- 43 minutes ago
Charles Darwin and his revolutionary theory of evolution through natural selection, looks at the broad spectrum of animals on our planet and how Charles Darwin attempted to explain this diversity.
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00:01Our Earth is the only known planet that sustains life,
00:05and it does so in abundance.
00:22I have been fortunate enough over the years
00:25to travel to some of the most extraordinary
00:28and remote places on Earth to find and film animals.
00:32This is the biggest flower in the world.
00:36The blue whale!
00:37It's the biggest creature that exists on the planet!
00:43The sheer number and variety of animals and plants is astonishing.
00:49Estimates of the number of different species vary from 6 million to 100 million.
00:55Nobody knows exactly how many different kinds of animals there are here.
01:00Wherever you look, there's life.
01:02There are often a multitude of variations on a single pattern.
01:07Nearly 200 different kinds of monkeys, for example.
01:12And 315 hummingbirds.
01:17Nearly 1,000 bats.
01:26And beetles, at least 350,000 species of them.
01:33Not to mention, a quarter of a million different kinds of flowering plants.
01:45The variety is astounding.
01:55Even in this one small English woodland, you might see 4 or 5 different kinds of finches.
02:07Why should there be such a dazzling variety?
02:11And how can we make sense of such a huge range of living organisms?
02:19200 years ago, a man was born who was to explain this astonishing diversity of life.
02:27In doing so, he revolutionized the way in which we see the world and our place in it.
02:33His name was Charles Darwin.
02:57This book, the Holy Bible, explains how this wonderful diversity came about.
03:05On the third day, after the creation of the world, God created plants.
03:11On the fifth day, fish and birds.
03:15And then, on the sixth day, mammals.
03:19And finally, man.
03:22That explanation was believed, literally, by pretty well the whole of Western Europe for the best part of 2,000
03:30years.
03:31And generations of painters pictured it for the faithful.
03:39This version was painted in Italy in the 16th century.
03:44Here is God in the Garden of Eden, which is now filled with all kinds of animals.
03:49Here, he is pulling Adam out of the earth.
03:55And here, creating the first woman by putting Adam to sleep and then taking one of his ribs and extracting
04:03Eve from his side.
04:07And she comes out assisted by two angels.
04:13And when God had finished, he said to Adam and Eve,
04:18Be fruitful and multiply and replenish the earth and subdue it and have dominion over the fish of the sea
04:26and over the fowl of the air and over every living thing that moveth upon the earth.
04:34That made it clear that, according to the Bible, humanity could exploit the natural world as they wished.
04:46This view of mankind's superiority still stood when, in 1831, a British surveying ship, the Beagle, set off on a
04:55voyage around the world.
04:56On board, as a companion to the captain, was the 22-year-old Charles Darwin.
05:04They crossed the Atlantic and made landfall on the coast of Brazil.
05:12There, the sheer abundance of tropical nature astonishes the newcomer, as I discovered when I retraced Darwin's steps 30 years
05:21ago for a television series about the diversity of nature.
05:26Darwin, as a boy, had been a fanatical collector of insects, and here he was enthralled almost to the point
05:34of ecstasy.
05:35In one day, in a small area, he discovered 69 different species of beetle.
05:43As he wrote in his journal, it's enough to disturb the composure of the entomologist's mind to contemplate the future
05:52dimension of a complete catalogue.
05:56They went south, rounded Cape Horn, and so reached the Pacific.
06:05And then, in September 1835, after they'd been away for almost four years, they landed on the little-known islands
06:13of the Galapagos.
06:16Here, they found creatures that existed nowhere else in the world.
06:21Cormorants that had lost the power of flight.
06:25Lizards that swam out through the surf to graze on the bottom of the sea.
06:33Darwin, who had studied botany and geology at Cambridge University, collected specimens of the animals and plants.
06:41And as usual, when he went ashore to investigate, described what he found in his journal.
06:49My servant himself were landed a few miles to the northeast in order that I might examine the district mentioned
06:59above as resembling chimneys.
07:04Volcanic chimneys, presumably.
07:06The comparison would have been more exact if I'd said the iron furnaces near Wolverhampton.
07:21The British resident in the Galapagos claimed that he knew from the shape of a giant tortoise's shell which island
07:28it had come from.
07:29If it had a rounded front, it came from a well-watered island where it fed on lush ground plants.
