Origins of Us (2011): Season 1, Episode 2 - Guts - full transcript
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.
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.