0:00:06 > 0:00:09The shape of your face.
0:00:09 > 0:00:12Walking on two legs.
0:00:12 > 0:00:15The way you see the world.
0:00:15 > 0:00:18What makes you the person you are?
0:00:22 > 0:00:26The story of each and every one of us
0:00:26 > 0:00:31can be traced back millions of years to the plains of ancient Africa.
0:00:33 > 0:00:36The answers to the question what makes us human
0:00:36 > 0:00:39lie buried in the ground in the fossils
0:00:39 > 0:00:41and other traces of our ancestors,
0:00:41 > 0:00:45but also lie deep within our own bodies,
0:00:45 > 0:00:48in our bones, flesh and genes.
0:00:51 > 0:00:55As an anatomist, I'm fascinated by the way our bodies
0:00:55 > 0:01:00have been sculpted by our ancestors' struggle for survival
0:01:06 > 0:01:10and what took us out of the forests, leaving the other apes behind,
0:01:10 > 0:01:14to spread out across the globe
0:01:14 > 0:01:17was our search for food.
0:01:17 > 0:01:19It's quite juicy.
0:01:19 > 0:01:23It's left its mark in our mouths
0:01:23 > 0:01:26and in our behaviour.
0:01:26 > 0:01:27Flame!
0:01:27 > 0:01:31Food makes us behave in the strangest ways.
0:01:33 > 0:01:37It's even driven the way we attract the opposite sex.
0:01:40 > 0:01:44The ways in which we find food and digest it
0:01:44 > 0:01:47have not only left their mark on our bodies,
0:01:47 > 0:01:50but underpin our success as a species.
0:02:18 > 0:02:21The warm waters off the coast of East Africa
0:02:21 > 0:02:25are home to an extraordinary creature.
0:02:28 > 0:02:32A link to our evolutionary past.
0:02:36 > 0:02:40This strange looking animal is known as a tunicate,
0:02:40 > 0:02:42or sea squirt,
0:02:42 > 0:02:46and, believe it or not, this is a distant relative of mine.
0:02:57 > 0:03:01It is quite hard to believe I've got anything at all in common with this sea squirt.
0:03:01 > 0:03:04It doesn't have eyes, it doesn't have arms and legs.
0:03:04 > 0:03:08In fact, pretty much all it does have is a gut.
0:03:08 > 0:03:12He's got an in hole to the gut there,
0:03:12 > 0:03:14and an out hole over there.
0:03:14 > 0:03:16It's a little U-shaped gut.
0:03:16 > 0:03:21This simple process of food in, waste out, gives us the blueprint
0:03:21 > 0:03:27for the guts that lie at the heart of every animal, including us.
0:03:27 > 0:03:30We humans like to think that we are so special,
0:03:30 > 0:03:34that we're so different from every other life form.
0:03:34 > 0:03:37And yet, there is something that unites us
0:03:37 > 0:03:39with every other animal on the planet
0:03:39 > 0:03:42and that is the search for food.
0:03:45 > 0:03:50And the quest to feed ourselves has driven changes in our bodies.
0:03:51 > 0:03:57The need for food hasn't just shaped sea squirts, it's shaped us as well,
0:03:57 > 0:04:01from our own guts, to the way we move, the way we behave
0:04:01 > 0:04:06and even the way in which we experience the world around us.
0:04:16 > 0:04:22But it's on land here in Africa that our story really begins.
0:04:24 > 0:04:28Over millions of years, our ancestors' bodies were shaped
0:04:28 > 0:04:32by the search for food as they crawled out onto land,
0:04:32 > 0:04:39evolving into reptiles, mammals and, eventually, monkeys.
0:04:44 > 0:04:47They are fast asleep.
0:04:47 > 0:04:50These are red colobus monkeys.
0:04:50 > 0:04:5430 million years ago, there weren't any humans on the planet,
0:04:54 > 0:04:57there weren't any apes, but there were monkeys.
0:05:14 > 0:05:19You and I evolved from monkeys which would have looked something like this.
0:05:19 > 0:05:23Propliopithecus, an ancient primate ancestor
0:05:23 > 0:05:28that lived in the trees on a diet of fruit and leaves.
0:05:30 > 0:05:32And their search for food
0:05:32 > 0:05:37has directly affected the way we see the world today.
0:05:39 > 0:05:43Most mammals wouldn't be able to tell the difference
0:05:43 > 0:05:45between these two tomatoes.
0:05:45 > 0:05:49But for you and me, the difference is obvious
0:05:49 > 0:05:53and this is all because of a crucial change in our ancestor's eyes
0:05:53 > 0:05:57that probably happened 30 to 40 million years ago.
0:06:01 > 0:06:07At the back of all mammals' eyes are light sensitive colour receptors called cones.
0:06:08 > 0:06:11Most mammals have only two types,
0:06:11 > 0:06:15that cover the blue and yellow parts of the spectrum.
0:06:16 > 0:06:22But 30 million years ago, a genetic mutation created a third,
0:06:22 > 0:06:27one that opened up a whole new range of colour...
0:06:31 > 0:06:34..Reds and greens.
0:06:42 > 0:06:46And with this, our full colour vision was born,
0:06:48 > 0:06:52revealing a rich and bountiful range of foods.
0:06:58 > 0:07:01If you're a leaf-eating primate, three colour receptors
0:07:01 > 0:07:06might help you pick out the slight paler, more yellow, tender leaves to eat.
0:07:06 > 0:07:10But for a fruit-eating primate, it means that you can pick up
0:07:10 > 0:07:12on the signals that the trees are giving you,
0:07:12 > 0:07:16that when something is ready to eat it turns red,
0:07:16 > 0:07:21and you know that it is full of sugar and more nutritious.
0:07:30 > 0:07:33Being able to tell when fruit was ripe,
0:07:33 > 0:07:36packed with life-giving sugar and energy,
0:07:36 > 0:07:41must've been a massive advantage in our ancestors' struggle for survival.
0:07:43 > 0:07:47Those animals with eyes tuned in to finding the richest foods
0:07:47 > 0:07:52were more likely to survive and pass on their genes
0:07:52 > 0:07:54and so colour vision spread,
0:07:54 > 0:07:58until their descendants, including us,
0:07:58 > 0:08:00were seeing in glorious Technicolor.