07:38Whereas one from a drier island had a peak at the front, which enabled it to reach up to higher
07:45vegetation.
07:49Were these tortoises, each on their separate islands, different species?
07:55And if so, was each one a separate act of divine creation?
08:03The differences that Darwin had noticed amongst these Galapagos animals were, of course, all tiny.
08:10But if they could develop, wasn't it possible that over the thousands or millions of years,
08:16a whole series of such differences might add up to one revolutionary change?
08:24On his voyage home, Darwin had time to ponder on these things.
08:29Could it be that species were not fixed for all time, but could in fact slowly change?
08:43On his return, he sorted out his specimens and sent them off to relevant experts
08:48so that each could be identified and classified.
08:56Most of the mammal bones and fossils he sent to Richard Owen.
09:02Owen was one of the most brilliant zoologists of his time.
09:06He was the first to recognise dinosaurs, and indeed had invented their very name.
09:11And he would later become the creator and first director
09:15of the Natural History Museum in London.
09:23Many of the specimens that Darwin collected are still preserved and treasured here,
09:28among the 70 million other specimens housed in the museum that Owen founded.
09:39And here is one of them.
09:43It's obviously the lower jaw of some great animal.
09:46And when Darwin discovered it, it had bits of skin and hair attached to it,
09:51so that at first it was thought to be the remains of some unknown living species.
09:55But now we know that it is a species that was extinct for some 10,000 years,
10:01a giant ground sloth.
10:04Owen examined it in great detail and eventually described it
10:09and gave it the name of Mylodon Darwinii in honour of its discoverer.
10:15But that mutual respect between two great men of science was not to last.
10:26Soon after his return from his voyage, Darwin made his home here in Down House in Kent.
10:33Here he wrote an account of his travels and worked on detailed scientific treatises
10:39about corals and barnacles and the geology and fossils of South America.
10:47But he also pondered deeply on what he had seen in the Galapagos and elsewhere.
10:53Maybe species were not fixed.
11:17Every day he took a walk in this small spinny that he had planted at the end of his garden.
11:25And it was here that he came to ponder on the problems of natural history,
11:30including that mystery of mysteries, how could one species turn into another?
11:38He noted that most, if not all animals, produce many more young than live to breed themselves.
11:47This female blue tit, for example, may well lay a dozen eggs a year, perhaps 50 or so in her
11:54lifetime.
11:55Yet only two of her chicks need to survive and breed themselves to maintain the numbers of the blue tit
12:01population.
12:02Those survivors, of course, are likely to be the healthiest and best suited to their particular environment.
12:08Their characteristics are then inherited, so perhaps over many generations,
12:14and particularly if there are environmental changes, species may well change.
12:21Only the fittest survive.
12:23And that was the key.
12:26He called the process natural selection.
12:38That would explain the differences that he had noted in the finches that he had brought back from the Galapagos.
12:46They were very similar except for their beaks.
12:50This one has a very thin, delicate beak which it uses to catch insects.
12:57This one, on the other hand, which came from an environment where there were a lot of nuts,
13:02has a big, heavy beak which enables it to crack them.
13:06So maybe, over the vastness of geological time, and particularly if species were invading new environments,
13:16those changes would amount to very radical changes indeed.
13:32Darwin drew a sketch in one of his notebooks to illustrate his idea,
13:38showing how a single ancestral species might give rise to several different ones,
13:44and then wrote above it a tentative, I think.
13:58Now he had to prove his theory, and he spent years gathering abundant and convincing evidence.
14:06He was an extraordinary letter writer.
14:08He wrote as many as a dozen letters a day to scientists and naturalists all over the world.
14:26He also realised that when people had first started domesticating animals,
14:32they had been doing experiments for him, for centuries.
14:40All domestic dogs are descended from a single ancestral species, the wolf.
14:46Dog breeders select those pups that have the characteristics that happen to please them.
14:52Nature, of course, selects those young animals that are best suited to a particular environment.
14:57But the process is essentially the same.
15:01And in both cases, it has produced astonishing variety.
15:12In effect, many of these different breeds could be considered different species,
15:18because they do not, indeed they cannot, interbreed for purely mechanical reasons.
15:24There's no way in which a Pekingese can mate with a Great Dane.
