Guts Origins of Us

The shape of your face.

Walking on two legs.

The way you see the world.

What makes you the person you are?

The story of each and every one of us

can be traced back millions of years to the plains of ancient Africa.

The answers to the question what makes us human

lie buried in the ground in the fossils

and other traces of our ancestors,

but also lie deep within our own bodies,

in our bones, flesh and genes.

As an anatomist, I'm fascinated by the way our bodies

have been sculpted by our ancestors' struggle for survival

and what took us out of the forests, leaving the other apes behind,

to spread out across the globe

was our search for food.

It's quite juicy.

It's left its mark in our mouths

and in our behaviour.

Flame!

Food makes us behave in the strangest ways.

It's even driven the way we attract the opposite sex.

The ways in which we find food and digest it

have not only left their mark on our bodies,

but underpin our success as a species.

The warm waters off the coast of East Africa

are home to an extraordinary creature.

A link to our evolutionary past.

This strange looking animal is known as a tunicate,

or sea squirt,

and, believe it or not, this is a distant relative of mine.

It is quite hard to believe I've got anything at all in common with this sea squirt.

It doesn't have eyes, it doesn't have arms and legs.

In fact, pretty much all it does have is a gut.

He's got an in hole to the gut there,

and an out hole over there.

It's a little U-shaped gut.

This simple process of food in, waste out, gives us the blueprint

for the guts that lie at the heart of every animal, including us.

We humans like to think that we are so special,

that we're so different from every other life form.

And yet, there is something that unites us

with every other animal on the planet

and that is the search for food.

And the quest to feed ourselves has driven changes in our bodies.

The need for food hasn't just shaped sea squirts, it's shaped us as well,

from our own guts, to the way we move, the way we behave

and even the way in which we experience the world around us.

But it's on land here in Africa that our story really begins.

Over millions of years, our ancestors' bodies were shaped

by the search for food as they crawled out onto land,

evolving into reptiles, mammals and, eventually, monkeys.

They are fast asleep.

These are red colobus monkeys.

30 million years ago, there weren't any humans on the planet,

there weren't any apes, but there were monkeys.

You and I evolved from monkeys which would have looked something like this.

Propliopithecus, an ancient primate ancestor

that lived in the trees on a diet of fruit and leaves.

And their search for food

has directly affected the way we see the world today.

Most mammals wouldn't be able to tell the difference

between these two tomatoes.

But for you and me, the difference is obvious

and this is all because of a crucial change in our ancestor's eyes

that probably happened 30 to 40 million years ago.

At the back of all mammals' eyes are light sensitive colour receptors called cones.

Most mammals have only two types,

that cover the blue and yellow parts of the spectrum.

But 30 million years ago, a genetic mutation created a third,

one that opened up a whole new range of colour...

..Reds and greens.

And with this, our full colour vision was born,

revealing a rich and bountiful range of foods.

If you're a leaf-eating primate, three colour receptors

might help you pick out the slight paler, more yellow, tender leaves to eat.

But for a fruit-eating primate, it means that you can pick up

on the signals that the trees are giving you,

that when something is ready to eat it turns red,

and you know that it is full of sugar and more nutritious.

Being able to tell when fruit was ripe,

packed with life-giving sugar and energy,

must've been a massive advantage in our ancestors' struggle for survival.

Those animals with eyes tuned in to finding the richest foods

were more likely to survive and pass on their genes

and so colour vision spread,

until their descendants, including us,

were seeing in glorious Technicolor.

With our three types of colour receptors,

our eyes can see up to a million different colours.

Our colour vision is a sensory gift.

There are relatively few other mammals that see all the rich and varied colours that we do.

And that goes all the way back to our monkey ancestors

searching out the most tender leaves,

the ripest fruits in those forests 30 million years ago.

Our ancestors flourished in those forests for millions of years,

with first monkeys, then apes exploiting the abundant food there.

And maybe they would've stayed in the trees

if it hadn't been for a series of major climate changes

that brought the search for food out of the trees

and down onto the ground.

