0:00:06 > 0:00:11Since the emergence of life more than three billion years ago,
0:00:11 > 0:00:13life on our planet has suffered
0:00:13 > 0:00:17a series of devastating mass extinction events.
0:00:17 > 0:00:21These have killed off uncountable species,
0:00:21 > 0:00:24and almost threatened to end life on Earth.
0:00:27 > 0:00:32I'm Professor Richard Fortey of London's Natural History Museum.
0:00:32 > 0:00:34I've spent all my working life
0:00:34 > 0:00:37studying the remains of animals long extinct.
0:00:38 > 0:00:42But now I'm setting off to discover
0:00:42 > 0:00:46why some animals and plants have survived.
0:00:46 > 0:00:47Hello, Snaky.
0:00:47 > 0:00:52I'm going in search of living fossils. Old timers.
0:00:52 > 0:00:54Here's the little face.
0:00:54 > 0:00:58That somehow managed to survive when so many others perished.
0:00:58 > 0:01:00Mm, excellent.
0:01:03 > 0:01:08In the process, I hope to find an answer to a profound question.
0:01:09 > 0:01:14Is being a survivor a question of having some very special features?
0:01:15 > 0:01:19Or nothing more than pure chance?
0:01:20 > 0:01:26From living fossils that are our most ancient relations
0:01:26 > 0:01:30to gigantic relics from the age of the dinosaurs.
0:01:31 > 0:01:37Life as we see it today is not just the product of evolution.
0:01:37 > 0:01:40It's also the consequence of mass extinction.
0:01:40 > 0:01:45We are all the sons and daughters of catastrophe.
0:01:45 > 0:01:47Oh, my goodness.
0:02:02 > 0:02:042.8 million years ago,
0:02:04 > 0:02:09triggered by changes in the Earth's orbit around the sun
0:02:09 > 0:02:13and shifts in its ocean currents, our world began to cool.
0:02:20 > 0:02:22Within a few thousand years,
0:02:22 > 0:02:26much of our planet was shrouded in a dense cloak of ice
0:02:26 > 0:02:31that would come and go until only 10,000 years ago.
0:02:31 > 0:02:33We call this age of ice the Pleistocene,
0:02:33 > 0:02:37and it transformed the hierarchy of nature.
0:02:44 > 0:02:48When ice sheets grow, animals and plants have a stark choice.
0:02:48 > 0:02:50They can adapt to the cold,
0:02:50 > 0:02:55they can move to stay with their own comfort zone, or they can die.
0:02:56 > 0:02:59And die many of them did.
0:03:02 > 0:03:04Even in the Arctic today,
0:03:04 > 0:03:08temperatures still regularly sink below minus 50 centigrade,
0:03:08 > 0:03:13and wind speeds have been known to reach 180 kilometres an hour.
0:03:15 > 0:03:19You might think nothing could live in such harsh conditions.
0:03:19 > 0:03:21But you'd be wrong.
0:03:22 > 0:03:26Strangely enough, when Pleistocene ice sheets grew,
0:03:26 > 0:03:28many animals saw it as an opportunity.
0:03:28 > 0:03:32New species evolved specially adapted to cold conditions.
0:03:33 > 0:03:37This is the story of how a few specialist species
0:03:37 > 0:03:41that evolved to live in the biting cold survived to the present day.
0:03:51 > 0:03:54It's summer in northern Norway.
0:03:56 > 0:03:59Here on the edge of the Arctic Circle,
0:03:59 > 0:04:02we can peer through a window back in time to a habitat
0:04:02 > 0:04:05that would not have been out of place in the Pleistocene.
0:04:08 > 0:04:10This is tundra.
0:04:10 > 0:04:12The word tundra comes from the Russian,
0:04:12 > 0:04:15meaning "treeless mountains".
0:04:15 > 0:04:19And it once covered huge tracts of the northern hemisphere.
0:04:21 > 0:04:25Summer here is short - a few months at most.
0:04:25 > 0:04:29Even in June, the temperature can drop below freezing.
0:04:29 > 0:04:31Daylight lasts more than 20 hours a day.
0:04:34 > 0:04:38With the ground below the surface still frozen solid in permafrost,
0:04:38 > 0:04:40no plant can sink deep roots.
0:04:41 > 0:04:46It's extraordinary how life can adapt to extremes.
0:04:46 > 0:04:52This little arctic birch I'm looking at crouches down away from the cold.
0:04:52 > 0:04:58A tiny little tree which is not much bigger than my hand,
0:04:58 > 0:04:59and it doesn't get much bigger.
0:04:59 > 0:05:03Yet it's related to trees that, in our garden,
0:05:03 > 0:05:05grow to 50 feet high or more.
0:05:05 > 0:05:09This is one strategy for coping with extreme conditions.
0:05:09 > 0:05:12Become miniature.
0:05:15 > 0:05:19Dwarf birch carry both male and female flowers,
0:05:19 > 0:05:22and its microscopic seeds are the result of wind pollination.
0:05:27 > 0:05:31And one thing you can always be certain of on these cold slopes
0:05:31 > 0:05:34is constant wind.
0:05:37 > 0:05:41But if trees shrink to adapt to the cold,
0:05:41 > 0:05:44the solution for many animals is the opposite.
0:05:45 > 0:05:52One way to cope with the onset of freezing conditions is to go large.
0:05:53 > 0:05:56That's because, as you grow bigger,
0:05:56 > 0:06:00volume increases disproportionately to surface area.
0:06:00 > 0:06:05In other words, if you're very big, you can hold in more heat.
0:06:05 > 0:06:08So, with the onset of icy conditions,
0:06:08 > 0:06:13several mammal groups in particular grew large.
0:06:13 > 0:06:16And for this reason, they're sometimes known as the mega-fauna.
0:06:21 > 0:06:25Great herds of mammoth, as well as woolly rhinoceroses,
0:06:25 > 0:06:28would once have lived in similar habitats.
0:06:30 > 0:06:35They have long gone, but one species of ice age mega-fauna
0:06:35 > 0:06:39that grazed alongside them still clings on in this special place.
0:06:43 > 0:06:46In this bleak and barren landscape,
0:06:46 > 0:06:50a landscape where the snow still lies
0:06:50 > 0:06:52every year for months at a time,
0:06:52 > 0:06:56it takes a very special creature to survive.
0:06:56 > 0:07:02There's little to eat except grass, lichens and a few herbs.
0:07:03 > 0:07:05And it's called the musk ox.
0:07:24 > 0:07:29Musk ox live in the Dovrefjell Sunndalsfjella National Park
0:07:29 > 0:07:34on land formerly used by NATO for war games and testing weapons.
0:07:36 > 0:07:38They are famously bad-tempered,
0:07:38 > 0:07:44and have been known to kill tourists and hikers, even charge trains.
0:07:44 > 0:07:47So to keep safe, I need the expertise
0:07:47 > 0:07:50of local Norwegian guide Johan Schonheyder.
0:07:53 > 0:07:56- Ah, so we're off. - Yeah. Now we're going.
0:08:06 > 0:08:11We're getting quite high here, and I can see the trees are thinning out.
0:08:11 > 0:08:14Is this the sort of place that musk ox might like to live?
0:08:14 > 0:08:17Yeah, it's not so often down here.
0:08:17 > 0:08:20But it comes in the springtime.
0:08:20 > 0:08:25It comes down to the valley here to give birth to their calves.
0:08:27 > 0:08:33So they live together, I guess, in small herds, with a dominant bull?
