- 1 day ago
Dr Roberts examines how our ancestors' search for food changed the shape of our faces, the way we see colour and even affects how we look for and keep a mate and who we find attractive.
早期灵长类祖先主要依赖大量植物纤维为生，拥有较长且复杂的肠道及盲肠以协助发酵和消化粗糙植物。随著环境变化，祖先开始摄入肉类和高能量食物, 高热量、易消化的肉类替代了低质大量的植物，让人类祖先的消化道逐渐变短，节省了大量用于消化的能量....
早期灵长类祖先主要依赖大量植物纤维为生，拥有较长且复杂的肠道及盲肠以协助发酵和消化粗糙植物。随著环境变化，祖先开始摄入肉类和高能量食物, 高热量、易消化的肉类替代了低质大量的植物，让人类祖先的消化道逐渐变短，节省了大量用于消化的能量....
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00:05The shape of your face, walking on two legs, the way you see the world, what makes you the person
00:17you are? The story of each and every one of us can be traced back millions of years to the
00:28plains of ancient Africa. The answers to the question, what makes us human, lie buried
00:37in the ground, in the fossils and other traces of our ancestors, but also lie deep within
00:44our own bodies, in our bones, flesh and genes. As an anatomist, I'm fascinated by the way
00:54our bodies have been sculpted by our ancestors' struggle for survival.
01:06And what took us out of the forests, leaving the other apes behind, to spread out across
01:13the globe, was our search for food. It's got duty. It's left its mark in our mouths, and
01:24in our behaviour. Flames. Food makes us behave in the strangest ways. It's even driven the
01:34way we attract the opposite sex. The ways in which we find food and digest it have not
01:44only left their mark on our bodies, but underpin our success as a species.
02:18The warm waters of the cate for the word of the cate for the cate for the cate for the
02:20Most of East Africa are home to an extraordinary creature.
02:28A link to our evolutionary past.
02:36This strange looking animal is known as a tunicate or sea squirt.
02:41And believe it or not, this is a distant relative of mine.
02:57It is quite hard to believe I've got anything at all in common with this sea squirt.
03:01It doesn't have eyes, it doesn't have arms and legs.
03:04In fact, pretty much all it does have is a gut.
03:08He's got an in hole to the gut there.
03:12And an out hole over there. It's a little U-shaped gut.
03:16This simple process of food in, waste out, gives us the blueprint for the guts that lie at the heart
03:23of every animal, including us.
03:27We humans like to think that we are so special, that we are so different from every other life form.
03:33And yet, there is something that unites us with every other animal on the planet.
03:39And that is the search for food.
03:45And the quest to feed ourselves has driven changes in our bodies.
03:52The need for food hasn't just shaped sea squirts, it's shaped us as well.
03:57From our own guts to the way we move, the way we behave, and even the way in which we
04:03experience the world around us.
04:17But it's on land, here in Africa, that our story really begins.
04:24Over millions of years our ancestors' bodies were shaped by the search for food.
04:30As they crawled out onto land, evolving into reptiles, mammals, and eventually, monkeys.
04:44They are fast asleep.
04:47These are red-collarpus monkeys.
04:5030 million years ago, there weren't any humans on the planet, there weren't any apes, but there were monkeys.
05:0730 million years ago.
05:13You and I evolved from monkeys which would have looked something like this.
05:20Procleopithecus, an ancient primate ancestor that lived in the trees on a diet of fruit and leaves.
05:30And their search for food has directly affected the way we see the world today.
05:39Most mammals wouldn't be able to tell the difference between these two tomatoes.
05:45But for you and me, the difference is obvious.
05:49And this is all because of a crucial change in our ancestors' eyes that probably happened 30 to 40 million
05:56years ago.
06:01At the back of all mammals' eyes are light-sensitive colour receptors called cones.
06:08Most mammals have only two types that cover the blue and yellow parts of the spectrum.
06:16But 30 million years ago, a genetic mutation created a third.
06:22One that opened up a whole new range of colour.
06:32Reds and greens.
06:33Reds and greens.
06:41And with this, our full colour vision was born.
