Original subtitles

PROFESSOR BRIAN COX: J1 2009 a new specles of spider was identified.

A spider with superpowers.

It was named exactly 150 years

after the publication of Darwin's On the Origin of Species,

in which he explained why life on Earth is so diverse and so complex.

Darwin's theory of evolution by natural selection

Was built on the work of naturalists

who were discovering thousands of new species across the world.

That process of finding species new to scilence and naming them

continues to this day and it's recognised

in the name of this newly-discovered arachnid.

Darwin's bark spider.

The spider occupies a unigue niche.

It can hunt where no other spider can.

That spider creates the largest webs found anywhere on Earth.

And in order to do that, it has to produce the strongest silk

of any spider, and it can span over 25 metres across lakes and rivers.

And, actually, no one knows how they get their webs

across such a large distance.

But Darwin's bark spider is Just one of thousands of unigue species

of animals and plants that you find in Madagascar.

The rainforests here

are öone of the most bio-diverse places on the planet.

And each year, more discoveriles are made,

as researchers try to understand

why this tiny corner of the universe is so prolific.

ALI of these living things were found within a five-minute walk

of this field station.

And the diversity is remarkable.

There's a chameleon there.

These are orchids.

This big green leaf is a Travellers Palm.

There are four species of mushroom on that branch alone.

Across Madagascar there are over 14,000 species of plants.

There are hundreds of species of mammals and birds and reptiles.

And over 9096 of them are unigue to this island.

(CHIRPING)

Now, how could it be that so many diverse living things

so beautifully adapted to their environment

could have emerged from a universe

that's governed by a simple set of natural laws?

The fact that we know the answer to that guestion

is one of the greatest achievements in science.

And in this film I want to explore how these endless forms most beautiful

have emerged from a lifeless cosmos.

Africa,

a whole continent full of creatures utterly different

from those in Madagascar.

But the diversity of life doesn't stop at what you see,

because within each individual

lies another hidden world of complexity.

(CUBS GROWLING)

This, believe it or not, is the top predator in Africa.

Or she will be when she's older. She's only about eight weeks old now.

Her body is built from a host of different molecules.

And by far the most diverse group are known as proteins.

You can see the proteins here. Those claws,

so vital to the lion's survival,

-are made of a protein called keratin. -(GROWLING)

Her eyes, also absolutely vital for her survival,

have a protein called opsin

which is bound to a pigment to make structures called rhodopsins,

which allow her to see in colour

and also allow her to see very well at night when she's hunting.

There are also proteins in her muscles. (CHUCKLES)

Myosin and actin. These are the things that allow her to run away.

The proteins in a lion come in countless different forms.

But they all share something in common -

a backbone of carbon.

An atom that's able to form long complex molecules.

Of all the 92 elements, there really is only one

that has that appetite for bonding its four electrons

to share them with other molecules.

Carbon will share those electrons with nitrogen, with oxygen, with hydrogen,

and, critically, with other carbons

to bulild up these immensely complex chains,

the amino acids and the proteins which are the building blocks oflife.

(GROWLING)

So to understand our planet's endless diversity,

we must begin by considering this life-giving element.

I've got a few scratches now because of you.

Because of your proteins.

After all, to build a lion, you must first build carbon.

And that's a story that stretches back to a time long before

there were even stars in the universe.

(EXPLOSION)

Thirteen and a half billion years ago,

Just a few hundred million years after the Big Bang,

the universe was a carbon-free zone.

An infinite sterile gloom of hydrogen and helium clouds.

Until one day,

those vast clouds began to collapse under the force of gravity.

(EXPLOSION)

And long before the solar system, Farth or life existed,

the first stars were born.

The birth of the first stars

did much more than just illuminate the universe,

because that set in train a seguence of events

which ultimately is necessary for the existence of life in the universe.

And we can still see that process

playing out in the universe today.

This is the brand-new South African Large Telescope.

