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动物文字稿
00:05Since the emergence of life more than 3 billion years ago, life on our planet has suffered
00:11a series of devastating mass extinction events. These have killed off uncountable species
00:20and almost threatened to end life on Earth.
00:27I'm Professor Richard Forty of London's Natural History Museum. I've spent all my working
00:33life studying the remains of animals, long extinct. But now I'm setting off to discover
00:41why some animals and plants have survived. I'm going in search of living fossils, old
00:51timers, his little face, that somehow managed to survive when so many others perished.
01:01In the process I hope to find an answer to a profound question. Is being a survivor a question
01:11of having some very special features. Or nothing more than pure chance.
01:19From living fossils that are our most ancient relations, to gigantic relics from the age of the dinosaurs.
01:30Life, as we see it today, is not just the product of evolution, it's also the consequence of mass extinction.
01:39We are all the sons and daughters of catastrophe.
01:43Life, as we see it. Oh, my goodness.
01:46Life, as we see it.
02:012.8 million years ago, triggered by changes in the Earth's orbit around the Sun and shifts in its ocean
02:08currents,
02:09our world began to cool.
02:19Within a few thousand years, much of our planet was shrouded in a dense cloak of ice
02:25that would come and go until only 10,000 years ago.
02:29We call this age of ice the Pleistocene, and it transformed the hierarchy of nature.
02:42When ice sheets grow, animals and plants have a stark choice.
02:47They can adapt to the cold, they can move to stay with their own comfort zone, or they can die.
02:55And die, many of them did.
03:01Even in the Arctic today, temperatures still regularly sink below minus 50 centigrade,
03:08and wind speeds have been known to reach 180 kilometres an hour.
03:14You might think nothing could live in such harsh conditions.
03:18But you'd be wrong.
03:22Strangely enough, when Pleistocene ice sheets grew, many animals saw it as an opportunity.
03:27New species evolved, specially adapted to cold conditions.
03:32This is the story of how a few specialist species that evolved to live in the biting cold, survive to
03:40the present day.
03:50It's summer in northern Norway.
03:55Here, on the edge of the Arctic Circle, we can peer through a window back in time to a habitat
04:01that would not have been out of place in the Pleistocene.
04:06This is tundra.
04:09The word tundra comes from the Russian meaning treeless mountains.
04:14And it once covered huge tracts of the northern hemisphere.
04:19Summer here is short, a few months at most.
04:23Even in June, the temperature can drop below freezing.
04:28Daylight lasts more than 20 hours a day.
04:33With the ground below the surface still frozen solid in permafrost, no plant can sink deep roots.
04:40It's extraordinary how life can adapt to extremes.
04:46This little Arctic birch I'm looking at crouches down away from the cold.
04:51A tiny little tree, which is not much bigger than my hand.
04:57And it doesn't get much bigger than that.
04:58Yet it's related to trees that in our garden grow to 50 feet high or more.
05:04This is one strategy for coping with extreme conditions.
05:09Become miniature.
05:13Dwarf birch carry both male and female flowers.
05:18And its microscopic seeds are the result of wind pollination.
05:26And one thing you can always be certain of on these cold slopes is constant wind.
05:36But if trees shrink to adapt to the cold, the solution for many animals is the opposite.
05:44One way to cope with the onset of freezing conditions is to go large.
05:52That's because as you grow bigger, volume increases disproportionately to surface area.
05:59In other words, if you're very big, you can hold in more heat.
06:03So with the onset of icy conditions, several mammal groups in particular grew large.
06:11And for this reason, they're sometimes known as the megafauna.
06:20Great herds of mammoth, as well as woolly rhinoceroses, would once have lived in similar habitats.
06:29They have long gone.
06:30But one species of ice age megafauna that grazed alongside them still clings on in this special place.
06:42In this bleak and barren landscape, a landscape where the snow still lies every year for months at a time,
06:51it takes a very special creature to survive.
06:55There's little to eat except grass, lichens, and a few herbs.
07:02And it's called the muskox.
07:24Muskox live in the Dovrefjell Sundalsfjell National Park,
07:28on land formerly used by NATO for war games and testing weapons.
07:35They are famously bad-tempered, and have been known to kill tourists and hikers, even charged trains.
07:42So to keep safe, I need the expertise of local Norwegian guide Johan Schönheder.
07:51Ah, so we're off.
07:53Yeah.
07:54Now we're going.
08:05We're getting quite high here, and I can see the trees are thinning out.
08:09So is this the sort of place that muskox might like to live?
08:13Yeah, it's not so often down here, but it comes in the springtime.
08:19They tend to, it comes down to the valley here to give birth to their calves.
