Galapagos with David Attenborough (2013) s01e03 Episode Script


x264-shortbrehd Hidden away in the vastness of the Pacific, and undiscovered by men until only a few centuries ago, lies a group of strange volcanic islands.
Each is a crucible where evolution proceeds at extraordinary speed.
Each island contains its own unique community.
The discovery of these creatures inspired an idea that changed our understanding of life on Earth Evolution.
And today, scientists on Galapagos are continuing to make discoveries that shed light on that crucial process and have revealed that human beings can be just as powerful a driving force for change as any other factor.
Something here was the catalyst that produced the most spectacular explosion of biological diversity in the world.
It's not just the number of species that appeared, but the rate at which they did so, and the result is so extraordinary, it inspired the most important of all biological theories, Charles Darwin's evolution by natural selection.
And now, 200 years later, we're beginning to understand the deep-lying forces that produced this biological wonderland.
One of those factors is isolation.
A part of Isabela Island, the largest of the 16 in the archipelago, is so difficult to get to, it's hardly ever visited.
Wolf Volcano.
Its giant crater lies exactly on the Equator, and is encircled internally by steep cliffs.
And on its flanks, evidence was discovered of a catastrophe that might, paradoxically, eventually lead to the creation of a new species.
This flow of recently solidified lava has created an impassable barrier 100 metres wide, right through the vegetation.
The fresh lava is razor-sharp, and almost impossible to cross.
On it lie bones.
Bleached white by the baking sun, they're those of giant tortoises.
Some animals that got stuck here are still clinging to life.
Tortoises are tough.
They can survive for months without any food or water.
And that worsened their fate, it will take them months to die.
Why so many tortoises tried to cross the lava barrier, nobody knows.
What drove them to keep attempting this impossible journey? Perhaps they were desperately trying to rejoin other members of their group.
Their deaths, however, are significant.
They illustrate a principle that applies to the whole of nature.
It's not unique to the Galapagos, but it's because of the Galapagos that we first came to understand it.
This tragic scene, filmed for the first time, may provide a clue as to how a new species may start to evolve.
The lava flow created an impassable physical barrier across the tortoises' territory, dividing it into two.
So two tortoise populations that were once one must now live apart.
If there is any significant difference, now or in the future, between their two territories, the tortoises may eventually become two different species.
Animals and plants are evolving throughout the natural world.
But it was the strange creatures of Galapagos that first revealed how that happens.
Nearly 200 years ago, the islands were visited by a young naturalist.
On September 16th 1835, HMS Beagle arrived in the Galapagos Islands, and the 26-year-old Charles Darwin stepped ashore to explore.
At the time, very little was known about the natural history of the islands.
Darwin, initially, was fascinated by its geology.
But it was the animals that gave him his historic insight.
Darwin was only on these islands for five weeks.
But in that short time, there were things he saw and conversations he had which stuck in his mind.
For example, the British vice-governor of Floreana Island said that he could tell which island a giant tortoise came from simply by the shape of its shell.
He pondered on the vice-governor's casual remark.
Why were populations of tortoises on separate islands all slightly different from one another? He set about making a collection of animals and plants from all the islands he visited.
Although it was the tortoises that first alerted Darwin to the differences between animals on different islands, it was his collection of these undramatic little birds, the finches, which provided him with the most substantial evidence for his great theory.
We now know that the ancestral Galapagos finches arrived in these islands about 2 million years ago.
Since then, they have diversified into a number of different species.
Today, there are 13 of them, distributed throughout the archipelago.
Each has its own special talents.
The woodpecker finch has discovered how to use a tool to winkle grubs out of their burrows in the branches of trees.
The vampire finch has learned how to extract blood from sitting birds.
Darwin, when he returned to England, brought back with him a wide variety of specimens of all kinds, and he spent years studying his collections.
He had a range of finches from several of the islands, and he noticed one particular way in which they differed.
They had beaks of different sizes.
Why? An idea grew in his mind.
It would also apply to tortoises, maybe to all animals and plants, wherever they occurred.
Painstakingly, meticulously, he started to accumulate evidence from all over the world to support his idea, and he called the process that produced new species "evolution by natural selection.
