0:00:02 > 0:00:05Of all the animals that live on our planet,
0:00:05 > 0:00:08one extraordinary group dominates.
0:00:10 > 0:00:12It has produced the largest...
0:00:12 > 0:00:14The blue whale!
0:00:15 > 0:00:17..the fastest,
0:00:17 > 0:00:21the most intelligent creatures that have ever lived.
0:00:21 > 0:00:23They're known as the vertebrates.
0:00:25 > 0:00:29And they all share one vital feature - a backbone.
0:00:31 > 0:00:35I'm travelling back in time to look for the key advances
0:00:35 > 0:00:37that drove their remarkable success.
0:00:40 > 0:00:44So far, I have seen the vertebrates grow from tiny origins
0:00:44 > 0:00:47to dominate the oceans,
0:00:47 > 0:00:48colonise the land...
0:00:50 > 0:00:52..and take to the skies.
0:00:54 > 0:00:58In this programme, I'm going to track the rise of a whole new branch
0:00:58 > 0:00:59of vertebrate life.
0:00:59 > 0:01:03The most complex animals yet to appear on Earth.
0:01:04 > 0:01:07They started as a group of tiny little creatures
0:01:07 > 0:01:09scarcely bigger than my little finger.
0:01:09 > 0:01:11Nocturnal animals.
0:01:11 > 0:01:14But they were to develop into some of the biggest creatures
0:01:14 > 0:01:17the planet has ever seen.
0:01:17 > 0:01:20It's a group that also contains us.
0:01:20 > 0:01:24This is the story of the mammals.
0:01:27 > 0:01:31I want to investigate how the mammals acquired a new set of key
0:01:31 > 0:01:36features that allowed them to thrive in every corner of our planet.
0:01:36 > 0:01:39Features we also have inherited.
0:01:40 > 0:01:44We'll find the evidence in a series of thrilling fossil discoveries
0:01:44 > 0:01:46and in living animals.
0:01:48 > 0:01:50With the latest scientific analysis,
0:01:50 > 0:01:54we'll be able to bring our ancient ancestors back to life.
0:02:17 > 0:02:22Today, animals with backbones dominate our planet
0:02:22 > 0:02:26on land, in the air and at sea.
0:02:26 > 0:02:31But how did that evolutionary takeover come about?
0:02:31 > 0:02:34There've been lots of gaps in the story.
0:02:34 > 0:02:36But in recent decades,
0:02:36 > 0:02:41exciting new discoveries have been made here in China,
0:02:41 > 0:02:43and I'm here to look at them.
0:02:46 > 0:02:50The rocks of China are yielding up the elusive missing links
0:02:50 > 0:02:52in the vertebrate story.
0:02:54 > 0:02:57Ancient creatures preserved as fossils.
0:02:59 > 0:03:03To find new evidence from the very start of the mammals' story,
0:03:03 > 0:03:06I'm travelling to the south of China,
0:03:06 > 0:03:08and the province of Yunnan.
0:03:19 > 0:03:22Fossils found here can reveal the kind of world
0:03:22 > 0:03:25those first mammals encountered, and the kind of animals
0:03:25 > 0:03:30they had to compete with to gain a foothold and survive.
0:03:32 > 0:03:37This area of southern China is known as the Lufeng Basin,
0:03:37 > 0:03:42and 180 million years ago, it was a vast natural hollow
0:03:42 > 0:03:46into which waters from all the surrounding hills flowed.
0:03:46 > 0:03:50And with those streams came sediment, which is now this,
0:03:50 > 0:03:54and they also brought the bodies of the animals that lived
0:03:54 > 0:03:58in those hills, including creatures like this one -
0:03:58 > 0:03:59a dinosaur.
0:04:05 > 0:04:10Excavators have uncovered hundreds of specimens like this one
0:04:10 > 0:04:12in the surrounding countryside.
0:04:17 > 0:04:21The local museum is crowded with one of the largest collections
0:04:21 > 0:04:24of complete dinosaur skeletons in the world.
0:04:34 > 0:04:37But a unique discovery here
0:04:37 > 0:04:39has revealed some of the earliest evidence
0:04:39 > 0:04:44for the origins of the animal group that would eventually succeed them.
0:04:46 > 0:04:50At the same time the dinosaurs were roaming in this area,
0:04:50 > 0:04:55there was another very different creature evolving in their shadow.
0:04:55 > 0:04:58One that was on a much, much smaller scale.
0:05:01 > 0:05:06Palaeontologist Wang Tao has spent his life exploring these hills.
0:05:08 > 0:05:13He's used to finding the remains of large dinosaurs.
0:05:13 > 0:05:16But on this hilltop site, he and his colleagues discovered
0:05:16 > 0:05:20something that didn't match the usual profile.
0:05:22 > 0:05:27TRANSLATION: I came to collect fossils with my colleagues
0:05:27 > 0:05:28in this area here.
0:05:30 > 0:05:32At the time, it was not like this.
0:05:32 > 0:05:35There were no crops growing here.
0:05:35 > 0:05:38After looking around, we followed this little slope.
0:05:38 > 0:05:44And finally we found a small fossil about two centimetres long.
0:05:46 > 0:05:48We thought it might be something special,
0:05:48 > 0:05:52so we sent it to the lab in Beijing to clean it up.
0:05:56 > 0:06:02I have travelled north to Beijing to see Wang Tao's discovery for myself.
0:06:02 > 0:06:06It's now stored in one of the world's leading institutes
0:06:06 > 0:06:08for the study of fossils.
0:06:13 > 0:06:15And this is it.
0:06:15 > 0:06:19And what seems extraordinary, near miraculous to me,
0:06:19 > 0:06:24is that anybody should notice that a tiny, tiny little thing like this
0:06:24 > 0:06:26is actually a fossil.
0:06:26 > 0:06:28But a fossil it is.
0:06:28 > 0:06:31It's the head of the tiny animal.
0:06:31 > 0:06:33There's the tip of its nose.
0:06:33 > 0:06:36That's the back of its neck.
0:06:36 > 0:06:40And you can also see it's got an eye socket.
0:06:40 > 0:06:43It's called Hadrocodium.
0:06:43 > 0:06:45If I turn it upside down
0:06:45 > 0:06:48you can see the bottom of its jaw.
0:06:49 > 0:06:55It might be the skull of a really minute little reptile.
0:06:55 > 0:06:56But it's not.
0:06:56 > 0:07:01Because reptiles have simple cone-shaped teeth,
0:07:01 > 0:07:05and this one has a tooth that is rather different.
0:07:05 > 0:07:10That has the shape of a little insect-eating mammal's tooth.
0:07:11 > 0:07:16So, this is one of the earliest mammal fossils we know of.
0:07:16 > 0:07:22And to that extent, it's the ancestor of all mammals alive today,
0:07:22 > 0:07:24including ourselves.
0:07:27 > 0:07:31As such, Hadrocodium holds a key position in the evolutionary story
0:07:31 > 0:07:34of the backboned animals, the vertebrates.