08:25So they live together, I guess, in small herds, with a dominant bull?
08:31Yeah, you can say that there is one ruler of the whole herd.
08:36Well, of course, the obvious question.
08:38Yeah.
08:39The name muskox refers to musk, which is an odour, a scent.
08:44Yeah.
08:45Is that to mark territory, or is that to establish dominance, or...?
08:51What's the story with the musk?
08:52Well, the only time we really can smell it is in the fall, when they have this mating period.
08:59OK, so it's to do with sex.
09:02Yeah, I think so.
09:03Yes.
09:15Well, I can see them now.
09:23A fully grown muskox bull can weigh half a ton and charge at 50 kilometres an hour over rough terrain.
09:32Here, in one of the last great cold wildernesses in the Northern Hemisphere, we creep closer,
09:39trying to peer back in time at a rare survivor our Stone Age ancestors might once have hunted for food
09:46and clothing.
09:48I think that the one we saw and the herd is behind this hill, so we have to be very
09:54careful,
09:55because they are walking against us, and they are watching us, and they know we are coming now.
10:01There are newly born calves, so we need to be extremely cautious.
10:05Now we are very close, and there are three ones on the other side of the river.
10:13It's over there, and they are waiting for each other on each side.
10:20Musk ox travel in small herds of about 20, but fording a fast-flowing river,
10:26this group have become separated, putting them on edge.
10:36Now we have to be careful, because we are now a little too close.
10:42He's really watching us now.
10:45Apparently, you know, indifferent, but actually they are very, very aware of everything we are doing.
10:49Oh, yeah.
10:51Such defensive behaviour dates back to the Ice Age, when giant bears still hunted them.
10:58They remain fiercely protective of their young.
11:02So is that a yearling, or how long old is the little calf?
11:06That's a yearling.
11:07When threatened, herds have sometimes been known to form into defensive circles,
11:12facing out at any potential foe.
11:16There we go. Yes, there we are.
11:19See how easily it goes in the water.
11:21Yes.
11:22Now it's going to be exciting to see what it does with the calf.
11:25I don't think the calf could make it across there, could it?
11:32Now it's crossing.
11:35With the calf.
11:38I mean, they obviously do go in for a lot of parental care, these animals.
11:41Yeah, because it's actually shading the...
11:46Maybe from crossing the river...
11:48So it's making an easy crossing for the...
11:50Yes.
11:51So really they are quite social animals.
11:54And operate very effectively together as a group.
12:01Normally always together, some more than one.
12:04Rarely you find a single one.
12:07So now they will regroup.
12:09Oh, that's great.
12:10Yeah.
12:14So that's a family.
12:19Being loyal, nurturing parents,
12:21it's a good evolutionary strategy for ensuring the survival of the next generation.
12:28But muskox have other tricks that help them survive in this bleak tundra.
12:35And see, they're grassing all the time.
12:3824 hours a day.
12:42They have this digest system that they have two hours eating grass and some flowers they're really low.
12:56And then after two hours, they have a quiet period of two hours where they're digesting the food they've had.
13:03Yes.
13:04And this they do 24 hours all the time.
13:07Once winter comes, they will conserve their energy by standing almost motionless for days on end.
13:16Not only can the muskox digestive system adjust itself to consume extremely tough foodstuffs in times of scarcity.
13:25But their liver and kidneys can slow down and shrink to half normal size to improve fat conservation.
13:38And there's yet another strategy for surviving the cold.
13:42If one way of coping with the ice age climate was to grow large, then another was to get woolly.
13:52This is muskox wool.
13:55It's very soft to the touch, but I can see little globules of rain on it which aren't absorbed.
14:03It's extremely water repellent and, yes, against my skin it's extremely warm and comfortable.
14:11This allows the muskox to cope with temperatures which can be as low as minus 50 degrees.
14:18It's incredible stuff.
14:20In short, if you want to survive a cold snap, get hairy.
14:29Although all attempts to domesticate them have failed, muskox steaks are a popular Norwegian delicacy,
14:36best enjoyed with a glass of red wine.
14:41And for me, their taste is a taxonomic revelation.
14:46Well, in taste it's not really like beef at all.
14:50It's more like mutton.
14:53Old, slightly older sheep.
14:55Well, perhaps that's not a surprise because the muskox is not really an ox.
15:01It's more closely related to the sheep and goats.
15:05It doesn't have the slightly rancid flavour that you sometimes get with goat.
15:16Well, we've heard of a wolf dressed up in sheep's clothing.
15:21Well, this is more like a sheep dressed up in cow's clothing.
15:33It's more like an antidepressant.
15:33It's more like a wolf.