From around three million years ago,

the global climate was fluctuating and becoming cooler and drier.

And we know from studies of ancient climate,

but also by looking at the animals that were around at the time,

that the woodlands were shrinking, whilst grasslands were expanding.

So, this was a really important potential habitat

if apes could manage to adapt and find food here.

And adapt they did.

Apes came down from the trees to walk on two legs

out across the savannah.

Fossil finds have revealed at least six different species

of upright, walking apes living in Africa around this time.

Exactly how they relate to each other, or to us,

no-one can be certain.

All we know comes from a few fragmented fossils

of species like Australopithecus africanus

and Paranthropus boisei.

But it's clear that their bodies were shaped by the search for food.

This peculiar looking creature is, believe it or not,

part of our ancestral family tree.

He was an upright walking ape, but only about a metre tall,

and he's got a tiny brain case here of less than a litre in capacity.

He's got an extremely wide face with flaring cheek bones

and a big muscle would have passed up here,

going right up on the side of the head,

to this crest on the top.

And that is temporalis muscle, which operates the jaw.

You can feel it on the side of your own head when you chew.

He's got absolutely massive jaws and teeth,

and although his proper name is Paranthropus boisei,

these earned him the nickname of Nutcracker Man.

From the shape of his face, it's long been thought

that Nutcracker Man survived on the dry savannah

by eating hard, dry foods, like nuts and seeds.

But, whatever they were eating, they eventually died out.

Whereas, it seems our ancestors were eating something very different.

And I'm on the hunt to find it.

The only trouble is the evidence is being guarded by a formidable predator.

Well, we're driving out to try to find some lions.

The clue I'm looking for is hidden deep within their food.

Oh, look there's a buffalo skull.

In fact, there's a whole skeleton

scattered around here.

Do you think we're getting close to them?

Yeah, we are getting closer.

There's one, look! There's a big male.

There's a magnificent male just lying there under the trees.

He's fantastic.

They're mating!

They have no shame, these lions.

They're just such huge animals.

And these were the predators

that our ancestors were sharing their environment with.

And the lions have found food.

It seems that he's worked up a bit of an appetite, which isn't surprising,

because when a female's in season they'll be mating six, seven times an hour.

Anyway, he's having a break now.

It's extraordinary to watch him tucking into this animal.

He's gone for the soft belly first of all, pulling out the guts,

and he's gradually working his way deeper and deeper into the flesh.

And the clue I'm looking for is actually hidden within that meat.

And that's because most of the animals that lions kill and eat

are carrying parasites.

And, as strange as it sounds,

those parasites can tell us something about our ancestors.

The meat lions eat is riddled with tapeworm larvae,

which grow into huge tapeworms inside the lion's gut

up to five metres long,

attaching themselves to their host with barbed hooks

and leaching off their food.

See that middle one?

Eugh!

Oh, these really are

disgusting animals, they're the stuff of nightmares.

Yet they're incredibly revealing.

Genetics studies have discovered that the lion tapeworm

is almost identical to a tapeworm found in humans.

In fact, it's so similar it seems likely that humans got this tapeworm from lions.

But you can't catch these parasites directly from another meat eater.

You can catch it by eating the same meat.

So, this suggests that humans, at some point,

were eating exactly the same animals that lions were eating,

big herbivores like antelopes in Africa.

Not only that, but it seems that we can pin a date on this.

Genetic studies suggest that that transfer of the tape

worm to a new host, to humans,

happened sometime before 800,000 to 1.7 million years ago.

For decades, the idea of our ancestors as meat eaters and hunters

has only been a theory, guessed at from fossil remains and stone tools.

But this is proof, not only for eating meat, but eating big game.

Proof that is living inside our guts today.

And by dating it, we're able to guess

who this meat eater was.

Homo erectus.

This is a replica of a fossil skull that was found here in Kenya in 1975.

