Guts Origins of Us


Guts

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The shape of your face.

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Walking on two legs.

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The way you see the world.

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What makes you the person you are?

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The story of each and every one of us

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

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The answers to the question what makes us human

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lie buried in the ground in the fossils

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and other traces of our ancestors,

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but also lie deep within our own bodies,

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in our bones, flesh and genes.

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

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have been sculpted by our ancestors' struggle for survival

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

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to spread out across the globe

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was our search for food.

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It's quite juicy.

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It's left its mark in our mouths

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and in our behaviour.

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Flame!

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Food makes us behave in the strangest ways.

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

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The ways in which we find food and digest it

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have not only left their mark on our bodies,

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but underpin our success as a species.

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The warm waters off the coast of East Africa

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are home to an extraordinary creature.

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A link to our evolutionary past.

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This strange looking animal is known as a tunicate,

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or sea squirt,

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

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

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

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

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

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and an out hole over there.

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It's a little U-shaped gut.

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

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

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We humans like to think that we are so special,

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

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And yet, there is something that unites us

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with every other animal on the planet

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and that is the search for food.

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

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

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

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

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

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Over millions of years, our ancestors' bodies were shaped

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

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evolving into reptiles, mammals and, eventually, monkeys.

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They are fast asleep.

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These are red colobus monkeys.

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

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

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

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Propliopithecus, an ancient primate ancestor

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

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And their search for food

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has directly affected the way we see the world today.

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Most mammals wouldn't be able to tell the difference

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between these two tomatoes.

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But for you and me, the difference is obvious

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

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that probably happened 30 to 40 million years ago.

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

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Most mammals have only two types,

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that cover the blue and yellow parts of the spectrum.

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

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

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..Reds and greens.

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And with this, our full colour vision was born,

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revealing a rich and bountiful range of foods.

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

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

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

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on the signals that the trees are giving you,

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that when something is ready to eat it turns red,

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

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Being able to tell when fruit was ripe,

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packed with life-giving sugar and energy,

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

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Those animals with eyes tuned in to finding the richest foods

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were more likely to survive and pass on their genes

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and so colour vision spread,

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until their descendants, including us,

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were seeing in glorious Technicolor.

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With our three types of colour receptors,

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our eyes can see up to a million different colours.

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Our colour vision is a sensory gift.

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

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And that goes all the way back to our monkey ancestors

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searching out the most tender leaves,

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the ripest fruits in those forests 30 million years ago.

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Our ancestors flourished in those forests for millions of years,

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

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And maybe they would've stayed in the trees

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

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that brought the search for food out of the trees

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and down onto the ground.

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From around three million years ago,

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the global climate was fluctuating and becoming cooler and drier.

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And we know from studies of ancient climate,

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

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that the woodlands were shrinking, whilst grasslands were expanding.

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So, this was a really important potential habitat

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if apes could manage to adapt and find food here.

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And adapt they did.

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Apes came down from the trees to walk on two legs

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out across the savannah.

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Fossil finds have revealed at least six different species

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

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

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no-one can be certain.

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All we know comes from a few fragmented fossils

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of species like Australopithecus africanus

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and Paranthropus boisei.

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

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This peculiar looking creature is, believe it or not,

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part of our ancestral family tree.

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

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

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

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and a big muscle would have passed up here,

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going right up on the side of the head,

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to this crest on the top.

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And that is temporalis muscle, which operates the jaw.

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

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He's got absolutely massive jaws and teeth,

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and although his proper name is Paranthropus boisei,

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these earned him the nickname of Nutcracker Man.

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

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that Nutcracker Man survived on the dry savannah

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

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

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

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And I'm on the hunt to find it.

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

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

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

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Oh, look there's a buffalo skull.

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In fact, there's a whole skeleton

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scattered around here.

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Do you think we're getting close to them?

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Yeah, we are getting closer.

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

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

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He's fantastic.

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They're mating!

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They have no shame, these lions.

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They're just such huge animals.

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And these were the predators

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that our ancestors were sharing their environment with.

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And the lions have found food.

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

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

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Anyway, he's having a break now.

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

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

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

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

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

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are carrying parasites.

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And, as strange as it sounds,

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those parasites can tell us something about our ancestors.

