the mouse was planning to go.
That's the pixellated blue blob.
Malcolm believes this reveals important clues
about the mouse's imagination.
- You can see that, essentially, we have the mouse thinking about
where it's getting to in the next little bit.
It's actually here, and this is where it's going to be soon,
and it seems to be thinking about where it might be in the future.
So, right now, the mouse's imagination of its location
and its actual location are very close.
- But then something remarkable happens.
The pixellated blue blob
moves away from the blue dot.
This suggests that the mouse is thinking
of where to go next to find food.
- Right here, it skips over to here,
and it starts to coalesce
around this next reward port
which, you'll see in a second,
is where it's going to go to next.
So, it appears to be thinking about...
This is a reward port, and it appears to be thinking about
the next reward port it's going to be visiting.
And that is really interesting,
because watch what happens after the mouse leaves this position,
after it's checked that reward port, it actually goes over
to exactly the location it seems to have been thinking about.
So, it's thinking of the future,
it's imagining the future, which is exactly what we'd hoped to see with
these more sophisticated behaviours that the arena is exhibiting.
- This is a bold claim -
that leaving water for land, where long-range vision makes planning
a matter of life or death,
may have led to the ability to imagine.
- If you're going to do the more complicated thing,
which is essentially representing the future and future opportunities
and threats, that requires a lot of neural power.
It's a massively intensive task.
So, this is one of the demands on the nervous system
that presumably feeds into this huge 10x increase in brain size
in the mammals and in the birds,
relative to ancestral aquatic organisms.
- Being able to visualise the future, to plan and solve problems,
powers enabled by the burgeoning neocortex,
would eventually come to give mammals
a huge evolutionary advantage.
- They survive, probably in large part because of their large brains,
their high intelligence, their ability to solve problems.
Within a few hundred thousand years,
we start seeing mammals the size of pigs.
Within about a million years,
we start to see mammals the size of cows.
So, as these mammals themselves are getting larger,
the brains are getting larger, but you can see it better on CAT scans.
These are the brains, you can kind of see them getting bigger.
And that grey bit at the top,
that's the same thing as the bump in Morganucodon, that's the neocortex,
but you can see it's getting bigger and bigger and bigger.
And as mammals continue to adapt
and evolve into dogs and cats and bats, whales, elephants, kangaroos,
all the mammals that we know, monkeys, apes,
and eventually humans, you know, that neocortex,
it came to envelop the surface of the brain.
- And so, most of what we regard as the brains of humans
actually emerged from that bump in Morgie?
- Exactly. That's the first whisper of a revolution,
a cognitive revolution, and we see in ourselves that same structure,
but a just much grander scale.
- So, how important, would you say, was the emergence
of warm-blooded animals in the evolution of the brain?
- To me, that was the single biggest, Big Bang instance
in the history of brain evolution.
So much about the brains that we have today were shaped
by our metabolism being evolved by our fossil ancestors.
- If Malcolm MacIver, Dan Dombeck and Steve Brusatte are right,
then the movement to land and the development of warm-bloodedness
are responsible for the single largest neural growth spurt
in 600 million years.
It gave us the greatest gift of all...
..the brain.
Next time -
foraging, tool-building, child-rearing, and relationships.
How our social lives have shaped the human brain.
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...
..and follow the links to the Open University.
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.
- SHE CHUCKLES - Some... Just a little bit!
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...
- LAUGHTER Exactly.
- 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?
Sorry, dear. - JULIE LAUGHS
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.
The poker face. - LAUGHTER
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?
- JIM LAUGHS - It's a long evening.
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,
LAUGHTER or, D, Jim Al-Khalili?
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.