0:08:33 > 0:08:37Yeah, you can say that. There is one ruler of the whole herd.
0:08:37 > 0:08:40Well, of course, the obvious question.
0:08:40 > 0:08:45The name musk ox refers to musk, which is an odour, a scent.
0:08:46 > 0:08:51Is that to mark territory, or is that to establish dominance?
0:08:51 > 0:08:53What's the story with the musk?
0:08:53 > 0:08:58The only time we really can smell it is in the fall
0:08:58 > 0:09:01when they have this mating period.
0:09:01 > 0:09:04- OK, so it's to do with sex? - Yeah, I think so.- Yes.
0:09:15 > 0:09:18Oh, I can see them now!
0:09:24 > 0:09:28A fully-grown musk ox bull can weigh half a ton
0:09:28 > 0:09:32and charge at 50 kilometres an hour over rough terrain.
0:09:33 > 0:09:37Here, in one of the last great cold wildernesses
0:09:37 > 0:09:40in the northern hemisphere, we creep closer,
0:09:40 > 0:09:44trying to peer back in time at a rare survivor
0:09:44 > 0:09:48our Stone Age ancestors might once have hunted for food and clothing.
0:09:48 > 0:09:54I think that the one we saw and the herd is behind this hill,
0:09:54 > 0:09:58so we have to be very careful, because they're walking against us,
0:09:58 > 0:10:01and they're watching us, and they know we are coming now.
0:10:01 > 0:10:05There are newly born calves, so we need to be extremely cautious.
0:10:07 > 0:10:10Now, we are very close.
0:10:10 > 0:10:13And the three mums are on the other side of the river.
0:10:13 > 0:10:16It's over there.
0:10:16 > 0:10:21And they're waiting for each other on each side.
0:10:21 > 0:10:25Musk ox travel in small herds of about 20.
0:10:25 > 0:10:30But fording a fast flowing river, this group have become separated,
0:10:30 > 0:10:31putting them on edge.
0:10:36 > 0:10:41Now we have to be careful, because we are now a little too close.
0:10:43 > 0:10:45He's really watching us now.
0:10:45 > 0:10:49Apparently indifferent, but they're aware of everything we're doing.
0:10:49 > 0:10:50Oh yes.
0:10:50 > 0:10:56Such defensive behaviour dates back to the ice age,
0:10:56 > 0:10:59when giant bears still hunted them.
0:10:59 > 0:11:03They remain fiercely protective of their young.
0:11:03 > 0:11:06So is that a yearling? How old is the little calf?
0:11:06 > 0:11:08That's a yearling.
0:11:08 > 0:11:11When threatened, herds have sometimes been known
0:11:11 > 0:11:14to form into defensive circles,
0:11:14 > 0:11:16facing out at any potential foe.
0:11:17 > 0:11:20Yes, there we are.
0:11:20 > 0:11:22See how easily it goes in the water.
0:11:22 > 0:11:26Now it's going to be exciting to see what it does with the calf.
0:11:26 > 0:11:29I don't think the calf could make it across there, could it?
0:11:33 > 0:11:36Now it's crossing with a calf.
0:11:39 > 0:11:43They obviously go in for a lot of parental care, these animals.
0:11:43 > 0:11:49Yes, it's actually shading the baby from crossing the river.
0:11:49 > 0:11:52- So it's making an easy crossing for the calf.- Yes.
0:11:52 > 0:11:55So really, they are quite social animals,
0:11:55 > 0:11:59and operate very effectively together as a group.
0:12:02 > 0:12:05Normally always together, some more than one.
0:12:05 > 0:12:08Rarely you find a single one.
0:12:08 > 0:12:11- So now, they will regroup. - That's great.
0:12:15 > 0:12:16So that's a family.
0:12:20 > 0:12:23Being loyal, nurturing parents,
0:12:23 > 0:12:26it's a good evolutionary strategy
0:12:26 > 0:12:29for ensuring the survival of the next generation.
0:12:29 > 0:12:31But musk ox have other tricks
0:12:31 > 0:12:34that help them survive in this bleak tundra.
0:12:35 > 0:12:42See, they are grazing all the time, 24-hours a day.
0:12:44 > 0:12:48They have this digestive system,
0:12:48 > 0:12:53they have two hours eating grass,
0:12:53 > 0:12:56and some flowers they really love,
0:12:56 > 0:12:59and then after two hours,
0:12:59 > 0:13:02they have a quiet period of two hours,
0:13:02 > 0:13:04where they're digesting the food they've had.
0:13:04 > 0:13:06This they do 24-hours, all the time.
0:13:09 > 0:13:12Once winter comes, they will conserve their energy
0:13:12 > 0:13:15by standing almost motionless, for days on end.
0:13:18 > 0:13:22Not only can the musk ox digestive system adjust itself
0:13:22 > 0:13:27to consume extremely tough food stuffs in times of scarcity,
0:13:27 > 0:13:30but their liver and kidneys can slow down,
0:13:30 > 0:13:35and shrink to half normal size to improve fat conservation.
0:13:39 > 0:13:43And there's yet another strategy for surviving the cold.
0:13:43 > 0:13:48If one way of coping with the ice age climate was to grow large,
0:13:48 > 0:13:51then another was to get woolly.
0:13:53 > 0:13:55This is musk ox wool.
0:13:56 > 0:13:59It's very soft to the touch,
0:13:59 > 0:14:04but I can see little globules of rain on it, which aren't absorbed.
0:14:04 > 0:14:06It's extremely water-repellent,
0:14:06 > 0:14:13and against my skin it's extremely warm and comfortable.
0:14:13 > 0:14:16This allows the musk oxen to cope with temperatures
0:14:16 > 0:14:19which can be as low as minus 50 degrees.
0:14:19 > 0:14:21It's incredible stuff.
0:14:21 > 0:14:26In short, if you want to survive a cold snap,
0:14:26 > 0:14:27get hairy.
0:14:29 > 0:14:33Although all attempts to domesticate them have failed,
0:14:33 > 0:14:38musk ox steaks are a popular Norwegian delicacy,
0:14:38 > 0:14:41best enjoyed with a glass of red wine.
0:14:41 > 0:14:47For me, their taste is a taxonomic revelation.
0:14:47 > 0:14:50Well, in taste it's not really like beef at all,
0:14:50 > 0:14:53it's more like mutton.
0:14:53 > 0:14:56Slightly older sheep.
0:14:56 > 0:14:59Well, perhaps that's not a surprise,
0:14:59 > 0:15:02because the musk ox is not really an ox,
0:15:02 > 0:15:06it's more closely related to the sheep and goats.
0:15:06 > 0:15:12It doesn't have the slightly rancid flavour you sometimes get with goat.
0:15:17 > 0:15:23Well, we've heard of a wolf dressed up in sheep's clothing,
0:15:23 > 0:15:28this is more like a sheep dressed up in cow's clothing.
0:15:34 > 0:15:377,000 kilometres west,
0:15:37 > 0:15:40in Yellowstone National Park,
0:15:40 > 0:15:44another giant ice age survivor has evolved a very different method
0:15:44 > 0:15:48of sustaining itself through the harsh winter months.
0:15:52 > 0:15:55Here in the United States, it's frequently called the buffalo,
0:15:55 > 0:15:58but its correct scientific name is the bison.