(MAN SPEAKING AFRIKAANS)

İts mirror is 11 metres wide,

making it the largest optical telescope in the Southern Hemisphere.

And it recently helped to pin down what's happening in an object

some 650 million light years from Farth.

This beautiful, almost lifelike system

is known simply as The Bird.

It's the spectacular result of what we used to think

were two galaxies colliding.

İt's events happening in the head of The Bird that are most interesting

from the perspective of life in the universe,

because the head is formed by another galaxy,

a third galaxy, an island of billions and billions of stars

colliding with the two galaxies that form the wings and the body

at a speed of around 250 miles a second.

Now, the turbulence, the disturbance that that creates

is causing many new stars to be formed.

(RUMBLING)

These stars begin their lives by burning hydrogen

to produce ever more helium.

But as they age, as the hydrogen runs out,

they turn to this helium.

The temperature at their core rises,

increasing the chances of three helium nuclei fusing together

to form a new elemeni, carbon.

That process has been going on

for almost the entire history of the universe, back 15 billion years.

And it's the formation of stars that is the vital first step

in the formation of life,

because stars produce the heavy elements in the universe, including carbon.

(EXPLOSION)

From the universe's earliest times,

carbon has been created inside ageing stars.

And over time, this carbon has built up, drifting through the cosmos as dust.

Until some of it was caught up in the formation of a planet called Farth.

And it's here that we can see this ancient carbon brought vividiy to life.

Today the universe is old enough that countless stars have lived and died.

And so there's been plenty of time

to synthesise the primordial hydrogen and helium into the heavy elements.

The guestion now is how does that carbon get into the web oflife?

Well, today it enters via one ingredient,

and I'm gonna measure İt using this balloon.

The ingredient is carbon dioxide,

which plays a key role in photosynthesis.

Fach night, the carbon dioxide concentration increases,

filling the air around the leaves at the top of the trees.

Now, this balloon has a carbon dioxide monitor in it which is going to measure

the change in the levels of CO2

at the top of the forest canopy as night turns to day.

As the sun rises, the trees begin to photosynthesise.

Now, at 6pm last night, so just after sunset,

the concentration was around 350 parts per million.

Around 10pm, so four hours after sunset,

the concentration had risen to about 400 parts per million.

And now, at about midday, the concentration

is back down to about three, four, five parts per million.

So that's a variation over a period of 18 hours

of, what, arocund 1096 in the concentration of carbon dioxide

Just in that piece of atmosphere at the top of the forest canopy.

So what you're seeing there is photosynthesis in action.

Every day, across the planet, photosynthesis uses sunlight

to turn carbon dioxide and water into simple sugars.

The overwhelming majority of the carbon is locked up inside long chains

of sugar molecules called cellulose and lignin.

Now, lignin is the stuff that gives wood its strength.

So in this form, and remember, that is most ofit,

it is very difficult indeed for animals to access.

For the energy and nutrients locked away

inside these long carbon chains

to move through the food web, they must be broken down.

And the best place to see that process in action is out on the open plain.

It's one vast larder for all manner of organisms.

But by far the most effective harvester of carbon

is actually one of the smallest creatures on the savannah.

Termites are social insects, working together to form a characteristic sight

seen all over the bush.

That's a termite mound, actually it's a tip of the iceberg.

The termite city extends way beyond that, underground.

And its function is fascinating.

İt's essentially an air-conditioning system.

What it does is maintain very specific conditions inside the mound,

the conditions of the rainforest.

When the termites first colonised the savannah some 30 million years ago,

they brought their rainforest with them

to support a form of life

that was already wonderfully adapted to living off dead wood.

This is what these termite mounds are all about.

Can you see those structures there? Those white honeycomb-like structures?

Those are called fungal combs.

They're wood pulp and possibly bits of dead grass

that the termites bring in and build into that structure.

And the reason the conditions have to be the same as the rainforest

is because they grow a particular genus of fungus

called Zermitomyces around those honeycombs.