15:347000 km west, in Yellowstone National Park.
15:39Another giant ice age survivor has evolved a very different method of sustaining itself through the harsh winter months.
15:50Here in the United States, it's frequently called the buffalo, but its correct scientific
15:55name is the bison.
16:03Yellowstone's bison live at an average height above sea level of 2,400 metres, where the
16:10temperature only briefly warms up into double figures.
16:14The lowest temperature ever recorded here was a staggering minus 54 degrees centigrade.
16:22To help fuel the bison through this bone-numbing cold, it grazes constantly, even when the ground
16:29is covered in snow and ice.
16:33But getting to the shrubs and grasses entombed beneath the snow can be a formidable challenge,
16:39one that bison have waged with the elements since the Ice Age.
16:46There's something extraordinarily primeval about these wonderful animals finding something
16:55to eat in this land.
16:58You can see them pushing through snow if they need to find food in the winter.
17:05They're really adapted to survive under the most harsh conditions you can imagine.
17:15Unlike muskox, bison don't store large reserves of fat for the cruel winter months.
17:22They feed all year round.
17:25But to dig in snow, you need traction, and to grip in the ice, bison have evolved a feature
17:31they share with deer, sheep and goats, but not horses.
17:37Their cloven hooves are split into two toes and help the bison grip when using their hugely muscular
17:44upper bodies, snow plows to uncover the grass concealed beneath.
17:57To get a closer peek at how bison are built for such feats of strength, I visit vet Don Warner,
18:04known locally as just Dock.
18:23Well done.
18:24So let's just have a quick look at the front of the head, rather flat.
18:28That's right.
18:29Relatively small horns compared with, say, a bovid like a cow.
18:34That's right.
18:35The male bison has a very large bonnet, a very thick hide in this area, and the horns kind
18:43of adorn the edge of that bonnet, and they use that for head-butting.
18:48Fighting is a lot of head-pushing, a lot of pushing each other around.
18:52One pushes one way and then the other pushes him back.
18:55It's a test of strength.
18:56It is.
18:56It is.
18:57And they're pushing hard.
18:58And then they try to come past the head and hook them in the side or the abdomen.
19:04But this is a female.
19:06And the base of the horn is quite a bit smaller.
19:12If I was to look at this straight off, I might think, that's a cow.
19:17And it's a bison.
19:18So how does this differ from other bovines, other cows?
19:23Well, the most obvious thing are these dorsal spinous processes.
19:29They're very long.
19:31A cow skeleton, they'd be about half that length.
19:34So this is what gives the sort of hump-like appearance.
19:37Correct.
19:38Another differentiation is the scapula.
19:42That's the shoulder.
19:43The shoulder blade.
19:44Right.
19:45That's quite a bit longer in a bison.
19:48This connection gives the buffalo a lot more leverage to move his skeleton and to move his
19:54whole body quickly.
19:56But what we're talking about here, of course, is a very heftily muscular area.
20:02Yes.
20:03There's muscle on each side connected to a large ligament that goes up and connects to the back
20:09of the skull.
20:10So I guess there must be a nice piece of meat in there.
20:13There is.
20:15That's the hump.
20:15It's very accessible.
20:17Peel back the skin.
20:18Peel back the skin.
20:19And you've got to...
20:19Cut it off.
20:20You've got a big steak.
20:21Take a big slab of the hump.
20:23So, well, if we put all this together, what we've got is an animal designed for survival
20:30through hard winters because all this muscle adds up to allowing the head to swish down
20:36through the snow and find buried vegetation.
20:39That's right.
20:40And it's just a big pendulum on a very strong anchoring system up at their back.
20:49And it allows them to forage in the wintertime through snow.
20:53So they can get through the really quite long winters you can have up on the prairie land.
20:58Yes.
21:15When it's cold, there's another advantage to being big.
21:20Big stomachs.
21:23Big stomachs.
21:25Big stomachs.
21:27Big stomachs.
21:33Big stomachs.
21:42What it does have in common with both of them, is its stomach.
21:47The moose is a ruminant.
21:48a herbivore whose stomach possesses four chambers.
21:54Ruminants use these extra stomachs to store bacteria
21:58that help to break down and ferment coarse, otherwise inedible plants.
22:05Their stomach contents can then be regurgitated, chewed again and redigested.
22:11A process called ruminating, or more simply, chewing the cud.
22:20But it wasn't just herbivores that found ways to adapt to a diet of frozen food.
22:29Scavenging in the ice is the speciality of the wolverine.
22:35And this Pleistocene survivor also possesses an ice-resistant pelt
22:39that is one of the most highly prized in the animal kingdom.