0:16:05 > 0:16:08Yellowstone's bison live at an average height above sea level
0:16:08 > 0:16:10of 2,400 metres,
0:16:10 > 0:16:12where the temperature only briefly
0:16:12 > 0:16:14warms up into double figures.
0:16:14 > 0:16:20The lowest temperature ever recorded here was a staggering minus 54C.
0:16:23 > 0:16:27To help fuel the bison through this bone-numbing cold,
0:16:27 > 0:16:29it grazes constantly,
0:16:29 > 0:16:32even when the ground is covered in snow and ice.
0:16:32 > 0:16:39But getting to the shrubs and grasses entombed beneath the snow
0:16:39 > 0:16:41can be a formidable challenge.
0:16:41 > 0:16:45One that bison have waged with the elements since the ice age.
0:16:49 > 0:16:52There's something extraordinarily primeval
0:16:52 > 0:16:54about these wonderful animals
0:16:54 > 0:16:57finding something to eat in this land.
0:16:59 > 0:17:01You can see them pushing through snow,
0:17:01 > 0:17:04if they need to find food in the winter.
0:17:05 > 0:17:09They're really adapted to survive under the most harsh
0:17:09 > 0:17:11conditions you can imagine.
0:17:15 > 0:17:17Unlike musk ox,
0:17:17 > 0:17:23bison don't store large reserves of fat for the cruel winter months.
0:17:23 > 0:17:26They feed all year round.
0:17:26 > 0:17:29But to dig in snow, you need traction,
0:17:29 > 0:17:32and to grip in the ice, bison have evolved a feature
0:17:32 > 0:17:36they share with deer, sheep and goats, but not horses.
0:17:37 > 0:17:42Their cloven hooves are split into two toes,
0:17:42 > 0:17:43and help the bison grip,
0:17:43 > 0:17:47when using their hugely muscular upper bodies.
0:17:47 > 0:17:51Snow ploughs, to uncover the grass concealed beneath.
0:17:59 > 0:18:03For a closer peek at how bison are built for such feats of strength,
0:18:03 > 0:18:08I visit vet Don Warner, known locally as just Doc.
0:18:24 > 0:18:25Well, Doc.
0:18:25 > 0:18:29So let's just have a quick look at the front of the head, rather flat.
0:18:29 > 0:18:32- That's right.- Relatively small horns,
0:18:32 > 0:18:35compared with say, a bovid, like a cow.
0:18:35 > 0:18:39That's right. The male bison has a very large bonnet.
0:18:39 > 0:18:43A very thick hide in this area,
0:18:43 > 0:18:47and the horns kind of adorn the edge of that bonnet,
0:18:47 > 0:18:49and they use that for head-butting.
0:18:49 > 0:18:53Fighting is a lot of head pushing, a lot of pushing each other around.
0:18:53 > 0:18:56One pushes one way, then the other pushes him back.
0:18:56 > 0:18:57It's a test of strength.
0:18:57 > 0:18:59It is, and they're pushing hard,
0:18:59 > 0:19:01and then they try to come past the head,
0:19:01 > 0:19:04and hook them in the side or the abdomen.
0:19:04 > 0:19:07But this is a female,
0:19:07 > 0:19:12and the base of the horn is quite a bit smaller.
0:19:12 > 0:19:15If I was to look at this straight off,
0:19:15 > 0:19:19I might think that's a cow - and it's bison.
0:19:19 > 0:19:24So how does this differ from other bovines?
0:19:24 > 0:19:30Well, the most obvious thing are these dorsal spinous processes.
0:19:30 > 0:19:31They're very long.
0:19:31 > 0:19:36A cow skeleton, they'd be about half that length.
0:19:36 > 0:19:39- So this is what gives the sort of hump-like appearance.- Correct.
0:19:39 > 0:19:42Another differentiation is the scapular.
0:19:42 > 0:19:45- That's the shoulder. - The shoulder blade, right.
0:19:45 > 0:19:49That's quite a bit longer in a bison.
0:19:49 > 0:19:53This connection gives the buffalo more leverage to move his skeleton,
0:19:53 > 0:19:57and to move his whole body quickly.
0:19:57 > 0:20:00What we're talking about here
0:20:00 > 0:20:04is a very heftily muscular area.
0:20:04 > 0:20:08Yes. There's muscle on each side, connected to a large ligament,
0:20:08 > 0:20:11that goes up and connects to the back of the skull.
0:20:11 > 0:20:14So I guess there must be a nice piece of meat in there.
0:20:14 > 0:20:17There is. That's the hump. It's very accessible.
0:20:17 > 0:20:20- Peel back the skin.- Peel back the skin and you've got...
0:20:20 > 0:20:22Cut it off, and you have a big steak.
0:20:22 > 0:20:24Take a big slab of the hump.
0:20:24 > 0:20:27If we put all this together, what we have is an animal
0:20:27 > 0:20:32designed for survival through hard winters,
0:20:32 > 0:20:36because all this muscle adds up to allowing the head
0:20:36 > 0:20:41to swish down through the snow and find buried vegetation.
0:20:41 > 0:20:45That's right. It's just a big pendulum
0:20:45 > 0:20:50on a very strong anchoring system up at their back,
0:20:50 > 0:20:53and it allows them to forage in the winter time, through snow.
0:20:53 > 0:20:57So they can get through the really quite long winters
0:20:57 > 0:21:00- you can have up on the prairie land.- Yes.
0:21:17 > 0:21:21When it's cold, there's another advantage to being big.
0:21:21 > 0:21:23Big stomachs.
0:21:24 > 0:21:29The moose is also a giant ice age survivor.
0:21:30 > 0:21:33It doesn't store fat like the musk ox,
0:21:33 > 0:21:38and it lacks the muscular shoulders, as in the bison.
0:21:38 > 0:21:41The moose browses for food on the move.
0:21:43 > 0:21:48What it does have in common with both of them is its stomach.
0:21:48 > 0:21:50The moose is a ruminant,
0:21:50 > 0:21:53a herbivore whose stomach possesses four chambers.
0:21:53 > 0:22:00Ruminants use these extra stomachs to store bacteria
0:22:00 > 0:22:04that help to break down and ferment coarse, otherwise inedible plants.
0:22:05 > 0:22:09Their stomach contents can then be regurgitated,
0:22:09 > 0:22:11chewed again and redigested.
0:22:12 > 0:22:16A process called ruminating,
0:22:16 > 0:22:18or more simply, chewing the cud.
0:22:21 > 0:22:23But it wasn't just herbivores that found ways to adapt
0:22:23 > 0:22:27to a diet of frozen food.
0:22:30 > 0:22:35Scavenging in the ice is the speciality of the wolverine,
0:22:35 > 0:22:38and this Pleistocene survivor
0:22:38 > 0:22:41also possesses an ice-resistant pelt
0:22:41 > 0:22:45that is one of the most highly prized in the animal kingdom.
0:22:47 > 0:22:50I'm with Debbie Harris,
0:22:50 > 0:22:53who looks after one of the few wolverines in captivity
0:22:53 > 0:22:56in the western United States.
0:22:59 > 0:23:01The wolverine.
0:23:01 > 0:23:03Sometimes known as "the glutton".
0:23:03 > 0:23:04Gulo gulo.
0:23:04 > 0:23:08What kind of adaptations does the wolverine have
0:23:08 > 0:23:14that might help it to become such a survivor?
0:23:14 > 0:23:17Well, one of the things is his fur does not absorb moisture.