It belongs to a species which is called Homo erectus,

or sometimes Homo ergaster, and

he looks very different from species that had gone before.

He has a smaller face, he would have been much taller

and would have had long legs, as well.

A lot more like you and I.

Homo erectus had a body shape almost identical to modern humans,

with long legs and a narrow waist.

He was amongst the earliest apes to deserve the name Homo,

meaning human.

And he used tools to butcher meat

and, perhaps, even to kill it, as a hunter.

And this idea of man the hunter

has been used to explain all sorts of changes

in intelligence, in bodies and behaviour.

One of the most obvious ways in which meat eating

is thought to have changed us is in the shape of our faces.

-Oh, this is a great collection.

-Thank you.

Dr Peter Ungar is a world authority on our ancestors' faces and teeth.

He's been looking at how a changing diet

might have affected the shape of our ancestors' jaws.

If you look at this earlier human ancestor,

they are large flat teeth and kind of bulbous in shape.

But when we move on to Homo erectus,

-what you see here is you see smaller teeth.

-Yep.

Thinner tooth enamel.

And, in fact, the face has responded, as well.

-It's much more slender, what we call gracile.

-Yeah.

Without big heavy chewing muscles.

-The cheekbones are very neat, aren't they?

-They are.

It's much more human-like in its general configuration.

Homo erectus' smaller teeth meant a smaller jaw.

And he lost that ape-like snout

of earlier ancestors like Australopithecus.

With a flatter face shape,

Homo erectus looks much more like a modern human.

To see how well our teeth and jaws are adapted to eating meat

we're going to put them to the test

with a machine designed by Jean Francois Meullenet, one of Peter's colleagues.

Known as the Bite Master,

this machine uses a sophisticated array of motors

to precisely mimic a natural chewing action.

First, we tried the large, flat teeth of Australopithecus.

I'm slightly nervous about this, it did look quite vicious!

-OK.

-That should do it.

Would they have been able to chew through meat?

It hasn't actually bitten through. It's just kind of squashed it.

Compressed it.

Those teeth aren't very well suited for sheering or slicing through tough foods like meat.

It's kind of like pounding steak with a hammer.

So, if our early ancestor's teeth can't cut it with meat, let's see

what three million years of evolution have done for meat eating with a cast of my teeth.

It feels quite odd to see my own teeth going into this machine.

Do you want to see what it does with a piece of meat?

Yeah, I am vegetarian, though.

I wonder if I've got meat-eating teeth?

-Let's give it a shot.

-Shall we have a try?

Good job.

Yeah, you see, it's eating through. That's amazing.

Take this piece of meat out now.

And that is amazing.

It hasn't quite pierced through,

but you can see the light through that piece of meat now.

-Absolutely.

-Wow.

The smaller, sharper teeth that evolved in all our mouths

seem well-adapted to shearing through

the tough muscle fibres of meat.

And these are the teeth of a vegetarian by choice!

By choice,

not by evolution.

But Peter's research doesn't stop there.

He's been using the latest technology to analyse the surface

of our ancestor's teeth at a microscopic level.

Tooth enamel is the hardest substance in the entire body,

but, incredibly, every time you eat your food leaves it's mark.

The evidence of your diet it etched onto the surface of your teeth in the forms of scratches and pits.

Right, look at that, that's gorgeous!

You're looking at an event that happened at a moment in time,

something like 3.3 or 3.4 million years ago.

The connection between yourself and your ancestors is right there.

It's like footprints, almost.

From these scratches, Peter can tell what our ancestors were eating,

and he's made a surprising discovery.

This is cool, get ready for this!

Boom! Look at those big, heavy pits.

-Yeah, they're like craters in the surface of the teeth.

-That's right.

-So, who's this?

-This is Homo erectus.

Here it is in three dimensions, and we can rotate it.

Look at that.

Big, heavy gouges taken out of that Homo erectus.

OK, so what's caused that?

Well, this particular individual unquestionably

ate something hard and brittle.

A nut, a seed, a root, a hard tuber, something like that.