22:48I'm with Debbie Harris, who looks after one of the few wolverines in captivity in the western United States.
22:58The wolverine, sometimes known as the glutton, gulo-gulo.
23:04What kind of adaptations does the wolverine have that might help it to become such a survivor?
23:12Well, one of the things is his fur does not absorb moisture.
23:16He has these very large paws with a lot of fur on them and they accommodate him like snowshoes
23:22because he lives very high in the mountains where there is a lot of snow.
23:25So he can run very fast on his little snowshoes.
23:32A fully grown wolverine may weigh around 20 kilograms.
23:36But it's an ice-aid giant of sorts.
23:39The wolverine is the largest mustelit in North America.
23:43In that family it includes the skunk, the otter, as well as the North American mink.
23:51Wolverines are weasels, the giants of the weasel family.
23:59Now, the wolverine has something of a reputation as a bit of a fierce creature.
24:03Is that reputation justified?
24:05That little wolverine at 30, 35 pounds can go out there and he can spook a grizzly bear as well
24:11as a pack of wolves
24:12if he's really willing to get out there and he's hungry enough to get that food that they've got.
24:17And believe me, he could do it.
24:22Ferocity is a useful survival strategy, even if this little chap seems unreasonably playful.
24:29But it helps to have the hardware to back threats up.
24:35In the case of the wolverine, it's the teeth that are its special secret.
24:40Of use not just against competitors and prey, but to help it feed in the freezing cold.
24:51Its rear molars are angled backwards so that the jaws can rip and tear deep frozen meat,
24:57making it a perfect ice-age scavenger.
25:01He also has a very powerful jaw capable of snapping bones so that he can eat the marrow from the
25:09bones.
25:09So they are animals adapted to cold conditions?
25:13Absolutely. They need that cold weather.
25:20Wolverines, bison, muskox and moose, all ice-age survivors that still cling on in the cold higher latitudes.
25:32But not all the Pleistocene megafauna lived in the Northern Hemisphere.
25:38And nor did they all live in ice.
25:43My next survivors live more than 16,000 kilometres away on the other side of the world.
25:52Back during the Pleistocene age, while the North was covered in glaciers, conditions were very different,
25:58but no less harsh in the Southern Hemisphere.
26:06To find out more, I join genetic scientist and caving enthusiast Alan Cooper in the Narra Court Caves of South
26:14Australia.
26:16Originally formed 200 million years ago from coral and marine fossils, the limestone has eroded, creating underground caves and holes
26:27on the surface that have entombed unwary animals.
26:31They are a World Heritage Site, a popular venue for caving adventures, and a mine of valuable environmental and ecological
26:39data.
26:41Despite my claustrophobia, Alan is eager to show me a paleontological site that contains evidence for what happened here while
26:50the Northern Hemisphere was covered in ice.
26:54So here we are in a bone pit.
26:58Layer after layer, fossils have been preserved in the floor of the cave, giving us a narrative of history of
27:05all hundreds of thousands of years.
27:08Layers of death.
27:11You're basically looking back through time, you know, potentially 40, 50,000 years of ecological dandruff, I suppose.
27:20How did they get there?
27:21Well, there was a hole in the surface through which animals tumbled.
27:26In other cases, predators brought bones in here to devour.
27:30But what kind of animals are there?
27:32Well, you've got a huge diversity of Australian megafauna here.
27:38We've got Tasmanian devils, which are still around today.
27:45Tasmanian tigers, which of course aren't.
27:48Short-faced kangaroos, we can see a skull there with the eye socket.
27:53Well, we're used to thinking in a kind of selfish way, us Europeans, as the ice age as if it's
27:59our ice age.
28:01But the fact is, the world is one great connected system.
28:06The problem in Australia, though, is we don't have the same sort of quality of fossil record that we do
28:11in the Northern Hemisphere.
28:12So trying to work out exactly what's happened is much more difficult.
28:16We do know it's a very cold, dry period during the glacial maximum, with sand dunes rolling across the interior
28:25of Australia.
28:26And life during that stage would be almost impossible.
28:34Life on the plains was especially harsh.
28:37So it's perhaps ironic that my next survivor began life, just as we probably did, in the trees.
28:52Some of the oldest kangaroo species are also the smallest and still live in forests.
28:59One of the secrets of their success was reproduction, something kangaroo foster mum, Tanya Melville, knows all about.
29:08Well, this is a very charming one. What's the species here?
29:12This one is called a swamp wallaby.
29:14So one of the important things about these in general is people tend to think of them as primitive, but
29:20actually they're not.
29:21They're really beautifully advanced, beautifully adapted.
29:24Definitely.
