BBC.Wonders.of.Life.3of5.Endless.Forms.Most.Beautiful
BBC.Wonders.of.Life.3of5.Endless.Forms.Most.Beautiful
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00:00In 2009, a new species of spider was identified.
00:28A spider with superpowers.
00:35It was named exactly 150 years after the publication of Darwin's On the Origin of Species,
00:50in which he explained why life on earth is so diverse and so complex.
00:55Darwin's theory of evolution by natural selection was built on the work of naturalists who were
01:09discovering thousands of new species across the world.
01:12That process of finding species new to science and naming them continues to this day,
01:22and it's recognised in the name of this newly discovered arachnid.
01:28Darwin's bark spider.
01:35The spider occupies a unique niche. It can hunt where no other spider can.
01:44That spider creates the largest webs found anywhere on earth,
01:48and in order to do that, it has to produce the strongest silk of any spider.
01:52They can span over 25 metres across lakes and rivers,
01:57and actually no one knows how they get their webs across such a large distance.
02:09But Darwin's bark spider is just one of thousands of unique species of animals and plants
02:15that you find in Madagascar.
02:18The rainforests here are one of the most biodiverse places on the planet.
02:31And each year, more discoveries are made as researchers try to understand why
02:36this tiny corner of the universe is so prolific.
02:42All of these living things were found within a five-minute walk of this field station,
02:46and the diversity is remarkable.
02:50There's a chameleon there.
02:52These are orchids. This big green leaf is a traveller's palm.
02:56There are four species of mushroom on that branch alone.
03:07Across Madagascar, there are over 14,000 species of plants.
03:12There are hundreds of species of mammals and birds and reptiles,
03:16and over 90% of them are unique to this island.
03:31How could it be that so many diverse living things,
03:35so beautifully adapted to their environment,
03:38could have emerged from a universe that's governed by a simple set of natural laws?
03:47The fact that we know the answer to that question
03:49is one of the greatest achievements in science.
03:53And in this film, I want to explore how these endless forms,
03:57most beautiful, have emerged from a lifeless cosmos.
04:46Africa, a whole continent full of creatures
04:50utterly different from those in Madagascar.
04:59But the diversity of life doesn't stop at what you see,
05:03because within each individual lies another hidden world of complexity.
05:16This, believe it or not, is the top predator in Africa.
05:19It's a huge predator.
05:21It's a huge predator.
05:22It's a huge predator.
05:24It's a huge predator.
05:25It's a huge predator.
05:27It's a huge predator.
05:28It's a huge predator.
05:29It's a huge predator.
05:31It's a huge predator.
05:32It's a huge predator.
05:34It's a huge predator.
05:35It's a huge predator.
05:37It's a huge predator.
05:38It's a huge predator.
05:40It's a huge predator.
05:41It's a huge predator.
05:42It's a huge predator.
05:44It's a huge predator.
05:46It's a huge predator.
05:49Left to Torres is the Perugian tortoise T.
05:55T.
05:56T.
05:58T.
05:59The tortoise bites people and Tom as well.
06:02T.
06:03T.
06:05And then one more.
06:06T.
06:07T.
06:08T.
06:10T.
06:11T.
06:13T.
06:14have a protein called opsin which is bound to a pigment to make structures called rhodopsins
06:20which allow her to see in colour and also allow her to see very well at night when she's hunting.
06:29There are also proteins in her muscles,
06:33myosin and actin which are the things that allow her to run away.
06:45The proteins in a lion come in countless different forms
06:51but they all share something in common, a backbone of carbon,
06:59an atom that's able to form long complex molecules.
07:03Of all the 92 elements there really is only one that has that appetite for bonding its four
07:10electrons to share them with other molecules. Carbon will share those electrons with nitrogen,
07:17with oxygen, with hydrogen and critically with other carbons to build up these immensely complex
07:25chains, the amino acids and the proteins which are the building blocks of life.
07:31So to understand our planet's endless diversity we must begin by considering this life-giving
07:37element. I've got a few scratches now because of you, because of your proteins.
07:46After a week or so, I'm going to have a look at a few of the proteins in the lion's body.
07:51After all, to build a lion you must first build carbon and that's a story that stretches back
07:58to a time long before there were even stars in the universe.
08:10Thirteen and a half billion years ago, just a few hundred million years after the big bang,
08:16just a few hundred million years after the big bang, the universe was a carbon-free zone.
