Darwin's Dangerous Idea (2009) s01e03 Episode Script
Life and Death
ANDREW MARR: Our planet is in the middle of a mass extinction.
It's estimated that every hour three species are lost forever.
That's 70 a day, 500 a week, 27,000 species every year, which would make it the fastest rate of extinction in the Earth's history.
And there's no doubt about the cause, it's us.
150 years ago, Charles Darwin gave us the key to understanding the intricate connections between all life on Earth.
Remove or damage one part of the delicate web of life, and you can cause catastrophic consequences elsewhere.
But we have been reluctant to listen and slow to act.
In this programme, I'm going to discover how Darwin opened our eyes to the beautiful but fragile relationship between all life on Earth, how we've struggled to understand and accept the full implications of his legacy, and how Darwin has given us the knowledge we need to help avert one of the greatest disasters in the history of our planet.
We are causing mass extinctions, including, perhaps, our own, because we're not alone.
We are part of a great web of life, and if we wreck that web, we go, too.
The answers to this challenge aren't easy, but they're not impossible either.
Just so long as we at last understand the scale and the urgency of Charles Darwin's dangerous idea.
In 1832, aged just 23, Charles Darwin arrived here in Argentina on board the government survey ship, H.
M.
S.
Beagle.
In this wild, seemingly empty landscape, he would make one of his most significant discoveries.
When the Beagle dropped anchor near the small military outpost of BahÃa Blanca, Charles Darwin was deeply unimpressed.
He wrote in his diary, "I never saw any place before so entirely destitute "of living creatures.
" But this admittedly rather bleak beach had a surprise in store.
It would help Darwin unlock some of the mysteries of the natural world.
And these clues came not from the living, but from the dead.
Strolling along this battered cliff face, Darwin came across some gigantic fossilised bones.
This was a big moment for Darwin.
The next morning, he came rushing back to see if he could find some more fossils, and this time he really struck lucky.
He spotted something much more impressive and he spent three hours digging it out.
"To my great joy," he noted, "I found the skull of some large animal embedded in a soft rock.
" It looked to him like some kind of giant mammal, but he wasn't entirely sure.
"As far as I can judge," he wrote, "it is allied to the rhinoceros.
" But it was unlike any rhinoceros living at the time.
Darwin was thrilled by the thought that, just possibly, the giant bones might belong to an ancient, extinct species.
The idea of extinction was still quite new.
Most people thought it was the result of the great flood sent by God to punish man, as described in the Bible story of Noah's Ark.
Darwin doubted this.
The evidence in the rocks suggested that his fossil species had not been killed by a violent Biblical catastrophe.
They seemed to have died during a state of tranquillity.
He was starting to think extinction might be a regular fact of nature.
And he found new evidence everywhere he looked.
Mingled among the fossilised bones of extinct mammals, he found fossilised seashells.
And yet, they were the same species of sea creature he could see happily living in the water nearby.
So, why did some animals become extinct and others survive? Big question, and Darwin would chew it over for years to come.
Heading out with the gauchos, Darwin revelled in sleeping rough and living off the land.
In a letter home, he said that his experiences in Argentina were giving him a most strange assemblage of ideas.
Out on the Argentine Pampas, Darwin came into close contact with the local wildlife, and he was particularly fond of the plucky little armadillo, which, perhaps sadly, was often served up for dinner.
One evening, picking through the bones on his dinner plate, Darwin realised that they were uncannily similar to the giant fossilised bones he'd been digging out of the ground.
Darwin now saw that he had some kind of extinct armadillo in his fossil collection.
Only, one the size of a small horse.
He also thought he had fossils of giant llamas and sloths, which would have stood three metres tall.
Eureka! Darwin saw a clear link between his ancient fossils and the animals now living on the Pampas.
Darwin became increasingly excited by what he called, "This wonderful relationship between the dead and the living.
" Why were modern species so similar to extinct ones? What was the connection between the still living and the long dead? Darwin would return to these questions again and again.
During the rest of his five-year voyage on the Beagle, he saw many extraordinary things that fuelled his curiosity about the nature of life on Earth.
But it was his discoveries here in Argentina that first gave him the idea that extinction was a vital and necessary part of the process of evolution.
By the time he left Argentina, Darwin was asking all sorts of questions about life and death and survival and extinction.
He always said that what he discovered in South America was crucial to his understanding of, what was for him, the mystery of mysteries.
The origin of species.
There wasn't a lot of space aboard the Beagle, so Darwin sent his strange, giant fossils home to England, back to his former Cambridge tutor, the reverend John Henslow.
"I trust they will be recognised," he wrote.
And they were.
Henslow was so excited that in Darwin's absence he arranged for them to go on show.
Towards the end of his voyage, Darwin got a letter from his sister saying that his fossil discoveries were already making him famous.
Now even great minds need a bit of great PR, and Darwin had plenty.
Henslow was already whipping up excitement among the Cambridge dons by reading extracts from Darwin's letters, and a very famous geologist called Adam Sedgwick went to see his father to announce that Charles was about to take his place among the leading scientific figures.
By the time Darwin returned to England in October 1836, his fossils had indeed made him a scientific celebrity.
He rather liked the attention at first, but burdened by his thoughts about life, death and extinction, he soon began to retreat from the limelight.
He knew he had the seed of a dangerous idea, one that would undermine the Bible and Christian teaching.
The accepted belief was that species were fixed, unchanged and unchangeable since their creation by God.
But ever since his time abroad, Darwin was having vague doubts about the permanence of species, and he began to believe that one species does change into another, and that species which didn't change would become extinct.
At first, Darwin kept his most provocative thoughts to himself, but he couldn't quite keep his mouth shut.
He needed help to develop his theory and he turned to the botanist Joseph Dalton Hooker, who later became director of the Royal Botanic Gardens at Kew.
Darwin was a cautious man with a deep fear of public humiliation and rejection, but he felt to close Joseph Hooker, comfortable with him, and he began to give him the first details of his dangerous idea.
There's a letter to Hooker, in January 1844, which reveals Darwin's deep dread of the work he was engaged in.
"I am almost convinced," he wrote, "quite contrary to the opinion I first had, "that species are not immutable.
"They do change.
" And he confided, "It is like confessing a murder.
" Darwin suspected his theory of evolution would upset, even enrage, many fellow Victorians, and it was a tough message.
He saw that, in nature, only a tiny fraction of those born survived to produce offspring themselves.
He thought the natural forces limiting the chances of survival might also drive species to change.
Darwin saw that life was a struggle for existence, but that this struggle was a fight not just between individuals or even between species, but with the physical conditions of life.
The environment.
Those animals well-adapted to their environment would live and produce offspring and pass on their useful adaptations to the next generation.
Those not well-adapted would die.
Darwin believed he'd discovered the mechanism which drove evolutionary change.
He had, and it gave him a profound insight, one that would later lead us to a deeper understanding of our relationship with the environment.
He saw that all life is connected through the struggle for survival.
Relationships exist between members of the same species, between predator and prey, and between the living world and the physical environment.
Darwin wrote that all living things are bound together by a web of complex relations.
But Darwin was a cautious man and he spent the next 15 years gathering evidence to support his theory.
Unknown to Darwin, thousands of miles away in the jungles of Indonesia, an explorer and naturalist called Alfred Russel Wallace was soon wrestling with exactly the same ideas.
The two men could hardly have been more different.
Darwin was a wealthy member of the scientific élite.
Wallace struggled to make ends meet, often paying his way by collecting animals to sell to rich naturalists like Darwin.