15:34Of course, it's true that if you used artificial insemination,
15:38you could get crosses between almost any of these breeds,
15:42but that's because human beings have been selecting between dogs for only a few centuries.
15:48Nature has been selecting between animals for millions of years,
15:53tens of millions, even hundreds of millions of years.
15:57So what might have started out as we would consider to be breeds,
16:01have now become so different, they are species.
16:25Darwin, sitting in Down House, wrote to pigeon fanciers and rabbit breeders,
16:31asking all kinds of detailed questions.
16:34about their methods and results.
16:36He himself, being a country gentleman and running an estate,
16:40knew about breeding horses and sheep and cattle.
16:44And he also conducted careful experiments with plants in his greenhouse.
16:53But Darwin knew that the idea that species could appear without divine intervention
16:59would appall society in general.
17:01And it was also contrary to the beliefs of his wife, Emma,
17:05who was a devout Christian.
17:08Perhaps for that reason, he was keen to keep the focus of his work scientific.
17:15He made a point of not being drawn in public about his religious beliefs,
17:20but in the latter part of his life, he withdrew from attending church.
17:25On Sundays, he would escort Emma and the children here to the parish church in Down.
17:31But while they went into the circus, he remained outside and went for a walk in the country lanes.
17:46Perhaps because he feared that his theory would cause outrage in some quarters,
17:51he delayed publishing it year after year after year.
17:55But he wrote a long abstract of it.
17:58And then on July the 5th, 1844, he wrote this letter to his wife.
18:04My dear Emma, I have just finished this sketch of my species theory.
18:09Some sketch. It was 240 pages long.
18:13I therefore write this in case of my sudden death that you will devote 400 pounds to its publication.
18:21He then goes on to list his various naturalist friends who would be asked to edit it and check it.
18:29And he ends the letter charmingly.
18:31My dear wife, yours affectionately, C.R. Darwin.
18:46He continued to accumulate evidence and refine his theory for the next 14 years.
18:57But then his hand was forced.
19:00In June 1858, 22 years after he got back from the Galapagos,
19:07here in his study in Down, he received a package from a naturalist who was working in what is now
19:14Indonesia.
19:16His name was Alfred Russell Wallace.
19:22He had been corresponding with Darwin for some years.
19:26But this package was different.
19:29It contained an essay that set out exactly the same idea as Darwin's,
19:34of evolution by natural selection.
19:39The idea had come to Wallace as he lay in his hut, semi-delurious in a malarial fever.
19:46But although his idea of natural selection was the same as Darwin's,
19:51he had not spent 20 years gathering the mountain of evidence to support it, as Darwin had done.
19:59But whose idea was it?
20:02In the end, the senior members of the Lenean Society decided that the fairest thing was for a brief outline
20:08of the theory from each of them to be read out, one after the other,
20:12at a meeting of the Society here in Burlington House in London.
20:17The Lenean, then as now, was the place where scientists studying the natural world held regular meetings to present and
20:25discuss papers about their observations and thoughts.
20:30The one held on July 1st, 1858, was attended by only about 30 people.
20:38Neither of the authors were present.
20:41Wallace was 10,000 miles away in the East Indies, and Darwin was ill and devastated by the death a
20:49few days earlier of his infant son.
20:51So he was still at his home in Kent.
20:55As a consequence, the two papers had to be read by the secretary.
21:00And as far as we can tell, they made very little impression on anyone.
21:08Darwin had spent the next year writing out his theory in detail.
21:12Then he sent the manuscript to his publisher, John Murray, whose firm then as now had offices in Albemarle Street,
21:20just off Piccadilly in London.
21:22Murray was the great publisher of his day and dealt with the works of Jane Austen and Lord Byron, whose
21:31first editions still line these office walls.
21:34Darwin regarded his work as simply a summary, but even so, it's 400 pages.
21:41It was published on November the 24th, 1859.
21:47This is not a first edition, more's the pity.
21:51First editions are worth, literally, hundreds of thousands of pounds.
21:55This is the sixth edition, my copy, which I bought as a boy.
22:00When I was 18, I noticed, and it cost me the princely sum of one shilling.
22:10The first edition of 1,250 copies sold out immediately.
22:15And it went for a reprint, and then another reprint, and another reprint.
22:19It's a book that contains very few technical terms.
22:23It's easily understood by anybody.