0:08:09 > 0:08:11With our three types of colour receptors,
0:08:11 > 0:08:15our eyes can see up to a million different colours.
0:08:21 > 0:08:24Our colour vision is a sensory gift.
0:08:24 > 0:08:30There are relatively few other mammals that see all the rich and varied colours that we do.
0:08:30 > 0:08:34And that goes all the way back to our monkey ancestors
0:08:34 > 0:08:37searching out the most tender leaves,
0:08:37 > 0:08:41the ripest fruits in those forests 30 million years ago.
0:08:48 > 0:08:53Our ancestors flourished in those forests for millions of years,
0:08:53 > 0:08:58with first monkeys, then apes exploiting the abundant food there.
0:09:04 > 0:09:07And maybe they would've stayed in the trees
0:09:07 > 0:09:12if it hadn't been for a series of major climate changes
0:09:12 > 0:09:16that brought the search for food out of the trees
0:09:16 > 0:09:19and down onto the ground.
0:09:26 > 0:09:29From around three million years ago,
0:09:29 > 0:09:33the global climate was fluctuating and becoming cooler and drier.
0:09:33 > 0:09:35And we know from studies of ancient climate,
0:09:35 > 0:09:39but also by looking at the animals that were around at the time,
0:09:39 > 0:09:45that the woodlands were shrinking, whilst grasslands were expanding.
0:09:45 > 0:09:49So, this was a really important potential habitat
0:09:49 > 0:09:53if apes could manage to adapt and find food here.
0:09:59 > 0:10:00And adapt they did.
0:10:04 > 0:10:09Apes came down from the trees to walk on two legs
0:10:09 > 0:10:11out across the savannah.
0:10:14 > 0:10:18Fossil finds have revealed at least six different species
0:10:18 > 0:10:23of upright, walking apes living in Africa around this time.
0:10:23 > 0:10:26Exactly how they relate to each other, or to us,
0:10:26 > 0:10:28no-one can be certain.
0:10:28 > 0:10:32All we know comes from a few fragmented fossils
0:10:32 > 0:10:37of species like Australopithecus africanus
0:10:37 > 0:10:40and Paranthropus boisei.
0:10:41 > 0:10:46But it's clear that their bodies were shaped by the search for food.
0:10:49 > 0:10:52This peculiar looking creature is, believe it or not,
0:10:52 > 0:10:55part of our ancestral family tree.
0:10:55 > 0:11:00He was an upright walking ape, but only about a metre tall,
0:11:00 > 0:11:05and he's got a tiny brain case here of less than a litre in capacity.
0:11:05 > 0:11:10He's got an extremely wide face with flaring cheek bones
0:11:10 > 0:11:13and a big muscle would have passed up here,
0:11:13 > 0:11:15going right up on the side of the head,
0:11:15 > 0:11:18to this crest on the top.
0:11:18 > 0:11:20And that is temporalis muscle, which operates the jaw.
0:11:20 > 0:11:25You can feel it on the side of your own head when you chew.
0:11:25 > 0:11:29He's got absolutely massive jaws and teeth,
0:11:29 > 0:11:33and although his proper name is Paranthropus boisei,
0:11:33 > 0:11:38these earned him the nickname of Nutcracker Man.
0:11:40 > 0:11:43From the shape of his face, it's long been thought
0:11:43 > 0:11:46that Nutcracker Man survived on the dry savannah
0:11:46 > 0:11:50by eating hard, dry foods, like nuts and seeds.
0:11:54 > 0:11:58But, whatever they were eating, they eventually died out.
0:12:01 > 0:12:06Whereas, it seems our ancestors were eating something very different.
0:12:10 > 0:12:13And I'm on the hunt to find it.
0:12:19 > 0:12:24The only trouble is the evidence is being guarded by a formidable predator.
0:12:31 > 0:12:34Well, we're driving out to try to find some lions.
0:12:40 > 0:12:44The clue I'm looking for is hidden deep within their food.
0:13:09 > 0:13:12Oh, look there's a buffalo skull.
0:13:12 > 0:13:14In fact, there's a whole skeleton
0:13:14 > 0:13:16scattered around here.
0:13:16 > 0:13:18Do you think we're getting close to them?
0:13:18 > 0:13:19Yeah, we are getting closer.
0:13:31 > 0:13:33There's one, look! There's a big male.
0:13:35 > 0:13:40There's a magnificent male just lying there under the trees.
0:13:41 > 0:13:43He's fantastic.
0:13:45 > 0:13:47They're mating!
0:13:49 > 0:13:52They have no shame, these lions.
0:13:55 > 0:13:59They're just such huge animals.
0:14:01 > 0:14:03And these were the predators
0:14:03 > 0:14:06that our ancestors were sharing their environment with.
0:14:15 > 0:14:17And the lions have found food.
0:14:20 > 0:14:24It seems that he's worked up a bit of an appetite, which isn't surprising,
0:14:24 > 0:14:28because when a female's in season they'll be mating six, seven times an hour.
0:14:28 > 0:14:30Anyway, he's having a break now.
0:14:30 > 0:14:33It's extraordinary to watch him tucking into this animal.
0:14:33 > 0:14:37He's gone for the soft belly first of all, pulling out the guts,
0:14:37 > 0:14:40and he's gradually working his way deeper and deeper into the flesh.
0:14:40 > 0:14:45And the clue I'm looking for is actually hidden within that meat.
0:14:45 > 0:14:50And that's because most of the animals that lions kill and eat
0:14:50 > 0:14:53are carrying parasites.
0:14:53 > 0:14:56And, as strange as it sounds,
0:14:56 > 0:15:02those parasites can tell us something about our ancestors.
0:15:10 > 0:15:14The meat lions eat is riddled with tapeworm larvae,
0:15:14 > 0:15:17which grow into huge tapeworms inside the lion's gut
0:15:17 > 0:15:20up to five metres long,
0:15:20 > 0:15:24attaching themselves to their host with barbed hooks
0:15:24 > 0:15:26and leaching off their food.
0:15:26 > 0:15:28See that middle one?
0:15:29 > 0:15:31Eugh!
0:15:31 > 0:15:33Oh, these really are
0:15:33 > 0:15:37disgusting animals, they're the stuff of nightmares.