During one of his expeditions, Wallace was struck down with malaria.
In February 1858, burning up with a malarial fever, Wallace was facing his own mortality.
Stuck out in a little hut in the middle of the jungle, he also began to ask why some die and some live, and he came to the conclusion that those animals capable of adapting to the changing conditions around them would survive, while unmodified creatures would die out and disappear.
Wallace recovered from his fever and then he wrote a letter to Charles Darwin.
Darwin was horrified, shaken to the core.
"All my originality will be smashed," he wrote.
Wallace had arrived at the same conclusion that Darwin had been sitting on for nearly 20 years.
Darwin's friends and allies urged him to finish his book as quickly as possible.
Faced with the threat of being pipped to the post, at last he found the courage to go public.
In November 1859, Darwin finally published his earth-shaker, On the Origin of Species.
Darwin ensured his place in world history by presenting to the public his laws of life, what became known as the theory of evolution by natural selection.
And Wallace, poor guy, became the forgotten man of evolution.
Just as Darwin feared, his book was greeted with outrage.
The uproar rested almost entirely on the suggestion that man is an animal, and that we are related to apes.
At the time, Darwin's vital insight into the intricate connections of life on Earth was almost entirely overlooked.
One of his most fervent supporters, a German scientist called Ernst Haeckel, did see behind the immediate shock headlines.
Darwin's ideas inspired him to define a whole new science.
He called it ecology and described it as the study of all those complex interrelations referred to by Darwin as the conditions of the struggle for existence.
For many decades to come, the science of ecology was hardly more than a word, but working away in the jungles of Indonesia, Alfred Russel Wallace was one of the first to witness the ecological implications of Darwin's web of interconnections.
Wallace agreed that extinction was a natural part of evolution, but as the Indonesian rainforests were felled to make way for tea plantations, Wallace began to see that extinction was something that could also be brought about when mankind interfered with what he called the nicely balanced relations of nature.
Decades ahead of his time, Alfred Russel Wallace warned that if ever mankind penetrated the recesses of the virgin forest, he would bring about the extinction of numerous forms of life.
Humanity now had the power to change the environment so fast that many ancient species would lose the struggle to survive.
Charles Darwin's awareness of the profound and surprising connections that exist between species was, to start with, pushed to one side, but for the rest of his life, he continued to explore these linkages in nature.
Darwin discovered that many species depend on each other with far-reaching implications for our own survival.
At the age of 72, just a year before his death, Darwin published his final book.
Its subject matter had captivated him for more than 40 years, most of them spent working here at Down House, his home in Kent.
Darwin's last book was about worms.
He gave it a catchy little title, The Formation of Vegetable Mould by the Action of Worms, With Observations on Their Habits.
Unlike Darwin's earlier work, his worm book was widely applauded and celebrated.
During his lifetime, it hugely outsold The Origin of Species.
In it, he wrote that, "The humble earthworm "has played a more important part in the history of the world "than most persons would at first suppose.
" Darwin conducted endless experiments on his garden worms, studying their anatomy and behaviour with fascination.
He revealed how earthworms carry out their stupendous work as nature's ploughmen.
He saw that worms prepare the ground, recycle nutrients and help the germination of seeds.
Darwin traced the impact of the humble earthworm and concluded that these little wrigglers play a vital role in our lives.
In his autobiography, Charles Darwin wrote that he was superior to the common run of men in noticing things which easily escape attention.
Even at the end of his life, his astute observations were giving us vital clues about how our survival depends on what he called an invisible web of complex relations.
Even the loss of an organism as apparently lowly as the earthworm would make large parts of this planet hostile to human survival.
Darwin's dangerous idea contained a vital insight into mankind's relationship with the world around us, and it came at an important moment in history.
Britain was changing very fast.
The look, sounds and smells of much of the country were being overwhelmed by the development of the steam engine and the rise of the factory system.
The Industrial Revolution was literally casting an ominous shadow over the environment.
By the 1880s, voices of concern were being raised, but not by scientists.
The artist, writer and Utopian socialist William Morris was among the leading Victorians to publicly question the benefits of industrialisation.
William Morris was enraged by the appalling living and working conditions being forced on the industrial working classes.
But he also had grave concerns about our changing relationship with nature.
"The latest danger civilisation is threatened with," he said, "is a danger of her own breeding.
" And in one of his famous lectures, he said that, "The beauty of the face of the Earth "was disappearing beneath a crust of unutterable grime.
" Morris campaigned to preserve the beauty of the countryside for the enjoyment of the working classes.
At this stage, Darwin's insights still hadn't been used to shed light on the wider impact of industrialisation.
Enter an amateur moth collector called James W.
Tutt.
He was about to apply Darwin's ideas to solve one of the great environmental mysteries of the industrial age.
James W.
Tutt was an enthusiastic Darwinist who devoted his life to the study of moths.
Devoted, enthusiastic, more than 900 articles, mainly on moths.
Twenty books, moths again.
But he's remembered for just one thing he noticed about one moth.
Biston betularia, or the peppered moth.
Peppered moths had excellent pale camouflage and were almost invisible on pale, lichen-covered trees.
But there was also a dark form of the moth.
This was much rarer than the pale variety, as it was easily spotted and eaten by birds.
By the mid-1800s, entomologists were puzzled by something strange.
In areas pumping out foul, sooty smoke, the darker form of the peppered moth had dramatically increased in number.
James Tutt noticed that the pale peppered moth stood out against the dark, soot-blackened trees, very conspicuous, easy for birds to pick off.
But the darker version was now very well camouflaged and it thrived and multiplied.
Tutt suggested that by polluting the environment, humanity was now directly affecting natural selection for the peppered moth.
By 1896, when Tutt published his book, British Moths, 98% of peppered moths in the polluted industrial north were black.
His study remains the classic textbook example of Darwinian selection in action.
Tutt had shown that by radically changing the environment, humanity had the power to change the course of evolution.
Charles Darwin understood that environmental change was a significant motor behind evolution.
"When a country undergoes some physical change," he wrote, "the original inhabitants must cease to be as perfectly adapted "to the changed conditions.
" But he thought this happened slowly.
What James Tutt had witnessed was a much faster process, now driven by us.
(ENGINE REVVING) By the early 20th century, we were just beginning to grasp the wider implications of Darwin's understanding of the web of life.
In the 1920s, a rebellious young zoologist called Charles Elton was one of the first to study the relationship between animal populations and the environment.
The science of ecology was at last about to come into its own.
In 1926, Elton set out with three colleagues and 20 mousetraps to begin a detailed study of the rodent population in Bagley Woods, near Oxford.
When Charles Elton came to check his traps on the first morning of the study, big disappointment.
Three mice, one vole.
But they were persistent fellows, he and his team, and over the next three years, they set 70,000 such traps and collected data on innumerable thousands of specimens.
They called themselves the Mouse Society.
Elton discovered that the size of the rodent population fluctuated with astounding regularity.
He saw how changes in the environment, such as weather, food availability and disease could directly affect the size of animal populations, and this could have highly disruptive impacts on the local ecology.
The rat is a public enemy.
He takes our food and endangers our health.
ANNOUNCER: If there are rats in your home or business premises, please let us know.
We can help you to rout the rat.
During the Second World War, the government turned to Elton for his knowledge of animal populations.
Their problem was that the huge food storage depots essential to the war effort were being overrun by rats and mice.
(SQUEAKING) They were eating the equivalent of a shipload of food every month.
Not what the ministry had planned for.
They drafted in Elton to help control the pest problem, and that set him thinking about what he called ecological explosions.