But this is Homo erectus with its smaller teeth

that we wouldn't expect to be eating really hard foods.

That's right.

But here's a different one.

Check this out, here's another Homo erectus.

This individual ate tough foods.

So, what do you think these Homo erectus individuals

could have been eating to get scratches like that?

Well, it could be grasses, or in this case it could be meat.

Right.

But I think what's most important here is that

if we take the whole range of Homo erectus specimens,

it looks very much like

a species with a very variable diet.

So this is really interesting,

because previous theories of human evolution

have put forward meat eating

as being this real fundamental change that happened.

And what we seem to be saying here is that, OK,

meat was perhaps part of the diet,

but the real key to it was that the diet is getting much broader.

Absolutely. I think meat is part of it, but there's more to the story.

Meat might have shaped our teeth,

but our ancestors were eating much more.

And we don't have to go far

from teeth to find out what else was in that varied diet.

I'm a vegetarian, so I know that it's possible for a human being

to survive for a number of years without eating any meat at all.

So, I'm not surprised that meat eating

wasn't the only change in our ancestor's diets.

There's some very interesting new evidence

which suggests we adapted to a new source of food

which was crucial to our survival.

And the evidence is found in our mouths, in our own saliva.

Our spit.

Scientists have been comparing our saliva

with that of chimpanzees

with whom we share a common ancestor going back about six million years.

Whilst our early ancestors were probably

eating a diet similar to that of chimpanzees today,

we have since evolved to live on different foods

and our saliva has changed.

Zoo manager Kris Hern has trained the chimps at Twycross Zoo

to open their mouths for dental checks

so we can try to get a sample of their saliva.

I'm going to ask him to open his mouth on a cue,

which is like that, and he should open his mouth.

And then I'm going to take a swab.

-Hopefully he's got some saliva in there for us.

-Yep.

And we'll take it from there.

-I'll get some gloves on, ready to take the swab.

-Open.

Oh, Kip, you're being ever so good.

'Chimp saliva, like ours, is packed with enzymes

'which starts to digest our food even before we've swallowed it.'

-Thank you, Kip.

-Thank you Kip. There you are.

-Wonderful. Right, OK, let's go and test this saliva.

-OK.

Any differences in the enzymes between their saliva and mine

can tell us about the specific foods we've evolved to eat.

Right, now I'm going to try and wring out the chimp spit.

And this is looking great.

Now I've just got to produce some of my own.

Excuse me.

Then I add flour and iodine.

This test should show how much of an enzyme called amylase

is in each sample of saliva.

The lighter the colour, the more salivary amylase is present.

After just a few minutes, the chimp sample has turned black,

whereas my human sample is still yellow,

clearly showing that my saliva has much more amylase.

Now, this is really interesting

and I'm thrilled this little experiment has worked

because it reflects the results of the much larger study

which actually looked at the levels of the enzyme amylase

in human saliva and chimpanzee saliva

and found that we, humans, have six to eight times

as much of this enzyme in our saliva as chimpanzees do.

Amylase breaks starch down into sugars.

It suggests that we are specifically adapted to eating starchy foods.

It means that at some point in our evolutionary journey

starch must have become really important to us.

To find out why we need to go back to where we came from.

This remote part of East Africa has been home to humans for millennia.

I'm on my way to meet an extraordinary group of people

who live here in Eastern Tanzania.

They're called the Hadza, and they're a modern people,

but they're living in a similar environment

and eating similar things to our ancestors.

The Hadza are some of the last nomadic hunter gatherers on Earth,

and in the 21st century

their diet still harks back to that of our ancient ancestors.

Oh, there's it. Look, look, look, there's some little children.

Oh, this is amazing!

ALL GREET EACH OTHER

The Hadza live in mobile camps, moving on every few months,

and they live on what they can find

in this arid environment.

Meat is prized above all

and the men go out hunting most days.

I'm really excited this morning

because one of the hunters had agreed

to take me out with him hunting,

which is just so unusual.