0:15:37 > 0:15:40Yet they're incredibly revealing.
0:15:40 > 0:15:43Genetics studies have discovered that the lion tapeworm
0:15:43 > 0:15:49is almost identical to a tapeworm found in humans.
0:15:50 > 0:15:57In fact, it's so similar it seems likely that humans got this tapeworm from lions.
0:15:57 > 0:16:02But you can't catch these parasites directly from another meat eater.
0:16:02 > 0:16:06You can catch it by eating the same meat.
0:16:06 > 0:16:09So, this suggests that humans, at some point,
0:16:09 > 0:16:13were eating exactly the same animals that lions were eating,
0:16:13 > 0:16:17big herbivores like antelopes in Africa.
0:16:17 > 0:16:20Not only that, but it seems that we can pin a date on this.
0:16:20 > 0:16:24Genetic studies suggest that that transfer of the tape
0:16:24 > 0:16:27worm to a new host, to humans,
0:16:27 > 0:16:33happened sometime before 800,000 to 1.7 million years ago.
0:16:38 > 0:16:42For decades, the idea of our ancestors as meat eaters and hunters
0:16:42 > 0:16:47has only been a theory, guessed at from fossil remains and stone tools.
0:16:47 > 0:16:54But this is proof, not only for eating meat, but eating big game.
0:16:54 > 0:16:57Proof that is living inside our guts today.
0:17:01 > 0:17:04And by dating it, we're able to guess
0:17:04 > 0:17:07who this meat eater was.
0:17:15 > 0:17:17Homo erectus.
0:17:28 > 0:17:33This is a replica of a fossil skull that was found here in Kenya in 1975.
0:17:33 > 0:17:37It belongs to a species which is called Homo erectus,
0:17:37 > 0:17:40or sometimes Homo ergaster, and
0:17:40 > 0:17:44he looks very different from species that had gone before.
0:17:44 > 0:17:48He has a smaller face, he would have been much taller
0:17:48 > 0:17:50and would have had long legs, as well.
0:17:50 > 0:17:53A lot more like you and I.
0:17:56 > 0:18:01Homo erectus had a body shape almost identical to modern humans,
0:18:01 > 0:18:04with long legs and a narrow waist.
0:18:05 > 0:18:09He was amongst the earliest apes to deserve the name Homo,
0:18:09 > 0:18:11meaning human.
0:18:11 > 0:18:14And he used tools to butcher meat
0:18:14 > 0:18:17and, perhaps, even to kill it, as a hunter.
0:18:19 > 0:18:22And this idea of man the hunter
0:18:22 > 0:18:25has been used to explain all sorts of changes
0:18:25 > 0:18:29in intelligence, in bodies and behaviour.
0:18:31 > 0:18:33One of the most obvious ways in which meat eating
0:18:33 > 0:18:37is thought to have changed us is in the shape of our faces.
0:18:48 > 0:18:50- Oh, this is a great collection. - Thank you.
0:18:51 > 0:18:55Dr Peter Ungar is a world authority on our ancestors' faces and teeth.
0:18:55 > 0:19:00He's been looking at how a changing diet
0:19:00 > 0:19:03might have affected the shape of our ancestors' jaws.
0:19:03 > 0:19:07If you look at this earlier human ancestor,
0:19:07 > 0:19:12they are large flat teeth and kind of bulbous in shape.
0:19:12 > 0:19:15But when we move on to Homo erectus,
0:19:15 > 0:19:18- what you see here is you see smaller teeth.- Yep.
0:19:18 > 0:19:20Thinner tooth enamel.
0:19:20 > 0:19:22And, in fact, the face has responded, as well.
0:19:22 > 0:19:26- It's much more slender, what we call gracile.- Yeah.
0:19:26 > 0:19:28Without big heavy chewing muscles.
0:19:28 > 0:19:31- The cheekbones are very neat, aren't they?- They are.
0:19:31 > 0:19:34It's much more human-like in its general configuration.
0:19:36 > 0:19:41Homo erectus' smaller teeth meant a smaller jaw.
0:19:44 > 0:19:47And he lost that ape-like snout
0:19:47 > 0:19:49of earlier ancestors like Australopithecus.
0:19:55 > 0:19:57With a flatter face shape,
0:19:57 > 0:20:00Homo erectus looks much more like a modern human.
0:20:07 > 0:20:10To see how well our teeth and jaws are adapted to eating meat
0:20:10 > 0:20:12we're going to put them to the test
0:20:12 > 0:20:16with a machine designed by Jean Francois Meullenet, one of Peter's colleagues.
0:20:18 > 0:20:20Known as the Bite Master,
0:20:20 > 0:20:24this machine uses a sophisticated array of motors
0:20:24 > 0:20:29to precisely mimic a natural chewing action.
0:20:29 > 0:20:33First, we tried the large, flat teeth of Australopithecus.
0:20:34 > 0:20:37I'm slightly nervous about this, it did look quite vicious!
0:20:37 > 0:20:39- OK.- That should do it.
0:20:39 > 0:20:42Would they have been able to chew through meat?
0:20:51 > 0:20:55It hasn't actually bitten through. It's just kind of squashed it.
0:20:55 > 0:20:56Compressed it.
0:20:56 > 0:21:01Those teeth aren't very well suited for sheering or slicing through tough foods like meat.
0:21:01 > 0:21:04It's kind of like pounding steak with a hammer.
0:21:09 > 0:21:14So, if our early ancestor's teeth can't cut it with meat, let's see
0:21:14 > 0:21:20what three million years of evolution have done for meat eating with a cast of my teeth.
0:21:22 > 0:21:25It feels quite odd to see my own teeth going into this machine.
0:21:25 > 0:21:27Do you want to see what it does with a piece of meat?
0:21:27 > 0:21:30Yeah, I am vegetarian, though.
0:21:30 > 0:21:33I wonder if I've got meat-eating teeth?
0:21:33 > 0:21:36- Let's give it a shot. - Shall we have a try?
0:21:40 > 0:21:41Good job.
0:21:41 > 0:21:44Yeah, you see, it's eating through. That's amazing.
0:21:50 > 0:21:52Take this piece of meat out now.
0:21:52 > 0:21:54And that is amazing.