08:25An infinite sterile gloom of hydrogen and helium clouds
08:31until one day those vast clouds began to collapse under the force of gravity.
08:36And long before the solar system, earth or life existed, the first stars were born.
09:07The birth of the first stars did much more than just illuminate the universe,
09:12because that set in train a sequence of events
09:16which ultimately is necessary for the existence of life in the universe.
09:28And we can still see that process playing out in the universe today.
09:37This is the brand new South African Large Telescope.
09:48Its mirror is 11 meters wide, making it the largest optical telescope in the southern hemisphere.
09:56And it recently helped to pin down what's happening in an object
10:00some 650 million light years from earth.
10:07This beautiful, almost lifelike system is known simply as the bird.
10:15It's the spectacular result of what we used to think were two galaxies colliding.
10:25It's events happening in the head of the bird that are most interesting
10:28from the perspective of life in the universe,
10:30because the head is formed by another galaxy,
10:34a third galaxy, an island of billions and billions of stars,
10:40colliding with the two galaxies that form the wings and the body
10:45at a speed of around 250 miles a second.
10:49Now, the turbulence, the disturbance that that creates
10:53is causing many new stars to be formed.
10:57These stars begin their lives by burning hydrogen to produce ever more helium.
11:05But as they age, as the hydrogen runs out, they turn to this helium.
11:12The temperature at their core rises,
11:14increasing the chances of three helium nuclei fusing together to form a new element,
11:21carbon dioxide.
11:23That process has been going on for almost the entire history of the universe,
11:28back 13 billion years,
11:30and it's the formation of stars that is the vital first step in the formation of life,
11:37because stars produce the heavy elements in the universe, including carbon.
11:43From the universe's earliest times,
11:46carbon has been created inside ageing stars.
11:55And over time, this carbon has built up,
11:58drifting away from the surface of the earth,
12:01and becoming more and more dense.
12:04It's a process that has been going on for thousands of years,
12:08and it's a process that has been going on for billions of years.
12:12It's a process that has been going on for billions of years.
12:16And it's a process that has been carrying through the cosmos as dust.
12:22Until some of it was caught up in the formation of a planet called Earth.
12:33And it's here that we can see this ancient carbon brought vividly to life.
12:42Today, the universe is old enough that countless stars have lived and died, and so there's
12:54been plenty of time to synthesise the primordial hydrogen and helium into the heavy elements.
13:02The question now is how does that carbon get into the web of life? Well, today, it enters
13:09via one ingredient, and I'm going to measure it using this balloon.
13:22The ingredient is carbon dioxide, which plays a key role in photosynthesis. Each night,
13:32the carbon dioxide concentration increases, filling the air around the leaves at the top
13:37of the trees. Now, this balloon has a carbon dioxide monitor in it, which is going to
13:45measure the change in the levels of CO2 at the top of the forest canopy as night turns
13:51to day. As the sun rises, the trees begin to photosynthesise. Now, at 6pm last night,
14:08so just after sunset, the concentration was around 350 parts per million. Around 10pm,
14:16so four hours after sunset, the concentration had risen to about 400 parts per million.
14:23And now, at about midday, the concentration is back down to about 345 parts per million.
14:32So that's a variation over a period of 18 hours of, what, around 10% in the concentration
14:39of carbon dioxide, just in that piece of atmosphere at the top of the forest canopy. So what you're
14:44seeing there is photosynthesis in action. Every day across the planet, photosynthesis
14:56uses sunlight to turn carbon dioxide and water into simple sugars. The overwhelming majority
15:08of the carbon is locked up inside long chains of sugar, molecules called cellulose and lignin.
15:16Now, lignin is the stuff that gives wood its strength. So in this form, and remember, that
15:26is most of it, it is very difficult indeed for animals to access. For the energy and
15:37nutrients locked away inside these long carbon chains to move through the food web, they
15:42must be broken down. And the best place to see that process in action is out on the open
15:53plain. It's one vast larder for all manner of organisms. But by far the most effective
16:07harvester of carbon is actually one of the smallest creatures on the savannah. Termites
16:19are social insects, working together to form a characteristic sight seen all over the bush.