The job of that fungus

is to break down the lignin and the cellulose inside the wood

and convert it into a form that the termites can eat.

Which actually you can see there, they're the little white nodules

Just present on the honeycomb structure.

The termites lack the enzymes to break down the wood efficiently,

so they've become farmers,

tending to öone giant social stomach.

So there's a very intense relationship between the termites and the fungus.

You don't find that fungus anywhere else, actually,

in the world, as far as we know,

other than inside termite mounds.

And it's thought that up to 9096 of the carbon locked up in lignin

in this part of Africa is released back into the food chain again

solely by those termites and that fungus.

So the termites deal with most of the lignin.

But that still leaves a vast store of carbon in the form of cellulose.

Across Africa, herds of mammals graze on grasses and leaves,

turning this cellulose into meat.

Many are a iype of mammal known as a ruminant.

The largest of which is öne of the easiest animals to spot on safari.

MAN: Giraffe there as well.

Giraffes live off a diet that's similar to termites.

They eat cellulose.

Primarily, actually, the tops of the acacia trees that you see here,

scattering the African savannah. And they face that same problem,

they've got to break those difficult carbon bonds down.

And they've come up with a very similar solution,

which is to cultivate bacteria and fungi.

But they do it inside their stomachs, and ruminants, like giraffes,

have had to build a very complex system in order to do that.

They've got four stomachs.

One of them contains their culture of bacteria and fungi,

and they allow them to digest that difficult cellulose.

Even with all this hardware,

ruminants must feed for over two-thirds of the day.

But there are other creatures here that have found a shortcut.

After all, if plant fibres are hard to digest,

why not let someone else do the work and simply steal a meal?

He's coming for us.

Oh, my God!

(ENGİNE STARTING)

Look what we've just found.

We were out looking for giraffe this morning,

we've found about 10 of them Just over there.

But, in looking for the giraffe, we've just found a leopard.

This is one of the top predators out here.

He's got very little to fear, apart from other leopards and maybe lions.

He's having a good look. He certainly doesn't care about us.

He's around two years old and, at the moment,

he doesn't have his own territory, he's too young for that.

And so he is İying low.

(ENGİNE STARTING)

He'll have to make about two kills a week

to stay in good condition, so maybe he'd catch an impala

every three or four days.

And he's obviously doing that

because look at him. (CHUCKLES)

Now he's looking for protein.

And I'm alittle bit worried because I'm protein.

-0Oh, wow! -MAN: It's that boom.

He's after the boom

He's coming really close to us

because he's after the soundman's boom pole.

Which he's... Oh.

It's...(CHUCKLES) That's incredible.

(WHISPERING INDISTINCTLY)

(LAUGHS)

From its origin in the death of stars...

its capture by plants...

through insects, mammals and on...

the carbon cycle is the real circle of life.

(DISTANT ROAR)

Out there tonight,

the relentless recycling of carbon through the food chain will continue.

As night falls, you can almost sense it,

the change in the sounds and the atmosphere.

Some will die so that others can live,

as carbon leaps from branch to branch across the great tree of life.

And guülding it on its way is just one very special form of chemistriy.

Every living thing is just a temporary home for carbon atoms

that existed long before there was life on Earth

and will exist long after Africa and Earth are gone.

But the pattern of life, the information needed to build

a zebra or a tree

or a human being or alion persists.

İt's passed on from generation to generation in a molecule,

a helical molecule with a backbone of carbon, called DNA.

There was a time when Farth appeared empity.

(# ATMOSPHERE BY JOY DIVISION)

Yet despite appearances, 3.8 billion years ago

life was already underway in the form of tiny living specks

that probabiy all shared the same biochemistıy.

We know that every living thing on the planet today,

so every piece of food you eat, every animal you've seen,

everyone you've ever known or will know,

in fact, every living thing that will ever exist on this planet

was descended from that one speck.

We call it the last universal common ancestor, or LUCA.