0:07:36 > 0:07:39The first creature with the beginnings of a backbone
0:07:39 > 0:07:42lived over 500 million years ago.
0:07:43 > 0:07:45Then fish,
0:07:45 > 0:07:47amphibians
0:07:47 > 0:07:49and reptiles evolved.
0:07:50 > 0:07:54It's from the reptile line that the first mammals emerge.
0:07:56 > 0:08:01The Hadrocodium fossil dates to 195 million years ago.
0:08:03 > 0:08:06These simple origins led to the vast diversity of mammals
0:08:06 > 0:08:08we see around us today.
0:08:10 > 0:08:15Over 5,700 living species have adapted to survive
0:08:15 > 0:08:17in every corner of the planet.
0:08:20 > 0:08:24We humans dominate and are the most numerous of the large mammals.
0:08:29 > 0:08:32This astonishing journey was built on a series
0:08:32 > 0:08:37of key evolutionary advances that began in very early forms
0:08:37 > 0:08:38like Hadrocodium.
0:08:43 > 0:08:47We only have its skull, but we can work out from modern mammals
0:08:47 > 0:08:50what the rest of its skeleton was like.
0:09:08 > 0:09:12So, how did this minute animal gain a foothold
0:09:12 > 0:09:14in the age of the dinosaurs?
0:09:23 > 0:09:26Kunming city in southern China.
0:09:28 > 0:09:30I've come to this late-night market
0:09:30 > 0:09:35to observe one of the first crucial steps in the mammals' story.
0:09:38 > 0:09:41The development of an amazing feature
0:09:41 > 0:09:43that gave them a key advantage.
0:09:43 > 0:09:45But only after dark.
0:09:49 > 0:09:52The mammals found a niche for themselves
0:09:52 > 0:09:55not so much in space as in time - at night,
0:09:55 > 0:09:58when the reptiles are not active.
0:09:59 > 0:10:01A simple experiment with two pets
0:10:01 > 0:10:04that happened to be for sale in the market tonight
0:10:04 > 0:10:06can demonstrate why this is so.
0:10:07 > 0:10:10This is a thermal camera,
0:10:10 > 0:10:15and it will show a cold body as a black or very dark.
0:10:15 > 0:10:19So, this lizard which is on the table is cold-blooded,
0:10:19 > 0:10:23and it appears to be very much the same temperature as the table.
0:10:24 > 0:10:30Reptiles get much of their energy directly from the sun as warmth.
0:10:30 > 0:10:32But there is no sun at night.
0:10:32 > 0:10:36As a consequence, it's scarcely got the energy to move.
0:10:36 > 0:10:38This puppy, on the other hand,
0:10:38 > 0:10:41is very active.
0:10:41 > 0:10:43And when you look at him with the camera,
0:10:43 > 0:10:47you can see that his body is very warm indeed.
0:10:47 > 0:10:49And you mustn't eat the lizard!
0:10:51 > 0:10:54The mammals, very early in their history, developed
0:10:54 > 0:11:00the remarkable ability to generate heat within their bodies.
0:11:00 > 0:11:01They became warm-blooded,
0:11:01 > 0:11:05and they achieved this by driving their metabolism
0:11:05 > 0:11:07at a much higher rate.
0:11:07 > 0:11:11But to do that, you need extra fuel, extra food.
0:11:13 > 0:11:18A reptile like a lizard can go for many days without eating.
0:11:18 > 0:11:23But if a mammal is denied its food for several days, it will die.
0:11:23 > 0:11:26So, in order to keep their fuel bills down,
0:11:26 > 0:11:31the mammals used a technique familiar to any householder -
0:11:31 > 0:11:32insulation.
0:11:32 > 0:11:35They coated their bodies, as this puppy has,
0:11:35 > 0:11:37with fur.
0:11:43 > 0:11:46With warm blood and a covering of hair,
0:11:46 > 0:11:50Hadrocodium was free to hunt for insects in the cool of the night.
0:11:53 > 0:11:55But now came a new challenge -
0:11:55 > 0:11:58to find its way around in pitch darkness.
0:12:05 > 0:12:09Detailed analysis of Hadrocodium's skull is revealing remarkable
0:12:09 > 0:12:13new evidence of a set of ingenious solutions to this problem.
0:12:15 > 0:12:19The clues are tiny and invisible to outside scrutiny.
0:12:21 > 0:12:25But professor Zhe-Xi Luo, an expert on early mammals,
0:12:25 > 0:12:30is using a micro CT scanner to unlock the skull's inner secrets.
0:12:31 > 0:12:34X-rays penetrate the rock
0:12:34 > 0:12:37and pick out detailed fossil structures within.
0:12:38 > 0:12:42A computer then builds a 3D model of the bones,
0:12:42 > 0:12:45and, in particular, the cavity that once held the brain.
0:12:49 > 0:12:52Professor Luo is able to identify an area that is clearly
0:12:52 > 0:12:55much larger than its equivalent in a reptile.
0:12:57 > 0:13:00If you look at the CT scan here,
0:13:00 > 0:13:06you can tell that, despite a tiny little skull, the brain is enormous.
0:13:08 > 0:13:12But one of the most striking features of this particular fossil
0:13:12 > 0:13:17is that it has very large olfactory bulbs.
0:13:18 > 0:13:21When you say olfactory bulbs,
0:13:21 > 0:13:24- those are the part of the brain that detects smell.- Correct.
0:13:24 > 0:13:31This mammal must have had very refined sensory detection
0:13:31 > 0:13:37of all kinds of smell, allowing it to be active in the dark of the night.
0:13:40 > 0:13:45This powerful sense of smell would have helped Hadrocodium pick out
0:13:45 > 0:13:48the scent of the worms and insects it fed on.
0:13:51 > 0:13:56The scanners have also revealed a radical advance in a second sense
0:13:56 > 0:13:57that's vital in the dark.
0:13:57 > 0:13:59Hearing.
0:14:00 > 0:14:05The tell-tale clue lies, surprisingly, in Hadrocodium's jaw.
0:14:05 > 0:14:08One very interesting feature
0:14:08 > 0:14:12that's so unique about this fossil mammal is...
0:14:12 > 0:14:15very flat jaw.
0:14:15 > 0:14:21The surface on the inside of the jaw is perfectly flat.
0:14:21 > 0:14:23In the primitive,
0:14:23 > 0:14:28pre-mammalian forms, there are big grooves.
0:14:30 > 0:14:34Grooves like these indicate the presence of two key bones
0:14:34 > 0:14:37that are attached to the jaw of a reptile.
0:14:39 > 0:14:42Seen here in green and red.
0:14:42 > 0:14:46A third bone, coloured blue, transmits sound waves in its ear.
0:14:47 > 0:14:52In a mammal there has been a truly amazing evolutionary development.
0:14:52 > 0:14:56The two jawbones have shifted to form, with the third...
0:14:58 > 0:14:59..the middle ear.
0:15:01 > 0:15:03This three-bone arrangement
0:15:03 > 0:15:05opens up a range of higher-pitched frequencies
0:15:05 > 0:15:08that a reptile cannot hear.