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The meat lions eat is riddled with tapeworm larvae,

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which grow into huge tapeworms inside the lion's gut

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up to five metres long,

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attaching themselves to their host with barbed hooks

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and leaching off their food.

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See that middle one?

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Eugh!

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Oh, these really are

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disgusting animals, they're the stuff of nightmares.

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Yet they're incredibly revealing.

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Genetics studies have discovered that the lion tapeworm

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is almost identical to a tapeworm found in humans.

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

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

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You can catch it by eating the same meat.

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So, this suggests that humans, at some point,

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were eating exactly the same animals that lions were eating,

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big herbivores like antelopes in Africa.

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

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Genetic studies suggest that that transfer of the tape

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worm to a new host, to humans,

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

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

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

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

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Proof that is living inside our guts today.

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And by dating it, we're able to guess

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who this meat eater was.

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Homo erectus.

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

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It belongs to a species which is called Homo erectus,

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or sometimes Homo ergaster, and

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he looks very different from species that had gone before.

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

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and would have had long legs, as well.

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A lot more like you and I.

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

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with long legs and a narrow waist.

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

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meaning human.

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And he used tools to butcher meat

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

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And this idea of man the hunter

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has been used to explain all sorts of changes

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in intelligence, in bodies and behaviour.

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One of the most obvious ways in which meat eating

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

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-Oh, this is a great collection.

-Thank you.

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

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He's been looking at how a changing diet

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might have affected the shape of our ancestors' jaws.

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If you look at this earlier human ancestor,

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

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But when we move on to Homo erectus,

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-what you see here is you see smaller teeth.

-Yep.

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Thinner tooth enamel.

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

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

-Yeah.

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Without big heavy chewing muscles.

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

-They are.

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

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Homo erectus' smaller teeth meant a smaller jaw.

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And he lost that ape-like snout

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of earlier ancestors like Australopithecus.

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With a flatter face shape,

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Homo erectus looks much more like a modern human.

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

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we're going to put them to the test

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

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Known as the Bite Master,

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this machine uses a sophisticated array of motors

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to precisely mimic a natural chewing action.

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

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

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-OK.

-That should do it.

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Would they have been able to chew through meat?

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

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Compressed it.

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

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

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

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

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

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

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Yeah, I am vegetarian, though.

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

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-Let's give it a shot.

-Shall we have a try?

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Good job.

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

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Take this piece of meat out now.

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And that is amazing.

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It hasn't quite pierced through,

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

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-Absolutely.

-Wow.

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The smaller, sharper teeth that evolved in all our mouths

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seem well-adapted to shearing through

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the tough muscle fibres of meat.

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And these are the teeth of a vegetarian by choice!

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By choice,

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not by evolution.

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But Peter's research doesn't stop there.

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

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of our ancestor's teeth at a microscopic level.

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Tooth enamel is the hardest substance in the entire body,

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

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

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Right, look at that, that's gorgeous!

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

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something like 3.3 or 3.4 million years ago.

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The connection between yourself and your ancestors is right there.

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It's like footprints, almost.

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

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and he's made a surprising discovery.

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This is cool, get ready for this!

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Boom! Look at those big, heavy pits.

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

-That's right.

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-So, who's this?

-This is Homo erectus.

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

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Look at that.

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Big, heavy gouges taken out of that Homo erectus.

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OK, so what's caused that?

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Well, this particular individual unquestionably

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ate something hard and brittle.

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

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But this is Homo erectus with its smaller teeth

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

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That's right.

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But here's a different one.

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Check this out, here's another Homo erectus.

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This individual ate tough foods.

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So, what do you think these Homo erectus individuals

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could have been eating to get scratches like that?

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

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Right.

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But I think what's most important here is that

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if we take the whole range of Homo erectus specimens,

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it looks very much like

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a species with a very variable diet.

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So this is really interesting,

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because previous theories of human evolution

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have put forward meat eating

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as being this real fundamental change that happened.

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

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meat was perhaps part of the diet,

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

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

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Meat might have shaped our teeth,

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but our ancestors were eating much more.

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And we don't have to go far

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

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

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

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So, I'm not surprised that meat eating

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

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There's some very interesting new evidence

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which suggests we adapted to a new source of food

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which was crucial to our survival.