29:26Kangaroos reproduce like a well-timed production line.
29:30Females can control their fertility.
29:32So, while one joey is in the pouch, another fertilised egg can be waiting to develop.
29:39They can hold an embryo and reserve, as it were.
29:42Definitely.
29:43And when conditions improve, it can complete the rest of the development process.
29:49That's it. So what that means is when the conditions fall bad, so, you know, the water dries up or
29:54not much food around, she can drop off the joey on the foot, she can drop off the joey in
29:59the pouch, but she'll still have that embryo waiting.
30:02So as soon as the conditions fall good again, it's bang, give birth straight away and start that whole breeding
30:08process off again.
30:09And, of course, they always try and scramble back in, don't they?
30:13Yeah, the mother will usually call if there's any sign of danger, and as soon as the joey hears that
30:19call, it's a mad scramble back in the pouch again.
30:22And she's actually got a drawstring-like muscle, so she can close it or she can open it, depending on
30:28what she feels like.
30:29It's all about slamming the door, really. Definitely, yep, you stay in.
30:32Don't you just stay in here?
30:33Yep, for sure.
30:45Many of Australia's marsupials had also become giants during the good times.
30:54As climate became more arid, they needed to toughen up to survive.
31:01Well, we know kangaroos' system of reproduction is extremely efficient, but what else helped them to survive, do you think,
31:09when climate changed in this drastic way?
31:11One of the big advantages of the marsupials is their metabolic rate is very slow.
31:16They can survive on much less food in much harsher conditions than, for example, the placental mammals.
31:23And quite often, people tend to think of the marsupials as being more primitive, and that's why they could only
31:28survive in Australia, because there was no competition.
31:31And perhaps in many ways, this very harsh, arid environment meant that something like the kangaroos, with their unique skills,
31:39were ideally suited,
31:41whereas placental mammals might have actually had a much harder time surviving here.
31:49Like its cold-adapted mammalian counterparts, kangaroos also chew the cud.
31:55But while the bison and the muskox build muscles or store fat, the kangaroo can extract water from the meanest
32:03shrub.
32:05So long as they could find even the driest plants, they could go for months on end without a drop.
32:15Interred in the Naracourt Caves are fossils of some of the giant marsupials that were contemporaries of the Ice Age
32:22mammals in the Northern Hemisphere.
32:26Hippopotamus-sized herbivores like Zygomaturus, the wolf-like Thylacine, sometimes called the Tasmanian Tiger, and the metre-and-a-half
32:36-long Thylacoleo,
32:38largest of all known marsupial predators, superficially resembling a cross between a lion and a bear.
32:46And what about Thylacoleo, the so-called marsupial lion?
32:51Yeah, a remarkable beast. We've got one here. Here's the skull. And as you can tell very quickly by looking
33:00at the teeth, this is no placental mammal.
33:04The two in size at the front, quite unique in this modified slicing molar down the side here.
33:12And look at the strength, the thickness in the skull.
33:15Looking at the feet, some new research has shown that it appears to be climbing, spending a lot of its
33:22time, or certainly capable of climbing trees.
33:24All right.
33:25You can imagine this, you know, 100 kilos coming down with those teeth on top of you.
33:29Except that it would be hunting presumably possums and things like that?
33:32We're talking possums, small wallabies, this sort of medium-sized animal.
33:36So they drag them into the cave, perhaps, for leisurely?
33:40Presumably, yeah. We really, even despite the evolutionary adaptations, which is so remarkable,
33:46it's actually still quite difficult to work out what this thing is doing.
33:50But these exotic marsupial giants lacked the survival trait that would make the kangaroo king of the continent.
33:58It was by hopping out of the forests, 15 million years ago, that kangaroos came to dominate Dry Age Australia.
34:07Hopping is one of the most effective means of locomotion in the animal kingdom.
34:12And the largest kangaroo species alive today can reach speeds in excess of 65 kilometres per hour.
34:27Such speed is useful for escaping from predators.
34:30But recent studies suggest the real survival bonus hopping gives kangaroos is range.
34:39This supremely efficient mode of locomotion allows mobs of kangaroos to cover vast ranges in pursuit of scarce grazing food,
34:48perhaps the best way to cope with conditions of drought.
34:58Plants, too, began to suffer from the tough, dry conditions.
35:04Yet the extreme aridity provided the perfect opportunity for another of Australia's most iconic dry-adapted species
35:14to spread across vast stretches of the continent.
35:22Eucalyptus trees.
35:25Their secret survival weapon is a tolerance to one of the bush's most regular and feared natural phenomena.
35:37Fire.
35:40Eucalyptus trees have adapted to cope with periodic fires.