Normally it's forbidden for women to go along and hunt.

So, I'm in a really privileged position.

THEY GREET EACH OTHER IN LOCAL LANGUAGE

Yeah, Alice.

Click languages, like Hadzane,

may be close to the earliest human languages.

We can set off now? Are you ready?

Fantastic.

Nyanza, what are you looking for?

Are you looking mainly for birds, or are you looking for other animals?

Nyanza is one of the camp's best hunters

and, like most Hadza men, usually hunts on his own.

A Hadza hunter will focus on big game if he can,

but finding anything in this parched bush land is hard.

It tends to be the older men, in their 40s and 50s,

who bring back most meat.

Experience counts for a lot here.

Temperatures are already soaring and it's only mid morning.

A Hadza hunter may cover about six miles in his search for food.

Well, this is certainly hot and tiring

and I'm not even keeping as alert as Nyanza is.

He's constantly on the lookout for any movement

that might tell him that there's an animal about.

(Close.)

(That was so close, a tiny bird.)

We're two hours in and still no luck.

The Hadza love meat when they can have it,

but it's not a reliable source of food.

Only one in 29 Hadza hunts

is successful in terms of the men coming home with big game.

It's clear I'm slowing Nyanza down,

so I let him continue while I head back to camp.

So, Nyanza, thank you so much for letting me come with you

and I'll let you go off on your own now. Thank you.

See you later.

But back at the camp the women don't seem to be that concerned

about the lack of meat for supper

because they've got plans of their own.

THEY GREET EACH OTHER

Every day the women head out on the search for food themselves.

I'm Alice. Alice.

-Alice.

-Alice. Yeah.

-Nibala?

-Nibala.

-Nibala.

Unlike the men, who hunt alone, the women work together

and spend around four hours a day out gathering fruit and roots.

The first port of call?

Berries.

Oh, masses of berries!

So, you squeeze it to get it out of the shell?

Ah, I see, right, OK.

It's like a tiny, sweet, slimy lychee.

Mmm.

There's quite a honey sweetness to it.

I like it.

It's lovely.

But fruits like these aren't available all year round.

Luckily, there is something else that is always there,

something they can rely on all through the year,

tubers.

Ah, OK.

So, these leaves belong to the plant that has the tubers underground,

and if you trace these back

it's these great big vine-like branches here

which go down and then, hopefully, somewhere under the ground there,

Nibala's going to find some tubers.

Is that a bit there?

Is that it? Yeah?

Tug it? Ooh, wow!

That's the end of it.

Look at that.

It looks like a cross between a, I don't know, a root

and a bit of a spindly sweet potato, maybe.

And just like a potato, this tuber is a staple food,

packed full of energy in the form of starch.

Oh, thank you, thank you.

It's not unpleasant.

It's quite nice. Mmm.

It's quite juicy, actually.

When you first bite into it, it's a bit like celery,

but it would be the most fibrous, tough celery you'd ever eaten.

It's got a lovely nutty flavour to it.

It's nice.

And, of course, I've got that very powerful saliva

with plenty of amylase in it,

so I can immediately start breaking down the starch

and benefiting from the sugars it contains.

So, in an uncertain world, where men often come home empty handed,

the humble tuber is sometimes all there is to eat.

We don't know exactly how our ancestors lived

millions of years ago,

but we can assume they were living on similar foods.

And it's likely the enzymes we all have in our saliva

evolved because tubers were so often on the menu.

I'd like to ask everyone if they think the women bring more food in than the men?

In fact, women bring in about 60% of the calories for the entire group.

Without them and the tuber,

survival here would be impossible.

When food is scarce, being able to eat a broad and flexible diet

is an obvious advantage and it meant

that early humans, like Homo erectus, became experts at survival.

But it didn't stop there.

The ability to survive by eating a great variety of different foods,

from fruit and tubers to meat,

meant that our ancestors

weren't restricted to one particular type of environment.