22:26And predictably, it caused an outrage, not only throughout this country, but indeed all the civilised world.
22:36What scandalised people most, it seems, was the implication that human beings were not specially created by God, as the
22:45Book of Genesis stated,
22:46but were descended from ape-like ancestors.
22:50A notion that provided a lot of scope for cartoonists.
22:56The leaders of the church, headed by Samuel Wilberforce, the Bishop of Oxford, attacked it on the grounds that it
23:02demoted God,
23:03and contradicted the story of creation as told by the Bible.
23:09That Mr. Darwin should have wandered from this broad highway of nature's works into the jungle of fanciful assumption is
23:18no small evil.
23:20I have read your book with more pain than pleasure.
23:23It is the frenzied inspiration of the inhaler of mephitic gas.
23:27Fails utterly.
23:33Darwin's theory implied that life had originated in simple forms and had then become more and more complex.
23:41He knew perfectly well that the whole idea of evolution raised a lot of questions.
23:48In fact, some of those questions would not be answered until comparatively recently.
23:54But in his own time, many distinguished scientists raised what seemed to be insuperable difficulties.
24:02And foremost among them was Richard Owen.
24:05The man who, twenty years earlier, had named the extinct ground sloth in honour of Darwin.
24:13Over the years, the two men had developed a deep personal dislike of one another, and had quarreled frequently.
24:22It wasn't that Owen thought that the story of the Garden of Eden was literally correct.
24:28But nonetheless, he was a deeply religious man.
24:38He had, after all, ensured that his museum, which would display the wonders of creation, echoed in its design the
24:46great Christian cathedrals of medieval Europe.
24:59And Owen knew about the diversity of life.
25:03Indeed, he had spent his whole career cataloguing it.
25:07But even so, he refused to believe that a species could change over time.
25:15He and other pioneer Victorian geologists, as they established their comparatively new science, recognised that the outlines of the history
25:24of life could be deduced by examining the land around them.
25:31Look at these rocks in northern Scotland.
25:35We know from fossils that are associated with them that they are very ancient.
25:41And they are sandstones.
25:43Compacted sand that was laid down at the bottom of the sea, layer upon layer upon layer.
25:50But look how many layers there are!
25:53But look how many layers there are!
26:09Clearly, those at the top must have been laid down after those beneath them.
26:14So, as you descend from layer to layer, you are, in effect, going back in time.
26:22So, a fossil species, if it comes from a particular layer, is of a particular age.
26:28And if you can recognise each one, then you can begin to piece together the outlines of life's history.
26:39Ah, my craster.
26:40The ability to identify fossils and place them in their geological time zone was still an essential skill when I
26:48was at university a century later.
26:52We worked our way through drawers like these, which are full of fossils of one sort or another.
26:59But none of them have labels, only numbers.
27:02So, you were expected to be able to pick up one and say,
27:09yes, that's a belemnite.
27:12Actually, which belemnite it is, I can't remember now.
27:15And when you came to your practical exam, your examiners would produce one of these and say,
27:21OK, what's that?
27:23And you either knew or you didn't.
27:25And the way you knew was because of all the work you did in drawers like these, hour after hour.
27:36Owen did not deny the sequence in which all these different species appeared,
27:41but he believed that each was separate, each divinely created.
27:46Darwin's theory, however, required that there should be connections,
27:51not just between similar species, but between the great animal groups.
27:58If fishes and reptiles and birds and mammals had all evolved from one another,
28:05then surely there must be intermediate forms between those great groups.
28:10And they were missing.
28:12And then, just two years after the publication of the origin of species,
28:18Richard Owen himself purchased the most astonishing fossil for his museum.
28:27It had been found in this limestone quarry in Bavaria.
28:31The stone here splits into flat, smooth leaves
28:35that have been used as roofing tiles since Roman times.
28:41Most are blank.
28:43But occasionally, when you split them apart, they reveal a shrimp or a fish.
28:50It's almost impossible to resist the temptation of pulling down almost every boulder you see,
28:57and then opening it like a book to look at each unopened page
29:02to see whether maybe it contains yet another fossil.
29:13But this fossil was something unprecedented.
29:17It is still one of the greatest of the treasures that are stored in the Natural History Museum.
29:24And this is it.
29:26It's called Archaeopteryx.
29:29It has unmistakable feathers on its wings and down its tail.