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

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Our spit.

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Scientists have been comparing our saliva

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with that of chimpanzees

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

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Whilst our early ancestors were probably

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eating a diet similar to that of chimpanzees today,

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we have since evolved to live on different foods

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and our saliva has changed.

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Zoo manager Kris Hern has trained the chimps at Twycross Zoo

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to open their mouths for dental checks

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

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

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

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And then I'm going to take a swab.

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

-Yep.

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And we'll take it from there.

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

-Open.

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

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'Chimp saliva, like ours, is packed with enzymes

0:26:440:26:47

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

0:26:470:26:50

-Thank you, Kip.

-Thank you Kip. There you are.

0:26:500:26:53

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

-OK.

0:26:530:26:58

Any differences in the enzymes between their saliva and mine

0:27:000:27:04

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

0:27:040:27:08

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

0:27:090:27:13

And this is looking great.

0:27:130:27:16

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

0:27:210:27:23

Excuse me.

0:27:230:27:25

Then I add flour and iodine.

0:27:310:27:36

This test should show how much of an enzyme called amylase

0:27:360:27:39

is in each sample of saliva.

0:27:390:27:42

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

0:27:420:27:45

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

0:27:480:27:52

whereas my human sample is still yellow,

0:27:550:27:58

clearly showing that my saliva has much more amylase.

0:27:580:28:02

Now, this is really interesting

0:28:040:28:06

and I'm thrilled this little experiment has worked

0:28:060:28:09

because it reflects the results of the much larger study

0:28:090:28:12

which actually looked at the levels of the enzyme amylase

0:28:120:28:16

in human saliva and chimpanzee saliva

0:28:160:28:19

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

0:28:190:28:23

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

0:28:230:28:27

Amylase breaks starch down into sugars.

0:28:270:28:31

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

0:28:310:28:37

It means that at some point in our evolutionary journey

0:28:440:28:47

starch must have become really important to us.

0:28:470:28:50

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

0:28:520:28:57

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

0:29:000:29:05

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

0:29:110:29:14

who live here in Eastern Tanzania.

0:29:140:29:16

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

0:29:160:29:20

but they're living in a similar environment

0:29:200:29:23

and eating similar things to our ancestors.

0:29:230:29:26

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

0:29:330:29:36

and in the 21st century

0:29:360:29:39

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

0:29:390:29:43

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

0:29:460:29:50

Oh, this is amazing!

0:29:500:29:51

ALL GREET EACH OTHER

0:29:590:30:00

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

0:30:160:30:20

and they live on what they can find

0:30:200:30:22

in this arid environment.

0:30:220:30:26

Meat is prized above all

0:30:260:30:29

and the men go out hunting most days.

0:30:290:30:31

I'm really excited this morning

0:30:350:30:37

because one of the hunters had agreed

0:30:370:30:40

to take me out with him hunting,

0:30:400:30:42

which is just so unusual.

0:30:420:30:44

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

0:30:440:30:47

So, I'm in a really privileged position.

0:30:470:30:50

THEY GREET EACH OTHER IN LOCAL LANGUAGE

0:30:510:30:53

Yeah, Alice.

0:31:000:31:01

Click languages, like Hadzane,

0:31:080:31:11

may be close to the earliest human languages.

0:31:110:31:14

We can set off now? Are you ready?

0:31:140:31:17

Fantastic.

0:31:170:31:19

Nyanza, what are you looking for?

0:31:270:31:29

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

0:31:290:31:33

Nyanza is one of the camp's best hunters

0:31:500:31:53

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

0:31:530:31:58

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

0:31:590:32:03

but finding anything in this parched bush land is hard.

0:32:030:32:08

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

0:32:130:32:17

who bring back most meat.

0:32:170:32:19

Experience counts for a lot here.

0:32:190:32:22

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

0:32:390:32:46

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

0:32:460:32:51

Well, this is certainly hot and tiring

0:32:560:32:58

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

0:32:580:33:01

He's constantly on the lookout for any movement

0:33:010:33:04

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

0:33:040:33:07

(Close.)

0:33:250:33:26

(That was so close, a tiny bird.)