0:23:17 > 0:23:19He has these very large paws,
0:23:19 > 0:23:21with a lot of fur of them,
0:23:21 > 0:23:23and they're like snow shoes.
0:23:23 > 0:23:25He lives very high in the mountains,
0:23:25 > 0:23:26where there's a lot of snow.
0:23:26 > 0:23:29So he can run very fast on his little snow shoes.
0:23:33 > 0:23:37A fully grown wolverine may weigh around 20 kilograms.
0:23:37 > 0:23:42But it's an ice age giant - of sorts.
0:23:42 > 0:23:45The wolverine is the largest mustelid in North America,
0:23:45 > 0:23:49and that family includes the skunk, the otter,
0:23:49 > 0:23:52as well as the North American mink.
0:23:52 > 0:23:54Wolverines are weasels.
0:23:54 > 0:23:56The giants of the weasel family.
0:23:59 > 0:24:02Now, the wolverine has something of a reputation
0:24:02 > 0:24:04as a bit of a fierce creature.
0:24:04 > 0:24:06Is that reputation justified?
0:24:06 > 0:24:10That little wolverine at 30, 35 pounds, he can go out there,
0:24:10 > 0:24:13and he can spook a grizzly bear as well as pack of wolves
0:24:13 > 0:24:15if he's really willing to get out there
0:24:15 > 0:24:18and he's hungry enough to get that food that they've got.
0:24:18 > 0:24:20Believe me, he could do it.
0:24:22 > 0:24:26Ferocity is a useful survival strategy,
0:24:26 > 0:24:29even if this little chap seems unreasonably playful.
0:24:30 > 0:24:34But it helps to have the hardware to back threats up.
0:24:36 > 0:24:38In the case of the wolverine,
0:24:38 > 0:24:42it's the teeth that are its special secret.
0:24:42 > 0:24:45Of use not just against competitors and prey,
0:24:45 > 0:24:48but to help it feed in the freezing cold.
0:24:50 > 0:24:53Its rear molars are angled backwards,
0:24:53 > 0:24:58so that the jaws can rip and tear deep frozen meat,
0:24:58 > 0:25:01making it a perfect ice age scavenger.
0:25:04 > 0:25:06He also has a very powerful jaw,
0:25:06 > 0:25:08capable of snapping bones,
0:25:08 > 0:25:10so that he can eat the marrow from the bones.
0:25:10 > 0:25:14So they are animals adapted to cold conditions.
0:25:14 > 0:25:16Absolutely. They need that cold weather.
0:25:20 > 0:25:25Wolverines, bison, musk ox and moose.
0:25:25 > 0:25:31All ice age survivors that still live in the cold higher latitudes.
0:25:33 > 0:25:37But not all the Pleistocene mega-fauna
0:25:37 > 0:25:38lived in the northern hemisphere.
0:25:38 > 0:25:41Nor did they all live in ice.
0:25:43 > 0:25:48My next survivors live more than 16,000 kilometres away,
0:25:48 > 0:25:51on the other side of the world.
0:25:52 > 0:25:55Back during the Pleistocene Age,
0:25:55 > 0:25:57while the north was covered in glaciers,
0:25:57 > 0:26:01conditions were very different, but no less harsh,
0:26:01 > 0:26:03in the southern hemisphere.
0:26:07 > 0:26:08To find out more,
0:26:08 > 0:26:13I join genetic scientist and caving enthusiast Alan Cooper
0:26:13 > 0:26:16in the Naracoorte Caves of South Australia.
0:26:17 > 0:26:21Originally formed 200 million years ago
0:26:21 > 0:26:22from coral and marine fossils,
0:26:22 > 0:26:25the limestone has eroded,
0:26:25 > 0:26:27creating underground caves
0:26:27 > 0:26:31and holes on the surface that have entombed unwary animals.
0:26:31 > 0:26:36They're a World Heritage Site, a popular venue for caving adventures,
0:26:36 > 0:26:41and a mine of valuable environmental and ecological data.
0:26:41 > 0:26:44Despite my claustrophobia,
0:26:44 > 0:26:48Alan is eager to show me a palaeontological site
0:26:48 > 0:26:51that contains evidence for what happened here
0:26:51 > 0:26:54while the northern hemisphere was covered in ice.
0:26:56 > 0:26:59So here we are in a bone pit.
0:26:59 > 0:27:01Layer after layer,
0:27:01 > 0:27:04fossils have been preserved in the floor of the cave,
0:27:04 > 0:27:09giving us a narrative of history of hundreds of thousands of years.
0:27:09 > 0:27:11Layers of death.
0:27:11 > 0:27:13You're basically looking back through time,
0:27:13 > 0:27:21potentially 40-50,000 years of ecological dandruff, I suppose.
0:27:21 > 0:27:23How did they get there?
0:27:23 > 0:27:25Well, there was a hole in the surface
0:27:25 > 0:27:27through which animals tumbled.
0:27:27 > 0:27:31In other cases, predators brought bones in here to devour.
0:27:31 > 0:27:34But what kind of animals are there?
0:27:34 > 0:27:39You have a huge diversity of Australian mega-fauna here.
0:27:39 > 0:27:43We have Tasmanian devils,
0:27:43 > 0:27:46which are still around today.
0:27:46 > 0:27:50Tasmanian tigers, which of course aren't.
0:27:50 > 0:27:52Short-faced kangaroos. We can see a skull there,
0:27:52 > 0:27:55with the eye socket.
0:27:55 > 0:27:59We're used to thinking, in a selfish way, us Europeans,
0:27:59 > 0:28:02of the ice age as if it's our ice age.
0:28:02 > 0:28:06But the fact is the world is one great connected system.
0:28:06 > 0:28:10The problem with Australia is we don't have the same sort of quality
0:28:10 > 0:28:13of fossil record that we do in the northern hemisphere,
0:28:13 > 0:28:17so trying to work out exactly what's happened is much more difficult.
0:28:17 > 0:28:23We do know it's a very cold, dry period during the glacial maximum,
0:28:23 > 0:28:27with sand dunes rolling across the interior of Australia,
0:28:27 > 0:28:30and life during that stage would be almost impossible.
0:28:35 > 0:28:38Life on the plains was especially harsh.
0:28:38 > 0:28:41So it's perhaps ironic my next survivor began life,
0:28:41 > 0:28:44just as we probably did,
0:28:44 > 0:28:45in the trees.
0:28:52 > 0:28:57Some of the oldest kangaroo species are also the smallest,
0:28:57 > 0:29:00and still live in forests.
0:29:00 > 0:29:04One of the secrets of their success was reproduction.
0:29:04 > 0:29:08Something kangaroo foster mum Tania Melville knows all about.
0:29:09 > 0:29:11This is a very charming one.
0:29:11 > 0:29:13What's the species here?
0:29:13 > 0:29:14This one is a swamp wallaby.
0:29:14 > 0:29:17So one of the important things about these in general,
0:29:17 > 0:29:22is people tend to think of them as primitive, but actually they're not.
0:29:22 > 0:29:24They're beautifully advanced,
0:29:24 > 0:29:26- beautifully adapted.- Definitely.
0:29:26 > 0:29:30Kangaroos reproduce like a well-timed production line.
0:29:30 > 0:29:33Females can control their fertility,
0:29:33 > 0:29:36so while one joey is in the pouch,
0:29:36 > 0:29:39another fertilised egg can be waiting to develop.
0:29:39 > 0:29:42They can hold an embryo en reserve, as it were.