(SQUEAKING) Elton pointed out that by gathering so much food in one place, humans had changed the rats' normal environment, in this case, causing an explosion in numbers.
This wartime experience inspired Charles Elton to study population explosions around the world.
He saw that human activity could alter local environments, often with devastating and unpredictable effects.
He was the first to grasp the scale of man's impact on the web of life.
Elton spelt out the consequences of mankind's growing interference in the natural world.
He issued an early environmental warning cry.
"We are living in a period in the world's history," he wrote, "when the mingling of thousands of kinds of organisms "from different parts of the world is setting up "terrific dislocations in nature.
" And our impact on the planet was about to accelerate.
To increase food production after the Second World War, there was a massive expansion in intensive, mechanised farming.
This in turn caused an explosion of pests.
Scientists thought they'd come up with a fail-safe, high-tech answer.
Pesticide sprays! But in our attempts to manipulate nature, we were finally forced to come to terms with the full implications of Darwin's web of life.
In 1956, the United States' Department of Agriculture began spraying millions of acres with the chemical insecticide DDT.
DDT was dropped indiscriminately on ponds and waterways, livestock, even on children.
There were reports that one beekeeper lost 800 colonies of bees, and a horse seen drinking from its water trough was found dead hours later.
The local wildlife was devastated.
One ecologist called it "an amazing rain of death".
In the small town of West Southport, in Maine, a biologist called Rachel Carson received a letter from a friend telling her that all the birds in her garden had died soon after the sprayers had flown over.
Carson started investigating.
She discovered that the indiscriminate spraying of pesticides was killing not just pests, but insects beneficial to agriculture.
And that was just the start of the story.
We poison the caddis flies in the stream, and the poison travels from link to link of the food chain, and soon the birds of the lake margins become its victims, and the following springs are silent of robin song.
Rachel Carson was ill at the time.
She was fighting breast cancer, but she felt she had to do something about what she saw as an impending ecological catastrophe.
"I seem now to have, as writers should, "a sense of urgency and passing time," she wrote, "and so much to say.
" In 1962, Rachel Carson published one of the most influential books of the 20th century, Silent Spring.
Silent Spring was a surprise bestseller.
In it, Carson used Darwin's theory of evolution to explain the far-reaching effects of spraying DDT.
Using his key insight that animals adapt to changing environments, she came to a chilling conclusion.
Carson dug up the fact that the pest insects were developing a resistance to the insecticide, something she described as a triumphant vindication of Darwin's principle of survival of the fittest.
She pointed out that the insects had evolved super races immune to the particular insecticide used, so that a deadlier one has always to be developed, and then a deadlier one than that.
So this was an arms race against nature that man could never win.
Silent Spring triggered intense debate about the indiscriminate use of pesticides.
Many scientists from the chemical industry briskly rejected her findings.
The major claims in Ms Rachel Carson's book, Silent Spring, are gross distortions of the actual facts.
MARR: Carson was subjected to a sustained and personal attack.
Struggling with her own illness, she defended her discoveries with steely determination.
One U.
S.
Government scientist accused her of "reckless misinterpretation of the scientific facts".
And in a sinister echo of the McCarthy era, a politician simply branded her a communist.
The intensity of the attacks on Rachel Carson were compared directly to the assault on Charles Darwin when he published The Origin of Species.
The New York Times summed up the mood with a headline, "Silent Spring Is Now Noisy Summer.
" MARR: Not everyone rejected Carson's claims.
When asked at a press conference about the long-term effects of DDT, President John F.
Kennedy referred to Rachel Carson's work.
The U.
S.
Government then launched a full investigation.
Silent Spring was found to be a disturbingly accurate and, if anything, understated account of the situation.
Our eyes were finally opened to the urgency of Darwin's discoveries about the interconnections in nature.
Two years after Silent Spring was published, Rachel Carson died at the age of 56.
Decades on, her book is regarded as the original battle cry for the modern environmental movement.
COMMENTATOR: The rocket is beginning to rise agonisingly slowly, and here we go, we're on our way into space.
MARR: At the dawn of the 1960s, as we started to unlock the secrets of the solar system, Darwin's dangerous idea was about to go far out.
(ON RADIO) Oh, that view is tremendous.
MARR: In the small Wiltshire village of Bowerchalke, a scientist called James Lovelock was working freelance for NASA.
Studying data on the Martian atmosphere, Lovelock was exploring the possibility of life on the Red Planet.
The more Lovelock learned that Mars' atmosphere was hostile to life, the more amazed he became about our planet's ability to sustain life.
Working away in this cottage, what his bosses at NASA called his thatched lab, Lovelock began to wonder.
How was it that the Earth's atmosphere was able to sustain exactly the right composition of gasses over so many millions of years to allow life to flourish? His answer would propel Charles Darwin's ideas about life on Earth into the space age.
Darwin showed us how living organisms are connected to their local environment through the struggle for existence.
James Lovelock took this much further.
Describing his theory as an offshoot of Darwin's great vision, he believed that the vital connections existed also on a huge scale, right across the planet.
Ever since his school days, Lovelock had been inspired by Charles Darwin, but he was now uncovering a much deeper relationship between life and the planet than anything Darwin could have imagined.
Lovelock was developing a theory that the Earth as a whole was behaving like a self-regulating living organism.
He was the first to describe a global ecosystem.
Lovelock believed that plants and animals help regulate the physical environment of the Earth.
He called this biological feedback, and he suggested that the oceans, the land, the atmosphere and all living things form a vast, delicately balanced system of interconnections.
Lovelock was keen to share his ideas.
As it happened, one of his neighbours was the author, William Golding, who wrote Lord of the Flies.
The two men spent afternoons chatting about space research and science fiction.
One winter morning in 1967, James Lovelock was walking along on his way to the post office when he bumped into William Golding.
And he began excitedly to tell the novelist about his ideas of the Earth being a self-regulating entity.
Golding was impressed and he told Lovelock, "If you're going to propagate a large idea about the Earth, "you'd better give it a proper name.
" He thought back to the Greek goddess of the Earth and suggested "Gaia".
(ROCK MUSIC PLAYING) Lovelock's Gaia hypothesis was almost too much in keeping with the spirit of the age.
As the hippy movement swept through Europe and America, its followers seized his ideas and decided that the Earth herself was a living thing.
Along with free love and flower power, Gaia became a gospel of the hippy age, and it wasn't long before the world was to see Gaia in all her glory.
ANNOUNCER 1: The engines are on.
Four, three, two, one, zero.
- We have liftoff.
- ANNOUNCER 2: The clock is running.
MARR: On Christmas eve, 1968, the astronauts of Apollo 8 circled the moon and saw for the first time the Earth rising over the lunar landscape.
They read aloud the story of creation from Genesis, the first book of the Bible.
WILLIAM ANDERS: "In the beginning, God created the heaven and the earth.
"And the earth was without form, and void: "And darkness was upon the face of the deep.
"And God said, 'Let there be light'.
"And God saw that it was good.
" MARR: This one image proved to be a pivotal moment in the rise of environmentalism.
Here is everything we have.
We could now see with beautiful simplicity that we are all part of one world.
We are all connected.
For the first time, humankind was able to see our whole planet.
Lonely and isolated in the darkness of the cosmos, the pale blue dot that is our home looked fragile.
This image of earthrise made people look at the world in a new way.
It emphasised the Earth's vulnerability and it helped to create a new kind of politics, one which put the environment at its heart.
In the latter part of the 20th century, Darwin's knowledge of the relationships linking plants, animals and the physical environment would help us understand the impact we as a species are having on the whole planet.