" And nowhere his its workings more vividly more evident, than here where it first occurred to him, in the Galapagos.
He realised why it was that there were several species of giant tortoises.
That original species probably had a high-domed shell, like this one, and that's very useful on well watered islands like this, where you have to barge your way through the vegetation.
But on other islands, there are other problems.
In the southeast corner of the archipelago lies Espanola Island.
Here, there is virtually no edible vegetation at all.
Except, that is, for this prickly pear cactus, opuntia.
But this species of opuntia is very tall.
And it has a tough, woody trunk.
The only parts worth eating are the fleshy leaves and flowers at the top.
Any giant tortoise that could reach them could get a meal.
Tortoises with low, round fronts to their shells couldn't do that.
But those with a peak at the front of their shell, and long necks, could just manage it.
So they were the ones that survived and produced young.
Over many thousands of generations and millions of years, the shell shape of the Espanola tortoise became more and more exaggerated.
Now, the peak at the front of the shell is shaped like a saddle.
Such a change didn't happen just on Espanola, different islands had their own versions.
Eventually, there were 15 different species on the islands, all descended from a single founder.
But why should the environments of the islands be so different? Well, a hint of that reason may come from looking at films I shot right here, back in 1978.
(SPEAKING IN 1978) In these programmes, we're going to survey the immeasurable number of animals that have been produced by natural selection, and look at them not as isolated oddities That image of me, shot 30 years ago, indicates something extraordinary.
In that time, the rock on which I was sitting has moved its position by about a metre from where I was then to where I am now.
In fact, the whole of this island is drifting across the surface of the globe at a rate of about three centimetres a year, roughly the rate at which my fingernails grow.
That may not sound much, but in the 3 million odd years since this island emerged above the surface of the ocean, it has drifted in a south-easterly direction by about 60 miles.
Movements in the Earth's crust are the key to understanding the archipelago's extraordinary evolutionary history.
A giant hotspot, rising from the Earth's molten core, began to build the Galapagos 4 million years ago.
But, as the island drifted away from it, other volcanoes replaced it, one after the other.
Each was built from an accumulation of ash and lava.
But then, as each moved away, eruptions ceased.
So a group of islands appeared, one after the other.
The islands were separated from one another by water, so their populations can't, for the most part, mix.
But they're just close enough for an occasional animal to float across and so seed a newly emerging island.
Because the islands are of different ages, they contain between them a great variety of environments.
And each has moulded its inhabitants in its own way.
That is why their animals are so diverse.
Each is a separate evolutionary community.
Darwin had noticed some of the clearest differences.
But there are many others that are less obvious.
An isolated population of animals can change not only in their anatomy, but in their behaviour.
Little lizards like this are found throughout the archipelago.
Each island has its own distinct species.
And they differ not so much in the way they look as the way they behave.
This is a lava lizard.
There are lots of them on the rocks around here.
And in the breeding season, which is now, the males are competing with one another, both for territory and for females.
And the way they do so is with press-ups.
Actually, this is a model that is used by scientists to investigate the way in which these lizards communicate with one another.
Let's see how he gets on.
And there's a response.
These press-ups vary, both in the number and the intensity, the speed at which they do it, and how high they bob their heads.
The interesting thing is that the responses vary from species to species.
In other words, each species has its own language of gestures.
There are slight physical differences between the species of lava lizard on different islands.
But now, because they have developed different gestures, they can't interbreed, even if they meet.
They're separated by a language barrier.
New technologie, now enables scientists to investigate the workings of evolution, in ways that Darwin could hardly have ever imagined.
X Rays are being used to work out what's happened to one of the least impressive animals on the island, a tiny land snail.
It's been known for a long time, that there are many different snail species, all closely related.
But a recent study of their shells, using x-rays, has demonstrated just how diverse they have become.
The length of the shell compared to the diameter of the tube inside is marginally different in different populations.
It's certainly different enough to define them as different species.
And there is an extraordinary large number of them throughout the islands with what seem to be very complex interrelationships.
In fact, there are more species of them than any other kind of animal on the islands.
Even one small island may contain several different species.
But why? It has all to do with the different microclimates that occur even within a single small island.