0:21:54 > 0:21:57It hasn't quite pierced through,
0:21:57 > 0:22:02but you can see the light through that piece of meat now.
0:22:02 > 0:22:04- Absolutely.- Wow.
0:22:05 > 0:22:10The smaller, sharper teeth that evolved in all our mouths
0:22:10 > 0:22:13seem well-adapted to shearing through
0:22:13 > 0:22:15the tough muscle fibres of meat.
0:22:15 > 0:22:18And these are the teeth of a vegetarian by choice!
0:22:18 > 0:22:20By choice,
0:22:20 > 0:22:22not by evolution.
0:22:25 > 0:22:29But Peter's research doesn't stop there.
0:22:30 > 0:22:34He's been using the latest technology to analyse the surface
0:22:34 > 0:22:38of our ancestor's teeth at a microscopic level.
0:22:41 > 0:22:45Tooth enamel is the hardest substance in the entire body,
0:22:45 > 0:22:49but, incredibly, every time you eat your food leaves it's mark.
0:22:51 > 0:22:58The evidence of your diet it etched onto the surface of your teeth in the forms of scratches and pits.
0:23:00 > 0:23:03Right, look at that, that's gorgeous!
0:23:03 > 0:23:06You're looking at an event that happened at a moment in time,
0:23:06 > 0:23:09something like 3.3 or 3.4 million years ago.
0:23:09 > 0:23:13The connection between yourself and your ancestors is right there.
0:23:13 > 0:23:15It's like footprints, almost.
0:23:17 > 0:23:21From these scratches, Peter can tell what our ancestors were eating,
0:23:21 > 0:23:24and he's made a surprising discovery.
0:23:24 > 0:23:26This is cool, get ready for this!
0:23:26 > 0:23:29Boom! Look at those big, heavy pits.
0:23:29 > 0:23:33- Yeah, they're like craters in the surface of the teeth.- That's right.
0:23:33 > 0:23:36- So, who's this? - This is Homo erectus.
0:23:36 > 0:23:38Here it is in three dimensions, and we can rotate it.
0:23:38 > 0:23:41Look at that.
0:23:41 > 0:23:44Big, heavy gouges taken out of that Homo erectus.
0:23:44 > 0:23:46OK, so what's caused that?
0:23:46 > 0:23:49Well, this particular individual unquestionably
0:23:49 > 0:23:51ate something hard and brittle.
0:23:51 > 0:23:55A nut, a seed, a root, a hard tuber, something like that.
0:23:55 > 0:23:57But this is Homo erectus with its smaller teeth
0:23:57 > 0:24:00that we wouldn't expect to be eating really hard foods.
0:24:00 > 0:24:01That's right.
0:24:01 > 0:24:03But here's a different one.
0:24:03 > 0:24:05Check this out, here's another Homo erectus.
0:24:05 > 0:24:08This individual ate tough foods.
0:24:08 > 0:24:11So, what do you think these Homo erectus individuals
0:24:11 > 0:24:13could have been eating to get scratches like that?
0:24:13 > 0:24:16Well, it could be grasses, or in this case it could be meat.
0:24:16 > 0:24:18Right.
0:24:18 > 0:24:21But I think what's most important here is that
0:24:21 > 0:24:24if we take the whole range of Homo erectus specimens,
0:24:24 > 0:24:26it looks very much like
0:24:26 > 0:24:29a species with a very variable diet.
0:24:29 > 0:24:31So this is really interesting,
0:24:31 > 0:24:34because previous theories of human evolution
0:24:34 > 0:24:36have put forward meat eating
0:24:36 > 0:24:39as being this real fundamental change that happened.
0:24:39 > 0:24:42And what we seem to be saying here is that, OK,
0:24:42 > 0:24:45meat was perhaps part of the diet,
0:24:45 > 0:24:49but the real key to it was that the diet is getting much broader.
0:24:49 > 0:24:53Absolutely. I think meat is part of it, but there's more to the story.
0:24:56 > 0:24:58Meat might have shaped our teeth,
0:24:58 > 0:25:01but our ancestors were eating much more.
0:25:01 > 0:25:02And we don't have to go far
0:25:02 > 0:25:07from teeth to find out what else was in that varied diet.
0:25:19 > 0:25:22I'm a vegetarian, so I know that it's possible for a human being
0:25:22 > 0:25:26to survive for a number of years without eating any meat at all.
0:25:26 > 0:25:28So, I'm not surprised that meat eating
0:25:28 > 0:25:31wasn't the only change in our ancestor's diets.
0:25:31 > 0:25:34There's some very interesting new evidence
0:25:34 > 0:25:37which suggests we adapted to a new source of food
0:25:37 > 0:25:39which was crucial to our survival.
0:25:39 > 0:25:44And the evidence is found in our mouths, in our own saliva.
0:25:44 > 0:25:46Our spit.
0:25:49 > 0:25:52Scientists have been comparing our saliva
0:25:52 > 0:25:53with that of chimpanzees
0:25:53 > 0:25:57with whom we share a common ancestor going back about six million years.
0:25:57 > 0:26:01Whilst our early ancestors were probably
0:26:01 > 0:26:03eating a diet similar to that of chimpanzees today,
0:26:03 > 0:26:08we have since evolved to live on different foods
0:26:08 > 0:26:09and our saliva has changed.
0:26:11 > 0:26:15Zoo manager Kris Hern has trained the chimps at Twycross Zoo
0:26:15 > 0:26:18to open their mouths for dental checks
0:26:18 > 0:26:20so we can try to get a sample of their saliva.
0:26:20 > 0:26:24I'm going to ask him to open his mouth on a cue,
0:26:24 > 0:26:27which is like that, and he should open his mouth.
0:26:27 > 0:26:29And then I'm going to take a swab.
0:26:29 > 0:26:31- Hopefully he's got some saliva in there for us.- Yep.
0:26:31 > 0:26:33And we'll take it from there.
0:26:33 > 0:26:35- I'll get some gloves on, ready to take the swab.- Open.
0:26:41 > 0:26:44Oh, Kip, you're being ever so good.
0:26:44 > 0:26:47'Chimp saliva, like ours, is packed with enzymes
0:26:47 > 0:26:50'which starts to digest our food even before we've swallowed it.'