06:48Revealing a rich and bountiful range of foods.
06:58If you're a leaf-eating primate, three colour receptors might help you pick out the slightly paler, more yellow, tender
07:05leaves to eat.
07:06But for a fruit-eating primate, it means that you can pick up on the signals that the trees are
07:11giving you.
07:12That when something is ready to eat, it turns red.
07:16And you know that it is full of sugar and more nutritious.
07:30Being able to tell when fruit was ripe, packed with life-giving sugar and energy,
07:36must have been a massive advantage in our ancestors' struggle for survival.
07:43Those animals with eyes tuned in to finding the richest foods were more likely to survive and pass on their
07:51genes.
07:52And so colour vision spread until their descendants, including us, were seeing in glorious technicolour.
08:08With our three types of colour receptors, our eyes can see up to a million different colours.
08:21Our colour vision is a sensory gift. There are relatively few other mammals that see all the rich and varied
08:28colours that we do.
08:29And that goes all the way back to our monkey ancestors searching out the most tender leaves, the ripest fruits,
08:38in those forests 30 million years ago.
08:48Our ancestors flourished in those forests for millions of years, with first monkeys, then apes, exploiting the abundant food there.
09:04And maybe they would have stayed in the trees if it hadn't been for a series of major climate changes
09:11that brought the search for food out of the trees and down onto the ground.
09:26From around three million years ago, the global climate was fluctuating and becoming cooler and drier.
09:33And we know from studies of ancient climate, but also by looking at the animals that were around at the
09:38time, that the woodlands were shrinking whilst grasslands were expanding.
09:44So this was a really important potential habitat if apes could manage to adapt and find food here.
09:58And adapt they did.
10:04Apes came down from the trees to walk on two legs out across the savannah.
10:14Fossil finds have revealed at least six different species of upright walking apes living in Africa around this time.
10:23Exactly how they relate to each other, or to us, no one can be certain.
10:28All we know comes from a few fragmented fossils of species like Australopithecus africanus and Paranthropus boise.
10:41But it's clear that their bodies were shaped by the search for food.
10:49This peculiar looking creature is, believe it or not, part of our ancestral family tree.
10:55He was an upright walking ape, but only about a metre tall.
10:59And he's got a tiny brain case here of less than a litre in capacity.
11:05He's got an extremely wide face with flaring cheekbones.
11:11And a big muscle would have passed up here, going right up on the side of the head to this
11:15crest on the top.
11:17And that is temporalis muscle, which operates the jaw.
11:20You can feel it on the side of your own head when you chew.
11:25He's got absolutely massive jaws and teeth.
11:30And although his proper name is Paranthropus boise, these earned him the nickname of Nutcracker Man.
11:40From the shape of his face, it's long been thought that Nutcracker Man survived on the dry savannah by eating
11:46hard, dry foods like nuts and seeds.
11:53But whatever they were eating, they eventually died out.
12:01Whereas it seems our ancestors were eating something very different.
12:10And I'm on the hunt to find it.
12:18The only trouble is the evidence is being guarded by a formidable predator.
12:30Well, we're driving out to try to find some lions.
12:40The clue I'm looking for is hidden deep within their food.
12:44The clue I'm looking for is hidden deep within their food.
13:09Well, look, there's a buffalo skull and, in fact, there's a whole skeleton of this autre ko aligned with the
13:14dragon Veil J Squee.
13:14Scattered around here, so do you think we're getting close to them?
13:17Yeah, we are getting closer.
13:30There's one! Look, there's a big male.
13:36There's a magnificent male just lying there under the trees.
13:41He's fantastic.
13:45They're mating!
13:49They have no shame, these lions.
13:54They're just such huge animals.
14:00And these were the predators that our ancestors were sharing their environment with.
14:14And the lions have found food.
14:47Most of the animals that lions kill and eat are carrying parasites.
14:52And as strange as it sounds, those parasites can tell us something about our ancestors.
15:09The meat lions eat is riddled with tapeworm larvae, which grow into huge tapeworms inside the lion's gut, up to
15:18five metres long.