16:27That's a termite mound. Actually, it's a tip of the iceberg. The termite city extends way
16:33beyond that underground. And its function is fascinating. It's essentially an air conditioning
16:40system. What it does is maintain very specific conditions inside the mound, the conditions
16:47of the rainforest. When the termites first colonised the savannah some 30 million years
16:54ago, they brought the rainforest with them to support a form of life that was already
17:00wonderfully adapted to living off dead wood. And this is what these termite mounds are
17:06all about. Can you see those structures there, those white honeycomb-like structures? Those
17:12are called fungal combs. They're wood pulp and possibly bits of dead grass that the termites
17:19bring in and build into that structure. And the reason the conditions have to be the same
17:24as the rainforest is because they grow a particular genus of fungus called termitomyces around
17:33those honeycombs. The job of that fungus is to break down the lignin and the cellulose
17:43inside the wood and convert it into a form that the termites can eat, which actually
17:47you can see there that are little white nodules just present on the honeycomb structure. The
17:58termites lack the enzymes to break down the wood efficiently, so they've become farmers,
18:05tending to one giant social stomach. So there's a very intense relationship between the termites
18:13and the fungus. You don't find that fungus anywhere else, actually in the world as far
18:19as we know, other than inside termite mounds. And it's thought that up to 90% of the carbon
18:29locked up in lignin in this part of Africa is released back into the food chain again
18:36solely by those termites and that fungus.
18:40So the termites deal with most of the lignin, but that still leaves a vast store of carbon
19:08in the form of cellulose. Across Africa, herds of mammals graze on grasses and leaves,
19:15turning this cellulose into meat. Many are a type of mammal known as a ruminant,
19:25the largest of which is one of the easiest animals to spot on safari.
19:55Giraffes live off a diet that's similar to termites. They eat cellulose, primarily,
20:08actually, the tops of the acacia trees that you see here scattering the African savannah.
20:14And they face that same problem. They've got to break those difficult carbon bonds down.
20:20And they come up with a very similar solution, which is to cultivate bacteria and fungi,
20:25but they do it inside their stomachs. And ruminants, like giraffes, have had to build a
20:32very complex system in order to do that. They've got four stomachs. One of them contains their
20:38culture of bacteria and fungi, and they allowed them to digest that difficult cellulose.
20:44Even with all this hardware, ruminants must feed for over two-thirds of the day.
20:54But there are other creatures here that have found a shortcut. After all, if plant fibres
21:00are hard to digest, why not let someone else do the work and simply steal a meal?
21:14He's coming for us. Oh, my God.
21:35Look what we've just found. We were out looking for giraffe this morning. We've
21:40found about ten of them just over there. But in looking for the giraffe, we've just found a
21:46leopard. This is one of the top predators out here. He's got very little to fear, apart from
21:53other leopards and baby lions. He's having a good look. He certainly doesn't care about us.
22:03He's around two years old, and at the moment he doesn't have his own territory. He's too
22:09young for that, and so he's lying low. He'll have to make about two kills a week
22:21to stay in good condition, so maybe catch an impala every three or four days,
22:28and he's obviously doing that, because look at him.
22:34Now he's looking for protein, and I'm a little bit worried, because I'm protein.
22:50He's coming really close to us, because he's after the sound man's boom pole,
22:54which is... That's incredible.
22:58From its origin in the death of stars...
23:28...it's capture by plants...
23:38...through insects, mammals and on.
23:49The carbon cycle is the real circle of life.
23:59Out there tonight, the relentless recycling of carbon through the food chain will continue.
24:06As night falls, you can almost sense it, the change in the sounds and the atmosphere.
24:16Some will die so that others can live, as carbon leaps from branch to branch across the great
24:24tree of life, and guiding it on its way is just one very special form of chemistry.
24:33Every living thing is just a temporary home for carbon atoms that existed
24:38long before there was life on Earth, and will exist long after Africa and Earth are gone.
24:44But the pattern of life, the information needed to build a zebra or a tree or a human being or a
24:52lion persists. It's passed on from generation to generation in a molecule, a helical molecule
25:00with a backbone of carbon called DNA.
25:03In a molecule, a helical molecule with a backbone of carbon called DNA.
25:34There was a time when Earth appeared empty.
25:51Yet despite appearances, 3.8 billion years ago, life was already underway in the form of tiny
25:59living specks that probably all shared the same biochemistry.
26:06We know that every living thing on the planet today, so every piece of food you eat, every
26:12animal you've seen, everyone you've ever known or will know, in fact every living thing that
26:17will ever exist on this planet, was descended from that one speck.
26:30We call it the last universal common ancestor, or LUCA. So just as the universe had its origin
26:37at the Big Bang, all life on this planet had its origin in that one moment.