35:46Some species, like these stringy bark eucalyptus, even have highly flammable loose bark
35:52that will erupt in flames with the smallest spark.
35:58The reason for this adaptation is as simple as it is efficient.
36:06Any plants that cannot cope with fire are incinerated.
36:12After the fire has passed, eucalyptus trees put out new shoots and regrow once more.
36:19The competition goes up in smoke.
36:28An even more special example of a fire-adapted plant is this wonderful bush.
36:39Named after an illustrious former president of the Royal Society, Banksia is the phoenix of the plant world.
36:48In fact, it can't live without fire because its seed pods burst when fire passes through,
36:55releasing the seeds to germinate in the newly enriched ground.
37:15The last extreme period of aridity started drawing to an end around 30,000 years ago.
37:21By then, Australia's landscape had been completely transformed,
37:26and many of the continent's large animals and plant species were beginning to disappear.
37:35Great transformations were also beginning elsewhere.
37:40Around 20,000 years ago, the great ice sheets that had covered much of the northern hemisphere
37:46for more than two million years began to melt.
37:52The end of the ice age would bring mass extinction.
37:57So what happened when the ice sheet finally retreated?
38:02The change in conditions made many of those specially adapted species go extinct.
38:09It was not the cold that killed them, it was the thaw.
38:19Some of the animals that did not survive can be found for sale in a fashionable street in Soho, New
38:25York City.
38:26They're carnivores that disappeared at the end of the Pleistocene Age.
38:31They were found preserved in tar pits in California.
38:36Extinct megafauna. These are the animals that didn't quite make it.
38:42Hunters all, these fell into the tar while in pursuit of the prey, which are also there.
38:49The sabre-toothed tiger, well I used to call it that, it's no tiger,
38:52but it does have these huge incisors, these great fangs for killing its prey.
38:58A lot of debate about how they worked.
39:01The dire wolf. The dire wolf, of course, hunted in packs just like the living wolf, but they were larger.
39:09Now extinct.
39:12The American lion. May come as a surprise to find lions in America, but there they were.
39:18Characteristic teeth, of course, on both jaws here.
39:22They didn't survive.
39:24These were all victims of a changing world.
39:35Just how dramatically the landscape changed can be seen in Yellowstone.
39:41This would once have been tundra, like the frozen north of Norway today.
39:46But as the ice began to retreat, so many species, long exiled further south, seized the opportunity to expand their
39:54dominion northwards.
39:57Yellowstone's tundra was conquered by an empire of conifers that took root across the northern hemisphere as the ice sheets
40:04receded.
40:08As the ice sheets waxed and waned, these cold-loving conifers could adapt their ranges in harmony.
40:20Warm times, they spread.
40:22Cold times, they contracted.
40:26Tough, enduring trees.
40:30And they're still with us today, of course, cladding every high mountainside.
40:40Modern conifer trees are descended from some of the oldest types of tree in the world.
40:45And conifers date back more than a hundred million years.
40:52To colonise new territory, the conifer uses cones to house its seeds.
40:59But in spite of their woody appearance, the cones are not impenetrable.
41:10So here's one of the cones that gives these trees their name.
41:14These have seeds tucked within them that form a food source for animals.
41:19Today, as they have done for millions of years.
41:27But the spread of conifer trees led to the decline of habitat for some tundra-dwelling animals.
41:54A woolly mammoth in the Ipswich Museum.
41:57A wonderful, gigantic relative of the elephant, but with differently shaped tusks.
42:04Curved into this elegant spiral.
42:08And these mammoths once roamed in their millions, all the way from East Anglia here to Siberia.
42:16They fared on a special kind of tundra vegetation, rich sedges.
42:24But they became extinct.
42:27A few diminutive mammoths lingered on in Wrangel Island in Arctic Siberia until almost historical times.
42:34The rest of the population became extinct as their special habitat declined.
42:40Their numbers went from millions to a few and then they died out.
42:53Small numbers of muskox survived by retreating with the tundra towards the inhospitable edge of the Arctic Circle.
43:04Whilst in North America, climate change was driving other animals towards extinction.
43:11With the thaw, tundra gave way eventually to prairie.
43:17Grasses quickly came to dominate the open landscape.
43:22Grasses are also a relative newcomer to the plant world, evolving around 23 million years ago, long after flowers.
43:34Grasses are special plants, continually regenerating their leaves from the base.
43:40So giving a continuous feed to grazing animals, like the bison.
43:46The bison survived, but only just.
43:50They were saved by chewing the cud.
43:53Their ruminant stomachs gave them the ability to extract nutrition from grasses,
43:58while mammoths, who were not ruminants, could not.