15:20Attaching themselves to their host with barbed hooks, and leeching off their food.
15:27Through that middle one.
15:29Oh, these really disgusting animals are the stuff of nightmares.
15:37But they're incredibly revealing, genetic studies have discovered that the lion tapeworm is almost identical to a tapeworm found in
15:47humans.
15:50In fact, it's so similar, it seems likely that humans got this tapeworm from lions, but you can't catch these
15:58parasites directly from another meat-eater.
16:02You can catch it by eating the same meat.
16:06So this suggests that humans at some point were eating exactly the same animals that lions were eating, big herbivores
16:15like antelopes in Africa.
16:17Not only that, but it seems that we can pin a date on this.
16:20It's genetic studies suggest that that transfer of the tapeworm to a new host, to humans, happened sometime before 800
16:29,000 to 1.7 million years ago.
16:38For decades, the idea of our ancestors as meat-eaters and hunters has only been a theory, guessed at from
16:45fossil remains and stone tools.
16:47But this is proof, not only for eating meat, but eating big game.
16:54Proof that is living inside our guts today.
17:01And by dating it, we're able to guess who this meat-eater was.
17:15Homo erectus.
17:28This is a replica of a fossil skull that was found here in Kenya in 1975.
17:34It belongs to a species which is called Homo erectus, or sometimes Homo agaster.
17:39And he looks very different from species that had gone before.
17:44He has a smaller face.
17:46He would have been much taller and would have had long legs as well.
17:50A lot more like you and I.
17:56Homo erectus had a body shape almost identical to modern humans, with long legs and a narrow waist.
18:05He was amongst the earliest apes to deserve the name Homo, meaning human.
18:10And he used tools to butcher meat, and perhaps even to kill it, as a hunter.
18:19And this idea of man the hunter has been used to explain all sorts of changes in intelligence, in bodies
18:28and behaviour.
18:30One of the most obvious ways in which meat-eating is thought to have changed us, is in the shape
18:36of our faces.
18:48Oh, this is a great collection.
18:51Dr. Peter Ungar is a world authority on our ancestors' faces and teeth.
18:57He's been looking at how a changing diet might have affected the shape of our ancestors' jaws.
19:03If you look at this earlier human ancestor, they are large, flat teeth, and kind of bulbous in shape.
19:12But when we move on to Homo erectus, what you see here is you see smaller teeth.
19:18Yeah.
19:19Thinner tooth enamel, and in fact the face has responded as well.
19:22It's much more slender, what we call gracile, without the big heavy chewing muscles.
19:28Yeah, the cheek bones are very neat, aren't they?
19:30Yes, they are. This is much more human-like in its general configuration.
19:36Homo erectus' smaller teeth meant a smaller jaw.
19:44And he lost that ape-like snout of earlier ancestors like Australopithecus.
19:54With a flatter face shape, Homo erectus looks much more like a modern human.
20:05To see how well our teeth and jaws are adapted to eating meat, we're going to put them to the
20:11test.
20:12With a machine designed by Jean-Francois Mullinet, one of Peter's colleagues.
20:19Known as the Bite Master, this machine uses a sophisticated array of motors to precisely mimic a natural chewing action.
20:29First, we try the large, flat teeth of Australopithecus.
20:34I'm slightly nervous about this, because it did look quite vicious.
20:38OK. That should do it.
20:39Would they have been able to chew through meat?
20:51Well, it hasn't actually bitten through, it's just kind of squashed it.
20:55Well, those teeth aren't very well suited for shearing or slicing through tough foods like meat.
21:01It's kind of like a pound of steak with a hammer.
21:09So, if our early ancestors' teeth can't cut it with meat, let's see what three million years of evolution have
21:16done for meat eating, with a cast of my teeth.
21:21It feels quite old to see my own teeth getting into this machine.
21:25You want to see what it does with a piece of meat?
21:28Yeah, I'm vegetarian though.
21:31What if I've got meat eating teeth?
21:33Let's give it a shot.
21:34Shall we have a try?
21:40Good job.
21:41Yeah, you can see it's slicing through, that's amazing.
21:50Take this piece of meat out now.