26:49Less than a billion years after its formation, there was already life on Earth.
27:00It's possible that some of it used biochemistry utterly different from the life we see today.
27:07If so, it has long been extinct.
27:13It's also possible that the first life may not have been cellular, just living chemistry in
27:19the porous rocks of some ancient ocean. We're not sure, but what's certain is that one day,
27:28a population of organisms showed up with biochemistry that we would recognise.
27:35This was LUCA, the first expression of a form of life that would, in time,
27:42throw up a group of humans who left their mark in this part of Africa.
27:47Now, we don't know what LUCA looked like. We don't know precisely where it lived or how it lived.
27:53But we do know this. If you start to trace my ancestral line back to my parents, to their
28:01parents, to their parents, to their parents, all the way back through geological time scales,
28:07over hundreds of thousands and millions and billions of years, there will be a
28:13unbroken line from me, all the way back to LUCA.
28:21We know that because every living thing on the planet today shares the same biochemistry.
28:28We all have DNA. It's made of the same bases, A, C, T and G. They code for the same amino acids.
28:36Those amino acids build the same proteins, the same proteins, the same proteins.
28:42They build the same proteins, which do very similar jobs, whether you're a plant,
28:47a bacterium or a bipedal hominid, like me.
28:56So all life uses the same fundamental biology.
29:01Those four bases, A, C, G and T, which code for just 20 amino acids,
29:08which in turn build each and every one of life's proteins.
29:16Be you bacteria, plant, bug or beast, your design comes from your DNA.
29:26So it's this molecule that must hold the key to understanding why life today is so diverse.
29:33We now know that the answer to the question, why is life on Earth so varied,
29:37is actually the answer to the question, why is the DNA molecule itself so varied?
29:43What are the natural processes that cause the structure of DNA to change?
29:48Well, part of the answer actually doesn't lie on Earth at all.
29:53It lies up there amongst the stars.
29:56And I can show you what I mean using this, which is a molecule called a DNA molecule.
30:03A DNA molecule is a cloud chamber, a piece of apparatus that has a unique place in the history of physics.
30:10I'm going to cool it down using dry ice, frozen carbon dioxide, just below minus 70 degrees Celsius.
30:23I'll put the top on.
30:27Hear that?
30:28That's the metal at the bottom of the tank cooling down very rapidly to minus 70.
30:37The cloud chamber works by having a super saturated vapour of alcohol inside the chamber.
30:45Plenty on there.
30:47Now I want to get that alcohol, I want to boil it off to get the vapour into the chamber,
30:52so I'm going to put a hot water bottle on top.
30:55I mean, this is the first genuine particle physics detector.
30:59It's the piece of apparatus that first saw antimatter.
31:03And it really does consist only of a fish tank, some alcohol, a bit of paper and a hot water bottle.
31:24There, look at that.
31:26You see that cloud, that vapour trail?
31:31That's a cosmic ray.
31:33That was initiated by a particle, probably a proton, that hit the Earth's atmosphere.
31:44It almost certainly was a cosmic ray.
31:47It almost certainly originated outside our solar system and was accelerated by the magnetic fields of our galaxy.
31:53It may even have begun its life beyond our galaxy.
32:17Now, imagine if one of those hits the DNA of a living thing.
32:22What that will do is cause a mutation.
32:25That mutation may be detrimental or, very, very occasionally, it might be beneficial.
32:37And I think it's quite wonderful to imagine that maybe one of the key mutations
32:45that was selected for over the millennia that led to some trait in me
32:51was caused by some particle that began its life, perhaps in a massive supernova explosion,
32:58perhaps outside our galaxy, and went and hit the DNA of something
33:03and caused some kind of beneficial mutation.
33:07We don't know, but you can dream, can't you?
33:15Mutations are an inevitable part of living on a planet like Earth.
33:22They're the first hint at how DNA and the genes that code for every living thing
33:28change from generation to generation.
33:44MUTATIONS
33:51Mutations are the spring from which innovation in the living world flows.
34:00But cosmic rays are not the only way in which DNA can be altered.
34:06There's natural background radiation from the rocks.
34:08There's the action of chemicals and free radicals.
34:12There can be errors when the code is copied
34:15and then all those changes can be shuffled by sex
34:19and, indeed, whole pieces of the code can be transferred from species to species.