0:15:11 > 0:15:16It's the system we have inherited inside our ears.
0:15:17 > 0:15:23So, in Hadrocodium, we get the earliest indication
0:15:23 > 0:15:28that the three ear bones so important for our hearing
0:15:28 > 0:15:32have already originated with this fossil.
0:15:36 > 0:15:41Now ears could pick up the faintest rustle in the undergrowth
0:15:41 > 0:15:46and guide Hadrocodium to any insects moving nearby.
0:15:48 > 0:15:52Professor Luo's analysis has also identified
0:15:52 > 0:15:56a spectacular advance in a third key sense.
0:15:56 > 0:16:00It also has very large areas
0:16:00 > 0:16:02responsible for skin touch.
0:16:02 > 0:16:06- For touch?- That's right. Mammals have hairs.
0:16:06 > 0:16:09One of the most important functions of the hair is actually
0:16:09 > 0:16:11to give us the sensory touch,
0:16:11 > 0:16:15and this animal has already developed that.
0:16:18 > 0:16:23The use of hairs as touch sensors is perhaps most obvious from the way
0:16:23 > 0:16:25modern mammals use their whiskers.
0:16:27 > 0:16:31This brown rat relies on them for finding its way around at night,
0:16:31 > 0:16:33or underground.
0:16:34 > 0:16:38At the base of each of those long hairs on its nose,
0:16:38 > 0:16:40there is a nerve receptor.
0:16:41 > 0:16:43And whenever the hair is touched,
0:16:43 > 0:16:46a message is sent up to the rat's brain.
0:16:48 > 0:16:50It's not just the whiskers, though.
0:16:50 > 0:16:54Hairs all over its body are wired up to its nervous system.
0:16:55 > 0:16:58This creates a sensory bubble,
0:16:58 > 0:17:02allowing the rat to map the world around it just by using its hairs.
0:17:06 > 0:17:08195 million years ago,
0:17:08 > 0:17:12the hairs on Hadrocodium must have been wired up in the same way.
0:17:19 > 0:17:23This remarkable little creature now had a whole array
0:17:23 > 0:17:27of new powers with which to meet the challenges of the night.
0:17:35 > 0:17:38A heightening of the senses powered by a growing brain
0:17:38 > 0:17:42had enabled the early mammals to survive in the shadow
0:17:42 > 0:17:46of the dinosaurs. And then, they also developed a radical new way
0:17:46 > 0:17:49of nourishing their young.
0:17:52 > 0:17:55We can look for clues to this next crucial step
0:17:55 > 0:17:59in our evolutionary story in Australia.
0:17:59 > 0:18:00Not in fossils,
0:18:00 > 0:18:04but in the bodies of two highly unusual creatures that live here.
0:18:13 > 0:18:15The first is the platypus,
0:18:15 > 0:18:19which uses its rubbery beak like a radar transmitter
0:18:19 > 0:18:22to hunt for shrimp or molluscs underwater.
0:18:26 > 0:18:28And the second is the echidna,
0:18:28 > 0:18:31which forages for ants and termites on land.
0:18:33 > 0:18:37The platypus and echidna are the only two survivors
0:18:37 > 0:18:40of a group of mammals called the "monotremes".
0:18:45 > 0:18:47Trace their genetic line back,
0:18:47 > 0:18:49and we discover they split from all other mammals
0:18:49 > 0:18:52around 200 million years ago.
0:18:55 > 0:18:58Because they retain traits from that distant time,
0:18:58 > 0:19:01they give us a remarkable insight into very early mammals
0:19:01 > 0:19:03like Hadrocodium.
0:19:08 > 0:19:12The most extraordinary feature of all is one that no other
0:19:12 > 0:19:14modern mammal has retained.
0:19:17 > 0:19:18They lay eggs.
0:19:20 > 0:19:22This echidna egg is tiny,
0:19:22 > 0:19:25only about the size of a marble.
0:19:26 > 0:19:30The hatching process itself has only rarely been captured on film.
0:19:40 > 0:19:43These are newly-hatched platypus young,
0:19:43 > 0:19:46filmed in their mother's burrow.
0:19:47 > 0:19:50They're only about the size of jelly beans.
0:19:52 > 0:19:55The early mammals must have laid eggs in the same way,
0:19:55 > 0:19:58and they inherited this trait from their reptile ancestors.
0:20:03 > 0:20:07This is a view inside a reptile egg.
0:20:07 > 0:20:11The embryo feeds on a supply of highly nutritious yolk.
0:20:15 > 0:20:17By the time reptiles hatch,
0:20:17 > 0:20:20they're sufficiently well-developed to go looking for their own food.
0:20:24 > 0:20:27But the platypus and echidna are very different.
0:20:27 > 0:20:30Their smaller eggs contain only a small amount of yolk,
0:20:30 > 0:20:34so their young hatch in a far less-developed state.
0:20:35 > 0:20:39They need a lot more nourishment if they're going to grow and survive.
0:20:43 > 0:20:45But at Healesville Sanctuary near Melbourne,
0:20:45 > 0:20:49we can find delightful evidence that platypus young do develop
0:20:49 > 0:20:53with great success without having to leave their mother's burrow.
0:20:56 > 0:20:58Four months after it hatched,
0:20:58 > 0:21:01a youngster is emerging for the first time.
0:21:03 > 0:21:08It has grown from a tiny hatchling to near adult size.
0:21:10 > 0:21:13And that is thanks to an amazing form of nourishment
0:21:13 > 0:21:17that is a defining feature of all mammals.
0:21:18 > 0:21:19Milk.
0:21:21 > 0:21:25This rich mixture of proteins, fats, carbohydrates and minerals
0:21:25 > 0:21:28oozes from the bellies of female platypus and echidna
0:21:28 > 0:21:30rather like sweat,
0:21:30 > 0:21:34and provides their young with everything they need to grow.
0:21:36 > 0:21:39It's likely that early mammals like Hadrocodium
0:21:39 > 0:21:42nourished their young in the same way.
0:21:42 > 0:21:45First with a reduced amount of yolk, and then with milk.
0:21:47 > 0:21:51So, what could explain this hugely significant step?
0:21:55 > 0:21:59New genetic analysis is providing the answer.
0:22:00 > 0:22:04Dr Henrik Kaessmann has been using the platypus to investigate
0:22:04 > 0:22:06the DNA of the early mammals.
0:22:07 > 0:22:10The platypus is really an amazing creature.
0:22:10 > 0:22:15It's really this crossover of a mammal and a reptile, right.
0:22:16 > 0:22:20And so it has a key position in the evolutionary analysis
0:22:20 > 0:22:21of all mammals.
0:22:23 > 0:22:26First, he looked at the reduction in egg yolk.
0:22:28 > 0:22:31Reptiles have at least three genes that together
0:22:31 > 0:22:33manufacture their large yolk.
0:22:34 > 0:22:37Dr Kaessmann has found that the platypus DNA
0:22:37 > 0:22:41records a dramatic change taking place in the early mammals.