Black lava rock has one species and sandy beaches close by, a very different one.
A dark cave has one sort and a leafy forrest growing arround his mouth, yet another kind.
And it seems to be connected to humidity.
At the one extreme, there are these with a wide mouth.
They come from relatively well watered islands.
And a wide mouth like that has a body which produces roughly a globular shell.
But on dry islands, the mouth has to be very small, to prevent evaporation and that produces a long conical shape.
So Galapagos' new species, range from the subtle like snails, to the obvious, like the marine iguanas.
In other parts of the world, evolution usually proceeds in a slow gradual way.
It can take millions of years for a new species to appear.
But in Galapagos, it's been happening in a evolutionary blink of an eye.
Galapagos, for its size, has more unique species than anywhere else on Earth.
And all have appeared in the islands' comparatively short history.
And that raises another intriguing question.
Why did such a great number appear so quickly? The answer has to do with the absence of some animals.
The few that are here, are all very small.
This is one of the most lethal.
A centipede.
It roams the underground searching for prey, which it kills by injecting venom, from the sharp claws on its front legs.
But it's only 30 centimeters long.
So its victims are mostly tiny.
Bigger animals like mockingbirds can easily subdue one.
They even feed centipedes to their chicks.
The greatest concentration of predators in the whole archipelago is found on the rocky island of Fernandina.
But they to of their kind are rather small and comparatively ineffectual.
The Galapagos racer.
They search for prey in the colonies of marine iguanas.
But all they can manage to do is to pick off the young, the weak or the dying.
And even that they find quite difficult.
They hunt in the rocks around the fringes of the colony.
They have to use a combination of both venom and constriction to make a kill.
And even then, because they're small snakes, it may take more than one to overcome a victim.
And then there's a tug of war between the winners to settle who has the prize.
There are other predators that prey on the iguanas from the air.
The Galapagos hawk.
But even this hunter is seldom powerful enough to subdue a big male.
It usually waits until it finds one that is weak or encumbered.
A pregnant female, trying to find a place to lay her eggs.
And there are not many hawks here.
Only 150 mated pairs, because there's only a limited number of nesting sites.
There are so few birds that they make very little impact on the iguana population.
So why are there no larger predators on Galapagos? Most of the Galapagos animals came from the rainforests of South America, 600 miles away.
There are plenty of big predators in these forests.
Reptiles got to Galapagos by floating across the ocean on rafts of vegetation.
Only hardy animals like the iguanas and tortoises could make that 600 mile voyage.
The great predators of the jungles, however, are mammals.
Big, fast, and warm-blooded, like jaguars.
If any of them had ever been carried away on a raft of vegetation, they would have perished out on the open ocean within a few days.
So now, while there are many kinds of herbivorous reptiles in the Galapagos, there are no large predatory mammals of any kind.
And this has had a profound effect on the animals that did get here.
It's something noticed by every visitor who comes to the islands.
All the animals here are amazingly tame.
Even the little finches are happy to bathe within inches of a stranger.
The lack of predators may have a surprisingly widespread effect.
It's not just that animals are not frightened of strangers, the so-called "island tameness", but that time that would be spent hiding from attackers can now be used to find food, find mates and raise young, and so produce more young, which hastens the progress of evolution.
There is no more impressive example of that than Fernandina's iguana colony.
With no significant predators around, these herbivores produce lots of young.
So many, that their problem is not how to defend themselves, but how to find enough food to support their great numbers.
So they ventured into the sea itself, to graze seaweed on the sea floor.
And although swimming in the cold sea cools them uncomfortably, with no predators around, they can soon put that right by stretching out in the sun.
The lack of big predators has had an effect on all the animals of the Galapagos.
They reproduce freely, so populations increase rapidly.
And so, consequently, does evolutionary change.
But island tameness has dangers.
If a major predator does appear, then wildlife will be ill-equipped to defend itself.
And one did.
In the year 1535, the most successful predatory animal of all arrived.
By the beginning of the 17th century, the islands had become a haven for pirates.
By the 19th century, whalers and merchantmen were calling here regularly, and all these ships had a disastrous effect.