29:37So, Owen had no hesitation in calling it a bird.
29:40But it was unlike any other bird that anyone knew of,
29:45because it had claws on the front of its wings,
29:49and as was later discovered, it didn't have a beak but jaws with teeth in it,
29:54and a line of bones supporting its tail.
29:59So, it was part reptile, part bird.
30:04Here was a link between those two great groups that was no longer missing.
30:11Gosh, you really can see the filaments there.
30:20Other examples of the same creature show its feathers even more clearly.
30:27We know from the bones of Archaeopteryx that it was, at best, a very poor flyer.
30:34So, it's not surprising that, eventually, it was superseded by more modern, more efficient birds.
30:42And that's the fate of these links between great groups.
30:46Eventually, they become extinct,
30:49and the only way we know they existed is from their fossilised remains.
30:54Even so, there is a bird, alive today,
30:58that illustrates the link between modern birds and reptiles.
31:06The hoatzin nests in the swamps of tropical South America.
31:11There are caiman in the water beneath, ready to snap up any chick that might fall from its nest,
31:16so an ability to hold on tight is very valuable.
31:20And the nestlings have a very interesting way of doing that.
31:25The young still have claws on the front of their wings, as Archaeopteryx did.
31:30Here is vivid evidence that the wings of birds are modified forelegs and once had toes with claws on them.
31:39There's another creature alive today that represents a link between the great animal groups,
31:44a descendant of a group of reptiles that took a different evolutionary course
31:48and evolved not feathers but fur, the platypus.
31:54When specimens of this creature first reached Europe from Australia at the very end of the 18th century,
32:00people refused to believe their eyes.
32:04They said it was a hoax.
32:07Bits and pieces of different creatures rather crudely sewn together.
32:12And yet, in a way, those early sceptics were right.
32:16The platypus is the most extraordinary mixture of different animals.
32:20It's part mammal and part reptile.
32:23And so it can give us some idea of how the first mammals developed.
32:29When it comes to breed, it does something that separates it from all other mammals except one.
32:35In its nest, deep in a burrow, it lays eggs.
32:39It's this that links the platypus with the reptiles,
32:43and this that entitles it to be regarded as the most primitive living mammal.
32:50So, the links between the great animal groups are not, in fact, missing,
32:55but exist both as fossils and as living animals.
33:00Although the fossil record provides an answer to the problem of missing links,
33:06it also posed a major problem.
33:10It started very abruptly.
33:13The earliest known fossils in Darwin's time
33:16came from a formation called the Cambrian.
33:20And there were two main kinds.
33:22These, which look like frets or blades, and are called graptolite.
33:27And these, like giant wood lice, which are called trilobites.
33:33Could it really be that life on Earth started with creatures as complex as these?
33:54As a boy, I was a passionate collector of fossils.
33:59I grew up in the city of Leicester.
34:02And I knew that in this area, not far from the city, called Childhood Forest,
34:08there were the oldest rocks in the world.
34:11Older even than the Cambrian.
34:13So, therefore, by definition, they would be without fossils.
34:18There was no point in me looking for fossils in these ancient rocks.
34:38There were, it's true, very rarely, some rather odd shapes in these rocks,
34:45like this one here.
34:46But they were dismissed as being some kind of mechanical aberration.
34:53I mean, after all, how could there be anything living in these extremely ancient rocks?
35:00And then, in 1957, a schoolboy with rather more patience and perspicacity than I had,
35:10found something really remarkable and undeniably the remains of a living creature.
35:20And here it is in Leicester Museum, where it's been brought for safekeeping.
35:26It's called Charnia.
35:28Who could doubt that this is the impression of a living organism?
35:34It has a central stem, branches on either side.
35:39In fact, it seems to have been something like the sea pens that today grow on coral reefs.
35:47Since its discovery, a whole range of organisms have been found in rocks of this extreme age,
35:56not only here in the Charnwood Forest, but in many other different parts of the world.
36:02Fossil hunters searching these rocks in the Ediacra hills of Australia had also been discovering other strange shapes.
36:13At first, many scientists refused to believe that these faint impressions were the remains of jellyfish.
36:20But by now, enough specimens have been discovered to make quite sure that that indeed is what they are.
36:34So now we know that life did not begin suddenly with those complex animals of the Cambrian.