0:29:42 > 0:29:45And when conditions improve
0:29:45 > 0:29:50it can complete the rest of the development process.
0:29:50 > 0:29:52That's it. What that means is when conditions fall bad,
0:29:52 > 0:29:56so the water dries up or not much food around,
0:29:56 > 0:29:59she can drop off the joey on foot,
0:29:59 > 0:30:02she can drop off the joey in the pouch,
0:30:02 > 0:30:03but she'll have that embryo waiting.
0:30:03 > 0:30:05So as soon as the conditions fall good again,
0:30:05 > 0:30:07it's bang, give birth straight away,
0:30:07 > 0:30:10and start the whole breeding process off again.
0:30:10 > 0:30:14And, of course, they always try and scramble back in, don't they?
0:30:14 > 0:30:18Yeah, the mother will usually call if there's any sign of danger
0:30:18 > 0:30:20and as soon as the joey hears that call,
0:30:20 > 0:30:23it's a mad scramble back in the pouch again.
0:30:23 > 0:30:25She's actually got a drawstring-like muscle
0:30:25 > 0:30:29so she can close it or she can open it, depending on what she feels like.
0:30:29 > 0:30:33- It's like slamming the door, really. - Definitely. Yup, "you stay in."
0:30:33 > 0:30:36- "Don't. You just stay in here." - Yup, for sure.
0:30:46 > 0:30:49Many of Australia's marsupials
0:30:49 > 0:30:52had also become giants during the good times.
0:30:55 > 0:31:00As climate became more arid, they needed to toughen up to survive.
0:31:02 > 0:31:05Well, we know kangaroos' system of reproduction
0:31:05 > 0:31:09is extremely efficient, but what else helped them to survive,
0:31:09 > 0:31:12do you think, when climate changed in this drastic way?
0:31:12 > 0:31:15One of the big advantages of the marsupials
0:31:15 > 0:31:17is their metabolic rate is very slow.
0:31:17 > 0:31:21They can survive on much less food and much harsher conditions
0:31:21 > 0:31:23than, for example, the placental mammals.
0:31:23 > 0:31:26And, quite often, people tend to think of the marsupials
0:31:26 > 0:31:28as being more primitive
0:31:28 > 0:31:31and that's why they could only survive in Australia
0:31:31 > 0:31:32because there was no competition.
0:31:32 > 0:31:36And, perhaps, in many ways this very harsh, arid environment
0:31:36 > 0:31:39meant that something like the kangaroos,
0:31:39 > 0:31:42with their unique skills, were ideally suited.
0:31:42 > 0:31:44Whereas placental mammals might have actually had
0:31:44 > 0:31:47a much harder time surviving here.
0:31:51 > 0:31:53Like its cold-adapted mammalian counterparts,
0:31:53 > 0:31:56kangaroos also chew the cud.
0:31:56 > 0:32:01But while the bison and the musk ox build muscles or store fat,
0:32:01 > 0:32:06the kangaroo can extract water from the meanest shrub.
0:32:06 > 0:32:09So long as they could find even the driest plants,
0:32:09 > 0:32:12they could go for months on end without a drop.
0:32:16 > 0:32:18Interred in the Naracoorte Caves
0:32:18 > 0:32:21are fossils of some of the giant marsupials
0:32:21 > 0:32:24that were contemporaries of the ice age mammals
0:32:24 > 0:32:26in the northern hemisphere.
0:32:27 > 0:32:31Hippopotamus-sized herbivores like zygomaturus.
0:32:31 > 0:32:36The wolf-like thylacine, sometimes called the Tasmanian tiger.
0:32:36 > 0:32:39And the meter-and-a-half-long thylacoleo,
0:32:39 > 0:32:42largest of all known marsupial predators,
0:32:42 > 0:32:46superficially resembling a cross between a lion and a bear.
0:32:48 > 0:32:53And what about thylacoleo, the so-called marsupial lion?
0:32:53 > 0:32:56Yeah, a remarkable beast, we've got one here.
0:32:56 > 0:32:59Here's the skull.
0:32:59 > 0:33:01And as you can tell very quickly by looking at the teeth,
0:33:01 > 0:33:05this is no placental mammal.
0:33:05 > 0:33:08The two incisors at the front, quite unique
0:33:08 > 0:33:12and this modified slicing molar down the side, here.
0:33:12 > 0:33:16And look at the strength, the thickness in the skull.
0:33:16 > 0:33:18Looking at the feet,
0:33:18 > 0:33:22some new research is showing that it appears to be climbing,
0:33:22 > 0:33:25spending a lot of time, or, certainly, capable of climbing trees.
0:33:25 > 0:33:26You can imagine this, you know,
0:33:26 > 0:33:29100 kilos coming down with those teeth on top of you.
0:33:29 > 0:33:32Except that it would be hunting, presumably,
0:33:32 > 0:33:33possums and things like that.
0:33:33 > 0:33:36We're talking possums, small wallabies,
0:33:36 > 0:33:37the, sort of, medium-size animal.
0:33:37 > 0:33:42- So, they drag them into the cave for leisurely...?- Presumably, yes.
0:33:42 > 0:33:45We really, even despite this, the evolutionary adaptations,
0:33:45 > 0:33:47which are so remarkable,
0:33:47 > 0:33:51it's still quite difficult to work out what this thing is doing.
0:33:51 > 0:33:56But these exotic, marsupial giants lacked the survival trait
0:33:56 > 0:33:58that would make the kangaroo king of the continent.
0:33:59 > 0:34:04It was by hopping out of the forests, 15 million years ago,
0:34:04 > 0:34:08that kangaroos came to dominate dry age Australia.
0:34:08 > 0:34:10Hopping is one of the most effective means of locomotion
0:34:10 > 0:34:12in the animal kingdom.
0:34:12 > 0:34:15And the largest kangaroo species alive today
0:34:15 > 0:34:19can reach speeds in excess of 65 kilometres per hour.
0:34:27 > 0:34:31Such speed is useful for escaping from predators
0:34:31 > 0:34:33but recent studies suggest
0:34:33 > 0:34:38the real survival bonus hopping gives kangaroos is range.
0:34:40 > 0:34:43This supremely efficient mode of locomotion
0:34:43 > 0:34:46allows mobs of kangaroos to cover vast ranges
0:34:46 > 0:34:48in pursuit of scarce, grazing food,
0:34:48 > 0:34:52perhaps the best way to cope with conditions of drought.
0:35:00 > 0:35:05Plants too began to suffer from the tough, dry conditions.
0:35:07 > 0:35:10Yet, the extreme aridity provided the perfect opportunity
0:35:10 > 0:35:15for another of Australia's most iconic dry-adapted species
0:35:15 > 0:35:18to spread across vast stretches of the continent.
0:35:23 > 0:35:25Eucalyptus trees.
0:35:27 > 0:35:30Their secret survival weapon is a tolerance
0:35:30 > 0:35:34to one of the bush's most regular and feared natural phenomena.
0:35:39 > 0:35:41Fire.
0:35:42 > 0:35:46Eucalyptus trees have adapted to cope with periodic fires.
0:35:48 > 0:35:51Some species like these stringybark Eucalyptus
0:35:51 > 0:35:53even have highly flammable, loose bark
0:35:53 > 0:35:57that will erupt in flames with the smallest spark.
0:35:59 > 0:36:04The reason for this adaptation is as simple as it is efficient.
0:36:08 > 0:36:12Any plants that cannot cope with fire are incinerated.