There is little or no fresh water on these islands, but they have a much rarer resource.
Giant tortoises can survive without food or water for very long periods, so ships could come here, collect the tortoises, stow them in the hold, and then after weeks at sea, bring one out, butcher it, and have a meal of fresh meat.
Slow, lumbering, and with no way of defending themselves, the tortoises were easy victims.
The population was decimated.
Between the 16th and 20th centuries, more than 100,000 were taken away and slaughtered.
And the ships brought other dangers.
They feasted on the tortoises eggs.
On the island of Pinzon rats consumed nearly every single egg, leaving the tortoise population on the brink of extinction.
But another island lost its tortoise population altogether.
Pinta, located on the shipping route around the northern fringe of the archipelago, was a favourite stopover for ships and their hungry crews.
And the unique Pinta tortoise was presumed extinct by the early 20th century.
But in 1972, an amazing discovery was made and filmed.
A living male Pinta tortoise was discovered in the undergrowth.
He was taken off to a protected enclosure on the main island, to live out his days in comfort and safety.
Here, he became an international celebrity, and he was given a name to reflect his state, Lonesome George.
He's about 80 years old, and he's getting a bit creaky in his joints As, indeed, am I.
He is arguably the rarest animal in the world.
Certainly, there can be none rarer, for he is the last of his kind.
His female died a long, long time ago.
When he dies, the Pinta species of Galapagos tortoise will be extinct.
But he is a very important animal.
Probably more than any other single creature, he's focused the attention of the world on the fragility of our environment, and he's stimulated science to look into whole new areas of research here in the Galapagos.
Just 14 days after we filmed Lonesome, he died in his sleep.
But he's not forgotten.
Lonesome George's story, like Darwin's fleeting but famous visit 200 years ago, has attracted many visitors to the islands.
Today, the archipelago is the basis of a multi-million dollar tourist industry.
30,000 people live here, in three small towns, and fleets of small boats take visitors on carefully-planned trips to see the islands' main sights.
It took animals and plants millions of years to find an colonize the Galapagos.
Now, new species of animals and plants of the world's continents can get here in a matter of hours And having got here, they often inadvertedly spread almost immediately through the islands.
Seeds of foreign plants hitch a ride on the air currents generated by passing traffic.
And the Galapagos' network of roads is now lined by foreign invaders.
Among them the common European blackberry.
A plant that can grow a centimeter a day, and create impenetrable thickets 4 meters thick.
They not only choke and kill native plants they even block the path of large animals, such as the tortoises.
Scientist are now trying to analyse the impact of human beings on the course of evolution in the islands.
And, surprisingly perhaps, the finches that Darwin made famous are still providing new insights.
Biologist Andrew Hendry is looking at how the finches' evolution may have been affected by human settlements.
When humans come into a new location, essentially what they do is change the environment, and that's changing selection that's acting on the populations.
Hendry is studying one particular species, the medium ground finch.
OK, yeah.
Remarkably, he's found that this finch, in its natural setting, is on the verge of dividing into two separate species.
The two are defined by the size of their beaks.
One is small, the other, large.
The difference between them has been caused by the types of food they eat.
So, if you feed on some small seed, you tend to have a small beak, and if you feed on large seed, you tend to have a really big beak and you tend to have a hard bite.
Remarkably, Hendry has found that among medium ground finches that live near human beings, the distinct big and small beak forms are getting fewer.
It's as if the two variants are here merging back into one.
The presence of human beings has stopped this finch from evolving.
We found that they feed a lot on human food, ranging from rice to fruit to grains to potato chips, and feeding on those types of different foods, doesn't really seem to matter what your beak size is any more.
So there isn't that pressure to have a small beak version and a large beak version and then there's no selection against those intermediate birds anymore.
There is plenty of food for them to eat.
So it seems like humans have caused a speciation reversal, they're fusing back together again as a result of human influences.
So, human beings can be just as much a part of nature as the forces that first shaped these islands and the organisms that live on them.
But human beings can not only destroy, they can conserve.
In the 1970s, the tortoise population reached an all-time low.
There were only a few thousand of them left.
But now, there's a major breeding programme for them.
The tortoise population today is increasing.