One of the habitats where this is becoming most obvious is the coral reef.
And the first person to write a scientific study on coral reefs? Charles Darwin.
Darwin was not a good swimmer, but when he saw his first coral reefs, he waded in to get a closer look, and he described what he saw as "mountains of stone", much more impressive than the vast dimensions of the pyramids, and yet built by an infinite number of minute architects.
By studying coral reefs, Darwin would learn key lessons about the relationship between life and the rest of the planet.
Darwin spent nearly two years writing up a detailed paper about how the various types of coral reef are formed.
He concluded that corals only flourish in shallow water, building amazing reef structures by growing on top of the rocky skeletons of previous generations.
Charles Darwin discovered that coral reefs are intricate and finely balanced living systems.
He recognised that sunlight, temperature, even the chemical composition of the oceans regulate the growth of these dazzling underwater cities.
But he gave us this warning, "Changes to the composition of the sea "not obvious to our senses may destroy the coral reefs.
" Just sometimes, you wish he hadn't been such a damned fine prophet.
Coral reefs all over the world are now facing an uncertain future.
With our knowledge of the interconnected web of life, we not only know why it's happening, but also that their loss could have dire effects on our planet as a whole.
Back in the 1950s, here in the Caribbean, the biologist Thomas F.
Goreau was the first to understand that corals have evolved an astonishing partnership.
Microscopic algae growing inside corals provide them with energy by converting the sunlight into sugars.
In turn, the corals give the algae somewhere safe to live.
But Goreau observed that even small changes in the ocean environment cause the corals to expel their algae helpers.
The coral then loses its colour and begins a slow death, a process called coral bleaching.
Thomas Goreau Jr continued and expanded his father's work, and he made an ominous discovery.
Fluctuations in ocean temperature were causing coral bleaching all over the world.
Throughout the 1980s and the 1990s, mass coral bleaching was occurring everywhere where the ocean temperature had been raised for a considerable period.
Goreau's work showed that the coral reefs were the global warning system for global warming.
We're all too aware that global warming is being caused by the accumulation of greenhouse gases like carbon dioxide in the atmosphere.
For millions of years, coral reefs have played a vital role in countering this effect, absorbing carbon dioxide from the ocean and locking it away in their rocky skeletons.
Thomas Goreau Jr showed that Darwin's prophecy about the vulnerability of corals to environmental change is now established fact, and their function as a regulator of the Earth's surface temperature is also being compromised.
Of all the world's living systems, coral reefs are among the most sensitive, and if the planet's temperatures carry on rising, they will be the first of the global habitats to die out completely.
Now, if the planet cools, they can regenerate, but at the moment, they're being simply overwhelmed.
And this is more than a pity, because if we lose the corals, we also lose their ability to absorb and lock away carbon dioxide, and we lose it forever.
In the 150 years since Darwin shared his dangerous idea, scientists have made great progress in grasping its wider implications for life, death and extinction.
But while we've been struggling to comprehend his insight, our impact on the planet has hugely increased.
In the tropical rainforests, mankind's assault on nature is having a catastrophic effect.
Rainforests cover just 6% of our planet's surface, but they're home to at least half of all the species living on Earth.
There's the lush canopy above, the shadowy forest floor below and the dense, multilayered structure of astounding complexity in between.
When Charles Darwin first saw a tropical rainforest, he was overcome.
He spoke afterwards of feelings of wonder, astonishment and devotion.
Sounds almost as if he was having a spiritual experience.
In time, his own work on the interconnectedness of nature would help unlock the secrets of these extraordinary places.
They really are the boiling cauldrons of evolution.
For more than 100 million years, rainforests have survived geological upheavals and severe climate change.
And throughout this time, they've been home to the fastest rate of evolution on Earth.
But now rainforest plants and animals face extinction.
In 1971, a Berkeley University biology student called Norman Myers was studying the impact of human activity on the rate of animal extinction.
The textbooks told him that the estimated global rate of extinction was around one species per year.
This was the level that Darwin saw as a normal part of the evolutionary process.
No cause for alarm.
Lounging around outside one morning, Norman Myers was going through the statistics on extinctions, and he noticed a ludicrous omission.
The extinction figures gave the rates for mammals, plants and birds, which you might have thought was a pretty comprehensive group, but together they comprise just 4% of all known species.
The rest are insects and other invertebrates.
The vast majority of species on the planet, and their fate had been forgotten.
Myers investigated further.
He spent the rest of the day rechecking the official estimates of the extinction rate.
And then he made a new calculation, this time including invertebrates.
Myers' research tools, he said, "were a pencil, a pocket calculator and curiosity".
But in the right hands, a pencil can be devastating.
Myers' calculations showed that species weren't becoming extinct at the rate of roughly one a year, but more like the rate of one every day.
The Earth was going through something terrible.
Darwin proposed that there's a fine balance between extinction and the birth of new species.
But on five occasions in the Earth's history, the fossil record suggests the rate of extinction increased so much, it threatened the future of life on Earth.
We call these catastrophic episodes mass extinctions.
There are many theories about what caused them, from global cooling, incredible volcanic activity, cataclysmic meteor strikes.
But whatever the reason, each event resulted in the extinction of between 65 and 95% of all living species on Earth.
Myers was now suggesting that we are in the middle of the sixth mass extinction, and this one is being caused by us.
Norman Myers estimated that this new mass extinction was the fastest loss of species ever seen on the planet, and the greatest number of casualties was from tropical rainforests.
The rainforests were filled with an abundance of especially well-adapted species.
Myers knew from Darwin that if the forests were destroyed, these species would then be poorly adapted to their changed environment and they'd face rapid extinction.
(CHAINSAW WHIRRING) By the mid-1970s, nearly half of the world's virgin rainforests had already been destroyed.
Much of this was caused by clearing forests to raise cattle for the fast-food industry.
What Myers called the hamburger connection.
And the yearly rate of destruction was increasing.
Darwin's legacy was helping us to understand the consequences of our actions, but it was also giving the tools to help save the planet from the full impact of this man-made mass extinction.
In 1988, Norman Myers came up with a plan.
Myers discovered that there are some areas around the world that contain super-high concentrations of animal and plant species, and he worked out that if we could preserve those places, we had a chance of saving up to a third of the 10 million or so species now alive on Earth.
In effect, he was proposing a little fleet of Darwinian Noah's Arks.
Myers called these areas biodiversity hotspots.
He identified 25 of them around the world, including here, across the islands of the Caribbean.
His hotspots conservation strategy has attracted nearly a billion dollars in funding, but it will be many years before we can judge its success.
This visionary, optimistic experiment is based absolutely on Darwin's original work on the interconnectedness of all life.
If we remove the rainforests, we also lose their extraordinary, supercharged ability to produce new species.
One scientist put it like this, "Death is one thing.
The end of birth is something else.
" Over the last 150 years, the implications of Charles Darwin's dangerous idea have slowly but decisively transformed our understanding of the living world.
His theory of evolution first caused outrage by challenging the belief in God.
His description of the survival of the fittest was then hijacked to attack democratic ideals of equality.
But his ideas also highlighted the connection and interdependence between all living things and the Earth's environment.
This vital part of his legacy has been the most difficult for us to accept and understand, and now it is a matter of life and death.
It's taken 150 years for us to catch up with the full significance of Darwin's theory of evolution by natural selection.
If we want to prolong our own existence, we have to preserve the environment, the natural world inside which we live.
And it's that, not equality or the existence or not of God, that is the most urgent message from Darwin's essential idea.