0:36:12 > 0:36:14After the fire has passed,
0:36:14 > 0:36:19Eucalyptus trees put out new shoots and re-grow once more.
0:36:20 > 0:36:23The competition goes up in smoke.
0:36:29 > 0:36:33An even more special example of a fire-adapted plant
0:36:33 > 0:36:34is this wonderful bush.
0:36:41 > 0:36:45Named after an illustrious former president of the Royal Society,
0:36:45 > 0:36:49Banksia is the phoenix of the plant world.
0:36:49 > 0:36:54In fact, it can't live without fire because its seed pods burst
0:36:54 > 0:36:58when fire passes through, releasing the seeds to germinate
0:36:58 > 0:37:00in the newly enriched ground.
0:37:16 > 0:37:20The last extreme period of aridity started drawing to an end
0:37:20 > 0:37:23around 30,000 years ago.
0:37:23 > 0:37:27By then, Australia's landscape had been completely transformed
0:37:27 > 0:37:29and many of the continent's large animals
0:37:29 > 0:37:32and plant species were beginning to disappear.
0:37:36 > 0:37:40Great transformations were also beginning elsewhere.
0:37:41 > 0:37:44Around 20,000 years ago, the great ice sheets
0:37:44 > 0:37:47that had covered much of the northern hemisphere
0:37:47 > 0:37:50for more than two million years began to melt.
0:37:53 > 0:37:57The end of the ice age would bring mass extinction.
0:37:59 > 0:38:03So, what happened when the ice sheet finally retreated?
0:38:03 > 0:38:05The change in conditions
0:38:05 > 0:38:09made many of those specially-adapted species go extinct.
0:38:09 > 0:38:14It was not the cold that killed them, it was the thaw.
0:38:21 > 0:38:23Some of the animals that did not survive
0:38:23 > 0:38:25can be found for sale in a fashionable street
0:38:25 > 0:38:27in Soho, New York City.
0:38:29 > 0:38:32They're carnivores that disappeared at the end of the Pleistocene Age.
0:38:32 > 0:38:36They were found preserved in tar pits in California.
0:38:37 > 0:38:43Extinct mega-fauna. These are the animals that didn't quite make it.
0:38:43 > 0:38:46Hunters all, these fell into the tar
0:38:46 > 0:38:49while in pursuit of the prey which are also there.
0:38:49 > 0:38:53The sabre-tooth tiger, well, I used to call it that, it's no tiger.
0:38:53 > 0:38:56But it does have these huge incisors,
0:38:56 > 0:38:59these great fangs for killing its prey.
0:38:59 > 0:39:01A lot of debate about how they worked.
0:39:02 > 0:39:03The dire wolf.
0:39:03 > 0:39:09The dire wolf, of course, hunted in packs, just like the living wolf,
0:39:09 > 0:39:12but they were larger. Now, extinct.
0:39:12 > 0:39:13The American lion.
0:39:13 > 0:39:16It may come as a surprise to find lions in America
0:39:16 > 0:39:18but there they were.
0:39:18 > 0:39:23Characteristic teeth, of course, on both jaws, here.
0:39:23 > 0:39:25They didn't survive.
0:39:25 > 0:39:28These were all victims of a changing world.
0:39:36 > 0:39:41Just how dramatically the landscape changed can be seen in Yellowstone.
0:39:43 > 0:39:44This would once have been tundra
0:39:44 > 0:39:47like the frozen north of Norway today.
0:39:47 > 0:39:51But as the ice began to retreat, so many species,
0:39:51 > 0:39:54long-exiled further south, seized the opportunity
0:39:54 > 0:39:57to expand their dominion northwards.
0:39:57 > 0:40:02Yellowstone's tundra was conquered by an empire of conifers
0:40:02 > 0:40:05that took root across the northern hemisphere
0:40:05 > 0:40:07as the ice sheets receded.
0:40:10 > 0:40:13As the ice sheets waxed and waned,
0:40:15 > 0:40:21these cold-loving conifers could adapt their ranges in harmony.
0:40:21 > 0:40:24Warm times, they spread.
0:40:24 > 0:40:26Cold times, they contracted.
0:40:28 > 0:40:30Tough, enduring trees.
0:40:31 > 0:40:34And they're still with us today, of course,
0:40:34 > 0:40:37cladding every high mountainside.
0:40:42 > 0:40:43Modern conifer trees are descended
0:40:43 > 0:40:47from some of the oldest types of tree in the world.
0:40:47 > 0:40:50And conifers date back more than 100 million years.
0:40:53 > 0:40:56To colonise new territory,
0:40:56 > 0:41:00the conifer uses cones to house its seeds.
0:41:00 > 0:41:03But, in spite of their woody appearance,
0:41:03 > 0:41:06the cones are not impenetrable.
0:41:11 > 0:41:15So, here's one of the cones that gives these trees their name.
0:41:15 > 0:41:19These have seeds tucked within them that form a food source
0:41:19 > 0:41:23for animals today as they have done for millions of years.
0:41:29 > 0:41:33But the spread of conifer trees led to the decline of habitat
0:41:33 > 0:41:36for some tundra-dwelling animals.
0:41:56 > 0:41:59A woolly mammoth in the Ipswich Museum.
0:41:59 > 0:42:03A wonderful, gigantic relative of the elephant
0:42:03 > 0:42:08but with differently-shaped tasks curved into this elegant spiral.
0:42:08 > 0:42:13And these mammoths once roamed in their millions
0:42:13 > 0:42:16all the way from East Anglia, here, to Siberia.
0:42:16 > 0:42:22They fed on a special kind of tundra vegetation, rich sedges.
0:42:26 > 0:42:28But they became extinct.
0:42:28 > 0:42:30A few diminutive mammoths lingered on
0:42:30 > 0:42:35in Wrangel Island in Arctic Siberia until almost historical times.
0:42:35 > 0:42:38The rest of the population became extinct
0:42:38 > 0:42:41as their special habitat declined.
0:42:41 > 0:42:45Their numbers went from millions to a few and then they died out.
0:42:54 > 0:42:58Small numbers of musk ox survived by retreating with the tundra
0:42:58 > 0:43:02towards the inhospitable edge of the Arctic Circle.
0:43:05 > 0:43:07Whilst, in North America,
0:43:07 > 0:43:12climate change was driving other animals towards extinction.
0:43:12 > 0:43:15With the thaw, tundra gave way, eventually, to prairie.
0:43:18 > 0:43:22Grasses quickly came to dominate the open landscape.
0:43:24 > 0:43:26Grasses are also a relative newcomer to the plant world,
0:43:26 > 0:43:30evolving around 23 million years ago, long after flowers.
0:43:35 > 0:43:38Grasses are special plants,
0:43:38 > 0:43:41continually regenerating their leaves from the base,
0:43:41 > 0:43:45so giving a continuous feed to grazing animals like the bison.
0:43:47 > 0:43:50The bison survived, but only just.
0:43:52 > 0:43:54They were saved by chewing the cud.
0:43:54 > 0:43:58Their ruminant stomachs gave them the ability to extract nutrition
0:43:58 > 0:44:03from grasses while mammoths, who were not ruminants, could not.
0:44:08 > 0:44:11Today in Yellowstone, the local bison have even adapted
0:44:11 > 0:44:14to eating the poisonous, sulphur-rich grass
0:44:14 > 0:44:16found around geysers.
0:44:16 > 0:44:20They can't endure it for long but when conditions are really icy,
0:44:20 > 0:44:23it temporarily keeps them from starvation.