0:33:260:33:28

We're two hours in and still no luck.

0:33:290:33:32

The Hadza love meat when they can have it,

0:33:370:33:41

but it's not a reliable source of food.

0:33:410:33:44

Only one in 29 Hadza hunts

0:33:440:33:47

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

0:33:470:33:53

It's clear I'm slowing Nyanza down,

0:34:080:34:10

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

0:34:100:34:13

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

0:34:150:34:18

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

0:34:180:34:21

See you later.

0:34:230:34:24

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

0:34:310:34:34

about the lack of meat for supper

0:34:340:34:36

because they've got plans of their own.

0:34:360:34:38

THEY GREET EACH OTHER

0:34:380:34:41

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

0:34:540:34:58

I'm Alice. Alice.

0:35:140:35:16

-Alice.

-Alice. Yeah.

0:35:160:35:19

-Nibala?

-Nibala.

-Nibala.

0:35:200:35:23

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

0:35:310:35:36

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

0:35:360:35:40

The first port of call?

0:35:480:35:50

Berries.

0:35:500:35:51

Oh, masses of berries!

0:35:580:36:00

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

0:36:020:36:05

Ah, I see, right, OK.

0:36:050:36:07

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

0:36:090:36:11

Mmm.

0:36:110:36:13

There's quite a honey sweetness to it.

0:36:140:36:16

I like it.

0:36:190:36:21

It's lovely.

0:36:240:36:26

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

0:36:280:36:32

Luckily, there is something else that is always there,

0:36:360:36:41

something they can rely on all through the year,

0:36:410:36:43

tubers.

0:36:430:36:45

Ah, OK.

0:36:450:36:47

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

0:36:470:36:51

and if you trace these back

0:36:510:36:53

it's these great big vine-like branches here

0:36:530:36:56

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

0:36:560:37:01

Nibala's going to find some tubers.

0:37:010:37:04

Is that a bit there?

0:37:090:37:10

Is that it? Yeah?

0:37:100:37:13

Tug it? Ooh, wow!

0:37:150:37:19

That's the end of it.

0:37:190:37:21

Look at that.

0:37:210:37:23

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

0:37:250:37:28

and a bit of a spindly sweet potato, maybe.

0:37:280:37:30

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

0:37:340:37:37

packed full of energy in the form of starch.

0:37:370:37:40

Oh, thank you, thank you.

0:37:420:37:45

It's not unpleasant.

0:37:490:37:51

It's quite nice. Mmm.

0:37:520:37:53

It's quite juicy, actually.

0:37:550:37:56

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

0:37:580:38:01

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

0:38:010:38:06

It's got a lovely nutty flavour to it.

0:38:080:38:10

It's nice.

0:38:100:38:12

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

0:38:120:38:15

with plenty of amylase in it,

0:38:150:38:17

so I can immediately start breaking down the starch

0:38:170:38:21

and benefiting from the sugars it contains.

0:38:210:38:23

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

0:38:280:38:32

the humble tuber is sometimes all there is to eat.

0:38:320:38:37

We don't know exactly how our ancestors lived

0:38:390:38:43

millions of years ago,

0:38:430:38:45

but we can assume they were living on similar foods.

0:38:450:38:48

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

0:38:480:38:53

evolved because tubers were so often on the menu.

0:38:530:38:57

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

0:38:580:39:05

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

0:39:320:39:38

Without them and the tuber,

0:39:380:39:40

survival here would be impossible.

0:39:400:39:43

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

0:39:480:39:52

is an obvious advantage and it meant

0:39:520:39:56

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

0:39:560:40:02

But it didn't stop there.

0:40:020:40:03

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

0:40:040:40:09

from fruit and tubers to meat,

0:40:090:40:11

meant that our ancestors

0:40:110:40:13

weren't restricted to one particular type of environment.

0:40:130:40:17

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

0:40:170:40:22

and, eventually, colonise the globe.

0:40:220:40:24

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

0:40:300:40:35

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

0:40:360:40:42

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

0:40:420:40:48

from arid savannah,

0:40:480:40:51

to the freezing Arctic,

0:40:530:40:55

to temperate woodland.

0:40:570:41:00

This is our old friend, Homo erectus.