We have to change our behaviour as a species.
If we don't, we now know what follows.
It's estimated that every hour three species are lost forever.
That's 70 a day, 500 a week, 27,000 species every year, which would make it the fastest rate of extinction in the Earth's history.
And there's no doubt about the cause, it's us.
150 years ago, Charles Darwin gave us the key to understanding the intricate connections between all life on Earth.
Remove or damage one part of the delicate web of life, and you can cause catastrophic consequences elsewhere.
But we have been reluctant to listen and slow to act.
In this programme, I'm going to discover how Darwin opened our eyes to the beautiful but fragile relationship between all life on Earth, how we've struggled to understand and accept the full implications of his legacy, and how Darwin has given us the knowledge we need to help avert one of the greatest disasters in the history of our planet.
We are causing mass extinctions, including, perhaps, our own, because we're not alone.
We are part of a great web of life, and if we wreck that web, we go, too.
The answers to this challenge aren't easy, but they're not impossible either.
Just so long as we at last understand the scale and the urgency of Charles Darwin's dangerous idea.
In 1832, aged just 23, Charles Darwin arrived here in Argentina on board the government survey ship, H.
M.
S.
Beagle.
In this wild, seemingly empty landscape, he would make one of his most significant discoveries.
When the Beagle dropped anchor near the small military outpost of BahÃa Blanca, Charles Darwin was deeply unimpressed.
He wrote in his diary, "I never saw any place before so entirely destitute "of living creatures.
" But this admittedly rather bleak beach had a surprise in store.
It would help Darwin unlock some of the mysteries of the natural world.
And these clues came not from the living, but from the dead.
Strolling along this battered cliff face, Darwin came across some gigantic fossilised bones.
This was a big moment for Darwin.
The next morning, he came rushing back to see if he could find some more fossils, and this time he really struck lucky.
He spotted something much more impressive and he spent three hours digging it out.
"To my great joy," he noted, "I found the skull of some large animal embedded in a soft rock.
" It looked to him like some kind of giant mammal, but he wasn't entirely sure.
"As far as I can judge," he wrote, "it is allied to the rhinoceros.
" But it was unlike any rhinoceros living at the time.
Darwin was thrilled by the thought that, just possibly, the giant bones might belong to an ancient, extinct species.
The idea of extinction was still quite new.
Most people thought it was the result of the great flood sent by God to punish man, as described in the Bible story of Noah's Ark.
Darwin doubted this.
The evidence in the rocks suggested that his fossil species had not been killed by a violent Biblical catastrophe.
They seemed to have died during a state of tranquillity.
He was starting to think extinction might be a regular fact of nature.
And he found new evidence everywhere he looked.
Mingled among the fossilised bones of extinct mammals, he found fossilised seashells.
And yet, they were the same species of sea creature he could see happily living in the water nearby.
So, why did some animals become extinct and others survive? Big question, and Darwin would chew it over for years to come.
Heading out with the gauchos, Darwin revelled in sleeping rough and living off the land.
In a letter home, he said that his experiences in Argentina were giving him a most strange assemblage of ideas.
Out on the Argentine Pampas, Darwin came into close contact with the local wildlife, and he was particularly fond of the plucky little armadillo, which, perhaps sadly, was often served up for dinner.
One evening, picking through the bones on his dinner plate, Darwin realised that they were uncannily similar to the giant fossilised bones he'd been digging out of the ground.
Darwin now saw that he had some kind of extinct armadillo in his fossil collection.
Only, one the size of a small horse.
He also thought he had fossils of giant llamas and sloths, which would have stood three metres tall.
Eureka! Darwin saw a clear link between his ancient fossils and the animals now living on the Pampas.
Darwin became increasingly excited by what he called, "This wonderful relationship between the dead and the living.
" Why were modern species so similar to extinct ones? What was the connection between the still living and the long dead? Darwin would return to these questions again and again.
During the rest of his five-year voyage on the Beagle, he saw many extraordinary things that fuelled his curiosity about the nature of life on Earth.
But it was his discoveries here in Argentina that first gave him the idea that extinction was a vital and necessary part of the process of evolution.
By the time he left Argentina, Darwin was asking all sorts of questions about life and death and survival and extinction.
He always said that what he discovered in South America was crucial to his understanding of, what was for him, the mystery of mysteries.
The origin of species.
There wasn't a lot of space aboard the Beagle, so Darwin sent his strange, giant fossils home to England, back to his former Cambridge tutor, the reverend John Henslow.
"I trust they will be recognised," he wrote.
And they were.
Henslow was so excited that in Darwin's absence he arranged for them to go on show.
Towards the end of his voyage, Darwin got a letter from his sister saying that his fossil discoveries were already making him famous.
Now even great minds need a bit of great PR, and Darwin had plenty.
Henslow was already whipping up excitement among the Cambridge dons by reading extracts from Darwin's letters, and a very famous geologist called Adam Sedgwick went to see his father to announce that Charles was about to take his place among the leading scientific figures.
By the time Darwin returned to England in October 1836, his fossils had indeed made him a scientific celebrity.
He rather liked the attention at first, but burdened by his thoughts about life, death and extinction, he soon began to retreat from the limelight.
He knew he had the seed of a dangerous idea, one that would undermine the Bible and Christian teaching.
The accepted belief was that species were fixed, unchanged and unchangeable since their creation by God.
But ever since his time abroad, Darwin was having vague doubts about the permanence of species, and he began to believe that one species does change into another, and that species which didn't change would become extinct.
At first, Darwin kept his most provocative thoughts to himself, but he couldn't quite keep his mouth shut.
He needed help to develop his theory and he turned to the botanist Joseph Dalton Hooker, who later became director of the Royal Botanic Gardens at Kew.
Darwin was a cautious man with a deep fear of public humiliation and rejection, but he felt to close Joseph Hooker, comfortable with him, and he began to give him the first details of his dangerous idea.
There's a letter to Hooker, in January 1844, which reveals Darwin's deep dread of the work he was engaged in.
"I am almost convinced," he wrote, "quite contrary to the opinion I first had, "that species are not immutable.
"They do change.
" And he confided, "It is like confessing a murder.
" Darwin suspected his theory of evolution would upset, even enrage, many fellow Victorians, and it was a tough message.
He saw that, in nature, only a tiny fraction of those born survived to produce offspring themselves.
He thought the natural forces limiting the chances of survival might also drive species to change.
Darwin saw that life was a struggle for existence, but that this struggle was a fight not just between individuals or even between species, but with the physical conditions of life.
The environment.
Those animals well-adapted to their environment would live and produce offspring and pass on their useful adaptations to the next generation.
Those not well-adapted would die.
Darwin believed he'd discovered the mechanism which drove evolutionary change.
He had, and it gave him a profound insight, one that would later lead us to a deeper understanding of our relationship with the environment.
He saw that all life is connected through the struggle for survival.
Relationships exist between members of the same species, between predator and prey, and between the living world and the physical environment.
Darwin wrote that all living things are bound together by a web of complex relations.
But Darwin was a cautious man and he spent the next 15 years gathering evidence to support his theory.
Unknown to Darwin, thousands of miles away in the jungles of Indonesia, an explorer and naturalist called Alfred Russel Wallace was soon wrestling with exactly the same ideas.
The two men could hardly have been more different.
Darwin was a wealthy member of the scientific élite.
Wallace struggled to make ends meet, often paying his way by collecting animals to sell to rich naturalists like Darwin.
During one of his expeditions, Wallace was struck down with malaria.