21:52And that is amazing.
21:54You can actually, it hasn't quite pierced through, but you can see the light through that piece of meat now.
22:02Absolutely.
22:03Wow.
22:05The smaller, sharper teeth that evolved in all our mouths seem well adapted to shearing through the tough muscle fibres
22:13of meat.
22:15And these are the teeth of a vegetarian, by choice.
22:18By choice.
22:20Not by evolution.
22:25But Peter's research doesn't stop there.
22:30He's been using the latest technology to analyze the surface of our ancestors' teeth at a microscopic level.
22:41Tooth enamel is the hardest substance in the entire body, but incredibly, every time you eat, your food leaves its
22:49mark.
22:51The evidence of your diet is etched onto the surface of your teeth in the forms of scratches and pits.
23:00Look at that.
23:01That's gorgeous.
23:02You're looking at an event that happened in a moment in time, something like 3.3 or 3.4 million
23:08years ago.
23:08You can't get, I mean, the connection between yourself and your ancestors is right there.
23:14I mean, it's like footprints almost.
23:16From these scratches, Peter can tell what our ancestors were eating.
23:20And he's made a surprising discovery.
23:24This is cool.
23:25Get ready for this.
23:27Boom.
23:28Look at those big, heavy pits.
23:30Yeah, they're like craters in the surface of the teeth.
23:33That's right.
23:33So who's this?
23:34This is Homo erectus.
23:36Here it is in three dimensions, and we can rotate it.
23:39Look at that.
23:41Big, heavy gouges taken out of that Homo erectus.
23:45Okay, so what's caused that?
23:47Well, this particular individual unquestionably ate something hard and brittle.
23:51A nut, a seed, a root, a hard tuber, something like that.
23:55But this is Homo erectus with its smaller teeth that we wouldn't expect to be eating these really, really hard
24:00foods.
24:01That's right, but here's a different one.
24:03Check this out. Here's another Homo erectus.
24:06This individual ate tough foods.
24:08So what do you think these Homo erectus individuals could have been eating them to get scratches like that?
24:14Well, it could be grasses, or in this case it could be meat.
24:17Right.
24:18But I think what's most important here is that if we take the whole range of Homo erectus specimens, it
24:25looks very much like a species with a very variable diet.
24:29So this is really interesting because previous theories of human evolution have put forward meat eating as being this real
24:37fundamental change that happened.
24:39And what we seem to be saying here is that, okay, meat was perhaps part of the diet, but the
24:46real key to it was that the diet is getting much broader.
24:49Absolutely. I think meat is part of it, but there's more to the story.
24:55Meat might have shaped our teeth, but our ancestors were eating much more.
25:01And we don't have to go far from teeth to find out what else was in that varied diet.
25:18I'm a vegetarian, so I know that it's possible for a human being to survive for a number of years
25:23without eating any meat at all.
25:25So I'm not surprised that meat eating wasn't the only change in our ancestors' diets.
25:31There's some very interesting new evidence which suggests we adapted to a new source of food which was crucial to
25:39our survival.
25:40And the evidence is found in our mouth, in our own saliva, our spit.
25:49Scientists have been comparing our saliva with that of chimpanzees, with whom we share a common ancestor going back about
25:56six million years.
25:58Whilst our early ancestors were probably eating a diet similar to that of chimpanzees today,
26:04we have since evolved to live on different foods, and our saliva has changed.
26:11Zoo manager Chris Hearn has trained the chimps at Twycor Zoo to open their mouths for dental checks,
26:18so we can try to get a sample of their saliva.
26:21I'm going to ask him to open his mouth on a cue, which is like that.
26:25And he should open his mouth.
26:27And then I'm going to take a swab. Hopefully he's got some saliva in us.
26:31And we'll take it from there.
26:33Got some gloves on, ready to take the swab.
26:40Oh, Kip, you're being ever so good.
26:44Look at that.
26:45Chimp's saliva, like ours, is packed with enzymes which start to digest our feed even before we've swallowed it.
26:50Thank you, Kip. Thank you, Kip.
26:52There you are. Wonderful.