0:44:31 > 0:44:34A more temperate world also signalled
0:44:34 > 0:44:39the return of flowers that had been pushed far to the south.
0:44:41 > 0:44:45Warmth encouraged species that needed long summers
0:44:45 > 0:44:47and suited their pollinators.
0:44:50 > 0:44:55These sunflowers almost seem to appreciate the light of the sun,
0:44:55 > 0:44:59following the course of it as it tracks across the sky.
0:45:12 > 0:45:17Flowers need their own, particular pollinators to help them set seed.
0:45:25 > 0:45:29Nowhere could escape the effects of the Pleistocene cold periods.
0:45:29 > 0:45:34Even in the tropics, rainforests contracted.
0:45:34 > 0:45:36That wasn't a problem for these butterflies,
0:45:36 > 0:45:40which could wing their way into refuges to see out the hard times.
0:45:42 > 0:45:45But, when the ice sheets began to contract,
0:45:45 > 0:45:49the rainforests began to expand to their present proportions.
0:45:53 > 0:45:56The very first ancestors of the butterflies
0:45:56 > 0:45:59were very inconspicuous at the time of the dinosaurs.
0:46:01 > 0:46:05Subsequent collaborative evolution between pollinators
0:46:05 > 0:46:08and flowering plants stimulated
0:46:08 > 0:46:13an unparalleled burst of invention in both insects and flowers.
0:46:15 > 0:46:19As a result, today, both pollinating insects and flowering plants
0:46:19 > 0:46:23are among the most varied and widespread of all species.
0:46:25 > 0:46:31Other animals were also released to a new freedom by changing climates.
0:46:33 > 0:46:36One young mammal had been confined to eastern Africa
0:46:36 > 0:46:38for most of its existence.
0:46:38 > 0:46:42But as temperatures warmed, it swiftly spread outwards.
0:46:44 > 0:46:48And this species is, perhaps, the ultimate Pleistocene survivor.
0:46:50 > 0:46:5513,000 years ago, another species moved into North America.
0:46:57 > 0:46:58Man.
0:46:58 > 0:47:01The same species arrived in Australia
0:47:01 > 0:47:03more than 40,000 years ago.
0:47:03 > 0:47:05And, in both cases, the mega-fauna,
0:47:05 > 0:47:09the large animals, seem to become extinct in a short time.
0:47:11 > 0:47:14Surely these events must be connected.
0:47:14 > 0:47:17Could it be that this new top predator,
0:47:17 > 0:47:22armed with a brilliant mind and a capacity to make tools
0:47:22 > 0:47:24is implicated in the demise
0:47:24 > 0:47:28of some of the most glamorous, large animals that have existed on Earth?
0:47:31 > 0:47:35The idea that as man arrived on new continents
0:47:35 > 0:47:37he hunted its large animals to extinction
0:47:37 > 0:47:41is called the overkill or sometimes blitzkrieg hypothesis.
0:47:43 > 0:47:48As the name suggests, it proposes that man advanced around the world
0:47:48 > 0:47:53like a division of Panzer tanks, annihilating everything in his path.
0:47:55 > 0:47:57After swiftly spreading to Europe and Asia,
0:47:57 > 0:48:02this new hunter reached Australia around 40,000 years ago,
0:48:02 > 0:48:05armed with fire.
0:48:07 > 0:48:09A weapon that would bring about the downfall
0:48:09 > 0:48:11of the last surviving giant marsupials.
0:48:15 > 0:48:18We know that these new interlopers had fire, don't we?
0:48:18 > 0:48:21Absolutely, you can see that in the archaeological record.
0:48:21 > 0:48:28And modern Aborigines used fire as a very effective hunting tool
0:48:28 > 0:48:29and, of course,
0:48:29 > 0:48:33that habitat alteration is going to have a huge impact on mega-fauna.
0:48:33 > 0:48:37So, I suppose there will be the perennial question of,
0:48:37 > 0:48:40was it all down to us humans?
0:48:40 > 0:48:45Or did us humans merely administer the final coup de grace?
0:48:45 > 0:48:49Certainly, in my opinion, from the genetic data that we've got,
0:48:49 > 0:48:51climate change is playing a major role
0:48:51 > 0:48:55and humans are, as you say, applying the final blow.
0:48:55 > 0:48:56And I think, in many cases,
0:48:56 > 0:49:00these species wouldn't have gone extinct, or might not have done,
0:49:00 > 0:49:03if humans hadn't been there to disrupt the environment
0:49:03 > 0:49:06and prevent populations from dispersing
0:49:06 > 0:49:08and reinforcing one another.
0:49:08 > 0:49:11I think it's the combined double blow that is the extinction.
0:49:14 > 0:49:16The only large marsupial that survived
0:49:16 > 0:49:18the duel ravages of climate change
0:49:18 > 0:49:22and the arrival of a new apex predator was the kangaroo.
0:49:25 > 0:49:28Its hopping, water efficient
0:49:28 > 0:49:32and ingenious reproductive ability gave it the tools to thrive.
0:49:35 > 0:49:38Today, there are almost three times as many kangaroos in Australia
0:49:38 > 0:49:40as there are people.
0:49:40 > 0:49:43By some estimates, nearly 60 million of them.
0:49:48 > 0:49:51The musk ox survived the appearance of man,
0:49:51 > 0:49:52but not here in Norway.
0:49:54 > 0:49:57In fact, these animals came from Greenland
0:49:57 > 0:49:59after the Second World War,
0:49:59 > 0:50:04reintroduced after the native population was hunted to extinction.
0:50:10 > 0:50:12Back in North America,
0:50:12 > 0:50:14the bison had evolved to dominate the Great Plains.
0:50:14 > 0:50:18And, for more than 10,000 years, successfully coexisted with man.
0:50:20 > 0:50:26Then, 200 years ago, a new arrival threatened to finally exterminate
0:50:26 > 0:50:29these great, ice age survivors.
0:50:29 > 0:50:34If I'd been sitting here 200 years ago, I would have seen behind me,
0:50:34 > 0:50:38not a few dozen, but tens of thousands, even millions of bison.
0:50:40 > 0:50:44It was the arrival of this object, the rifle,
0:50:44 > 0:50:48that changed its fortunes and almost drove it to extinction.
0:50:48 > 0:50:50Particularly after the American Civil War,
0:50:50 > 0:50:53when these rifles came into commission.
0:50:53 > 0:50:56It is a survivor but only by the skin of its teeth.
0:51:06 > 0:51:09Today, under the broad skies of Montana,
0:51:09 > 0:51:12250 kilometres north of Yellowstone National Park,
0:51:12 > 0:51:15ranchers like Tana Blackmore
0:51:15 > 0:51:20dedicate their lives to conserving the remaining herds of bison.
0:51:20 > 0:51:21Part Native American,
0:51:21 > 0:51:25she keeps more than 200 bison on her land in the Crow Reservation.
0:51:27 > 0:51:30And with Tana at my side, I can get far closer
0:51:30 > 0:51:32to these magnificent survivors
0:51:32 > 0:51:36than I would ever dare in Yellowstone.
0:51:36 > 0:51:41As a native woman, and doing the work that I was doing with the land
0:51:41 > 0:51:47and so forth, they literally, different people, literally,
0:51:47 > 0:51:50bought these baby buffalo and gifted them to me.
0:51:50 > 0:51:54And it's like, you should ask before you start giving people buffalo.