36:42It started much, much earlier, first with simple microscopic forms which eventually became bigger,
36:49but which were still so soft and delicate that they only very rarely left any mark in the rocks.
36:58The question of the age of the earth posed another problem for Darwin's theory.
37:05In the 17th century, an Irish bishop had used the genealogies recorded in the Bible that lead back to Adam
37:12to work out that the week of creation must have taken place in the year 4004 BC.
37:19That may seem to us to be a very naive way of doing things, but what other method was there
37:25anyway?
37:27The Victorian geologists had already concluded that the earth must be millions of years old.
37:33But how many millions? No one could say.
37:37Then, less than 50 years after the publication of the origin,
37:41a discovery was made in what seemed a totally disconnected branch of science
37:46that would ultimately provide the answer.
37:50A Polish woman working in Paris, Marie Curie,
37:54discovered that some rocks contained an element called uranium
37:57that decays over time at a steady rate through a process called radiation.
38:04Today, a century after she made her extraordinary discovery,
38:09the method of dating by measuring changes in radioactivity has become greatly refined.
38:18This is a sample taken from those very ancient rocks in Charmwood Forest.
38:24And these tiny crystals are revealed to be 562 million years old.
38:32That provides more than enough time for natural selection to produce the procession of fossils
38:38that eventually leads to the living animals and plants we know today.
38:45But there was another objection.
38:47If all animals within a group have a common origin,
38:52how is it that some kinds of animals are distributed throughout the continents of the world except Antarctica?
39:00How is it that, for example, frogs in Europe and Africa are also found here in South America on the
39:09other side of the Atlantic Ocean,
39:10bearing in mind that frogs have permeable skins and can't survive in seawater?
39:17Darwin himself had a couple of suggestions.
39:21One was that they might have floated across accidentally on rafts of vegetation,
39:25and the other is that maybe there were land bridges between the continents.
39:30But even he was not convinced by either explanation.
39:40Even as late as 1947, when I was a geology student here at Cambridge, there was no convincing explanation.
39:49It's true that back in 1912, a German geologist had suggested that at one time in the very remote distant
39:59past,
40:00all the continents of the Earth that we know today were grouped together to form one huge supercontinent,
40:07and that over time this broke up and the pieces drifted apart.
40:13That would have provided an answer.
40:17But when I asked the professor of geology here who was lecturing to us why he didn't tell us about
40:23that in his lectures,
40:24he replied rather loftily, I must say,
40:28when you can demonstrate to me that there is a force on Earth that can move the continents by a
40:35millimetre,
40:36I will consider it.
40:37But until then, the idea is sheer moonshine, dear boy.
40:44But then, in the 1960s, it became possible to map the sea floor in detail.
40:51And it was discovered not only that the continents have shifted in just the way that the German geologists had
40:58suggested,
40:59but that they were still moving.
41:03New rock wells up from deep below the Earth's crust and flows away on either side of the mid-ocean
41:09ridges,
41:10carrying the continents with it.
41:14Amphibians had originally evolved on this supercontinent,
41:17and had then travelled on each of its various fragments as they drifted apart.
41:22Problem solved.
41:28Perhaps the biggest problem of all for most people was the argument put forward for the existence of God
41:36at the beginning of the 19th century by an Anglican clergyman called William Paley.
41:42He said, supposing you were walking in the countryside and you picked up something like this.
41:50You would know, from looking at it, that it had been designed to tell the time.
41:59There must, therefore, be a designer.
42:02And the same argument would apply if you looked at one of the intricate structures found in nature,
42:08such as the human eye.
42:10And the only designer of the human eye could be God.
42:16Anti-Venutionists maintain that the eye would only work if it was complete in all its details.
42:24Darwin, on the other hand, argued that the eye had developed becoming increasingly complex over a long period of time.
42:33That would only work if each stage of development was an improvement on the previous one.
42:40And today, we know enough about the animal kingdom to know that that is indeed the case.
42:48Some very simple animals have nothing more than light-sensitive spots
42:53that enable them to tell the difference between light and dark.
42:56But if a patch of such spots formed even the shallowest of pits,
43:01one edge of the pit would throw a shadow and so reveal the direction of light.
43:07If the pit got deeper and started to close, then light would form a blurred image.
43:14Mucus secreted by the cells would bend the light and focus it.