So, just as the universe had its origin at the Big Bang,

all life on this planet had its origin in that one moment.

Lless than a billion years after its formation,

there was already life on Farth.

(THUNDER RUMBLING)

İt's possible that some of it used biochemistry

utterly different from the life we see today.

If so, it has long been extinct.

İt's also possible that the first life may not have been cellular,

just living chemistry in the porous rocks of some ancient ocean.

We're not sure.

But what's certain is that öone day a population of organisms showed up

With biochemistry that we would recognise.

This was LUCA,

the first expression of a form of life that would, in time,

throw up a group of humans who left their mark in this part of Africa.

Now, we don't know what LUCA looked like.

We don't know precisely where it lived or how it lived.

But we do know this,

if you start to trace my ancestral line back to my parents, to their parents,

to their parents, to their parents,

all the way back through geological timescales

over hundreds of thousands and millions and billions of years,

there will be an unbroken line from me all the way back to LUCA.

We know that, because every living thing on the planet today

shares the same biochemistry.

We all have DNA.

İt's made of the same bases - A, C Tand G.

They code for the same amino acids.

Those amino acids build the same proteins

which do very similar jobs, whether you're a plant, a bacterium

or a bipedal hominid like me.

So all life uses the same fundamental biology.

Those four bases, A, C€ Gand I,

which code for just 20 amino acids,

which in turn build each and every oöne of life's proterins.

Be you bacteria, plant, bug or beasi,

your design comes from your DNA.

So it's this molecule that must hold the key

to understanding why life today is so diverse.

We now know that the answer to the guestion,

"Why is life on Earth so varied?"

is actually the answer to the guestion,

"Why is the DNA molecule itself so varied?"

What are the natural processes

that cause the structure of DNA to change?

Well, part of the answer actually doesn't lie on Earth at all.

It lies up there amongst the stars.

And I can show you what I mean, using this, which is a cloud chamber,

a piece of apparatus that has a unigue place in the history of physics.

I'm gonna cool it down using dry ice,

frozen carbon dioxide,

jJust below minus 70 degrees Celsius.

-T'll put the top on. -(GLASS CREAKING)

-(SOUEALING) -Hear that?

That's the metal at the bottom of the tank cooling down very rapidliy

to minus 70.

The cloud chamber works by having

a super-saturated vapour of alcohol inside the chamber.

Plenty on there.

Now, I want to get that alcohol,

I want to boil it off to get the vapour into the chamber.

So I'm gonna put a hot-water bottle on top.

I mean, this is the first genuine particle physics detector.

İt's the piece of apparatus that first saw anti-matter.

And it really does consist only of a fish tank,

some alcohol, a bit of paper, and a hot-water bottle.

There, look at that.

You see that cloud, that vapour trail?

That's a cosmic ray.

That was initiated by a particle,

probably a proton, that hit the Earth's atmosphere.

It almost certainly originated outside our solar system

and was accelerated by the magnetic fields of our galaxy.

It may even have begun its life beyond our galaxy.

(EXPLOSION)

Now, imagine if one of those hits the DNA of aliving thing.

What that will do is cause a mutation.

That mutation may be detrimental, or, very, very occasionally,

it might be beneficial.

And I think it's gulte wonderful to imagine

that maybe one of the key mutations

that was selected for over the millennia,

that led to some trait in me,

was caused by some particle that began its life, perhaps,

in a massive supernova explosion,

perhaps outside our galaxy,

and went and hit the DNA of something

and caused some kind of beneficial mutation.

We don't know, but you can dream, can't you?

Mutations are an inevitable part of living on a planet like Farth.

They're the first hint at how DNA,

and the genes that code for every living thing,

change from generation to generation.

(MONKEYS HOWL)

Mutations are the spring

from which innovation in the living world flows.

But cosmic rays are not the only way in which DNA can be altered.

There's natural background radiation from the rocks,

there's the action of chemicals and free radicals.