In February 1858, burning up with a malarial fever, Wallace was facing his own mortality.
Stuck out in a little hut in the middle of the jungle, he also began to ask why some die and some live, and he came to the conclusion that those animals capable of adapting to the changing conditions around them would survive, while unmodified creatures would die out and disappear.
Wallace recovered from his fever and then he wrote a letter to Charles Darwin.
Darwin was horrified, shaken to the core.
"All my originality will be smashed," he wrote.
Wallace had arrived at the same conclusion that Darwin had been sitting on for nearly 20 years.
Darwin's friends and allies urged him to finish his book as quickly as possible.
Faced with the threat of being pipped to the post, at last he found the courage to go public.
In November 1859, Darwin finally published his earth-shaker, On the Origin of Species.
Darwin ensured his place in world history by presenting to the public his laws of life, what became known as the theory of evolution by natural selection.
And Wallace, poor guy, became the forgotten man of evolution.
Just as Darwin feared, his book was greeted with outrage.
The uproar rested almost entirely on the suggestion that man is an animal, and that we are related to apes.
At the time, Darwin's vital insight into the intricate connections of life on Earth was almost entirely overlooked.
One of his most fervent supporters, a German scientist called Ernst Haeckel, did see behind the immediate shock headlines.
Darwin's ideas inspired him to define a whole new science.
He called it ecology and described it as the study of all those complex interrelations referred to by Darwin as the conditions of the struggle for existence.
For many decades to come, the science of ecology was hardly more than a word, but working away in the jungles of Indonesia, Alfred Russel Wallace was one of the first to witness the ecological implications of Darwin's web of interconnections.
Wallace agreed that extinction was a natural part of evolution, but as the Indonesian rainforests were felled to make way for tea plantations, Wallace began to see that extinction was something that could also be brought about when mankind interfered with what he called the nicely balanced relations of nature.
Decades ahead of his time, Alfred Russel Wallace warned that if ever mankind penetrated the recesses of the virgin forest, he would bring about the extinction of numerous forms of life.
Humanity now had the power to change the environment so fast that many ancient species would lose the struggle to survive.
Charles Darwin's awareness of the profound and surprising connections that exist between species was, to start with, pushed to one side, but for the rest of his life, he continued to explore these linkages in nature.
Darwin discovered that many species depend on each other with far-reaching implications for our own survival.
At the age of 72, just a year before his death, Darwin published his final book.
Its subject matter had captivated him for more than 40 years, most of them spent working here at Down House, his home in Kent.
Darwin's last book was about worms.
He gave it a catchy little title, The Formation of Vegetable Mould by the Action of Worms, With Observations on Their Habits.
Unlike Darwin's earlier work, his worm book was widely applauded and celebrated.
During his lifetime, it hugely outsold The Origin of Species.
In it, he wrote that, "The humble earthworm "has played a more important part in the history of the world "than most persons would at first suppose.
" Darwin conducted endless experiments on his garden worms, studying their anatomy and behaviour with fascination.
He revealed how earthworms carry out their stupendous work as nature's ploughmen.
He saw that worms prepare the ground, recycle nutrients and help the germination of seeds.
Darwin traced the impact of the humble earthworm and concluded that these little wrigglers play a vital role in our lives.
In his autobiography, Charles Darwin wrote that he was superior to the common run of men in noticing things which easily escape attention.
Even at the end of his life, his astute observations were giving us vital clues about how our survival depends on what he called an invisible web of complex relations.
Even the loss of an organism as apparently lowly as the earthworm would make large parts of this planet hostile to human survival.
Darwin's dangerous idea contained a vital insight into mankind's relationship with the world around us, and it came at an important moment in history.
Britain was changing very fast.
The look, sounds and smells of much of the country were being overwhelmed by the development of the steam engine and the rise of the factory system.
The Industrial Revolution was literally casting an ominous shadow over the environment.
By the 1880s, voices of concern were being raised, but not by scientists.
The artist, writer and Utopian socialist William Morris was among the leading Victorians to publicly question the benefits of industrialisation.
William Morris was enraged by the appalling living and working conditions being forced on the industrial working classes.
But he also had grave concerns about our changing relationship with nature.
"The latest danger civilisation is threatened with," he said, "is a danger of her own breeding.
" And in one of his famous lectures, he said that, "The beauty of the face of the Earth "was disappearing beneath a crust of unutterable grime.
" Morris campaigned to preserve the beauty of the countryside for the enjoyment of the working classes.
At this stage, Darwin's insights still hadn't been used to shed light on the wider impact of industrialisation.
Enter an amateur moth collector called James W.
Tutt.
He was about to apply Darwin's ideas to solve one of the great environmental mysteries of the industrial age.
James W.
Tutt was an enthusiastic Darwinist who devoted his life to the study of moths.
Devoted, enthusiastic, more than 900 articles, mainly on moths.
Twenty books, moths again.
But he's remembered for just one thing he noticed about one moth.
Biston betularia, or the peppered moth.
Peppered moths had excellent pale camouflage and were almost invisible on pale, lichen-covered trees.
But there was also a dark form of the moth.
This was much rarer than the pale variety, as it was easily spotted and eaten by birds.
By the mid-1800s, entomologists were puzzled by something strange.
In areas pumping out foul, sooty smoke, the darker form of the peppered moth had dramatically increased in number.
James Tutt noticed that the pale peppered moth stood out against the dark, soot-blackened trees, very conspicuous, easy for birds to pick off.
But the darker version was now very well camouflaged and it thrived and multiplied.
Tutt suggested that by polluting the environment, humanity was now directly affecting natural selection for the peppered moth.
By 1896, when Tutt published his book, British Moths, 98% of peppered moths in the polluted industrial north were black.
His study remains the classic textbook example of Darwinian selection in action.
Tutt had shown that by radically changing the environment, humanity had the power to change the course of evolution.
Charles Darwin understood that environmental change was a significant motor behind evolution.
"When a country undergoes some physical change," he wrote, "the original inhabitants must cease to be as perfectly adapted "to the changed conditions.
" But he thought this happened slowly.
What James Tutt had witnessed was a much faster process, now driven by us.
(ENGINE REVVING) By the early 20th century, we were just beginning to grasp the wider implications of Darwin's understanding of the web of life.
In the 1920s, a rebellious young zoologist called Charles Elton was one of the first to study the relationship between animal populations and the environment.
The science of ecology was at last about to come into its own.
In 1926, Elton set out with three colleagues and 20 mousetraps to begin a detailed study of the rodent population in Bagley Woods, near Oxford.
When Charles Elton came to check his traps on the first morning of the study, big disappointment.
Three mice, one vole.
But they were persistent fellows, he and his team, and over the next three years, they set 70,000 such traps and collected data on innumerable thousands of specimens.
They called themselves the Mouse Society.
Elton discovered that the size of the rodent population fluctuated with astounding regularity.
He saw how changes in the environment, such as weather, food availability and disease could directly affect the size of animal populations, and this could have highly disruptive impacts on the local ecology.
The rat is a public enemy.
He takes our food and endangers our health.
ANNOUNCER: If there are rats in your home or business premises, please let us know.
We can help you to rout the rat.
During the Second World War, the government turned to Elton for his knowledge of animal populations.
Their problem was that the huge food storage depots essential to the war effort were being overrun by rats and mice.
(SQUEAKING) They were eating the equivalent of a shipload of food every month.
Not what the ministry had planned for.
They drafted in Elton to help control the pest problem, and that set him thinking about what he called ecological explosions.
(SQUEAKING) Elton pointed out that by gathering so much food in one place, humans had changed the rats' normal environment, in this case, causing an explosion in numbers.