0:22:41 > 0:22:45We found only one egg yolk gene in the platypus genome
0:22:45 > 0:22:50that really was functional and was producing the egg yolk protein.
0:22:50 > 0:22:54Presumably the fact that there was only one gene
0:22:54 > 0:22:57which was producing yolk accounts for the fact
0:22:57 > 0:22:59that the platypus egg is so small?
0:22:59 > 0:23:01Exactly.
0:23:01 > 0:23:05The early mammals must have started to switch off their yolk genes.
0:23:05 > 0:23:09And Dr Kaessmann has made a second key discovery.
0:23:10 > 0:23:14The trigger for this shutdown was the arrival of the genes
0:23:14 > 0:23:16that produce milk.
0:23:16 > 0:23:19So, you have the milk genes appearing that then allow
0:23:19 > 0:23:22for the subsequent loss of the egg yolk genes.
0:23:23 > 0:23:27The mammals began to favour milk over egg yolk as a way
0:23:27 > 0:23:28to nourish their young.
0:23:30 > 0:23:33And that is because milk has one key advantage.
0:23:34 > 0:23:39It's on tap, and that means that none of it need go to waste.
0:23:39 > 0:23:41And there's no limit on how much
0:23:41 > 0:23:44and for how long a mother can feed her young.
0:23:49 > 0:23:51Warm bodies, powerful senses,
0:23:51 > 0:23:55and now, milk, had allowed the early mammals like Hadrocodium
0:23:55 > 0:23:59to gain a foothold while the reptiles still ruled.
0:24:03 > 0:24:06But combining egg-laying with milk-feeding
0:24:06 > 0:24:08brought a new challenge.
0:24:08 > 0:24:12A mammal mother could not leave the eggs to hatch by themselves
0:24:12 > 0:24:14as most reptiles do today.
0:24:14 > 0:24:16She had to stay with them.
0:24:21 > 0:24:23Then came a truly astonishing solution.
0:24:26 > 0:24:28The egg, instead of being laid,
0:24:28 > 0:24:34was retained inside the body and started its development there,
0:24:34 > 0:24:37so that the young was born alive.
0:24:40 > 0:24:42Apart from the monotremes,
0:24:42 > 0:24:45there are two other major groups of modern mammals around today.
0:24:46 > 0:24:50Marsupials and placentals.
0:24:50 > 0:24:52It's thought that they first appeared
0:24:52 > 0:24:55around 160 million years ago.
0:24:56 > 0:24:59Both give birth to live young.
0:24:59 > 0:25:02But they do so in two very different ways.
0:25:05 > 0:25:10Spectacular fossil beds in the north of China have, in recent years,
0:25:10 > 0:25:14produced the earliest ancestors yet found of these two groups.
0:25:18 > 0:25:21This is Liaoning province.
0:25:24 > 0:25:27125 million years ago,
0:25:27 > 0:25:30volcanoes were erupting in this region.
0:25:35 > 0:25:39They left layer upon layer of yellow ash in these rocks.
0:25:46 > 0:25:50Excavations have revealed the fossilised remains of animals
0:25:50 > 0:25:54trapped in these layers and preserved in extraordinary detail.
0:25:55 > 0:25:59This is a fossil that's been called Sinodelphys.
0:26:00 > 0:26:04Its skeleton is very easily seen.
0:26:04 > 0:26:08But around its skeleton there are dark marks,
0:26:08 > 0:26:11and close examination shows that they are fur.
0:26:11 > 0:26:16So, we can be pretty sure that this is the fossil of a mammal.
0:26:16 > 0:26:19But its skeleton, and in particular, its teeth,
0:26:19 > 0:26:23make it clear that it was a marsupial.
0:26:27 > 0:26:31Marsupials were once distributed throughout the globe.
0:26:32 > 0:26:35But most are found today in Australia.
0:26:36 > 0:26:37And they allow us to see
0:26:37 > 0:26:42how their ancestors began to bring their young into the world alive.
0:26:47 > 0:26:51This is a sanctuary for breeding endangered species of wallaby
0:26:51 > 0:26:53through the use of foster mothers.
0:26:58 > 0:27:00Running the conservation project
0:27:00 > 0:27:04is Dr David Taggart of the University of Adelaide.
0:27:07 > 0:27:11Today, he and his team are conducting a health check
0:27:11 > 0:27:14on a newly arrived baby wallaby, known as a "joey".
0:27:18 > 0:27:23This joey looks like it's about two grams, so about 16 days old.
0:27:23 > 0:27:26So, 16 days ago, this young would have been born.
0:27:26 > 0:27:29All marsupial young are born very immature,
0:27:29 > 0:27:32so its ears are folded and the eyes are closed.
0:27:33 > 0:27:37Instead of being enclosed in an egg when leaving its mother
0:27:37 > 0:27:40like a baby echidna, this joey emerged
0:27:40 > 0:27:44directly from its mother's birth canal just 30 days after conception.
0:27:45 > 0:27:48Its front legs are more developed
0:27:48 > 0:27:51and strong enough for it to pull itself up through the fur
0:27:51 > 0:27:55and wriggle inside a feature that is unique to marsupials - a pouch.
0:28:03 > 0:28:07Here, there's a highly developed milk delivery system.
0:28:10 > 0:28:14The milk is channelled through long, fleshy tubes, teats.
0:28:17 > 0:28:19A wallaby mother has four of them,
0:28:19 > 0:28:23and can even feed young of different ages at the same time.
0:28:26 > 0:28:29She might have a young, just newly born,
0:28:29 > 0:28:31attached to one teat, and she'll have a young
0:28:31 > 0:28:34with its head in the pouch feeding from another teat.
0:28:34 > 0:28:36And those two teats will be producing a milk
0:28:36 > 0:28:40that is of different consistency.
0:28:40 > 0:28:44So, one will be to nourish a new-born young
0:28:44 > 0:28:47and the other's to nourish a young that's almost ready to wean.
0:28:47 > 0:28:48It's a great system.
0:28:50 > 0:28:53The long teats also give the young a way to cling
0:28:53 > 0:28:55onto their mother as she moves around.
0:29:00 > 0:29:04This opossum is a marsupial that lives in South America
0:29:04 > 0:29:05and it has no pouch.
0:29:07 > 0:29:10Its young seal their mouths so tightly round the teats,
0:29:10 > 0:29:13they stay firmly attached.
0:29:13 > 0:29:17This may well be how the early marsupials, like Sinodelphys,
0:29:17 > 0:29:19carried their young around.
0:29:21 > 0:29:24They were now no longer tied to a nest or a burrow
0:29:24 > 0:29:25like the egg-laying mammals.
0:29:27 > 0:29:29But this method had one obvious drawback.
0:29:30 > 0:29:32Outside their mother's body,
0:29:32 > 0:29:38the newborn young were vulnerable to accident and exposed to disease.
0:29:44 > 0:29:48In China, new evidence is emerging for the pioneers
0:29:48 > 0:29:50of an even more radical solution.