34:24So, bit by bit, in tiny steps from generation to generation,
34:30the code is constantly, randomly changing.
34:36Now, whilst there's no doubt that random mutation does alter DNA,
34:42evolution is anything but random.
34:45It can't be, because the chances of something with DNA as complex as this,
34:50appearing by look alone, are vanishingly small.
34:55Imagine you just changed one position in the code at random, a random mutation.
35:00There are four letters, A, T, C and G, so there are four possible combinations.
35:05If there are two places in the code, there are four combinations for each one,
35:11so that makes 16.
35:12If there are three, then there are 64 possibilities.
35:16By the time you get to a code with 150 letters in it,
35:20then there are more possible combinations in the code
35:24than there are atoms in the observable universe.
35:30Now, a hippo has a code with around three billion different letters,
35:37so the number of combinations of those letters,
35:41the chances of producing that code at random,
35:44are absolutely infinitesimally small.
35:48It's impossible.
35:54So, there must be a non-random element to evolution,
35:59a natural process which greatly restricts this universe of possibilities
36:04and shapes the outcome.
36:07We call it natural selection.
36:10And to see it in action, let's return to where we began,
36:14on the island of Madagascar.
36:37Around 65 million years ago,
36:39a group of seafarers were nearing the end of a long journey across the Indian Ocean.
36:44These were accidental travellers, a group of creatures from Africa,
36:49trapped on a natural raft and carried by the ocean currents.
36:54The land they found was verging green territory.
36:59Plants, insects, reptiles and birds had established themselves,
37:04but there were none of their own kind.
37:08The land they found was a wasteland,
37:10a wasteland where no one had ever lived before.
37:14The land they found was a wasteland,
37:16a wasteland where no one had ever lived before.
37:18Plants, insects, reptiles and birds had established themselves,
37:23but there were none of their own kind.
37:29They were caught up in a saga that tells of the great shifting of Earth's continental plates.
37:41It's impossible to understand the diversity of life on Earth today
37:44without understanding the shifting geography of our planet.
37:48The southern hemisphere, as it was 150 million years ago,
37:52and you see it's dominated by a single landmass called Gondwana.
37:57And then 90 million years ago,
37:59Gondwana had begun to break up, to separate into something that looks quite recognisably like Africa.
38:08And these two islands, Madagascar and India,
38:12now subsequently India has drifted northwards and bumped into Eurasia,
38:16raising the Himalayas, but crucially Madagascar has remained isolated.
38:22It's been an island surrounded by ocean for almost 90 million years.
38:36So when the seafarers arrived on their raft of trees and twigs and leaves,
38:42they had a blank canvas.
38:44This two, three, maybe even a single pregnant individuals had a whole island to roam across.
38:51And over 65 million years,
38:54they have blossomed into hundreds and thousands of individuals
38:58and become Madagascar's most iconic animals.
39:43Finding the descendants of those ancient mariners is not easy,
39:48but local guide Joseph has been tracking them for years
39:52and is going to help me find them.
40:13There at the top of the tree is an indri, which is the largest lemur in Madagascar.
40:19And it's just sat there watching us, quietly at the moment.
40:30This lemur here is a very special lemur.
40:33He has a name, he's called David.
40:37After Sir David Attenborough.
40:42David Attenborough
40:44David Attenborough
41:10Now we can only do this because
41:12Joseph has spent a lot of time with these lemurs.
41:16So they trust him.
41:20And therefore it seems they trust me.
41:38It's enormous hands.
41:41The reason it's thought that we find lemurs here in Madagascar, in Madagascar alone,
41:46is because there are no simians, there are no chimpanzees,
41:52none of my ancestral family dating back tens of millions of years to outcompete them.
41:58So what's thought happened is that around 65 million years ago,
42:05one of the lemurs' ancestors managed to sail across the Mozambique Channel and landed here.
42:14There were none of those competitors here, and so the lemurs have flourished ever since.
42:22There are now over 90 species of lemur, or subspecies, in Madagascar.
42:26No species of my lineage, the simians.
42:36Madagascar
42:46Over a vast sweep of time, the lemurs have diversified to fill all manner of different habitats.
42:56From the arid spiny forests of the south, to the rocky canyons in the north,
43:03there is something about this island that is allowing the lemurs' DNA to change in the most amazing ways.
43:11Madagascar
43:30We're on the hunt for an aye-aye, the most closely related of all the surviving lemurs to their common ancestor.
43:41Right there, see the vine moving?