And this meant, in turn, that they could spread out into new habitats

and, eventually, colonise the globe.

From around two million years ago, Homo erectus left Africa.

And they were just the first of several human species who would go on to populate the globe.

Their ability to eat a varied diet meant they could survive virtually anywhere,

from arid savannah,

to the freezing Arctic,

to temperate woodland.

This is our old friend, Homo erectus.

And, as far as we know,

these were the first people to expand out of Africa

and to spread right across Asia.

Then, 600,000 years ago, another species appears

in Africa and in Europe,

Homo heidelbergensis.

Thought to be descended from Homo erectus, he was similar in build,

but with a bigger brain

and it's thought that he in turn evolved into another species.

200,000 years ago someone else appears on the scene,

and this time it's us, Homo sapiens.

We originated in Africa

and then spread out right across the globe.

But, as well as population expansion,

there's something else very obvious going on here,

and that's an increase in brain size over time.

Large brains need a lot of energy

and it's always been thought that what fuelled brain growth was meat.

But a new idea suggests it might be linked

to something even more powerful.

Fire.

A flame!

Fantastic, I've started a fire.

There's something really magical about starting a fire from nothing.

I really don't think that we can underestimate the value of fire to our ancestors.

It would have offered them protection,

warmth during cold nights and in cold climates,

light after the sun had gone down.

But it's incredibly hard to know

when exactly our ancestors first learnt to control fire.

Fires are just so spectacular when they've burning, but, of course,

when they've burnt out there's so little left,

just a thin layer of ash on the ground,

so it's not surprising it's really difficult to pick up the traces

of the first fires that our ancestors would have controlled.

There's some evidence going back 1.5 million years ago

that our ancestors may have controlled fire, but,

by the time our own species, Homo sapiens, is around,

we're using fire all the time.

And we get an idea of what they were doing with fire

from charred remains.

Things like pieces of burnt bone, charred hazelnut shells.

They were cooking.

I've got these burdock roots. They're probably charred to nothing.

Well, I can truthfully say that roasted burdock root is quite tasty.

But cooking doesn't only make food more palatable.

Recent research suggests

it was cooking, not meat,

that fuelled the evolution of our big brains.

It was cooking that made us human.

This theory has given rise to a new wave of scientific research

investigating the advantages that cooked food has over raw.

And I'm going to demonstrate this in a very basic way,

first by eating a quarter of a day's calories in raw carrots.

Right, it's just taken me...

about five, six minutes to eat a single carrot.

So if I was trying to survive on raw carrots alone

I'd be munching my way through them for eight hours a day.

Not only does eating raw food take a long time...

Do you want to swap?

..but actually digesting it uses up energy.

For every 100 calories of raw food I eat,

I use up to 25 calories chewing and digesting it.

Right, that is the end of my last raw carrot,

and I'm really glad, because it's taken me hours to eat them.

And now to see the difference cooking makes.

There's so many of them they barely fit in the colander.

When you cook something like carrots, you're not actually altering the calorie content,

but there is something crucially different about them.

Well, I've nearly finished and this half of the experiment was much easier.

I can get through a cooked carrot in probably half the time

it would take me to chomp my way through a raw carrot.

Cooked food is much easier to digest than raw

and this simple fact holds the key

to why cooking has been so important in our evolution.

Not only is cooked food easier to chew, it takes less energy to digest it once it reaches our guts,

which means that we effectively get more energy from cooked food

because we put less into digesting it.

And although cooked food contains the same amount of calories as raw food...

we can get at more of those calories by cooking it -

with some foods up to 35% more.

And some scientists believe that it was this extra energy from cooking

that was crucial to supporting the growth of our big brains.

Over millions of years,

our search for food has taken us from fruit-eating monkeys in the forest

to hunters and gatherers, striding out onto the open plains.

It's driven the development of tools

and the control of fire that have taken us across the globe.

But it hasn't just changed us physically, it's done something else -

it has shaped our behaviour.