0:26:50 > 0:26:53- Thank you, Kip. - Thank you Kip. There you are.
0:26:53 > 0:26:58- Wonderful. Right, OK, let's go and test this saliva.- OK.
0:27:00 > 0:27:04Any differences in the enzymes between their saliva and mine
0:27:04 > 0:27:08can tell us about the specific foods we've evolved to eat.
0:27:09 > 0:27:13Right, now I'm going to try and wring out the chimp spit.
0:27:13 > 0:27:16And this is looking great.
0:27:21 > 0:27:23Now I've just got to produce some of my own.
0:27:23 > 0:27:25Excuse me.
0:27:31 > 0:27:36Then I add flour and iodine.
0:27:36 > 0:27:39This test should show how much of an enzyme called amylase
0:27:39 > 0:27:42is in each sample of saliva.
0:27:42 > 0:27:45The lighter the colour, the more salivary amylase is present.
0:27:48 > 0:27:52After just a few minutes, the chimp sample has turned black,
0:27:55 > 0:27:58whereas my human sample is still yellow,
0:27:58 > 0:28:02clearly showing that my saliva has much more amylase.
0:28:04 > 0:28:06Now, this is really interesting
0:28:06 > 0:28:09and I'm thrilled this little experiment has worked
0:28:09 > 0:28:12because it reflects the results of the much larger study
0:28:12 > 0:28:16which actually looked at the levels of the enzyme amylase
0:28:16 > 0:28:19in human saliva and chimpanzee saliva
0:28:19 > 0:28:23and found that we, humans, have six to eight times
0:28:23 > 0:28:27as much of this enzyme in our saliva as chimpanzees do.
0:28:27 > 0:28:31Amylase breaks starch down into sugars.
0:28:31 > 0:28:37It suggests that we are specifically adapted to eating starchy foods.
0:28:44 > 0:28:47It means that at some point in our evolutionary journey
0:28:47 > 0:28:50starch must have become really important to us.
0:28:52 > 0:28:57To find out why we need to go back to where we came from.
0:29:00 > 0:29:05This remote part of East Africa has been home to humans for millennia.
0:29:11 > 0:29:14I'm on my way to meet an extraordinary group of people
0:29:14 > 0:29:16who live here in Eastern Tanzania.
0:29:16 > 0:29:20They're called the Hadza, and they're a modern people,
0:29:20 > 0:29:23but they're living in a similar environment
0:29:23 > 0:29:26and eating similar things to our ancestors.
0:29:33 > 0:29:36The Hadza are some of the last nomadic hunter gatherers on Earth,
0:29:36 > 0:29:39and in the 21st century
0:29:39 > 0:29:43their diet still harks back to that of our ancient ancestors.
0:29:46 > 0:29:50Oh, there's it. Look, look, look, there's some little children.
0:29:50 > 0:29:51Oh, this is amazing!
0:29:59 > 0:30:00ALL GREET EACH OTHER
0:30:16 > 0:30:20The Hadza live in mobile camps, moving on every few months,
0:30:20 > 0:30:22and they live on what they can find
0:30:22 > 0:30:26in this arid environment.
0:30:26 > 0:30:29Meat is prized above all
0:30:29 > 0:30:31and the men go out hunting most days.
0:30:35 > 0:30:37I'm really excited this morning
0:30:37 > 0:30:40because one of the hunters had agreed
0:30:40 > 0:30:42to take me out with him hunting,
0:30:42 > 0:30:44which is just so unusual.
0:30:44 > 0:30:47Normally it's forbidden for women to go along and hunt.
0:30:47 > 0:30:50So, I'm in a really privileged position.
0:30:51 > 0:30:53THEY GREET EACH OTHER IN LOCAL LANGUAGE
0:31:00 > 0:31:01Yeah, Alice.
0:31:08 > 0:31:11Click languages, like Hadzane,
0:31:11 > 0:31:14may be close to the earliest human languages.
0:31:14 > 0:31:17We can set off now? Are you ready?
0:31:17 > 0:31:19Fantastic.
0:31:27 > 0:31:29Nyanza, what are you looking for?
0:31:29 > 0:31:33Are you looking mainly for birds, or are you looking for other animals?
0:31:50 > 0:31:53Nyanza is one of the camp's best hunters
0:31:53 > 0:31:58and, like most Hadza men, usually hunts on his own.
0:31:59 > 0:32:03A Hadza hunter will focus on big game if he can,
0:32:03 > 0:32:08but finding anything in this parched bush land is hard.
0:32:13 > 0:32:17It tends to be the older men, in their 40s and 50s,
0:32:17 > 0:32:19who bring back most meat.
0:32:19 > 0:32:22Experience counts for a lot here.
0:32:39 > 0:32:46Temperatures are already soaring and it's only mid morning.
0:32:46 > 0:32:51A Hadza hunter may cover about six miles in his search for food.
0:32:56 > 0:32:58Well, this is certainly hot and tiring
0:32:58 > 0:33:01and I'm not even keeping as alert as Nyanza is.
0:33:01 > 0:33:04He's constantly on the lookout for any movement
0:33:04 > 0:33:07that might tell him that there's an animal about.
0:33:25 > 0:33:26(Close.)
0:33:26 > 0:33:28(That was so close, a tiny bird.)
0:33:29 > 0:33:32We're two hours in and still no luck.
0:33:37 > 0:33:41The Hadza love meat when they can have it,
0:33:41 > 0:33:44but it's not a reliable source of food.
0:33:44 > 0:33:47Only one in 29 Hadza hunts
0:33:47 > 0:33:53is successful in terms of the men coming home with big game.
0:34:08 > 0:34:10It's clear I'm slowing Nyanza down,
0:34:10 > 0:34:13so I let him continue while I head back to camp.
0:34:15 > 0:34:18So, Nyanza, thank you so much for letting me come with you
0:34:18 > 0:34:21and I'll let you go off on your own now. Thank you.
0:34:23 > 0:34:24See you later.
0:34:31 > 0:34:34But back at the camp the women don't seem to be that concerned
0:34:34 > 0:34:36about the lack of meat for supper
0:34:36 > 0:34:38because they've got plans of their own.
0:34:38 > 0:34:41THEY GREET EACH OTHER
0:34:54 > 0:34:58Every day the women head out on the search for food themselves.