0:41:160:41:18

And, as far as we know,

0:41:200:41:22

these were the first people to expand out of Africa

0:41:220:41:26

and to spread right across Asia.

0:41:260:41:28

Then, 600,000 years ago, another species appears

0:41:280:41:32

in Africa and in Europe,

0:41:320:41:34

Homo heidelbergensis.

0:41:340:41:36

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

0:41:360:41:41

but with a bigger brain

0:41:410:41:43

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

0:41:430:41:47

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

0:41:470:41:51

and this time it's us, Homo sapiens.

0:41:510:41:54

We originated in Africa

0:42:000:42:01

and then spread out right across the globe.

0:42:010:42:05

But, as well as population expansion,

0:42:050:42:07

there's something else very obvious going on here,

0:42:070:42:11

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

0:42:110:42:14

Large brains need a lot of energy

0:42:140:42:16

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

0:42:160:42:21

But a new idea suggests it might be linked

0:42:210:42:23

to something even more powerful.

0:42:230:42:26

Fire.

0:42:280:42:29

A flame!

0:42:290:42:31

Fantastic, I've started a fire.

0:42:310:42:35

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

0:42:490:42:54

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

0:43:010:43:07

It would have offered them protection,

0:43:070:43:09

warmth during cold nights and in cold climates,

0:43:090:43:12

light after the sun had gone down.

0:43:120:43:16

But it's incredibly hard to know

0:43:160:43:19

when exactly our ancestors first learnt to control fire.

0:43:190:43:23

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

0:43:230:43:27

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

0:43:270:43:30

just a thin layer of ash on the ground,

0:43:300:43:32

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

0:43:320:43:36

of the first fires that our ancestors would have controlled.

0:43:360:43:40

There's some evidence going back 1.5 million years ago

0:43:400:43:45

that our ancestors may have controlled fire, but,

0:43:450:43:50

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

0:43:500:43:53

we're using fire all the time.

0:43:530:43:55

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

0:43:560:44:00

from charred remains.

0:44:000:44:02

Things like pieces of burnt bone, charred hazelnut shells.

0:44:020:44:07

They were cooking.

0:44:070:44:09

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

0:44:120:44:15

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

0:44:220:44:28

But cooking doesn't only make food more palatable.

0:44:280:44:33

Recent research suggests

0:44:360:44:37

it was cooking, not meat,

0:44:370:44:40

that fuelled the evolution of our big brains.

0:44:400:44:44

It was cooking that made us human.

0:44:460:44:50

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

0:44:580:45:02

investigating the advantages that cooked food has over raw.

0:45:020:45:07

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

0:45:070:45:11

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

0:45:110:45:15

Right, it's just taken me...

0:45:240:45:27

about five, six minutes to eat a single carrot.

0:45:270:45:31

So if I was trying to survive on raw carrots alone

0:45:310:45:34

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

0:45:340:45:39

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

0:45:390:45:44

Do you want to swap?

0:45:440:45:47

..but actually digesting it uses up energy.

0:45:470:45:51

For every 100 calories of raw food I eat,

0:45:530:45:56

I use up to 25 calories chewing and digesting it.

0:45:560:46:01

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

0:46:040:46:08

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

0:46:080:46:11

And now to see the difference cooking makes.

0:46:130:46:16

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

0:46:160:46:20

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

0:46:200:46:25

but there is something crucially different about them.

0:46:250:46:27

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

0:46:410:46:46

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

0:46:460:46:51

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

0:46:510:46:53

Cooked food is much easier to digest than raw

0:46:530:46:58

and this simple fact holds the key

0:46:580:47:01

to why cooking has been so important in our evolution.

0:47:010:47:05

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

0:47:050:47:11

which means that we effectively get more energy from cooked food

0:47:110:47:15

because we put less into digesting it.

0:47:150:47:17

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

0:47:170:47:22

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

0:47:220:47:25

with some foods up to 35% more.

0:47:250:47:29

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

0:47:290:47:33

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

0:47:330:47:38

Over millions of years,

0:47:440:47:46

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

0:47:460:47:52

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

0:47:520:47:57

It's driven the development of tools

0:47:570:48:00

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

0:48:000:48:05

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

0:48:050:48:10

it has shaped our behaviour.