Once-threatened species have been brought back from the brink.
And scientists are discovering just how important and influential this reintroduction programme might be.
On Alcedo Volcano, home for the largest population of free-roaming giant tortoises, a study has shown that they're crucial to the health of all the surrounding wildlife.
Today there are some 15,000 tortoises on the Galapagos and they are an essential element in the islands' ecosystem.
One study in particular, has shown how important they are.
Biologist Steve Blake uses satellite tags to track their movements.
They reveal, to most people's great surprise, that the tortoises migrate over huge distances, from the depths of the crater, right up to the rim.
It's just phenomenal.
Why would a 600lb reptile migrate from sea level to up to 1,000 metres on some islands? From the air, the routes the tortoises take are clearly visible.
And they use the same highways, year after year.
One of the fundamental drivers of the migration seems to be food.
Tortoises tend to come to the highlands at the coolest time of year.
Up in the highlands, they can feed on a year-round, low-quality food source.
But then when the rains kick in, the lowlands tend to green up, and the tortoises go down there, probably to fatten up.
But Blake's studies reveal much more about the tortoises than just where they go.
They demonstrate the extraordinary effect that tortoises have on their surrounding environment.
They create special conditions that suit all kinds of other animals.
They shape and prune the landscape.
They disperse seeds, trample down the undergrowth, and trim the lowest branches of the bushes.
And all that allows seeds to germinate.
It disturbs insects, so that they can be gathered by hungry predators.
Their dung is also crucial to the survival of many other creatures.
Beetles lay their eggs in it, and their larvae grow fat on the nutriment that it still contains.
Tortoises are definitely the megaformers of the islands.
They are like the elephants of Galapagos They are out there in great numbers, they got big bodies, They creating myriad microhabitats for other species, They truly are half gardeners of Galapagos.
That's probably the best way to sum up their ecological role.
The implications are very important, they suggest that the reintroduction of tortoises to islands where their numbers have been seriously reduced could restore the richness of the whole environment.
We have the chance to bring back the full glory of these fragile ecosystems.
Today, unlike many other tropical islands elsewhere, 95% of Galapagos's biodiversity still survives.
And amazingly, new species are still being discovered.
One was found just 35 miles north of Alcedo, on the giant, little-visited volcano, Wolf.
To get to Wolf, you really need a helicopter.
It's one of the most hostile and least-explored parts of the whole archipelago.
There had been rumours of something strange living up on these remote, high slopes.
Something that lived in burrows, and only emerged every now and then to feed.
A scientific team went up to investigate.
What they discovered astonished everybody.
A completely new and unknown species of reptile.
A pink iguana.
Until now, it was thought that the Galapagos possessed only three species of iguana.
The black marine iguana, that lives on the seashore.
And two species of yellow iguana that live inland, feeding on cacti and other vegetation.
This land iguana is certainly the most closely related to the newly discovered one.
Genetic studies of the 100 or so individuals that make up this tiny population have shown that it diverged from its land iguana cousins more than 5 million years ago.
So, amazingly, it has been here just as long as the other two, but has remained unknown to science until now.
The discovery also means, that it is older than Wolf volcano, where it now lives.
And of course, there is another great mystery that no-one has yet explained.
Nobody knows why it's pink.
Could it be that to be pink up here brings something good? We don't know.
Maybe this was once spread widely over the island, and this is just the relic population that's left.
Again, we don't know.
But there's one thing that is quite certain, and that is that there's a lot we have yet to learn about the enchanted islands, and about the animals that have evolved here.
And of one thing, I have no doubt, Charles Darwin would be delighted.
In just a few million years, this empty expanse of ocean was transformed.
A series of volcanoes broke the surface and built the islands.
Against heavy odds, a few species managed to reach them.
They adapted to what they found, and so evolved into a multitude of new species.
Each new discovery we make gives Darwin's theory a greater relevance.
But beyond the strange plants and bizarre animals, there is a greater significance.
What we've learned here has given us a greater understanding of our planet.
This small group of islands has revealed in microcosm the processes that have shaped all life on Earth.
Missing parts added, corrections and BluRay sync by: Rie van de Buggy's
Previous Episode