Darwin's Dangerous Idea

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 Bahía 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