0:29:52 > 0:29:56At the same time as the marsupials appeared,
0:29:56 > 0:30:00another branch developed on the family tree of the mammals,
0:30:00 > 0:30:03a branch that we belong to.
0:30:03 > 0:30:08And it had way of nurturing their young before birth.
0:30:14 > 0:30:18I'm travelling to Beijing and its museum of natural history,
0:30:18 > 0:30:22to see remarkably early evidence for this group.
0:30:30 > 0:30:32This is it.
0:30:35 > 0:30:37It's been called Juramaia,
0:30:37 > 0:30:40which means "Jurassic mother".
0:30:41 > 0:30:45Its bones, and in particular, its teeth,
0:30:45 > 0:30:49identify it as a member of the mammal group to which we belong.
0:30:50 > 0:30:53But the key thing about it is its date.
0:30:53 > 0:30:57It's Jurassic - 160 million years old.
0:30:58 > 0:31:02And this makes Juramaia the earliest creature we know of
0:31:02 > 0:31:06that could have nurtured its young in a revolutionary new way.
0:31:12 > 0:31:17Juramaia lived and hunted in a world still dominated by the dinosaurs.
0:31:23 > 0:31:26But it may have had a powerful advantage -
0:31:26 > 0:31:29the ability for a mother to carry her young,
0:31:29 > 0:31:32not outside her body like the marsupials...
0:31:34 > 0:31:36..but inside, in a womb.
0:31:41 > 0:31:45To understand how Juramaia could have achieved this, we can look at
0:31:45 > 0:31:48one of its living descendants, the one that carries its young inside
0:31:48 > 0:31:52for the longest period of all mammals, the elephant.
0:31:53 > 0:31:55This is Dokkoon.
0:31:56 > 0:32:00She is part of a breeding programme at Melbourne Zoo in Australia,
0:32:00 > 0:32:01and she is pregnant.
0:32:03 > 0:32:07Dr Thomas Hildebrandt, one of the world's leading experts
0:32:07 > 0:32:11in mammal birth, is monitoring progress with an ultrasound scanner.
0:32:12 > 0:32:16We study the longest pregnancy on the planet,
0:32:16 > 0:32:18which the elephant has with 22 months.
0:32:18 > 0:32:20And so ultrasound allows us
0:32:20 > 0:32:23non-invasively to see all the differences
0:32:23 > 0:32:25during the foetal development,
0:32:25 > 0:32:29which is quite exciting and was never done before.
0:32:31 > 0:32:34More detailed 3D scans give us
0:32:34 > 0:32:38a spectacular view inside her womb.
0:32:38 > 0:32:40Even at an early stage of development,
0:32:40 > 0:32:42the baby's trunk is visible and moving.
0:32:44 > 0:32:48But we can also see the presence of a remarkable organ
0:32:48 > 0:32:53that evolved to make it possible to feed a developing baby before birth.
0:32:54 > 0:32:56The placenta.
0:33:00 > 0:33:04This baby elephant was born in the zoo just three weeks ago
0:33:04 > 0:33:08and its placenta has been saved for analysis.
0:33:13 > 0:33:17Here we have the elephant placenta of the baby which is running
0:33:17 > 0:33:19outside the yard.
0:33:19 > 0:33:22These blood vessels form the umbilical cord,
0:33:22 > 0:33:25allowing to move all the nutrients to the baby
0:33:25 > 0:33:27and take all the waste material away.
0:33:29 > 0:33:32On the underside is a ring of sponge-like tissue
0:33:32 > 0:33:35that attaches to the lining of the mother's womb
0:33:35 > 0:33:40and allows nutriment to flow in and waste to flow out.
0:33:42 > 0:33:45But it also operates as a life-saving barrier.
0:33:46 > 0:33:50Because half of the unborn baby's genes are from its father,
0:33:50 > 0:33:54it was under threat in the womb from its mother's immune system.
0:33:54 > 0:33:58The baby is foreign materials and alien to the mother,
0:33:58 > 0:34:05and would be rejected if there's not this very specific system engaged
0:34:05 > 0:34:09which protects the baby against the maternal immune system.
0:34:10 > 0:34:13Because the tissues of the placenta are composed of cells
0:34:13 > 0:34:18from both mother and baby, and the two blood supplies never mix,
0:34:18 > 0:34:20the baby is protected.
0:34:21 > 0:34:24This allows it to remain inside the womb
0:34:24 > 0:34:27until it's ready to survive in the outside world.
0:34:29 > 0:34:32Mammals equipped with this miracle of evolutionary engineering
0:34:32 > 0:34:35are known as "placentals".
0:34:38 > 0:34:42It's likely that their earliest ancestors, like Juramaia,
0:34:42 > 0:34:45were the first to rear their young inside their bodies
0:34:45 > 0:34:48160 million years ago.
0:34:50 > 0:34:54By now, the mammals had acquired all the key characteristics
0:34:54 > 0:34:56that define them as a group.
0:34:56 > 0:34:58Hairy bodies,
0:34:58 > 0:34:59milk
0:34:59 > 0:35:01and live birth.
0:35:01 > 0:35:04And this combination would eventually provide them
0:35:04 > 0:35:09with the platform for an astonishing explosion in diversity.
0:35:11 > 0:35:14For millions of years, they remained the small,
0:35:14 > 0:35:17shrew-like creatures that we've encountered so far,
0:35:17 > 0:35:20skittering about around the feet of the dinosaurs.
0:35:20 > 0:35:24But then came a sudden global catastrophe
0:35:24 > 0:35:27that threatened to bring the whole history of the vertebrates
0:35:27 > 0:35:28to a sudden end.
0:35:35 > 0:35:40A meteor impact that sent shock waves around the world,
0:35:40 > 0:35:43and coincided with the extinction of the dinosaurs.
0:35:45 > 0:35:49We're still not exactly sure WHY the dinosaurs disappeared,
0:35:49 > 0:35:53but certainly 65 million years ago,
0:35:53 > 0:35:55they disappear from the fossil record.
0:35:56 > 0:35:59But many other vertebrates survived,
0:35:59 > 0:36:03and for them, the dominance of the world was now up for grabs.
0:36:07 > 0:36:11Scientists are unearthing stunning evidence in Germany
0:36:11 > 0:36:13for how the mammals seized this opportunity.
0:36:16 > 0:36:20This natural hollow is known as the Messel Pit.
0:36:22 > 0:36:25An entire community of animals was entombed here
0:36:25 > 0:36:28by an extraordinary freak of nature.
0:36:30 > 0:36:3247 million years ago,
0:36:32 > 0:36:36this was a lake fringed by a subtropical rainforest.
0:36:36 > 0:36:38But its waters held a dark secret.
0:36:40 > 0:36:43The lake was in fact a flooded volcanic crater.
0:36:45 > 0:36:48It's thought that lethal carbon dioxide gas
0:36:48 > 0:36:53released from its depths periodically bubbled to the surface,
0:36:53 > 0:36:57killing the creatures that drank at its shore or flew over its waters.