0:35:14 > 0:35:16I'm Alice. Alice.
0:35:16 > 0:35:19- Alice.- Alice. Yeah.
0:35:20 > 0:35:23- Nibala?- Nibala.- Nibala.
0:35:31 > 0:35:36Unlike the men, who hunt alone, the women work together
0:35:36 > 0:35:40and spend around four hours a day out gathering fruit and roots.
0:35:48 > 0:35:50The first port of call?
0:35:50 > 0:35:51Berries.
0:35:58 > 0:36:00Oh, masses of berries!
0:36:02 > 0:36:05So, you squeeze it to get it out of the shell?
0:36:05 > 0:36:07Ah, I see, right, OK.
0:36:09 > 0:36:11It's like a tiny, sweet, slimy lychee.
0:36:11 > 0:36:13Mmm.
0:36:14 > 0:36:16There's quite a honey sweetness to it.
0:36:19 > 0:36:21I like it.
0:36:24 > 0:36:26It's lovely.
0:36:28 > 0:36:32But fruits like these aren't available all year round.
0:36:36 > 0:36:41Luckily, there is something else that is always there,
0:36:41 > 0:36:43something they can rely on all through the year,
0:36:43 > 0:36:45tubers.
0:36:45 > 0:36:47Ah, OK.
0:36:47 > 0:36:51So, these leaves belong to the plant that has the tubers underground,
0:36:51 > 0:36:53and if you trace these back
0:36:53 > 0:36:56it's these great big vine-like branches here
0:36:56 > 0:37:01which go down and then, hopefully, somewhere under the ground there,
0:37:01 > 0:37:04Nibala's going to find some tubers.
0:37:09 > 0:37:10Is that a bit there?
0:37:10 > 0:37:13Is that it? Yeah?
0:37:15 > 0:37:19Tug it? Ooh, wow!
0:37:19 > 0:37:21That's the end of it.
0:37:21 > 0:37:23Look at that.
0:37:25 > 0:37:28It looks like a cross between a, I don't know, a root
0:37:28 > 0:37:30and a bit of a spindly sweet potato, maybe.
0:37:34 > 0:37:37And just like a potato, this tuber is a staple food,
0:37:37 > 0:37:40packed full of energy in the form of starch.
0:37:42 > 0:37:45Oh, thank you, thank you.
0:37:49 > 0:37:51It's not unpleasant.
0:37:52 > 0:37:53It's quite nice. Mmm.
0:37:55 > 0:37:56It's quite juicy, actually.
0:37:58 > 0:38:01When you first bite into it, it's a bit like celery,
0:38:01 > 0:38:06but it would be the most fibrous, tough celery you'd ever eaten.
0:38:08 > 0:38:10It's got a lovely nutty flavour to it.
0:38:10 > 0:38:12It's nice.
0:38:12 > 0:38:15And, of course, I've got that very powerful saliva
0:38:15 > 0:38:17with plenty of amylase in it,
0:38:17 > 0:38:21so I can immediately start breaking down the starch
0:38:21 > 0:38:23and benefiting from the sugars it contains.
0:38:28 > 0:38:32So, in an uncertain world, where men often come home empty handed,
0:38:32 > 0:38:37the humble tuber is sometimes all there is to eat.
0:38:39 > 0:38:43We don't know exactly how our ancestors lived
0:38:43 > 0:38:45millions of years ago,
0:38:45 > 0:38:48but we can assume they were living on similar foods.
0:38:48 > 0:38:53And it's likely the enzymes we all have in our saliva
0:38:53 > 0:38:57evolved because tubers were so often on the menu.
0:38:58 > 0:39:05I'd like to ask everyone if they think the women bring more food in than the men?
0:39:32 > 0:39:38In fact, women bring in about 60% of the calories for the entire group.
0:39:38 > 0:39:40Without them and the tuber,
0:39:40 > 0:39:43survival here would be impossible.
0:39:48 > 0:39:52When food is scarce, being able to eat a broad and flexible diet
0:39:52 > 0:39:56is an obvious advantage and it meant
0:39:56 > 0:40:02that early humans, like Homo erectus, became experts at survival.
0:40:02 > 0:40:03But it didn't stop there.
0:40:04 > 0:40:09The ability to survive by eating a great variety of different foods,
0:40:09 > 0:40:11from fruit and tubers to meat,
0:40:11 > 0:40:13meant that our ancestors
0:40:13 > 0:40:17weren't restricted to one particular type of environment.
0:40:17 > 0:40:22And this meant, in turn, that they could spread out into new habitats
0:40:22 > 0:40:24and, eventually, colonise the globe.
0:40:30 > 0:40:35From around two million years ago, Homo erectus left Africa.
0:40:36 > 0:40:42And they were just the first of several human species who would go on to populate the globe.
0:40:42 > 0:40:48Their ability to eat a varied diet meant they could survive virtually anywhere,
0:40:48 > 0:40:51from arid savannah,
0:40:53 > 0:40:55to the freezing Arctic,
0:40:57 > 0:41:00to temperate woodland.
0:41:16 > 0:41:18This is our old friend, Homo erectus.
0:41:20 > 0:41:22And, as far as we know,
0:41:22 > 0:41:26these were the first people to expand out of Africa
0:41:26 > 0:41:28and to spread right across Asia.
0:41:28 > 0:41:32Then, 600,000 years ago, another species appears
0:41:32 > 0:41:34in Africa and in Europe,
0:41:34 > 0:41:36Homo heidelbergensis.
0:41:36 > 0:41:41Thought to be descended from Homo erectus, he was similar in build,
0:41:41 > 0:41:43but with a bigger brain
0:41:43 > 0:41:47and it's thought that he in turn evolved into another species.
0:41:47 > 0:41:51200,000 years ago someone else appears on the scene,
0:41:51 > 0:41:54and this time it's us, Homo sapiens.
0:42:00 > 0:42:01We originated in Africa
0:42:01 > 0:42:05and then spread out right across the globe.
0:42:05 > 0:42:07But, as well as population expansion,
0:42:07 > 0:42:11there's something else very obvious going on here,
0:42:11 > 0:42:14and that's an increase in brain size over time.