44:06Today, in Yellowstone, the local bison have even adapted to eating the poisonous,
44:12sulphur-rich grass found around geezers.
44:15They can't endure it for long, but when conditions are really icy,
44:19it temporarily keeps them from starvation.
44:30A more temperate world also signalled the return of flowers that had been pushed far to the south.
44:40Warmth encouraged species that needed long summers and suited their pollinators.
44:50These sunflowers almost seem to appreciate the light of the sun,
44:54following the course of it as it tracks across the sky.
45:11Flowers need their own particular pollinators to help them set seed.
45:24Nowhere could escape the effects of the Pleistocene cold periods.
45:28Even in the tropics, rainforests contracted.
45:32That wasn't a problem for these butterflies,
45:34which could wing their way into refuges to see out the hard times.
45:40But when the ice sheets began to contract,
45:43the rainforests began to expand to their present proportions.
45:51The very first ancestors of the butterflies were very inconspicuous at the time of the dinosaurs.
46:01Subsequent collaborative evolution between pollinators and flowering plants stimulated an unparalleled burst of invention in both insects and flowers.
46:13As a result, today, both pollinating insects and flowering plants are among the most varied and widespread of all species.
46:24Other animals were also released to a new freedom by changing climates.
46:32One young mammal had been confined to eastern Africa for most of its existence,
46:36but as temperatures warmed, it swiftly spread outwards.
46:42And this species is perhaps the ultimate Pleistocene survivor.
46:4913,000 years ago, another species moved into North America.
46:56Man.
46:57The same species arrived in Australia more than 40,000 years ago.
47:01And in both cases, the megafauna, the large animals, seem to become extinct in a short time.
47:09Surely these events must be connected.
47:13Could it be that this new top predator, armed with a brilliant mind and a capacity to make tools,
47:21is implicated in the demise of some of the most glamorous large animals that have existed on Earth?
47:30The idea that as man arrived on new continents, he hunted its large animals to extinction,
47:36is called the overkill, or sometimes blitzkrieg hypothesis.
47:41As the name suggests, it proposes that man advanced around the world like a division of panzer tanks,
47:49annihilating everything in his path.
47:54After swiftly spreading to Europe and Asia,
47:57this new hunter reached Australia around 40,000 years ago, armed with fire.
48:05A weapon that would bring about the downfall of the last surviving giant marsupials.
48:13We know that these new interlopers had fire, don't we?
48:18Absolutely. You can see that in the archaeological record.
48:20And modern Aborigines used fire as a very effective hunting tool.
48:27And of course that habitat alteration is going to have a huge impact on megafauna.
48:32So I suppose there will be the perennial question of,
48:36was it all down to us humans?
48:39Or did us humans merely administer the final coup de grace?
48:44Certainly in my opinion, from the genetic data that we've got, climate change is playing a major role.
48:51And humans are, as you say, applying the final blow.
48:54And I think in many cases these species wouldn't have gone extinct, or might not have done,
48:58if humans hadn't been there to disrupt the environment and prevent populations from dispersing and reinforce one another.
49:06And I think it's the combined double blow that is the extinction.
49:12The only large marsupial that survived the dual ravages of climate change and the arrival of a new apex predator
49:20was the kangaroo.
49:23Its hopping, water efficient and ingenious reproductive ability gave it the tools to thrive.
49:33Today there are almost three times as many kangaroos in Australia as there are people.
49:39By some estimates, nearly 60 million of them.
49:46The musk ox survived the appearance of man, but not here in Norway.
49:53In fact, these animals came from Greenland after the Second World War,
49:58reintroduced after the native population was hunted to extinction.
50:08Back in North America, the bison had evolved to dominate the Great Plains,
50:13and for more than 10,000 years successfully co-existed with man.
50:19Then, 200 years ago, a new arrival threatened to finally exterminate these great Ice Age survivors.
50:28If I'd been sitting here 200 years ago, I would have seen behind me, not a few dozen, but tens
50:35of thousands, even millions of bison.
50:39It was the arrival of this object, the rifle, that changed its fortunes and almost drove it to extinction.
50:47Particularly after the American Civil War, when these rifles came into commission.
50:52It is a survivor, but only by the skin of its teeth.
51:05Today, under the broad skies of Montana, 250 kilometres north of Yellowstone National Park,
51:12ranchers like Tana Blackmore dedicate their lives to conserving the remaining herds of bison.
51:19Part Native American, she keeps more than 200 bison on her land in the Crow Reservation.
51:25And with Tana at my side, I can get far closer to these magnificent survivors than I would ever dare
51:32in Yellowstone.