There can be errors when the code is copied.

And then all those changes can be shuffled by sex,

and, indeed, whole pieces of the code

can be transferred from species to specles.

So, bit by bit,

in tiny steps from generation to generation,

the code is, constantly, randomly changing.

Now, whilst there's no doubt

that random mutation does alter DNA,

evolution is anything but random.

It can't be, because the chances of something with DNA as complex as this

appearing by luck alone are vanishingly small.

Imagine you just changed one position

in the code at random, a random mutation.

There are four letters - A,T, C, andG-

so there are four possible combinations.

If there are two places in the code,

there are four combinations for each one.

So that makes 16.

If there are three, then there are 64 possibilities.

By the time you get to a code with 150 letters in it,

then there are more possible combinations in the code

than there are atoms in the observable universe.

Now, a hippo has a code

with around three billion different letters.

So, the number of combinations of those letters,

their chances of producing that code at random

are absolutely infinitesimally small.

İt's impossible.

(SNORTING)

So there must be a non-random element to evolution,

a natural process, which greatly restricts

this universe of possibilities and shapes the outcome.

We call it natural selection.

And to see it in action,

let's return to where we began,

on the island of Madagascar.

Around 65 million years ago,

a group of seafarers were nearing the end of a long journey

across the Indian Ocean.

These were accidental travellers, a group of creatures from Africa

trapped on a natural raft and carried by the ocean currents.

The land they found was virgin, green territory.

Plants, insects, reptiles and birds had established themselves.

But there were none of their own kind.

They were caught up in a sağa that tellis of the great shifting

of Farth's continental plates.

İt's impossible to understand the diversity of life on Earth today

without understanding the shifting geography of our planet.

See, here's a map

of the Southern Hemisphere as it was 150 million years ago,

and you see it's dominated by a single land mass called Gondwana.

And then, 90 million years ago,

Gondwana had begun to break up,

to separate into something

that looks guite recognisably like Africa,

and these two islands -

Madagascar and India.

Now, subseguentiy, India has drifted northwards

and bumped into Eurasla, raising the Himalayas.

But, crucially,

Madagascar has remained isolated.

İt's been an iİsland surrounded by ocean

for almost 90 million years.

So, when those seafarers arrived on their raft

of trees and twigs and leaves, they had a blank canvas.

This two, three, maybe even a single pregnant, individuals,

had a whole island to roam across.

And over 65 million years,

they have blossomed into hundreds and thousands of individuals

and become Madagascar's most iconic animals.

(LEMUR SHRLEKING IN DISTANCE)

Finding the descendants of those ancient mariners is not easy.

But local gurde Joseph has been tracking them for years

and he's going to help me find them.

(LEMUR SHRLIEKING)

There, at the top of the tree, is an İndri,

which is the largest lemur in Madagascar.

And...

it's Just sat there watching us... guletly at the moment.

This lemur here is a very special lemur.

He has a name. He's called David.

After Sir David Attenborough.

(LEMUR SHRLIEKING)

(WHISPERING) Now, we could only do this

because Joseph has spent a lot of time with these lemurs,

so they trust him.

And therefore, it seems, they trust me.

Such enormous hands.

The reason, it's thought, that...

we find lemurs here in Madagascar, and Madagascar alone,

is because there are no simians.

There are no chimpanzees, none of my ancestral family

dating back tens of millions of years to out-compete them.

So, what's thought happened is that,

around 65 million years ago,

one of the lemurs' ancestors

managed to sail across the Mozambigue Channel and landed here.

There were none of those competitors here,

and so the lemurs have flourished ever since.

There are now over 90 species of lemur...

or subspecies, in Madagascar.

And no species...

of my lineage - the simians.

(LEMUR SHRLIEKING)

Över a vast sweep of time,

the lemurs have diversified

to fill all manner of different habitats.

From the arid spiny forests of the south,

to the rocky canyons in the north.