26:54Right. Okay.
26:56Let's go and test this saliva. Okay.
27:00Any differences in the enzymes between their saliva and mine can tell us about the specific foods we've evolved to
27:07eat.
27:09Right. Now I'm going to try and wring out the chimp spit.
27:14And this is looking great.
27:20Now I've just got to produce some of my own. Excuse me.
27:31Then I add flour and iodine.
27:35This test should show how much of an enzyme called amylase is in each sample of saliva.
27:42The lighter the colour, the more salivary amylase is present.
27:48After just a few minutes, the chimp sample has turned black.
27:54Whereas my human sample is still yellow, clearly showing that my saliva has much more amylase.
28:03Now this is really interesting and I'm thrilled that this little experiment has worked because it reflects the results of
28:11the much larger study which actually looked at the levels of the enzyme amylase in human saliva and chimpanzee saliva
28:19and found that we, humans, have six to eight times as much of this enzyme in our saliva as chimpanzees
28:27do.
28:27Amylase breaks starch down into sugars.
28:30It suggests that we are specifically adapted to eating starchy foods.
28:44It means that at some point in our evolutionary journey, starch must have become really important to us.
28:52To find out why, we need to go back to where we came from.
29:00This remote part of East Africa has been home to humans for millennia.
29:11I'm on my way to meet an extraordinary group of people who live here in eastern Tanzania.
29:17They're called the Hadza and they're a modern people but they're living in a similar environment and eating similar things
29:24to our ancestors.
29:32The Hadza are some of the last nomadic hunter-gatherers on earth and in the 21st century, their diet still
29:40harks back to that of our ancient ancestors.
29:45Oh, there's some little children.
29:49Oh, this is amazing.
29:51Oh, this is amazing.
30:16The Hadza live in mobile camps moving on every few months and they live on what they can find in
30:23this arid environment.
30:26Meat is prized above all and the men go out hunting most days.
30:35I'm really excited this morning because one of the hunters has agreed to take me out with him hunting, which
30:42is just so unusual.
30:44Normally, it's forbidden for women to go along and hunt, so I'm in a really privileged position.
31:08Click languages like Hadza may be close to the earliest human languages.
31:14We can set off now. You're ready? Fantastic.
31:27Nyanza, what are you looking for? Are you looking mainly for birds or are you looking for other animals?
31:32The tool is controlled for animals.
31:35I don't know about them. We come with
31:36them, we get rid of them, so dad hasagiaged them, and we can have another animal.
31:50Nyanza is one of the camp's best hunters and, like most Hadza men, usually hunts on his own.
31:59A Hadza hunter will focus on big game if he can, but finding anything in this parched
32:06bushland is hard.
32:12It tends to be the older men, in their 40s and 50s, who bring back most meat.
32:20Experience counts for a lot here.
32:40Temperatures are already soaring and it's only mid-morning.
32:46A Hadza hunter may cover about six miles in his search for food.
32:56This is certainly hot and tiring and I'm not even keeping as alert as Nyanza is, he's constantly
33:02on the lookout for any movement that might tell him that there's an animal about.
33:24So close, that was so close, a tiny bird.
33:29We're two hours in and still no luck.
33:37The Hadza love meat when they can have it, but it's not a reliable source of food.
33:43Only one in 29 Hadza hunts is successful in terms of the men coming home with big game.
34:08It's clear I'm slowing Nyanza down, so I let him continue while I head back to camp.
34:15So Nyanza, thank you so much for letting me come with you and I'll let you go off on your
34:19own there.
34:22See you later.
34:31But back at the camp, the women don't seem to be that concerned about the lack of meat
34:35food for supper, because they've got plans of their own.
34:53Every day, the women head out on the search for food themselves.
34:57And I have been waiting for quite a few months to have been allowed.
35:13I am Alice.
35:15Alice.
35:16Alice.
35:17Alice.
35:17Alice.
35:18Alice.
35:19Is it wrong?
35:20Is it wrong?
35:21Is it wrong?
35:21It wrong.
35:23Screeching.