0:51:54 > 0:51:56It's, it's kind of a responsibility, isn't it?
0:51:56 > 0:51:59It's a huge responsibility.
0:51:59 > 0:52:02You know, I wouldn't want to trust myself out there, somehow.
0:52:02 > 0:52:04They just look too massive and powerful.
0:52:06 > 0:52:09See the big bull? Look at the massive head on him.
0:52:14 > 0:52:16- There he is.- That is some animal.
0:52:18 > 0:52:22I mean, that bull really does look like he's in charge.
0:52:22 > 0:52:26Do you want some of that? You want some that?
0:52:26 > 0:52:28They look like they're being independent, here,
0:52:28 > 0:52:32but buffalo will stick together.
0:52:32 > 0:52:34They're never far from each other unless, you know,
0:52:34 > 0:52:38their particular band's... And once they hit about 100 head,
0:52:38 > 0:52:41they start to break into a new band.
0:52:43 > 0:52:47They have another survival trait that would have helped protect them
0:52:47 > 0:52:49from Pleistocene predators.
0:52:49 > 0:52:53Though, sadly, not hunters armed with long-range rifles.
0:52:53 > 0:52:55They've got incredible circular vision.
0:52:55 > 0:52:57Eyes in the sides of their heads.
0:52:57 > 0:53:00All they need to do is slightly turn their head
0:53:00 > 0:53:03and they can see what's going on back here, like rear-view mirrors.
0:53:04 > 0:53:09Yeah. Yeah. You want some of that? You want some of that?
0:53:09 > 0:53:13Today's bison are all descendants of a handful
0:53:13 > 0:53:16that survived the human cull of the 1800s.
0:53:16 > 0:53:18Hello, babies.
0:53:19 > 0:53:22They were brought back from the brink
0:53:22 > 0:53:24by breeding the remaining wild animals
0:53:24 > 0:53:26with some kept in the Bronx Zoo.
0:53:29 > 0:53:31After we finish our safari,
0:53:31 > 0:53:36I join Tana for what she insists is a truly free-range bison burger.
0:53:36 > 0:53:38So, it's my chance for a taste
0:53:38 > 0:53:41without having to pay the buffalo bill.
0:53:42 > 0:53:43Mmm.
0:53:44 > 0:53:49- Mmm. Excellent.- I'm glad you enjoy it. It has a very different flavour.
0:53:49 > 0:53:53It's a wholesome flavour, very robust and full, I believe.
0:53:53 > 0:53:57Of course, its history, the history of this animal, is not a happy one.
0:53:57 > 0:53:59I mean, it was a mass exploitation.
0:54:02 > 0:54:05Well, there's also another unhappy side to that too.
0:54:05 > 0:54:09And that has to do with the Indian Wars.
0:54:09 > 0:54:12The primary reason that the masses of buffalo were eliminated
0:54:12 > 0:54:16was to eliminate the food source for the native
0:54:16 > 0:54:19because it was the life force for the native people.
0:54:19 > 0:54:22And if they eliminated the food source,
0:54:22 > 0:54:27then they would also eliminate the threat from the Native American.
0:54:27 > 0:54:30Yes, I mean, it was a political, partly a political motivation,
0:54:30 > 0:54:32- no doubt.- Yes. Hmm.
0:54:32 > 0:54:36The flavour's, well, it's like beef, in a way,
0:54:36 > 0:54:39But, I would say, overall, sweeter.
0:54:42 > 0:54:44The burgers are certainly delicious.
0:54:44 > 0:54:49I wonder if a mammoth burger would have been half as nice.
0:54:49 > 0:54:52Hunting simply for food can't explain
0:54:52 > 0:54:56why so many of the other ice age giants died out.
0:54:56 > 0:55:00It was climate change and the disappearance of their habitat
0:55:00 > 0:55:01that caused their extinction.
0:55:07 > 0:55:09The link between habitat and survival
0:55:09 > 0:55:12has been one of the enduring themes of our series.
0:55:13 > 0:55:17Every survivor we have seen is just one small part
0:55:17 > 0:55:21of a vast and interconnected tree of life.
0:55:21 > 0:55:24Just one of the millions upon millions of species
0:55:24 > 0:55:28that have ever lived on our planet.
0:55:28 > 0:55:30But have we, in our small selection,
0:55:30 > 0:55:33discovered the secret to being a survivor?
0:55:37 > 0:55:40Luck alone may have helped propel some species
0:55:40 > 0:55:43over life's great hurdles.
0:55:45 > 0:55:47Like mammals inheriting the Earth
0:55:47 > 0:55:50when an asteroid killed off the dinosaurs.
0:55:50 > 0:55:53But there is more to long-term survival
0:55:53 > 0:55:56than just one lucky throw of the dice.
0:55:57 > 0:55:59Like adaptation.
0:56:00 > 0:56:04We've seen how exquisitely adapted to their way of life,
0:56:04 > 0:56:06everything from a musk ox
0:56:06 > 0:56:08to a duck-billed platypus can be.
0:56:08 > 0:56:12But plenty of animals that went extinct,
0:56:12 > 0:56:16from dinosaurs to trilobites,
0:56:16 > 0:56:19were probably just as finely adapted and that didn't save them.
0:56:23 > 0:56:26Some survivors, like the echidna or the turtle,
0:56:26 > 0:56:27seem to live a long time
0:56:27 > 0:56:32or invest a lot of effort in producing offspring.
0:56:32 > 0:56:37Stacking the odds in the survival of their own progeny.
0:56:37 > 0:56:42- Could I see where the head is right at the moment?- Right beside you.
0:56:42 > 0:56:46Others, like snakes and emus, can go without food for long periods.
0:56:48 > 0:56:52Or even go into suspended animation. Like nuts and seeds.
0:56:55 > 0:56:58But all living things have one need in common.
0:56:58 > 0:57:00Habitat.
0:57:02 > 0:57:05From the ancient time havens of the intertidal zone in Delaware
0:57:05 > 0:57:08and Hong Kong,
0:57:08 > 0:57:10the green refuge of Daintree,
0:57:12 > 0:57:14and the ice-covered mountains of the wolverine,
0:57:15 > 0:57:19persistence of habitat is the fundamental basis
0:57:19 > 0:57:21of persistence of a species.
0:57:27 > 0:57:32Today, Homo sapiens is master of all he surveys.
0:57:33 > 0:57:35We have transformed the natural world
0:57:35 > 0:57:38and are changing ancient and enduring habitats
0:57:38 > 0:57:41like never before,
0:57:41 > 0:57:44triggering a new era of man-made mass extinction.
0:57:46 > 0:57:48But by threatening habitats around the world
0:57:48 > 0:57:51we, ultimately, threaten the survival of our own kind.
0:57:53 > 0:57:56A big city is so full of energy, so full of excitement,
0:57:56 > 0:57:58so full of consumption.
0:57:58 > 0:58:03It seems that we humans have come a very long way
0:58:03 > 0:58:05in a very short time.
0:58:06 > 0:58:08And it might be the best place to ask
0:58:08 > 0:58:13whether mankind will burn himself out in an extravagant splash
0:58:13 > 0:58:18or is he, possibly, going to be one of the survivors?
0:58:20 > 0:58:23MUSIC: "Stayin' Alive" by Bee Gees
0:58:44 > 0:58:48Subtitles by Red Bee Media Ltd
0:58:48 > 0:58:52E-mail subtitling@bbc.co.uk