43:19If this mucus hardened, it would form a proper lens and transmit a brighter and clearer image.
43:27All these different fully functional stages at different levels of complexity
43:32are found in living animals today.
43:35This single-celled creature has one of those light-sensitive spots.
43:42Flatworms have a small pit containing light spots so they can detect the shadow of a predator.
43:49A snail's blurry vision is good enough to enable it to find its way to food.
43:55And the octopus has an eye with a proper lens and can see as much detail as we can.
44:05So the structure of the human eye does not demand the assistance of a supernatural designer.
44:11It can have evolved gradually with each stage bringing a real advantage, as Darwin's theory demands.
44:24Natural selection, of course, requires that an animal's characteristics are handed from one generation to the next.
44:32It's obvious that children resemble their parents. Anyone knows that.
44:37But when you come to think of it, how does that come about?
44:42In Darwin's time, nobody had the faintest idea about the mechanism or the rules that governed that process.
44:51Except, perhaps, for one man who was working in the city of Brno, in what is now the Czech Republic,
44:58at exactly the same time that Darwin was writing his book in Kent.
45:03That man's name was Gregor Mendel.
45:08He discovered the laws of inheritance by breeding thousands of pea plants
45:13and observing how they changed from one generation to the next.
45:18He found that while many characteristics were passed down directly from one generation to another,
45:25others could actually skip a generation. How could that happen?
45:30Mendel explained this by suggesting that each plant, each organism contained within it,
45:38factors which were responsible for creating those particular characteristics.
45:44Today, we call those things genes.
45:47But nobody had any idea how they worked until a hundred years after Mendel's time.
45:54And then the answer was discovered in Cambridge.
46:02In 1953, here in the Cavendish Laboratories, two young researchers,
46:08Francis Crick and James Watson, were building models like this.
46:13It was their way of thinking about and investigating the structure of a complex molecule
46:21that's found in the genes of all animals, DNA.
46:26The crucial bit are these chains which encircle the rod.
46:35And here is a second and entwine.
46:39This is the double helix.
46:44The workings of the DNA molecule are now understood in such detail that we can demonstrate something that is truly
46:52astounding.
46:54A gene taken from one animal can function in another.
46:59The gene that causes the jellyfish to be luminous, for example, transplanted into a mouse, will make that mouse luminous.
47:15The genetic code can also reveal relationships.
47:20Even our law courts accept that DNA fingerprinting can establish whether a man is the father of a particular child.
47:30And it can also reveal whether one kind of animal is related to another.
47:41It proves, for example, that kangaroos, ground-living animals that run with great leaps, are closely related to koalas that
47:51have taken to climbing trees.
47:54That insect-eating shrews have cousins that took to the air in search of insects, bats.
48:02And that one branch of the elephant family, way back in geological history, took to the water and became sea
48:09cows.
48:09So, 150 years after the publication of Darwin's revolutionary book, modern genetics has confirmed its fundamental truth.
48:22All life is related.
48:25And it enables us to construct with confidence the complex tree that represents the history of life.
48:34It began in the sea some 3,000 million years ago.
48:41Complex chemical molecules began to clump together to form microscopic blobs, cells.
48:50These were the seeds from which the tree of life developed.
48:55They were able to split, replicating themselves as bacteria do.
48:59And as time passed, they diversified into different groups.
49:05Some remained attached to one another so that they formed chains.
49:09We know them today as algae.
49:13Others formed hollow balls, which collapsed upon themselves, creating a body with an internal cavity.
49:20They were the first multi-celled organisms.
49:24Sponges are their direct descendants.
49:28As more variations appeared, the tree of life grew and became more diverse.
49:34Some organisms became more mobile and developed a mouth that opened into a gut.
49:43Others had bodies stiffened by an internal rod.
49:48They, understandably, developed sense organs around their front end.
49:53A related group had bodies that were divided into segments with little projections on either side that helped them to
50:00move around on the sea floor.
50:03Some of these segmented creatures developed hard protective skins, which gave their bodies some rigidity.
50:10So now the seas were filled with a great variety of animals.
50:16And then, around 450 million years ago, some of these armoured creatures crawled up out of the water and ventured
50:25onto land.
50:28And here, the tree of life branched into a multitude of different species that exploited this new environment in all
50:36kinds of ways.
50:39One group of them developed elongated flaps on their backs, which over many generations eventually developed into wings.