There is something about this island

that is allowing the lemurs' DNA to change

in the most amaziıng ways.

We're on the hunt for an aye-aye,

the most-closely related of all the surviving lemurs

to their common ancestor.

(INDISTINCTI CHATTER)

MAN: Right there.

-(WHISPERING) Oh, yeah, yeah. -MAN: Yeah, yeah.

COX: Oh, yeah.

I just shone the light up and saw these absolutely...

two bright, bright red eyes shining out.

She's very high up in her own little nest.

I don't want to lose sight of her in this forest,

which is very dark and dense.

The team have located a female aye-aye and her son.

They want to attach radio collars to track their movements

and better understand how far they range through these forests.

But first they must sedate them with a dart.

(MAN SPEAKING NATIVE DIALECT)

He's waiting for it to come down low enough to get that clean shot.

I mean, how you get a clean shot...

in this, I have no idea.

(INDISTINCTI CHATTER)

After two hours of traipsing through the treacherous forest,

the aye-ayes remain at large.

(OVERLAPPING CHATTER, LAUGHTER)

MAN: Oh, yeah!

Well, here is the aye-aye that was tranguilised last night.

They finally got her about half an hour after we left.

Ithink it was probably because we were disturbing her.

Apparently, as soon as we'd gone, she came down the tree

and she was tranguilised.

And, as you can see, she's pretty well sedated now,

which is fortunate for me because she has certain adaptations

that I wouldn't like to be deployed.

You can see there... her teeth.

Her teeth are very unusual for a primate.

In fact, unigue, because they carry on growing.

So she's much more like a rodent in that respect.

And that's so she can gnaw into wood.

You see, aye-ayes have filled a unigue niche on Madagascar.

İt's a niche that's filled by woodpeckers

in many other areas of the world.

What she does is she feeds on grubs and bugs inside trees.

And to do that, she has several unigue adaptations,

of which the teeth are one.

The most startling

is this central finger here. It's bizarre.

İt's got a ball and socket joint, for a start,

so İit has complete 360-degree movement.

It feels to me almost as İf it's broken, butit isn't.

İt's just, you can move İt around in any direction.

And she uses that finger, initially, to tap on the trunk of the tree.

And then listening to the echo from that tapping

with these huge ears, she can detect where the grubs are.

And then she gnaws through the wood

with those rodent-like teeth.

And then uses this finger again

to reach inside the hole

and get the bugs out.

So the guestion is, why?

How could an animal be so precisely adapted

to a particular lifestyle?

She's waking up now.

And the answer is,

natural selection.

See, what must have happened is, way back,

when the ancestors of the lemurs, the lemuriforms, arrived in Madagascar,

there must have been a mutation that...

lengthened the middle finger ever so slightly of one of those lemurs.

And that must have given it an advantage.

That must have allowed it, perhaps,

to reach into little holes and search for grubs.

There's some reason why that lengthened middle finger

meant that that gene was more likely to be passed to the next generation

and then down to the next generation.

So that landscape of possibilities is narrowed.

İt's narrowed because that gene persists.

And it's persisted now for at least 40 million years,

because this species has been on one branch of the tree of life now

for over 40 million years.

And so, over those years,

that middle finger has got more and more speclalised.

Natural selection has allowed the aye-aye's wonderfully mutated finger

to spread through the population.

And this same law applies to all life.

If you have a mutation that helps you in the struggle to survive,

you are more likely to leave more offspring.

And, in the next generation,

that mutation is more likely to survive.

So this animal is a beautiful example,

probably one of the best in the world,

of how the sieve of natural selection

produces animals that are perfectly adapted

to live in their environment.

Now, there are many reasons to study the aye-aye.

But here's a good one.

In the 1970s it was thought the aye-aye was extinct.

Now we know there are several thousand

in the forests of Madagascar - five, six, seven thousand.

Certainly less than 10, 000.

But over the last 50 years, 5096 of this forest has vanished.