35:31Unlike the men who hunt alone, the women work together and spend around four hours a day
35:38out gathering fruit and roots.
35:47The first port of call, berries.
35:58Masses of berries.
36:02So you squeeze it to get it out of the shell.
36:08It's like a tiny sweet slimy lychee.
36:11There's quite a honey sweetness to it.
36:17Karahaipi.
36:18Karahaipi.
36:19I like Karahaipi.
36:23It's lovely.
36:27But fruits like these aren't available all year round.
36:36Luckily there is something else that is always there.
36:40Something they can rely on all through the year.
36:44Tubers.
36:45Ah, okay.
36:47So these leaves belong to the plant that has the tubers underground.
36:51If you trace these back, it's these great big vine-like branches here which go down.
36:58And then hopefully somewhere under the ground there, Mabada's going to find some tubers.
37:04Aequa.
37:05Equa.
37:06Equa.
37:07Equa.
37:07Equa.
37:07Equa.
37:09Is that that bit there?
37:11Equa?
37:12Yeah.
37:14Tug it.
37:15Tug it?
37:16Oh!
37:18Wow!
37:19That's the end of it.
37:21Look at that.
37:24It looks like a cross between a root and a bit of a spindly sweet potato maybe.
37:33And just like a potato, this tuba is a staple food packed full of energy in the form of starch.
37:42Oh, thank you.
37:49It's not unpleasant.
37:50Mmm.
37:51It's quite nice.
37:53Mmm.
37:54It's quite juicy actually.
37:58When you first bite into it, it's a bit like celery, but it would be the most fibrous,
38:04tough celery you'd ever eaten.
38:07It's got a lovely nutty flavour to it.
38:10It's nice.
38:12And of course, I've got that very powerful saliva with plenty of amylase in it so I can immediately
38:17start breaking down the starch and benefiting from the sugars it contains.
38:28So in an uncertain world where men often come home empty handed, the humble tuba is sometimes
38:35all there is to eat.
38:39We don't know exactly how our ancestors lived millions of years ago, but we can assume they
38:46were living on similar foods.
38:47And it's likely the enzymes we all have in our saliva evolved because tubas were so often
38:56on the menu.
38:58I'd like to ask everyone if they think the women bring more food in than the men.
39:07The women bring in about 60 percent of the money and the women bring in about 60 percent of
39:12I think everyone has a very good friend and he's a very good friend.
39:24I think that my mother is a very good friend and the dad is a very good friend.
39:31In fact, women bring in about 60% of the calories for the entire group.
39:38Without them and the tuber, survival here would be impossible.
39:47When food is scarce, being able to eat a broad and flexible diet is an obvious advantage.
39:54And it meant that early humans, like Homo erectus, became experts at survival.
40:01But it didn't stop there.
40:04The ability to survive by eating a great variety of different foods, from fruit and tubers to meat,
40:11meant that our ancestors weren't restricted to one particular type of environment.
40:17And this meant in turn that they could spread out into new habitats and eventually colonise the globe.
40:29From around two million years ago, Homo erectus left Africa.
40:35And they were just the first of several human species who would go on to populate the globe.
40:42Their ability to eat a varied diet meant they could survive virtually anywhere.
40:47From arid savannah.
40:52To the freezing Arctic.
40:57To temperate woodland.
41:16This is our old friend, Homo erectus.
41:19And as far as we know, these were the first people to expand out of Africa.
41:25And to spread right across Asia.
41:28Then 600,000 years ago, another species appears in Africa and in Europe.
41:34Homo heidelbergensis.
41:37Thought to be descended from Homo erectus, he was similar in build but with a bigger brain.
41:43And it's thought that he, in turn, evolved into another species.
41:48200,000 years ago, someone else appears on the scene.
41:51And this time, it's us.
41:53Homo sapiens.
41:59We originated in Africa and then spread out right across the globe.
42:04But as well as population expansion, there's something else very obvious going on here.
42:10And that's an increase in brain size over time.
42:14Large brains need a lot of energy.
42:17And it's always been thought that what fueled brain growth was meat.
42:20But a new idea suggests it might be linked to something even more powerful.