0:37:00 > 0:37:02Their bodies drifted down to the bottom
0:37:02 > 0:37:05to be entombed in the muddy sediment.
0:37:09 > 0:37:11It's now one of the most remarkable
0:37:11 > 0:37:14fossil excavation sites in the world.
0:37:20 > 0:37:25Painstaking work is uncovering creatures sealed inside layers
0:37:25 > 0:37:26of the ancient lake bed.
0:37:30 > 0:37:33They're preserved in extraordinary detail.
0:37:41 > 0:37:45It's a unique snapshot of life after the dinosaurs.
0:37:47 > 0:37:50There are reptiles, like lizards and snakes.
0:37:54 > 0:37:56Here, too, are ancient birds,
0:37:56 > 0:37:59the vertebrate group that evolved from the dinosaurs.
0:38:01 > 0:38:04But the biggest changes are amongst the mammals.
0:38:04 > 0:38:07They have started to specialise.
0:38:08 > 0:38:12This, perhaps, is the least specialised of them.
0:38:12 > 0:38:16It's an insect-eater, a creature like a large shrew,
0:38:16 > 0:38:20and its teeth are still relatively simple.
0:38:21 > 0:38:24But then there are also animals like this.
0:38:28 > 0:38:32And this has very big, gnawing front teeth.
0:38:34 > 0:38:38This is an early rodent, a creature like a rat.
0:38:38 > 0:38:39And then bigger still...
0:38:42 > 0:38:43..is this animal.
0:38:45 > 0:38:50This has grinding molar teeth at the back,
0:38:50 > 0:38:52and long legs.
0:38:52 > 0:38:55It's beginning to stand up on its toes.
0:38:56 > 0:38:59This is an early horse.
0:38:59 > 0:39:02And perhaps the most specialised and remarkable of all
0:39:02 > 0:39:04at this still very early date
0:39:04 > 0:39:07is this extraordinary specimen.
0:39:08 > 0:39:11This, as you can see, is a bat.
0:39:11 > 0:39:15And the preservation is so remarkable
0:39:15 > 0:39:18that the skin can be easily seen,
0:39:18 > 0:39:20not only on its forelegs,
0:39:20 > 0:39:22which turns them into wings,
0:39:22 > 0:39:27but even you can see this large ear
0:39:27 > 0:39:29on the side of its head,
0:39:29 > 0:39:33which suggests that already it was beginning to echo-locate,
0:39:33 > 0:39:37to hear its own calls so it navigates during flying.
0:39:41 > 0:39:44The mammals were displaying an extraordinary ability
0:39:44 > 0:39:49to rapidly adapt their bodies to fill the range of niches left vacant
0:39:49 > 0:39:51by the death of the dinosaurs.
0:39:53 > 0:39:54They had new opportunities,
0:39:54 > 0:39:57but they also faced a new evolutionary pressure.
0:39:59 > 0:40:00Climate change.
0:40:03 > 0:40:06Ten million years of gradual global-warming
0:40:06 > 0:40:08had triggered a surge in plant life.
0:40:09 > 0:40:14The land became covered in forests that grew ever denser and darker.
0:40:16 > 0:40:19New mammals emerged with new features that helped them
0:40:19 > 0:40:22to thrive in this changed environment.
0:40:22 > 0:40:26Features that would have huge significance for humans.
0:40:28 > 0:40:32This is an early member of the group of mammals
0:40:32 > 0:40:34that was going to produce us.
0:40:34 > 0:40:36This is an early primate.
0:40:36 > 0:40:41And you can see that on its front legs, its hands,
0:40:41 > 0:40:43they have an opposable thumb,
0:40:43 > 0:40:45so it could grasp.
0:40:45 > 0:40:49And the same on the back legs - the big toe is also opposable.
0:40:50 > 0:40:53So, this animal was a climber.
0:40:55 > 0:40:59The primates could now reach food that was high up in trees.
0:41:01 > 0:41:04And it's thought that it was a new type of food that triggered
0:41:04 > 0:41:08another astonishing advance in their bodies.
0:41:08 > 0:41:11A major improvement in sight.
0:41:15 > 0:41:19Dr Sandra Engels is part of a team investigating
0:41:19 > 0:41:23the diet of the fossilised primate from the Messel Pit.
0:41:24 > 0:41:28Remarkably, she's able to examine the preserved contents of its gut.
0:41:30 > 0:41:35We have particles of the last meal of this primate,
0:41:35 > 0:41:39and we analysed it with very high magnification
0:41:39 > 0:41:44and we found the oval outline of a seed
0:41:44 > 0:41:46which is part of a fruit.
0:41:46 > 0:41:50And because we found it in the gut of this primate,
0:41:50 > 0:41:52we know that it fed on fruit.
0:41:52 > 0:41:573D scans of its teeth make it clear that fruit was a major part
0:41:57 > 0:42:02of its diet. This animal was a specialised fruit-eater.
0:42:03 > 0:42:06If we take a closer look to the shape of the teeth,
0:42:06 > 0:42:12we have structures as deep basins or rounder cusps
0:42:12 > 0:42:15that are the right tools to break up fruit.
0:42:18 > 0:42:2247 million years ago, large, fleshy fruit like this
0:42:22 > 0:42:25had only recently been developed by plants.
0:42:25 > 0:42:28It was one of the ways in which they had adapted
0:42:28 > 0:42:31to the new dense forest environments.
0:42:32 > 0:42:37Many early plants relied on the wind to distribute their seeds.
0:42:37 > 0:42:41But in the forest, there is little or no wind, so they had a problem.
0:42:42 > 0:42:46They solved it by recruiting the help of birds,
0:42:46 > 0:42:50and they did that by wrapping their seeds
0:42:50 > 0:42:53in an edible, sweet flesh, fruit.
0:42:54 > 0:42:57Birds carried the seeds in their stomachs
0:42:57 > 0:43:01and eventually deposited them elsewhere in the forest.
0:43:03 > 0:43:08The primates had clearly begun to exploit this cosy arrangement,
0:43:08 > 0:43:12but to take full advantage, they needed to improve their vision.
0:43:14 > 0:43:16During the age of the dinosaurs,
0:43:16 > 0:43:18when the mammals were largely nocturnal,
0:43:18 > 0:43:21they had developed better night vision,
0:43:21 > 0:43:24but sacrificed a feature not needed in the dark.
0:43:24 > 0:43:26The ability to see colour.
0:43:28 > 0:43:34Today, most mammals still see the world largely in black and white.
0:43:34 > 0:43:37But the reptiles and their cousins, the birds,
0:43:37 > 0:43:39retained excellent colour vision.
0:43:42 > 0:43:44And the fruit-bearing plants
0:43:44 > 0:43:48had evolved a signalling arrangement to match.
0:43:51 > 0:43:54There's no point in having your seeds distributed
0:43:54 > 0:43:55before they're fully formed.
0:43:55 > 0:43:58So, the plants evolved a colour-coding system
0:43:58 > 0:44:00to show when that was.