This is an animal that's been around as a species

for over 40 million years.

So, it's important to know

how these animals are doing

and how they're surviving in this diminishing habitat.

Whilst natural selection explains how the aye-aye evolvedi,

it alone can't explain how a small group of individuals

over 60 million years ago

gave rise to over 90 different species of lemur today.

But there is another form of life

that can offer us a clue.

Up here in the high forest canopy,

we're in a very different environment to the one down there

on the forest floor.

İt's a more arid environment,

it's almost like a desert.

İt's exposed to the sun, water is harder to come by.

And so this is a sea

of different niches

that are able to be occupied and exploited

by animals that are different

to the ones you'll find down there on the floor.

So, in a very real sense,

this is an island, an island to be colonised.

And sure enough,

there are settlers to be found even here.

You see that thing that looks like a muddy ball there on the branch?

Well, that's an ant's nest.

It's home to a species of Crematogaster ants,

that are unigue, not only to Madagascar,

but to the forest canopy.

You see, what makes those ants unigue

is that they can build their own nests.

There are very few species of ants that can do that.

So, that is an island,

that is a niche,

and it's allowed that species of ants to develop

because they're isolated from the rest of the ecosystem.

And, astonishingly, within this niche,

another form of life, new to science, has been discovered.

A beetle that manages to survive here unharmed by the ants.

How it does it is a mystery.

But what is known

is that this particular species has only ever been found

inside these nests.

So, that really is its own mini ecosystem

with species living in it that are unigue to that island.

We live on an ever-shifting dynamic world

that creates islands in abundance.

Farth's mountain ranges,

river valleys and canyons all create islands for life.

And it's these islands

that those ancestors of the lemurs found when they arrived in Madagascar.

Empty niches, where populations became isolated.

And, over great swathes of time,

evolved into such wonderfully diverse forms.

(CHİLDREN CHATTERIİNG)

A hundred and fifty years on from the Origin of Species,

the subtlety and beauty of Darwin's insight

is still revealing itself to us.

It describes how our beautiful complex tree of life has grown

from a once-desolate universe.

The chemistry of carbon

allows for the existence of a molecule that is able to replicate itself

and pass information on from generation to generation.

There can be random changes in the structure of that molecule,

mutations,

and they're tested by their interaction

with the environment and otherliving things.

The ones that pass that test survive

and the ones that fail that test are lost.

The separation and isolation of living things onto islands,

which may be physical like Madagascar,

or just the single branch of a single tree,

results in speciation,

the explosion of living forms,

highly specialised to occupy niches within niches.

And this is the explanation

for the diversity of life on Earth.

There is grandeur in this view of life, as Darwin wrote,

and understanding how it happened

surely only adds to the wonder.

As precise as Einstein's theorles of relativity,

and as profound as thermodynamics,

Darwin has given us another universal law -

evolution by natural selection.

And if evolution is the law on this island,

then it will apply throughout the cosmos.

Which begs a big guestion.

Could there be other trees of life most beautiful

amongst the stars?

In 2011 we discovered a rocky planet

orbiting around a distant star with daytime temperatures

not too dissimilar to those found on Earth.

Now, there must be millions,

if not billions, of such planets out there in the universe.

And it's inconcelivable to me

that none of them will have trees of life

as complex or even more complex than our own.

But that doesn't devalue the existence of our tree,

because our tree İs unigue.

It consists of thousands of branches,

all interdependent on thousands of others,

and the precise structure depends on chance events,

like the passage of the lemurs across the ocean 65 million years ago.

So when you go outside tomorrow,

just take a look at a little piece of your world,

in a corner of your garden, or a park,

or even the grass that's growing in a crack in the pavement,

because there will be life there and it will be unigue.

There will be nowhere like that anywhere else in the universe.

And that makes our tree,

from the sturdiest branch to the most fragile twig,

indescribably valuable.

(# ÜNDERNEATH THE STARS BY KATE RUSBY)