This wartime experience inspired Charles Elton to study population explosions around the world.
He saw that human activity could alter local environments, often with devastating and unpredictable effects.
He was the first to grasp the scale of man's impact on the web of life.
Elton spelt out the consequences of mankind's growing interference in the natural world.
He issued an early environmental warning cry.
"We are living in a period in the world's history," he wrote, "when the mingling of thousands of kinds of organisms "from different parts of the world is setting up "terrific dislocations in nature.
" And our impact on the planet was about to accelerate.
To increase food production after the Second World War, there was a massive expansion in intensive, mechanised farming.
This in turn caused an explosion of pests.
Scientists thought they'd come up with a fail-safe, high-tech answer.
Pesticide sprays! But in our attempts to manipulate nature, we were finally forced to come to terms with the full implications of Darwin's web of life.
In 1956, the United States' Department of Agriculture began spraying millions of acres with the chemical insecticide DDT.
DDT was dropped indiscriminately on ponds and waterways, livestock, even on children.
There were reports that one beekeeper lost 800 colonies of bees, and a horse seen drinking from its water trough was found dead hours later.
The local wildlife was devastated.
One ecologist called it "an amazing rain of death".
In the small town of West Southport, in Maine, a biologist called Rachel Carson received a letter from a friend telling her that all the birds in her garden had died soon after the sprayers had flown over.
Carson started investigating.
She discovered that the indiscriminate spraying of pesticides was killing not just pests, but insects beneficial to agriculture.
And that was just the start of the story.
We poison the caddis flies in the stream, and the poison travels from link to link of the food chain, and soon the birds of the lake margins become its victims, and the following springs are silent of robin song.
Rachel Carson was ill at the time.
She was fighting breast cancer, but she felt she had to do something about what she saw as an impending ecological catastrophe.
"I seem now to have, as writers should, "a sense of urgency and passing time," she wrote, "and so much to say.
" In 1962, Rachel Carson published one of the most influential books of the 20th century, Silent Spring.
Silent Spring was a surprise bestseller.
In it, Carson used Darwin's theory of evolution to explain the far-reaching effects of spraying DDT.
Using his key insight that animals adapt to changing environments, she came to a chilling conclusion.
Carson dug up the fact that the pest insects were developing a resistance to the insecticide, something she described as a triumphant vindication of Darwin's principle of survival of the fittest.
She pointed out that the insects had evolved super races immune to the particular insecticide used, so that a deadlier one has always to be developed, and then a deadlier one than that.
So this was an arms race against nature that man could never win.
Silent Spring triggered intense debate about the indiscriminate use of pesticides.
Many scientists from the chemical industry briskly rejected her findings.
The major claims in Ms Rachel Carson's book, Silent Spring, are gross distortions of the actual facts.
MARR: Carson was subjected to a sustained and personal attack.
Struggling with her own illness, she defended her discoveries with steely determination.
One U.
S.
Government scientist accused her of "reckless misinterpretation of the scientific facts".
And in a sinister echo of the McCarthy era, a politician simply branded her a communist.
The intensity of the attacks on Rachel Carson were compared directly to the assault on Charles Darwin when he published The Origin of Species.
The New York Times summed up the mood with a headline, "Silent Spring Is Now Noisy Summer.
" MARR: Not everyone rejected Carson's claims.
When asked at a press conference about the long-term effects of DDT, President John F.
Kennedy referred to Rachel Carson's work.
The U.
S.
Government then launched a full investigation.
Silent Spring was found to be a disturbingly accurate and, if anything, understated account of the situation.
Our eyes were finally opened to the urgency of Darwin's discoveries about the interconnections in nature.
Two years after Silent Spring was published, Rachel Carson died at the age of 56.
Decades on, her book is regarded as the original battle cry for the modern environmental movement.
COMMENTATOR: The rocket is beginning to rise agonisingly slowly, and here we go, we're on our way into space.
MARR: At the dawn of the 1960s, as we started to unlock the secrets of the solar system, Darwin's dangerous idea was about to go far out.
(ON RADIO) Oh, that view is tremendous.
MARR: In the small Wiltshire village of Bowerchalke, a scientist called James Lovelock was working freelance for NASA.
Studying data on the Martian atmosphere, Lovelock was exploring the possibility of life on the Red Planet.
The more Lovelock learned that Mars' atmosphere was hostile to life, the more amazed he became about our planet's ability to sustain life.
Working away in this cottage, what his bosses at NASA called his thatched lab, Lovelock began to wonder.
How was it that the Earth's atmosphere was able to sustain exactly the right composition of gasses over so many millions of years to allow life to flourish? His answer would propel Charles Darwin's ideas about life on Earth into the space age.
Darwin showed us how living organisms are connected to their local environment through the struggle for existence.
James Lovelock took this much further.
Describing his theory as an offshoot of Darwin's great vision, he believed that the vital connections existed also on a huge scale, right across the planet.
Ever since his school days, Lovelock had been inspired by Charles Darwin, but he was now uncovering a much deeper relationship between life and the planet than anything Darwin could have imagined.
Lovelock was developing a theory that the Earth as a whole was behaving like a self-regulating living organism.
He was the first to describe a global ecosystem.
Lovelock believed that plants and animals help regulate the physical environment of the Earth.
He called this biological feedback, and he suggested that the oceans, the land, the atmosphere and all living things form a vast, delicately balanced system of interconnections.
Lovelock was keen to share his ideas.
As it happened, one of his neighbours was the author, William Golding, who wrote Lord of the Flies.
The two men spent afternoons chatting about space research and science fiction.
One winter morning in 1967, James Lovelock was walking along on his way to the post office when he bumped into William Golding.
And he began excitedly to tell the novelist about his ideas of the Earth being a self-regulating entity.
Golding was impressed and he told Lovelock, "If you're going to propagate a large idea about the Earth, "you'd better give it a proper name.
" He thought back to the Greek goddess of the Earth and suggested "Gaia".
(ROCK MUSIC PLAYING) Lovelock's Gaia hypothesis was almost too much in keeping with the spirit of the age.
As the hippy movement swept through Europe and America, its followers seized his ideas and decided that the Earth herself was a living thing.
Along with free love and flower power, Gaia became a gospel of the hippy age, and it wasn't long before the world was to see Gaia in all her glory.
ANNOUNCER 1: The engines are on.
Four, three, two, one, zero.
- We have liftoff.
- ANNOUNCER 2: The clock is running.
MARR: On Christmas eve, 1968, the astronauts of Apollo 8 circled the moon and saw for the first time the Earth rising over the lunar landscape.
They read aloud the story of creation from Genesis, the first book of the Bible.
WILLIAM ANDERS: "In the beginning, God created the heaven and the earth.
"And the earth was without form, and void: "And darkness was upon the face of the deep.
"And God said, 'Let there be light'.
"And God saw that it was good.
" MARR: This one image proved to be a pivotal moment in the rise of environmentalism.
Here is everything we have.
We could now see with beautiful simplicity that we are all part of one world.
We are all connected.
For the first time, humankind was able to see our whole planet.
Lonely and isolated in the darkness of the cosmos, the pale blue dot that is our home looked fragile.
This image of earthrise made people look at the world in a new way.
It emphasised the Earth's vulnerability and it helped to create a new kind of politics, one which put the environment at its heart.
In the latter part of the 20th century, Darwin's knowledge of the relationships linking plants, animals and the physical environment would help us understand the impact we as a species are having on the whole planet.