42:27Fire.
42:29The flame.
42:31Fantastic.
42:33I've started a fire.
42:48There's something really magical about starting a fire from nothing.
43:01I really don't think that we can underestimate the value of fire to our ancestors.
43:06It would have offered them protection, warmth during cold nights and in cold climates.
43:12Light after the sun has gone down.
43:16But it's incredibly hard to know when exactly our ancestors first learnt to control fire.
43:24Fires are just so spectacular when they're burning, but of course when they've burnt out,
43:28there's so little left, just a thin layer of ash on the ground.
43:32And so it's not surprising that it's really difficult to pick up the traces
43:36of the first fires that our ancestors would have controlled.
43:40There's some evidence going back one and a half million years ago that our ancestors may have controlled fire.
43:49But by the time our own species Homo sapiens is around, we're using fire all the time.
43:56And we get an idea of what they were doing with fire from charred remains.
44:01Things like pieces of burnt bone, charred hazelnut shells.
44:07They were cooking.
44:11I've got these burdock roots, they're probably charred to nothing.
44:22Well, I can truthfully say that roasted burdock root is quite tasty.
44:28But cooking doesn't only make food more palatable.
44:35Recent research suggests it was cooking, not meat, that fuelled the evolution of our big brains.
44:46It was cooking that made us human.
44:57This theory has given rise to a new wave of scientific research,
45:02investigating the advantages that cooked food has over raw.
45:06And I'm going to demonstrate this in a very basic way.
45:10First, by eating a quarter of a day's calories in raw carrots.
45:25Right. It's just taken me about five, six minutes to eat a single carrot.
45:31So if I was trying to survive on raw carrots alone, I'd be munching my way through them for eight
45:37hours a day.
45:40Not only does eating raw food take a long time.
45:44Do you want to swallow?
45:47But actually digesting it uses up energy.
45:53For every hundred calories of raw food I eat, I use up to 25 calories chewing and digesting it.
46:04Right. That is the end of my last raw carrot.
46:08And I'm really glad because it's taken me hours to eat them.
46:13And now to see the difference cooking makes.
46:16There's so many of them, they barely fit in the colander.
46:20When you cook something like carrots, you're not actually altering the calorie content.
46:25But there is something crucially different about them.
46:41Well, I've nearly finished.
46:42And this half of the experiment was much easier.
46:46I can get through a cooked carrot in probably half the time it would take me to chomp my way
46:52through a raw carrot.
46:54Cooked food is much easier to digest than raw.
46:58And this simple fact holds the key to why cooking has been so important in our evolution.
47:05Not only is cooked food easier to chew, it takes less energy to digest it once it reaches our guts.
47:11Which means that we effectively get more energy from cooked food because we put less into digesting it.
47:18And although cooked food contains the same amount of calories as raw food.
47:22We can get at more of those calories by cooking it, with some foods up to 35% more.
47:29And some scientists believe that it was this extra energy from cooking that was crucial to supporting the growth of
47:37our big brains.
47:44Over millions of years, our search for food has taken us from fruit eating monkeys in the forest, to hunters
47:52and gatherers striding out onto the open plains.
47:57It's driven the development of tools and the control of fire that have taken us across the globe.
48:04But it hasn't just changed us physically, it's done something else.
48:09It has shaped our behaviour.
48:20We evolved as hunter-gatherers, living on similar foods to the Hadza.
48:46Finding food shapes their society, but it has affected all of us.
48:56It seems that the Hadza, and presumably our ancestors too, found a very efficient and effective way of surviving here.
49:04Men and women each have different and distinctive roles.
49:10So the women go digging for tubers and collecting berries, whilst the men go out hunting for meat and honey.
49:18They'll eat some of it while they're out in the bush, but they bring a lot of it back home
49:22to share.
49:23So it makes sense to pair up.
49:28Having a partner to share food with is a massive advantage in this harsh environment.
49:34And many Hadza men and women marry for life.
49:48Sharing food like this is thought to be the origin of pairing up and staying together.
50:01Bukulu, how did you get married? Was there a ceremony?