0:44:01 > 0:44:05This plant, for example, here is a young fruit still growing.
0:44:05 > 0:44:10Its flesh is hard and bitter, and it's green.
0:44:10 > 0:44:13But this fruit is fully formed.
0:44:13 > 0:44:16Its flesh is good to eat, soft,
0:44:16 > 0:44:20and the seed within is ready to go.
0:44:20 > 0:44:21And it's red.
0:44:23 > 0:44:26To spot a flash of red colour in amongst the green foliage
0:44:26 > 0:44:29is easy for a bird or a reptile.
0:44:31 > 0:44:34But for a mammal, with their night-time vision,
0:44:34 > 0:44:36red and green are indistinguishable.
0:44:38 > 0:44:39Then, remarkably,
0:44:39 > 0:44:44some of the primates managed a feat no other mammal has achieved.
0:44:45 > 0:44:50They put evolution into reverse and re-acquired colour vision.
0:44:52 > 0:44:56The common ancestor of this monkey, and of me,
0:44:56 > 0:44:59lived up in the trees in the daylight.
0:44:59 > 0:45:05And they quickly evolved the ability to see colour,
0:45:05 > 0:45:08and therefore, to know which was ripe and which was unripe fruit,
0:45:08 > 0:45:11and so take advantage of the system
0:45:11 > 0:45:13that had already been worked out
0:45:13 > 0:45:16between the birds and the plants.
0:45:17 > 0:45:20Let's just see what she thinks about that.
0:45:21 > 0:45:23Which of those do you like?
0:45:23 > 0:45:24There's it.
0:45:30 > 0:45:34After the dinosaur extinctions of 65 million years ago,
0:45:34 > 0:45:37the mammals were using their spectacular adaptability
0:45:37 > 0:45:41to evolve and diversify at an astonishing rate.
0:45:44 > 0:45:46In the process, they laid the foundations
0:45:46 > 0:45:49for the major mammal groups we see today.
0:45:54 > 0:46:00But then, around 47 million years ago, came a new set of problems.
0:46:02 > 0:46:04The Earth's climate changed yet again.
0:46:04 > 0:46:08Many places became drier, and where that happened,
0:46:08 > 0:46:11the forest thinned out and was replaced
0:46:11 > 0:46:14by low, scattered bushes and grass.
0:46:14 > 0:46:18And those new environments presented new challenges to animals
0:46:18 > 0:46:22and ushered in the age of the mammal monsters.
0:46:26 > 0:46:29Scientists are finding stunning evidence of this change
0:46:29 > 0:46:32in the Great Plains of North America.
0:46:38 > 0:46:44This dramatic country in South Dakota is known as the Badlands.
0:46:45 > 0:46:50Streams and rivers have eroded the rocks into fantastic shapes.
0:46:54 > 0:46:55But 40 million years ago,
0:46:55 > 0:47:00these were layers of sediment laid down across an open flood plain.
0:47:04 > 0:47:07Palaeontologist Clint Boyd is looking here
0:47:07 > 0:47:10for the fossilised remains of creatures from that ancient time.
0:47:12 > 0:47:15And he's finding mammals that are giants.
0:47:18 > 0:47:23This is part of the bone we call the femur or the upper-thigh bone,
0:47:23 > 0:47:27and this round surface right here is for the hip socket.
0:47:27 > 0:47:28And so you can see it's very large.
0:47:28 > 0:47:31We'd be talking about a very large animal.
0:47:31 > 0:47:35And not only do we have the thigh bone but we've got ankle bones
0:47:35 > 0:47:38spread out over here, and then cascading down from that spot,
0:47:38 > 0:47:40we've got some of the tail bones coming down.
0:47:40 > 0:47:43So, if we add all this up together, based on the size,
0:47:43 > 0:47:45we're looking at an animal that's probably
0:47:45 > 0:47:47about two metres tall at the hips.
0:47:49 > 0:47:53The creature is known as a Titanothere.
0:47:53 > 0:47:54It was a herbivore.
0:47:54 > 0:47:58It fed on the lush vegetation that once covered this area
0:47:58 > 0:48:00of the United States.
0:48:03 > 0:48:06A range of different specimens have been collected
0:48:06 > 0:48:09at Denver Museum of Nature and Science.
0:48:10 > 0:48:12And they reveal that the first Titanotheres
0:48:12 > 0:48:16were built on a much smaller scale.
0:48:16 > 0:48:19When Titanotheres first appear on the scene, they look like this.
0:48:19 > 0:48:22This is the lower jaw of one of the first Titanotheres,
0:48:22 > 0:48:24and it's one of these sheep-sized animals.
0:48:24 > 0:48:26In only five million years,
0:48:26 > 0:48:29members of the group go from sheep-sized...
0:48:30 > 0:48:33..to about the size of a small horse.
0:48:34 > 0:48:38Within only 15 million years of their first appearance,
0:48:38 > 0:48:40Titanotheres look like this.
0:48:40 > 0:48:44Here you can see the skull of one of these Titanotheres.
0:48:46 > 0:48:51In evolutionary terms, the size increase is astonishingly quick.
0:48:52 > 0:48:54But what drove this remarkable change?
0:48:58 > 0:49:01Another fossil could provide an explanation.
0:49:01 > 0:49:05It dates back to the time of the first and smallest Titanotheres,
0:49:05 > 0:49:07but it's a very different type of mammal.
0:49:09 > 0:49:12This is the skull of Malfelis Badwaterensis,
0:49:12 > 0:49:14the "bad cat from Badwater".
0:49:14 > 0:49:16This was the largest predator at the time.
0:49:16 > 0:49:20This is the skull. This large crest is for large jaw muscles
0:49:20 > 0:49:24which would've given a powerful shearing bite that ran these
0:49:24 > 0:49:28blade-like teeth, perfect for chopping up a Titanothere.
0:49:28 > 0:49:31And what's interesting is that Malfelis was exactly
0:49:31 > 0:49:35the same size as the top herbivores of the time, like Titanotheres.
0:49:39 > 0:49:43The earliest Titanotheres could hide from these bad cats
0:49:43 > 0:49:46in the dense forest environments.
0:49:46 > 0:49:49But as those forests began to thin out,
0:49:49 > 0:49:52the Titanotheres were more vulnerable to attack.
0:49:52 > 0:49:56One way to improve their chances was to grow bigger.
0:49:57 > 0:50:00An herbivore is much more likely to survive an encounter
0:50:00 > 0:50:02with a predator if it's a little bit larger.
0:50:02 > 0:50:03And so there was a bit of an arms race
0:50:03 > 0:50:05between the predators and the prey.
0:50:05 > 0:50:09And animals like Titanotheres were able to escape this predator pressure
0:50:09 > 0:50:13by becoming the super-sized giants we see 35 million years ago.
0:50:16 > 0:50:20Fossilised remains of Titanotheres from the Badlands of South Dakota
0:50:20 > 0:50:23and elsewhere across the Great Plains
0:50:23 > 0:50:26allow us to reconstruct its rapid growth spurt.