50:48The insects had arrived.
50:51Life moved into the air and diversified into myriad forms.
50:59Life moved into the air, and then found a small mass.
51:00Meanwhile, back in the seas, those creatures with a stiffening rod in their bodies had strengthened it by encasing it
51:06in bone.
51:09A skull developed with a hinged jaw that could grab and hold onto prey.
51:15They grew bigger and developed fins equipped with muscles
51:19that enabled them to swim with speed and power.
51:23So fish now dominated the waters of the world.
51:28One group of them developed the ability to gulp air from the water surface.
51:36Their fleshy fins became weight-supporting legs
51:39and 375 million years ago a few of these backbone creatures
51:45followed the insects onto the land.
51:48They were amphibians with wet skins and they had to return to water to lay their eggs.
51:54But some of their descendants evolved dry, scaly skins
51:59and broke their link with water by laying eggs with watertight shells.
52:05These creatures, the reptiles, were the ancestors of today's tortoises, snakes, lizards and crocodiles.
52:13And of course they included the group that back then came to dominate the land, the dinosaurs.
52:22But 65 million years ago a great disaster overtook the Earth.
52:32Whatever its cause, a great proportion of animals were exterminated.
52:37All the dinosaurs disappeared except for one branch,
52:40whose scales had become modified into feathers.
52:45They were the birds.
52:47While they spread through the skies,
52:49a small, seemingly insignificant group of survivors
52:52began to increase in numbers on the ground beneath.
52:57These creatures differed from their competitors
53:00in that their bodies were warm and insulated with coats of fur.
53:04They were the first mammals.
53:07With much of the land left vacant after the great catastrophe,
53:10they now had their chance.
53:13Their warm, insulated bodies enabled them to be active at all times,
53:18at night as well as during the day,
53:20and in all places,
53:22from the Arctic to the tropics,
53:25in water as well as on land,
53:29on grassy plains and up in the trees.
53:34And the birds of the sea will be the most beautiful birds.
54:13There can be no doubt about our close relationship to these chimpanzees.
54:20Our bodies are so similar.
54:22The proportions of our limbs or our faces may differ,
54:26but otherwise we are very, very similar.
54:29The arrangement of our internal organs, the chemistry of our blood,
54:34the way our bodies work, all these are almost identical,
54:39and DNA confirms that.
54:43Indeed, we are as closely related to chimpanzees and the rest of the apes and monkeys
54:49as, say, lions are to tigers and to the rest of the cat family.
55:18Suddenly, an image from our remote past becomes vivid little light.
55:24The time when our distant ancestors, in order to keep up with the changing environment,
55:29had to wade and keep their heads above water in order to find food.
55:34That crucial moment when our far distant ancestors took a step away from being apes
55:41and a step towards humanity.
55:59The Natural History Museum is one of the most important museums of its kind in the world.
56:05Richard Owen brought it into existence,
56:08but over a century later, discoveries from many branches of science
56:12have shown that his belief that species can never change
56:16but always remain exactly the same was mistaken.
56:39It was Charles Darwin's profound insights that have proved to be true.
56:45And now, to mark the 200th anniversary of his birth,
56:50his statue is being taken from its out-of-the-way location
56:54to be placed centre stage in the main hall.
56:59Keep around in there now.
57:03All right.
57:15Darwin's great insight revolutionised the way in which we see the world.
57:19We now understand why there are so many different species,
57:23why they are distributed in the way they are around the world,
57:27and why their bodies and our bodies are shaped in the way that they are.
57:32Because we understand that bacteria evolve,
57:36we can devise methods of dealing with the diseases they cause.
57:40And because we can disentangle the complex relationships
57:43between animals and plants in a natural community,
57:46we can foresee some of the consequences
57:49when we start to interfere with those communities.
57:53But above all, Darwin has shown us
57:56that we are not apart from the natural world.
58:00we do not have dominion over it.
58:03We are subject to its laws and processes,
58:08as are all other animals on Earth,
58:11to which indeed we are related.
58:13for...
58:14if nothing was�emic,
58:22If anything was brought to us to heaven,
58:22think we would do this again...
58:22don't want bare politeness,
58:22it's�� derivates to home
58:46Music coming up on BBC Four, Hot Chocolate, Yazoo and Simple Minds on Top of the Pops 1982.
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