43:53Oh yeah, yes, yeah, yeah.
43:56Oh yes.
44:04I've just shut the light off and saw these absolutely two bright, bright red eyes.
44:10I'll show you that.
44:12She's very high up at the moment.
44:18They're on the loose side of her in this forest, where she's very dark and dense.
44:26The team have located a female aye-aye and her son.
44:31They want to attach radio collars to track their movements and better understand how far they range through these forests.
44:40But first, they must sedate them with a dart.
44:46What I'm going to do is wait for it to come down low enough to get that clean shot.
44:49I mean, how do you get a clean shot in this?
44:53I've got no idea.
45:00After two hours of traipsing through the treacherous forest, the aye-ayes remain at large.
45:16Some people sit around the fire.
45:18Oh yeah.
45:24Well, here is the aye-aye that was tranquilized last night.
45:28They finally got her about half an hour after we left.
45:31I think it was probably because we were disturbing her.
45:34Apparently, as soon as we'd gone, she came down the tree and she was tranquilized.
45:38And as you can see, she's pretty well sedated now,
45:42which is fortunate for me, because she has certain adaptability.
45:47You can see there, her teeth.
45:50Her teeth are very unusual for a primate.
45:53In fact, unique, because they carry on growing.
45:56So she's much more like a rodent in that respect.
45:59And that's so she can gnaw into wood.
46:02See, aye-ayes have filled a unique niche on Madagascar.
46:06It's a niche that's been around for thousands of years.
46:09It's a niche that's been around for thousands of years.
46:12It's a niche that's been around for thousands of years.
46:15It's a niche that's been around for thousands of years.
46:18It's a niche that's been around for thousands of years.
46:21What she does is she feeds on grubs and bugs inside trees.
46:24And to do that, she has several unique adaptations of which the teeth are one.
46:29The most startling is this central finger here.
46:33It's bizarre.
46:35It's got a ball and socket joint for a start.
46:39So it has complete 360-degree movement.
46:43It feels to me almost as if it's broken, but it isn't.
46:46It's just you can move it around in any direction.
46:49And she uses that finger initially to tap on the trunk of the tree.
46:54And then listening to the echo from that tapping with these huge ears,
46:59she can detect where the grubs are.
47:02And then she gnaws through the wood with those rodent-like teeth
47:06and then uses this finger again to reach inside the hole and get the bugs out.
47:13So the question is, why?
47:15How could an animal be so precisely adapted to a particular lifestyle?
47:22She's waking up now.
47:25And the answer is natural selection.
47:28See, what must have happened is way back
47:32when the ancestors of the lemurs, the lemuriformes, arrived in Madagascar,
47:36there must have been a mutation that lengthened the middle finger ever so slightly of one of those lemurs.
47:44And that must have given it an advantage.
47:47That must have allowed it perhaps to reach into little holes and search for grubs.
47:51There's some reason why that lengthened middle finger meant that that gene
47:56was more likely to be passed to the next generation and then down to the next generation.
48:01That landscape of possibilities is narrowed.
48:04It's narrowed because that gene persists.
48:07And it's persisted now for at least 40 million years
48:12because this species has been on one branch of the tree of life now for over 40 million years.
48:20And so over those years, that middle finger has got more and more specialised.
48:25Natural selection has allowed the aye-aye's wonderfully mutated finger to spread through the population.
48:33And this same law applies to all life.
48:38If you have a mutation that helps you in the struggle to survive,
48:43you are more likely to leave more offspring.
48:47And in the next generation, that mutation is more likely to survive.
48:54So this animal is a beautiful example,
48:59probably one of the best in the world,
49:02of how the sieve of natural selection produces animals that are perfectly adapted to live in their environment.
49:24Now, there are many reasons to study the aye-aye, but here's a good one.
49:29In the 1970s, it was thought the aye-aye was extinct.
49:32Now we know there are several thousand in the forest of Madagascar,
49:36five, six, seven thousand, certainly less than 10,000.
49:40But over the last 50 years, 50% of the aye-aye has been extinct.
49:44And we know that the aye-aye is a very rare species.
49:48Five, six, seven thousand, certainly less than 10,000.
49:51But over the last 50 years, 50% of this forest has vanished.
50:10This is an animal that's been around as a species for over 40 million years.
50:15So it's important to know how these animals are doing,
50:19and how they're surviving in this diminishing habitat.