0:50:39 > 0:50:41From modest beginnings,
0:50:41 > 0:50:43they increased their bulk ten times over...
0:50:44 > 0:50:47..till the largest stood over eight feet tall.
0:50:58 > 0:51:02On the open grasslands that increasingly covered the Earth,
0:51:02 > 0:51:04many other giant mammals emerged.
0:51:05 > 0:51:08Together, they're known as the "Megafauna".
0:51:12 > 0:51:15This giant sloth was found in California.
0:51:23 > 0:51:27In China, I've come to see the remains of mammoths.
0:51:31 > 0:51:35And a remarkable creature that was the largest land mammal
0:51:35 > 0:51:37to walk this Earth.
0:51:38 > 0:51:43This great beast is called Paraceratherium.
0:51:43 > 0:51:48It stood five metres tall and nearly eight metres long.
0:51:48 > 0:51:50Those furry little mammals
0:51:50 > 0:51:54scampering about in the shadows had produced descendants
0:51:54 > 0:51:57that could stare the biggest dinosaur in the eye.
0:52:08 > 0:52:12Today, the elephant is one of the few species of Megafauna
0:52:12 > 0:52:14to have survived.
0:52:15 > 0:52:17But those outsized versions
0:52:17 > 0:52:20have otherwise disappeared from the planet.
0:52:22 > 0:52:24So, what happened to them?
0:52:26 > 0:52:31Their eventual extinction coincides with another key event
0:52:31 > 0:52:32in the history of the Earth.
0:52:39 > 0:52:42From around two and a half million years ago,
0:52:42 > 0:52:45ice sheets spread down from the North and up from the South
0:52:45 > 0:52:48to cover vast areas of the continents.
0:52:54 > 0:52:57But it was only when the ice finally retreated,
0:52:57 > 0:53:01just 10,000 years ago, that the Megafauna vanished.
0:53:02 > 0:53:06Some have blamed that on the rise and falls of the temperature
0:53:06 > 0:53:09as the Ice Age finally came to a close.
0:53:09 > 0:53:13But others have sought the culprit amongst the mammals themselves.
0:53:15 > 0:53:17A newly-evolved super predator.
0:53:25 > 0:53:29To see some of the earliest evidence for its arrival in China,
0:53:29 > 0:53:30I've returned to Beijing.
0:53:34 > 0:53:38These fossilised remains belong to a primate.
0:53:42 > 0:53:46It's been dated to around 68,000 years ago.
0:53:48 > 0:53:52This primate had two new evolutionary features.
0:53:52 > 0:53:54First, its pelvis.
0:53:54 > 0:53:56An animal with a pelvis like this
0:53:56 > 0:53:58would have been able to walk upright.
0:53:59 > 0:54:01Secondly, the skull.
0:54:01 > 0:54:05Its brain case is enormous.
0:54:05 > 0:54:07In proportion to the size of its body,
0:54:07 > 0:54:10it's six times the average mammal size.
0:54:10 > 0:54:13And that would have brought great intelligence.
0:54:15 > 0:54:18And this creature, of course, was a human being.
0:54:20 > 0:54:25The early humans put their new intelligence to deadly use.
0:54:27 > 0:54:29They worked out how to make weapons.
0:54:31 > 0:54:34These stones, carefully chipped to form sharp blades,
0:54:34 > 0:54:37were found alongside human remains.
0:54:39 > 0:54:42And they developed new powers of communication
0:54:42 > 0:54:46that enabled them to join forces and hunt in teams.
0:54:47 > 0:54:50This was a new kind of predator.
0:54:50 > 0:54:53It first appeared in Africa
0:54:53 > 0:54:56and then spread to all the other continents,
0:54:56 > 0:54:59and each time its appearance in that continent
0:54:59 > 0:55:03coincided more or less with the disappearance of the Megafauna.
0:55:03 > 0:55:06Which suggests, at the very least,
0:55:06 > 0:55:10that this creature had something to do with that event.
0:55:18 > 0:55:20To conclude my journey in China,
0:55:20 > 0:55:23and find the last step in our evolutionary story,
0:55:23 > 0:55:28I'm back in Kunming city to visit one of its busiest maternity wards.
0:55:34 > 0:55:38An enlarged brain brought us huge advantages,
0:55:38 > 0:55:43but its size also presented a basic design problem at birth.
0:55:45 > 0:55:47The bony skull encasing the brain
0:55:47 > 0:55:50still had to make it out through the mother's birth canal.
0:55:55 > 0:55:58A new addition to our species, just 12 hours old,
0:55:58 > 0:56:00can reveal how this is possible.
0:56:04 > 0:56:08This little boy's name is Shao Bao.
0:56:08 > 0:56:11It means "little treasure".
0:56:11 > 0:56:16He was born because of a special feature in his skull.
0:56:16 > 0:56:19Mammal skulls are made up of separate bones.
0:56:19 > 0:56:24And in most species those are fused together at the time of birth
0:56:24 > 0:56:30to form a hard, bony box to protect that most special organ, the brain.
0:56:31 > 0:56:35But not so with Shao Bao and other human beings.
0:56:35 > 0:56:37They remain separate,
0:56:37 > 0:56:41and that allowed his head to slightly change shape
0:56:41 > 0:56:45and squeeze through the aperture of his mother's pelvis.
0:56:49 > 0:56:53This also allows the brain to continue to grow and develop
0:56:53 > 0:56:55after birth.
0:56:57 > 0:57:00In fact, the plates won't start to fuse
0:57:00 > 0:57:03until Shao Bao is around two years old.
0:57:06 > 0:57:08It's one of the most recent
0:57:08 > 0:57:11in a long line of remarkable evolutionary developments
0:57:11 > 0:57:15that allowed the vertebrates, animals with a backbone,
0:57:15 > 0:57:19to create the dazzling diversity we see around us today.
0:57:21 > 0:57:25Shao Bao's ancestry, like that of all of us,
0:57:25 > 0:57:28stretches back over 500 million years
0:57:28 > 0:57:33to a tiny little wormlike creature swimming in the bottom of the sea.
0:57:36 > 0:57:39His backbone and jaw came from the early fish.
0:57:41 > 0:57:44His limbs and lungs from amphibians.
0:57:46 > 0:57:49The reptiles gave him his watertight skin.
0:57:53 > 0:57:56Tiny nocturnal mammals donated a bigger brain...
0:57:57 > 0:57:59..sharper senses...
0:58:00 > 0:58:02..and the manner in which he was born.
0:58:05 > 0:58:09His hands and colour vision came from the fruit-eating primates.
0:58:10 > 0:58:15And his larger brain and greater intelligence, from the first humans.
0:58:17 > 0:58:21So, all our features of our body can be traced back
0:58:21 > 0:58:23to our ancient ancestors,
0:58:23 > 0:58:26and there's much more we have yet to learn about them.
0:58:28 > 0:58:29But one thing is certain -
0:58:29 > 0:58:33the evolution of the vertebrates has not yet come to an end.
0:59:01 > 0:59:04Subtitles by Red Bee Media Ltd