0:42:14 > 0:42:16Large brains need a lot of energy
0:42:16 > 0:42:21and it's always been thought that what fuelled brain growth was meat.
0:42:21 > 0:42:23But a new idea suggests it might be linked
0:42:23 > 0:42:26to something even more powerful.
0:42:28 > 0:42:29Fire.
0:42:29 > 0:42:31A flame!
0:42:31 > 0:42:35Fantastic, I've started a fire.
0:42:49 > 0:42:54There's something really magical about starting a fire from nothing.
0:43:01 > 0:43:07I really don't think that we can underestimate the value of fire to our ancestors.
0:43:07 > 0:43:09It would have offered them protection,
0:43:09 > 0:43:12warmth during cold nights and in cold climates,
0:43:12 > 0:43:16light after the sun had gone down.
0:43:16 > 0:43:19But it's incredibly hard to know
0:43:19 > 0:43:23when exactly our ancestors first learnt to control fire.
0:43:23 > 0:43:27Fires are just so spectacular when they've burning, but, of course,
0:43:27 > 0:43:30when they've burnt out there's so little left,
0:43:30 > 0:43:32just a thin layer of ash on the ground,
0:43:32 > 0:43:36so it's not surprising it's really difficult to pick up the traces
0:43:36 > 0:43:40of the first fires that our ancestors would have controlled.
0:43:40 > 0:43:45There's some evidence going back 1.5 million years ago
0:43:45 > 0:43:50that our ancestors may have controlled fire, but,
0:43:50 > 0:43:53by the time our own species, Homo sapiens, is around,
0:43:53 > 0:43:55we're using fire all the time.
0:43:56 > 0:44:00And we get an idea of what they were doing with fire
0:44:00 > 0:44:02from charred remains.
0:44:02 > 0:44:07Things like pieces of burnt bone, charred hazelnut shells.
0:44:07 > 0:44:09They were cooking.
0:44:12 > 0:44:15I've got these burdock roots. They're probably charred to nothing.
0:44:22 > 0:44:28Well, I can truthfully say that roasted burdock root is quite tasty.
0:44:28 > 0:44:33But cooking doesn't only make food more palatable.
0:44:36 > 0:44:37Recent research suggests
0:44:37 > 0:44:40it was cooking, not meat,
0:44:40 > 0:44:44that fuelled the evolution of our big brains.
0:44:46 > 0:44:50It was cooking that made us human.
0:44:58 > 0:45:02This theory has given rise to a new wave of scientific research
0:45:02 > 0:45:07investigating the advantages that cooked food has over raw.
0:45:07 > 0:45:11And I'm going to demonstrate this in a very basic way,
0:45:11 > 0:45:15first by eating a quarter of a day's calories in raw carrots.
0:45:24 > 0:45:27Right, it's just taken me...
0:45:27 > 0:45:31about five, six minutes to eat a single carrot.
0:45:31 > 0:45:34So if I was trying to survive on raw carrots alone
0:45:34 > 0:45:39I'd be munching my way through them for eight hours a day.
0:45:39 > 0:45:44Not only does eating raw food take a long time...
0:45:44 > 0:45:47Do you want to swap?
0:45:47 > 0:45:51..but actually digesting it uses up energy.
0:45:53 > 0:45:56For every 100 calories of raw food I eat,
0:45:56 > 0:46:01I use up to 25 calories chewing and digesting it.
0:46:04 > 0:46:08Right, that is the end of my last raw carrot,
0:46:08 > 0:46:11and I'm really glad, because it's taken me hours to eat them.
0:46:13 > 0:46:16And now to see the difference cooking makes.
0:46:16 > 0:46:20There's so many of them they barely fit in the colander.
0:46:20 > 0:46:25When you cook something like carrots, you're not actually altering the calorie content,
0:46:25 > 0:46:27but there is something crucially different about them.
0:46:41 > 0:46:46Well, I've nearly finished and this half of the experiment was much easier.
0:46:46 > 0:46:51I can get through a cooked carrot in probably half the time
0:46:51 > 0:46:53it would take me to chomp my way through a raw carrot.
0:46:53 > 0:46:58Cooked food is much easier to digest than raw
0:46:58 > 0:47:01and this simple fact holds the key
0:47:01 > 0:47:05to why cooking has been so important in our evolution.
0:47:05 > 0:47:11Not only is cooked food easier to chew, it takes less energy to digest it once it reaches our guts,
0:47:11 > 0:47:15which means that we effectively get more energy from cooked food
0:47:15 > 0:47:17because we put less into digesting it.
0:47:17 > 0:47:22And although cooked food contains the same amount of calories as raw food...
0:47:22 > 0:47:25we can get at more of those calories by cooking it -
0:47:25 > 0:47:29with some foods up to 35% more.
0:47:29 > 0:47:33And some scientists believe that it was this extra energy from cooking
0:47:33 > 0:47:38that was crucial to supporting the growth of our big brains.
0:47:44 > 0:47:46Over millions of years,
0:47:46 > 0:47:52our search for food has taken us from fruit-eating monkeys in the forest
0:47:52 > 0:47:57to hunters and gatherers, striding out onto the open plains.
0:47:57 > 0:48:00It's driven the development of tools
0:48:00 > 0:48:05and the control of fire that have taken us across the globe.
0:48:05 > 0:48:10But it hasn't just changed us physically, it's done something else -
0:48:10 > 0:48:12it has shaped our behaviour.
0:48:21 > 0:48:26We evolved as hunter-gatherers, living on similar foods to the Hadza.
0:48:45 > 0:48:49Finding food shapes their society,
0:48:49 > 0:48:52but it is has affected all of us.
0:48:56 > 0:48:59It seems that the Hadza, and presumably our ancestors too,
0:48:59 > 0:49:05found a very efficient and effective way of surviving here.
0:49:05 > 0:49:09Men and women each have different and distinctive roles,
0:49:09 > 0:49:13so the women go digging for tubers and collecting berries,
0:49:13 > 0:49:17whilst the men go out hunting for meat and honey.
0:49:17 > 0:49:21They'll eat some of it while they're out in the bush,
0:49:21 > 0:49:24but they bring a lot of it back home to share,
0:49:24 > 0:49:26so it makes sense to pair up.