One of the habitats where this is becoming most obvious is the coral reef.
And the first person to write a scientific study on coral reefs? Charles Darwin.
Darwin was not a good swimmer, but when he saw his first coral reefs, he waded in to get a closer look, and he described what he saw as "mountains of stone", much more impressive than the vast dimensions of the pyramids, and yet built by an infinite number of minute architects.
By studying coral reefs, Darwin would learn key lessons about the relationship between life and the rest of the planet.
Darwin spent nearly two years writing up a detailed paper about how the various types of coral reef are formed.
He concluded that corals only flourish in shallow water, building amazing reef structures by growing on top of the rocky skeletons of previous generations.
Charles Darwin discovered that coral reefs are intricate and finely balanced living systems.
He recognised that sunlight, temperature, even the chemical composition of the oceans regulate the growth of these dazzling underwater cities.
But he gave us this warning, "Changes to the composition of the sea "not obvious to our senses may destroy the coral reefs.
" Just sometimes, you wish he hadn't been such a damned fine prophet.
Coral reefs all over the world are now facing an uncertain future.
With our knowledge of the interconnected web of life, we not only know why it's happening, but also that their loss could have dire effects on our planet as a whole.
Back in the 1950s, here in the Caribbean, the biologist Thomas F.
Goreau was the first to understand that corals have evolved an astonishing partnership.
Microscopic algae growing inside corals provide them with energy by converting the sunlight into sugars.
In turn, the corals give the algae somewhere safe to live.
But Goreau observed that even small changes in the ocean environment cause the corals to expel their algae helpers.
The coral then loses its colour and begins a slow death, a process called coral bleaching.
Thomas Goreau Jr continued and expanded his father's work, and he made an ominous discovery.
Fluctuations in ocean temperature were causing coral bleaching all over the world.
Throughout the 1980s and the 1990s, mass coral bleaching was occurring everywhere where the ocean temperature had been raised for a considerable period.
Goreau's work showed that the coral reefs were the global warning system for global warming.
We're all too aware that global warming is being caused by the accumulation of greenhouse gases like carbon dioxide in the atmosphere.
For millions of years, coral reefs have played a vital role in countering this effect, absorbing carbon dioxide from the ocean and locking it away in their rocky skeletons.
Thomas Goreau Jr showed that Darwin's prophecy about the vulnerability of corals to environmental change is now established fact, and their function as a regulator of the Earth's surface temperature is also being compromised.
Of all the world's living systems, coral reefs are among the most sensitive, and if the planet's temperatures carry on rising, they will be the first of the global habitats to die out completely.
Now, if the planet cools, they can regenerate, but at the moment, they're being simply overwhelmed.
And this is more than a pity, because if we lose the corals, we also lose their ability to absorb and lock away carbon dioxide, and we lose it forever.
In the 150 years since Darwin shared his dangerous idea, scientists have made great progress in grasping its wider implications for life, death and extinction.
But while we've been struggling to comprehend his insight, our impact on the planet has hugely increased.
In the tropical rainforests, mankind's assault on nature is having a catastrophic effect.
Rainforests cover just 6% of our planet's surface, but they're home to at least half of all the species living on Earth.
There's the lush canopy above, the shadowy forest floor below and the dense, multilayered structure of astounding complexity in between.
When Charles Darwin first saw a tropical rainforest, he was overcome.
He spoke afterwards of feelings of wonder, astonishment and devotion.
Sounds almost as if he was having a spiritual experience.
In time, his own work on the interconnectedness of nature would help unlock the secrets of these extraordinary places.
They really are the boiling cauldrons of evolution.
For more than 100 million years, rainforests have survived geological upheavals and severe climate change.
And throughout this time, they've been home to the fastest rate of evolution on Earth.
But now rainforest plants and animals face extinction.
In 1971, a Berkeley University biology student called Norman Myers was studying the impact of human activity on the rate of animal extinction.
The textbooks told him that the estimated global rate of extinction was around one species per year.
This was the level that Darwin saw as a normal part of the evolutionary process.
No cause for alarm.
Lounging around outside one morning, Norman Myers was going through the statistics on extinctions, and he noticed a ludicrous omission.
The extinction figures gave the rates for mammals, plants and birds, which you might have thought was a pretty comprehensive group, but together they comprise just 4% of all known species.
The rest are insects and other invertebrates.
The vast majority of species on the planet, and their fate had been forgotten.
Myers investigated further.
He spent the rest of the day rechecking the official estimates of the extinction rate.
And then he made a new calculation, this time including invertebrates.
Myers' research tools, he said, "were a pencil, a pocket calculator and curiosity".
But in the right hands, a pencil can be devastating.
Myers' calculations showed that species weren't becoming extinct at the rate of roughly one a year, but more like the rate of one every day.
The Earth was going through something terrible.
Darwin proposed that there's a fine balance between extinction and the birth of new species.
But on five occasions in the Earth's history, the fossil record suggests the rate of extinction increased so much, it threatened the future of life on Earth.
We call these catastrophic episodes mass extinctions.
There are many theories about what caused them, from global cooling, incredible volcanic activity, cataclysmic meteor strikes.
But whatever the reason, each event resulted in the extinction of between 65 and 95% of all living species on Earth.
Myers was now suggesting that we are in the middle of the sixth mass extinction, and this one is being caused by us.
Norman Myers estimated that this new mass extinction was the fastest loss of species ever seen on the planet, and the greatest number of casualties was from tropical rainforests.
The rainforests were filled with an abundance of especially well-adapted species.
Myers knew from Darwin that if the forests were destroyed, these species would then be poorly adapted to their changed environment and they'd face rapid extinction.
(CHAINSAW WHIRRING) By the mid-1970s, nearly half of the world's virgin rainforests had already been destroyed.
Much of this was caused by clearing forests to raise cattle for the fast-food industry.
What Myers called the hamburger connection.
And the yearly rate of destruction was increasing.
Darwin's legacy was helping us to understand the consequences of our actions, but it was also giving the tools to help save the planet from the full impact of this man-made mass extinction.
In 1988, Norman Myers came up with a plan.
Myers discovered that there are some areas around the world that contain super-high concentrations of animal and plant species, and he worked out that if we could preserve those places, we had a chance of saving up to a third of the 10 million or so species now alive on Earth.
In effect, he was proposing a little fleet of Darwinian Noah's Arks.
Myers called these areas biodiversity hotspots.
He identified 25 of them around the world, including here, across the islands of the Caribbean.
His hotspots conservation strategy has attracted nearly a billion dollars in funding, but it will be many years before we can judge its success.
This visionary, optimistic experiment is based absolutely on Darwin's original work on the interconnectedness of all life.
If we remove the rainforests, we also lose their extraordinary, supercharged ability to produce new species.
One scientist put it like this, "Death is one thing.
The end of birth is something else.
" Over the last 150 years, the implications of Charles Darwin's dangerous idea have slowly but decisively transformed our understanding of the living world.
His theory of evolution first caused outrage by challenging the belief in God.
His description of the survival of the fittest was then hijacked to attack democratic ideals of equality.
But his ideas also highlighted the connection and interdependence between all living things and the Earth's environment.
This vital part of his legacy has been the most difficult for us to accept and understand, and now it is a matter of life and death.
It's taken 150 years for us to catch up with the full significance of Darwin's theory of evolution by natural selection.
If we want to prolong our own existence, we have to preserve the environment, the natural world inside which we live.
And it's that, not equality or the existence or not of God, that is the most urgent message from Darwin's essential idea.
We have to change our behaviour as a species.
If we don't, we now know what follows.