We evolved as hunter-gatherers, living on similar foods to the Hadza.

Finding food shapes their society,

but it is has affected all of us.

It seems that the Hadza, and presumably our ancestors too,

found a very efficient and effective way of surviving here.

Men and women each have different and distinctive roles,

so the women go digging for tubers and collecting berries,

whilst the men go out hunting for meat and honey.

They'll eat some of it while they're out in the bush,

but they bring a lot of it back home to share,

so it makes sense to pair up.

Having a partner to share food with is a massive advantage in this harsh environment,

and many Hadza men and women marry for life.

Sharing food like this is thought to be the origin

of pairing up and staying together.

How did you get married?

Was there a ceremony?

Do Hadzabe men always just have one wife at one time?

How long have you and Pendo been married?

And people outside your family, how might they know that you're married?

Pendo, what do you think the benefits of being a married woman will be?

And are you looking forward to having children together?

Hadza women typically have around five children, which is hard work.

It takes a Hadza woman around 13 million calories

to raise a child from conception until it's weaned.

And she can't physically do it without support,

so choosing the right partner

is one of the most important decisions a woman here has to make.

So what do you think makes a good Hadzabe man?

What would make you love him?

Anything else? A nice face, maybe? A tall man?

'Hadza women work hard to bring in food for the family

'and they want a partner who will do the same.'

I think it makes perfect sense in this environment

for the women to be so choosy about the men whom they marry,

because if those men aren't good hunters, good providers,

the women have a lot to lose.

And women's preference for good hunters

is thought to have shaped the way men behave, wherever they live.

Even when there's nothing to hunt,

men can still find ways to show off their prowess to women.

The latest research shows that men are in some way hard-wired

to show potential partners they've got what it takes.

And they do it by taking risks.

And we're going to show you how with some of Britain's best skateboarders.

Rather strangely, we've asked them to try to perform a trick

that they're not very good at, that they're still struggling to learn,

and that, in fact, they're likely to fail at.

The important thing is that they're taking a risk.

Whilst practicing their difficult tricks,

there's a moment when the skateboarder makes an unconscious decision

either to play it safe and give up on the trick by kicking the board away so they can land safely,

or to live dangerously, to stick with the trick

and try to land the board, which is risky.

To start with, a male researcher monitors how often they take a risk

and how often they play it safe.

What happens when we introduce some attractive young women into the equation?

In the presence of female observers, the men seem to be gambling more.

In fact, the original research

showed that risk-taking almost doubled when an attractive woman was present.

And that, it seems, comes down to testosterone.

Scientists have found

that having women around increases the skateboarder's levels of testosterone by up to 40%,

forcing the men to display their potential

for the modern day version of a good hunter.

Men showing off to women by taking risks could be a throwback

to the food gathering strategies of our ancestors.

By taking risks, men are signalling that they're likely to be good providers

and therefore better mates.

So it seems that men have an excuse for behaving the way they do.

They're designed to be show-offs.

It turns out that food has driven the evolutionary journey

of both the men and women of our species, Homo sapiens.

So much about us today, from the way we feel about each other

to the ways in which we think and behave, and even the way we look,

we can trace back to our hunter-gatherer ancestors in Africa

and their search for food.

But since then we have spread out to every corner of the globe

and our population has exploded.

And what enabled that was farming.

In the last 10,000 years, we've gone from being nomadic hunter-gatherers

to large-scale industrial farmers.

That has enabled a population explosion...

..and changed the face of our planet,

with over a third of the land on Earth taken over by farming.

Our relationship with food has had a powerful effect on us,

shaping the structure of our bodies and our societies,

and having a massive impact on the environment around us.

We've gone from being forest-dwelling, fruit-eating apes

to becoming a species that can survive finding food just about anywhere

because we put it there.

We're naturally able to eat a diverse variety of foods

and, through the use of culture, through cooking and farming,

we've widened that range even further

and that underpins our success as a global species.

Subtitles by Red Bee Media Ltd

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