50:39Whilst natural selection explains how the aye-aye evolved,
50:43it alone can't explain how a small group of individuals over 60 million years ago
50:50gave rise to over 90 different species of lemur today.
50:58But there is another form of life that can offer us a clue.
51:04Up here in the high forest canopy, we're in a very different environment to the one down there on the forest floor.
51:12It's a more arid environment. It's almost like a desert.
51:15It's exposed to the sun. Water is harder to come by.
51:19And so this is a sea of different niches that are able to be occupied and exploited
51:26by animals that are different to the ones you will find down there on the floor.
51:30So in a very real sense, this is an island, an island to be colonised.
51:37And sure enough, there are settlers to be found even here.
51:43You see that thing that looks like a muddy ball there on the branch?
51:47Well, that's an ant's nest. It's home to a species of chromatogaster ants
51:52that are unique, not only to Madagascar, but to the forest canopy.
51:57You see, what makes those ants unique is that they can build their own nests.
52:02There are very few species of ants that can do that.
52:06So that is an island. That is a niche.
52:09And it's allowed that species of ants to develop because they're isolated from the rest of the ecosystem.
52:17And astonishingly, within this niche, another form of life new to science has been discovered.
52:26A beetle that manages to survive here unharmed by the ants.
52:32How it does it is a mystery.
52:36But what is known is that this particular species has only ever been found inside these nests.
52:44So that really is its own mini-ecosystem with species living in it that are unique to that island.
52:53We live on an ever-shifting, dynamic world that creates islands in abundance.
53:11Earth's mountain ranges.
53:14The ocean.
53:17Earth's mountain ranges, river valleys and canyons all create islands for life.
53:29And it's these islands that those ancestors of the lemurs found when they arrived in Madagascar.
53:37Empty niches where populations became isolated.
53:42And over great swathes of time, evolved into such wonderfully diverse forms.
54:07A hundred and fifty years on from the origin of species,
54:11the subtlety and beauty of Darwin's insight is still revealing itself to us.
54:20It describes how our beautiful, complex tree of life has grown from a one-hundred-year-old tree.
54:29It describes how our beautiful, complex tree of life has grown from a once-desolate universe.
54:39The chemistry of carbon allows for the existence of a molecule that is able to replicate itself
54:45and pass information on from generation to generation.
54:49There can be random changes in the structure of that molecule, mutations,
54:55and they are tested by their interaction with the environment and other living things.
55:00The ones that pass that test survive, and the ones that fail that test are lost.
55:10The separation and isolation of living things onto islands, which may be physical, like Madagascar,
55:17or just the single branch of a single tree, results in speciation.
55:22The explosion of living forms highly specialised to occupy niches within niches.
55:28And this is the explanation for the diversity of life on Earth.
55:33There is grandeur in this view of life, as Darwin wrote,
55:37and understanding how it happened surely only adds to the wonder.
55:52As precise as Einstein's theories of relativity, and as profound as thermodynamics,
56:00Darwin has given us another universal law.
56:07Evolution by natural selection.
56:12And if evolution is the law on this island, then it will apply throughout the cosmos.
56:22Which begs a big question.
56:28Could there be other trees of life most beautiful amongst the stars?
56:35In 2011, we discovered a rocky planet orbiting around a distant star
56:40with daytime temperatures not too dissimilar to those found on Earth.
56:45Now, there must be millions, if not billions, of stars orbiting around the planet.
56:51But we don't know how many there are.
56:54We don't know how many stars are orbiting around the planet.
56:59Now, there must be millions, if not billions, of such planets out there in the universe.
57:05And it's inconceivable to me that none of them will have trees of life
57:10as complex, or even more complex, than our own.
57:14But that doesn't devalue the existence of our tree.
57:18Because our tree is unique.
57:21It consists of thousands of branches, all interdependent on thousands of others,
57:26and the precise structure depends on chance events,
57:30like the passage of the lemurs across the ocean 65 million years ago.
57:43So when you go outside tomorrow, just take a look at a little piece of your world,
57:48a corner of your garden, or a park,
57:53or even the grass that's growing in a crack in the pavement.
57:57Because there will be life there, and it will be unique.
58:01There will be nowhere like that anywhere else in the universe.
58:05And that makes our tree, from the sturdiest branch to the most fragile twig,
58:10indescribably valuable.
58:43The results of the Man U game versus Everton and Aston Villa up against West Ham.
58:48Match of the day two is coming up next.