0:49:28 > 0:49:34Having a partner to share food with is a massive advantage in this harsh environment,
0:49:34 > 0:49:38and many Hadza men and women marry for life.
0:49:47 > 0:49:51Sharing food like this is thought to be the origin
0:49:51 > 0:49:54of pairing up and staying together.
0:50:00 > 0:50:03How did you get married?
0:50:03 > 0:50:04Was there a ceremony?
0:50:23 > 0:50:28Do Hadzabe men always just have one wife at one time?
0:50:38 > 0:50:40How long have you and Pendo been married?
0:50:43 > 0:50:47And people outside your family, how might they know that you're married?
0:51:00 > 0:51:05Pendo, what do you think the benefits of being a married woman will be?
0:51:20 > 0:51:23And are you looking forward to having children together?
0:51:38 > 0:51:42Hadza women typically have around five children, which is hard work.
0:51:44 > 0:51:50It takes a Hadza woman around 13 million calories
0:51:50 > 0:51:53to raise a child from conception until it's weaned.
0:52:09 > 0:52:14And she can't physically do it without support,
0:52:14 > 0:52:17so choosing the right partner
0:52:17 > 0:52:22is one of the most important decisions a woman here has to make.
0:52:25 > 0:52:28So what do you think makes a good Hadzabe man?
0:52:28 > 0:52:30What would make you love him?
0:52:41 > 0:52:45Anything else? A nice face, maybe? A tall man?
0:53:00 > 0:53:03'Hadza women work hard to bring in food for the family
0:53:03 > 0:53:06'and they want a partner who will do the same.'
0:53:06 > 0:53:09I think it makes perfect sense in this environment
0:53:09 > 0:53:13for the women to be so choosy about the men whom they marry,
0:53:13 > 0:53:17because if those men aren't good hunters, good providers,
0:53:17 > 0:53:20the women have a lot to lose.
0:53:20 > 0:53:23And women's preference for good hunters
0:53:23 > 0:53:27is thought to have shaped the way men behave, wherever they live.
0:53:33 > 0:53:35Even when there's nothing to hunt,
0:53:35 > 0:53:39men can still find ways to show off their prowess to women.
0:53:46 > 0:53:50The latest research shows that men are in some way hard-wired
0:53:50 > 0:53:54to show potential partners they've got what it takes.
0:53:54 > 0:53:57And they do it by taking risks.
0:53:58 > 0:54:03And we're going to show you how with some of Britain's best skateboarders.
0:54:04 > 0:54:09Rather strangely, we've asked them to try to perform a trick
0:54:09 > 0:54:12that they're not very good at, that they're still struggling to learn,
0:54:12 > 0:54:14and that, in fact, they're likely to fail at.
0:54:14 > 0:54:19The important thing is that they're taking a risk.
0:54:24 > 0:54:27Whilst practicing their difficult tricks,
0:54:27 > 0:54:31there's a moment when the skateboarder makes an unconscious decision
0:54:31 > 0:54:36either to play it safe and give up on the trick by kicking the board away so they can land safely,
0:54:36 > 0:54:40or to live dangerously, to stick with the trick
0:54:40 > 0:54:44and try to land the board, which is risky.
0:54:44 > 0:54:49To start with, a male researcher monitors how often they take a risk
0:54:49 > 0:54:51and how often they play it safe.
0:54:56 > 0:55:01What happens when we introduce some attractive young women into the equation?
0:55:20 > 0:55:25In the presence of female observers, the men seem to be gambling more.
0:55:25 > 0:55:27In fact, the original research
0:55:27 > 0:55:31showed that risk-taking almost doubled when an attractive woman was present.
0:55:37 > 0:55:40And that, it seems, comes down to testosterone.
0:55:42 > 0:55:44Scientists have found
0:55:44 > 0:55:50that having women around increases the skateboarder's levels of testosterone by up to 40%,
0:55:50 > 0:55:53forcing the men to display their potential
0:55:53 > 0:55:56for the modern day version of a good hunter.
0:56:00 > 0:56:04Men showing off to women by taking risks could be a throwback
0:56:04 > 0:56:07to the food gathering strategies of our ancestors.
0:56:07 > 0:56:13By taking risks, men are signalling that they're likely to be good providers
0:56:13 > 0:56:15and therefore better mates.
0:56:15 > 0:56:20So it seems that men have an excuse for behaving the way they do.
0:56:20 > 0:56:23They're designed to be show-offs.
0:56:27 > 0:56:30It turns out that food has driven the evolutionary journey
0:56:30 > 0:56:35of both the men and women of our species, Homo sapiens.
0:56:37 > 0:56:42So much about us today, from the way we feel about each other
0:56:42 > 0:56:46to the ways in which we think and behave, and even the way we look,
0:56:46 > 0:56:51we can trace back to our hunter-gatherer ancestors in Africa
0:56:51 > 0:56:52and their search for food.
0:56:52 > 0:56:57But since then we have spread out to every corner of the globe
0:56:57 > 0:57:00and our population has exploded.
0:57:00 > 0:57:03And what enabled that was farming.
0:57:09 > 0:57:13In the last 10,000 years, we've gone from being nomadic hunter-gatherers
0:57:13 > 0:57:17to large-scale industrial farmers.
0:57:22 > 0:57:27That has enabled a population explosion...
0:57:31 > 0:57:34..and changed the face of our planet,
0:57:34 > 0:57:39with over a third of the land on Earth taken over by farming.
0:57:48 > 0:57:52Our relationship with food has had a powerful effect on us,
0:57:52 > 0:57:56shaping the structure of our bodies and our societies,
0:57:56 > 0:58:00and having a massive impact on the environment around us.
0:58:00 > 0:58:04We've gone from being forest-dwelling, fruit-eating apes
0:58:04 > 0:58:09to becoming a species that can survive finding food just about anywhere
0:58:09 > 0:58:12because we put it there.
0:58:12 > 0:58:17We're naturally able to eat a diverse variety of foods
0:58:17 > 0:58:21and, through the use of culture, through cooking and farming,
0:58:21 > 0:58:24we've widened that range even further
0:58:24 > 0:58:29and that underpins our success as a global species.
0:58:47 > 0:58:50Subtitles by Red Bee Media Ltd
0:58:50 > 0:58:53E-mail subtitling@bbc.co.uk