51:35As a native woman, and doing the work that I was doing with the land and so forth, they literally,
51:44different people literally bought these baby buffalo and gifted them to me.
51:50And it's kind of like, you should ask before you start giving people buffalo.
51:52It's a kind of a responsibility, isn't it?
51:55It's a huge responsibility.
51:59I wouldn't want to trust myself out there somehow. They just look too massive and powerful.
52:05See the big bull? Look at the massive head on him.
52:13There he is.
52:14That is some animal.
52:17I mean, that bull really does look like he's in charge.
52:21You want some of that?
52:24You want some of that?
52:25They look like they're being independent here, but buffalo will stick together.
52:30They're never far from each other unless, you know, their particular bands.
52:35And once they hit about a hundred head, they start to break into a new band.
52:42They have another survival trait that would have helped protect them from Pleistocene predators, though sadly not hunters armed with
52:50long-range rifles.
52:52They've got incredible circular vision, eyes on the sides of their heads.
52:57All they need to do is slightly turn their head and they can see what's going on back here, like
53:01rear-view mirrors.
53:04Yeah? Yeah? You want some of that? You want some of that?
53:09Today's bison are all descendants of a handful that survived the human cull of the 1800s.
53:15Hello, babies.
53:17They were brought back from the brink by breeding the remaining wild animals with some kept in the Bronx Zoo.
53:28After we finish our safari, I join Tana for what she insists is a truly free-range bison burger.
53:35So it's my chance for a taste without having to pay the buffalo bill.
53:41Mmm.
53:43Mmm, excellent.
53:45I'm glad you enjoy. It has a very different flavour. It's a wholesome flavour. Very robust and full, I believe.
53:52Of course, it's history. The history of this animal is not a happy one.
53:55I mean, it was a mass exploitation.
53:59Well, there's also another unhappy side to that too, and that has to do with the Indian Wars.
54:08The primary reason that the masses of buffalo were eliminated was to eliminate the food source for the native,
54:15because it was the life force for the native people.
54:19And if they eliminated the food source, then they would also eliminate the threat from the Native American.
54:26Yes. I mean, it was a political, partly a political motivation, no doubt.
54:31Mmm.
54:31The flavours, well, it's like beef in a way, but I would say overall sweeter.
54:40The burgers are certainly delicious. I wonder if a mammoth burger would have been half as nice.
54:48Hunting simply for food can't explain why so many of the other Ice Age giants died out.
54:54It was climate change and the disappearance of their habitat that caused their extinction.
55:04The link between habitat and survival has been one of the enduring themes of our series.
55:12Every survivor we have seen is just one small part of a vast and interconnected tree of life.
55:19Just one of the millions upon millions of species that have ever lived on our planet.
55:27But have we, in our small selection, discovered the secret to being a survivor?
55:36Luck alone may have helped propel some species over life's great hurdles.
55:43Like mammals inheriting the Earth when an asteroid killed off the dinosaurs.
55:49But there is more to long-term survival than just one lucky throw of the dice.
55:56Like adaptation.
55:58We've seen how exquisitely adapted to their way of life everything from a muskox to a duck-billed platypus can
56:07be.
56:08But plenty of animals that went extinct, from dinosaurs to trilobites,
56:14were probably just as finely adapted and that didn't save them.
56:21Some survivors, like the echidna or the turtle, seem to live a long time or invest a lot of effort
56:29in producing offspring.
56:31Stacking the odds in the survival of their own progeny.
56:36Can I see where the head is right at the moment?
56:39Right beside you.
56:40Others, like snakes and emus, can go without food for long periods.
56:46Or even go into suspended animation, like nuts and seeds.
56:53But all living things have one need in common.
56:57Habitat.
57:00From the ancient time havens of the intertidal zone in Delaware and Hong Kong.
57:06The green refuge of Daintree.
57:09And the ice-covered mountains of the Wolverine.
57:14Persistence of habitat is the fundamental basis of persistence of a species.
57:26Today, Homo sapiens is master of all he surveys.
57:32We have transformed the natural world and are changing ancient and enduring habitats like never before.
57:39Triggering a new era of man-made mass extinction.
57:44But by threatening habitats around the world, we ultimately threaten the survival of our own kind.
57:52A big city is so full of energy, so full of excitement, so full of consumption.
57:58It seems that we humans have come a very long way in a very short time.
58:05And it might be the best place to ask whether mankind will burn himself out in an extravagant splash.
58:12Or is he possibly going to be one of the survivors?
58:37Tomorrow night, taking you back to more recent history and the lost kingdoms of Africa, specifically the Zulu tribe.
58:44That's at 7 here on BBC HD.
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