50:23Do you Hadza men always just have one wife at one time?
50:28When I was a kid, I was a kid, I was a kid, I was a kid, I was a
50:35kid.
50:37Madhulu, how long have you and Pendo been married?
50:41I was married.
50:43And people outside your family, how might they know that you're married?
51:00Pendo, what do you think the benefits of being a married woman will be?
51:20And are you looking forward to having children together?
51:37Hadza women typically have around five children, which is hard work.
51:45It takes a Hadza woman around 13 million calories
51:49to raise a child from conception until it's weaned.
52:09And she can't physically do it without support.
52:15So choosing the right partner is one of the most important decisions a woman here has to make.
52:24So what do you think makes a good Hadza man?
52:28What would make you love him?
52:41Anything else? A nice face? Maybe a tall man?
52:45Anything else? A nice face? Maybe a tall man?
52:58I'm so soft.
53:00Hadza women work hard to bring in food for the family,
53:04and they want a partner who will do the same.
53:06I think it makes perfect sense in this environment for the women to be so choosy about the men whom
53:12they marry.
53:14Because if those men aren't good hunters, good providers, the women have a lot to lose.
53:20And women's preference for good hunters is thought to have shaped the way men behave wherever they live.
53:32Even when there's nothing to hunt, men can still find ways to show off their prowess to women.
53:46The latest research shows that men are in some way hardwired to show potential partners they've got what it takes.
53:54And they do it by taking risks.
53:58And we're going to show you how with some of Britain's best skateboarders.
54:04Rather strangely, we've asked them to try to perform a trick that they're not very good at,
54:10that they're still struggling to learn, and that in fact they're likely to fail at.
54:15The important thing is that they're taking a risk.
54:24Whilst practising their difficult tricks, there's a moment when the skateboarder makes an unconscious decision
54:29either to play it safe and give up on the trick by kicking the board away so they can land
54:35safely,
54:36or to live dangerously, to stick with the trick and try to land the board, which is risky.
54:45To start with, a male researcher monitors how often they take a risk and how often they play it safe.
54:56What happens when we introduce some attractive young women into the equation?
55:20In the presence of female observers, the men seem to be gambling more.
55:25In fact, the original research showed that risk-taking almost doubled
55:29when an attractive woman was present.
55:36And that, it seems, comes down to testosterone.
55:42Scientists have found that having women around increases the skateboarders' levels of testosterone by up to 40%,
55:50forcing the men to display their potential as a modern-day version of a good hunter.
56:00Men showing off to women by taking risks could be a throwback to the food-gathering strategies of our ancestors.
56:07By taking risks, men are signalling that they're likely to be good providers,
56:13and therefore better mates.
56:15So it seems that men have an excuse for behaving the way they do.
56:20They're designed to be show-offs.
56:26It turns out that food has driven the evolutionary journey of both the men and women of our species, Homo
56:34sapiens.
56:37So much about us today, from the way we feel about each other, to the ways in which we think
56:44and behave,
56:45and even the way we look, we can trace back to our hunter-gatherer ancestors in Africa and their search
56:51for food.
56:52But since then, we have spread out to every corner of the globe, and our population has exploded.
56:59And what enabled that was farming.
57:08In the last 10,000 years, we've gone from being nomadic hunter-gatherers to large-scale industrial farmers.
57:22That has enabled a population explosion.
57:30And changed the face of our planet, with over a third of the land on Earth taken over by farming.
57:48Our relationship with food has had a powerful effect on us, shaping the structure of our bodies and our societies,
57:55and having a massive impact on the environment around us.
57:59We've gone from being forest-dwelling, fruit-eating apes, to becoming a species that can survive,
58:07finding food just about anywhere, because we put it there.
58:12We're naturally able to eat a diverse variety of foods.
58:17And through the use of culture, through cooking and farming, we've widened that range even further.
58:23And that underpins our success as a global species.
58:31And Alice is back on BBC HD tomorrow night at nine, with the final part of The Origins of Us.
58:37Next this evening, we have a crack at uncovering the secret life of ice.
58:43The Origins of Us
58:44The Origins of Us
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