0:48:100:48:12

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

0:48:210:48:26

Finding food shapes their society,

0:48:450:48:49

but it is has affected all of us.

0:48:490:48:52

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

0:48:560:48:59

found a very efficient and effective way of surviving here.

0:48:590:49:05

Men and women each have different and distinctive roles,

0:49:050:49:09

so the women go digging for tubers and collecting berries,

0:49:090:49:13

whilst the men go out hunting for meat and honey.

0:49:130:49:17

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

0:49:170:49:21

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

0:49:210:49:24

so it makes sense to pair up.

0:49:240:49:26

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

0:49:280:49:34

and many Hadza men and women marry for life.

0:49:340:49:38

Sharing food like this is thought to be the origin

0:49:470:49:51

of pairing up and staying together.

0:49:510:49:54

How did you get married?

0:50:000:50:03

Was there a ceremony?

0:50:030:50:04

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

0:50:230:50:28

How long have you and Pendo been married?

0:50:380:50:40

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

0:50:430:50:47

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

0:51:000:51:05

And are you looking forward to having children together?

0:51:200:51:23

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

0:51:380:51:42

It takes a Hadza woman around 13 million calories

0:51:440:51:50

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

0:51:500:51:53

And she can't physically do it without support,

0:52:090:52:14

so choosing the right partner

0:52:140:52:17

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

0:52:170:52:22

So what do you think makes a good Hadzabe man?

0:52:250:52:28

What would make you love him?

0:52:280:52:30

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

0:52:410:52:45

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

0:53:000:53:03

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

0:53:030:53:06

I think it makes perfect sense in this environment

0:53:060:53:09

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

0:53:090:53:13

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

0:53:130:53:17

the women have a lot to lose.

0:53:170:53:20

And women's preference for good hunters

0:53:200:53:23

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

0:53:230:53:27

Even when there's nothing to hunt,

0:53:330:53:35

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

0:53:350:53:39

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

0:53:460:53:50

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

0:53:500:53:54

And they do it by taking risks.

0:53:540:53:57

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

0:53:580:54:03

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

0:54:040:54:09

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

0:54:090:54:12

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

0:54:120:54:14

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

0:54:140:54:19

Whilst practicing their difficult tricks,

0:54:240:54:27

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

0:54:270:54:31

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

0:54:310:54:36

or to live dangerously, to stick with the trick

0:54:360:54:40

and try to land the board, which is risky.

0:54:400:54:44

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

0:54:440:54:49

and how often they play it safe.

0:54:490:54:51

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

0:54:560:55:01

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

0:55:200:55:25

In fact, the original research

0:55:250:55:27

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

0:55:270:55:31

And that, it seems, comes down to testosterone.

0:55:370:55:40

Scientists have found

0:55:420:55:44

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

0:55:440:55:50

forcing the men to display their potential

0:55:500:55:53

for the modern day version of a good hunter.

0:55:530:55:56

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

0:56:000:56:04

to the food gathering strategies of our ancestors.

0:56:040:56:07

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

0:56:070:56:13

and therefore better mates.

0:56:130:56:15

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

0:56:150:56:20

They're designed to be show-offs.

0:56:200:56:23

It turns out that food has driven the evolutionary journey

0:56:270:56:30

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

0:56:300:56:35

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

0:56:370:56:42

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

0:56:420:56:46

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

0:56:460:56:51

and their search for food.

0:56:510:56:52

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

0:56:520:56:57

and our population has exploded.

0:56:570:57:00

And what enabled that was farming.

0:57:000:57:03

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

0:57:090:57:13

to large-scale industrial farmers.

0:57:130:57:17

That has enabled a population explosion...

0:57:220:57:27

..and changed the face of our planet,

0:57:310:57:34

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

0:57:340:57:39

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

0:57:480:57:52

shaping the structure of our bodies and our societies,

0:57:520:57:56

and having a massive impact on the environment around us.

0:57:560:58:00

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

0:58:000:58:04

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

0:58:040:58:09

because we put it there.

0:58:090:58:12

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

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

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we've widened that range even further

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and that underpins our success as a global species.

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0:58:470:58:50

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