Browse content similar to What Darwin Didn't Know. Check below for episodes and series from the same categories and more!
Line | From | To | |
---|---|---|---|
We live in a world of exquisite diversity, | 0:00:08 | 0:00:13 | |
with more species than we can possibly count. | 0:00:13 | 0:00:17 | |
Here in Lake Malawi, for instance, | 0:00:18 | 0:00:21 | |
there are hundreds of different fish that are found nowhere else. | 0:00:21 | 0:00:26 | |
Why so many? | 0:00:26 | 0:00:29 | |
Why so different? | 0:00:29 | 0:00:30 | |
150 years ago Charles Darwin published On The Origin Of Species. | 0:00:37 | 0:00:43 | |
And in that one great book he asked the right question... | 0:00:43 | 0:00:48 | |
..and gave the right answer... | 0:00:48 | 0:00:50 | |
Where, asked Darwin, does all this diversity come from? | 0:00:56 | 0:00:59 | |
And answered that it must be the product of evolution. | 0:01:00 | 0:01:06 | |
Species, he argued, give rise to other species | 0:01:06 | 0:01:10 | |
and as they do so, they change. | 0:01:10 | 0:01:13 | |
The changes are minute and subtle, | 0:01:13 | 0:01:16 | |
but given enough time the results could be spectacular. | 0:01:16 | 0:01:19 | |
And so they are. | 0:01:19 | 0:01:22 | |
Darwin's explanation for life on earth | 0:01:24 | 0:01:26 | |
was so seductive and so simple that it seems obvious today. | 0:01:26 | 0:01:32 | |
And yet, Darwin's explanation of how evolution works | 0:01:32 | 0:01:37 | |
was riddled with holes. | 0:01:37 | 0:01:40 | |
Its logical foundations were shaky. | 0:01:40 | 0:01:43 | |
His evidence was weak. | 0:01:43 | 0:01:45 | |
There was so much he did not, | 0:01:45 | 0:01:48 | |
could not, know. | 0:01:48 | 0:01:50 | |
Darwin trusted that future generations of scientists | 0:01:52 | 0:01:56 | |
would complete his work and prove the essential truth of his vision. | 0:01:56 | 0:02:00 | |
And for 150 years that is what we have been doing. | 0:02:00 | 0:02:06 | |
In this film, I'll chart the decline, fall | 0:02:07 | 0:02:10 | |
and ultimate triumph of Darwin's ideas. | 0:02:10 | 0:02:13 | |
And I'll show how evolutionary theory has itself evolved, | 0:02:15 | 0:02:18 | |
so that it is now far more vast and subtle than ever he imagined. | 0:02:18 | 0:02:24 | |
In September 1835 | 0:02:38 | 0:02:41 | |
Charles Darwin arrived in the Galapagos Archipelago... | 0:02:41 | 0:02:45 | |
..and did what he always did when arriving in a new place - | 0:02:47 | 0:02:52 | |
he got out his gun and began to collect. | 0:02:52 | 0:02:56 | |
Among the many inhabitants of the Galapagos that Darwin | 0:02:59 | 0:03:03 | |
pinned, pickled, shot, or stuffed are these four birds. | 0:03:03 | 0:03:08 | |
They don't look like much, but look at them closely. | 0:03:10 | 0:03:15 | |
Look at them as Darwin looked at them, | 0:03:15 | 0:03:19 | |
and you can see the beginnings of evolution. | 0:03:19 | 0:03:23 | |
They are mocking birds. | 0:03:25 | 0:03:28 | |
Each comes from a different island, | 0:03:28 | 0:03:30 | |
and each is subtly different from the others. | 0:03:30 | 0:03:33 | |
They differ in the shape of their bills and the size of their bodies, | 0:03:33 | 0:03:38 | |
and the colour of their plumage. | 0:03:38 | 0:03:41 | |
It was these differences that first caused Darwin to wonder | 0:03:41 | 0:03:46 | |
whether species might transform over time. | 0:03:46 | 0:03:50 | |
Darwin surmised that the birds were variants of the same species | 0:03:52 | 0:03:57 | |
and must therefore descend from a common ancestor - | 0:03:57 | 0:04:01 | |
a mocking bird which had somehow | 0:04:01 | 0:04:03 | |
found its way to the Galapagos many years earlier. | 0:04:03 | 0:04:07 | |
That was Darwin's hunch, | 0:04:09 | 0:04:13 | |
but how to prove it? | 0:04:13 | 0:04:15 | |
He certainly couldn't produce the hypothetical ancestor - | 0:04:15 | 0:04:19 | |
it was lost in time. | 0:04:19 | 0:04:22 | |
So he did what scientists do when they don't have the data - | 0:04:22 | 0:04:27 | |
he appealed to an analogy. | 0:04:27 | 0:04:30 | |
Darwin bred pigeons. | 0:04:39 | 0:04:42 | |
They were, for him, a microcosm of evolution. | 0:04:42 | 0:04:45 | |
They showed how any creature could, given enough time, | 0:04:52 | 0:04:56 | |
be transformed into something very different from its ancestor. | 0:04:56 | 0:05:01 | |
For, implausible though it may seem, | 0:05:06 | 0:05:08 | |
these gorgeous, monstrous, inbred aristocrats of the avian world - | 0:05:08 | 0:05:13 | |
the Scandaroon, the Frillback, the Jacobin, not to forget the Mookee - | 0:05:13 | 0:05:19 | |
are all descended from this - the plebeian rock pigeon. | 0:05:19 | 0:05:24 | |
All pigeons are, at birth, subtly different from each other. | 0:05:27 | 0:05:32 | |
Breeders select those with desirable features to survive and reproduce... | 0:05:32 | 0:05:38 | |
..and they cull the rest. | 0:05:38 | 0:05:41 | |
The desirable features accumulate from generation to generation | 0:05:43 | 0:05:48 | |
and become exaggerated. | 0:05:48 | 0:05:50 | |
And so, remarkably quickly, the birds evolve. | 0:05:50 | 0:05:56 | |
Nature, Darwin said, works like that. | 0:05:56 | 0:06:00 | |
It favours some features and permits others to whither away. | 0:06:00 | 0:06:06 | |
He called this process natural selection. | 0:06:06 | 0:06:10 | |
All this explains why the first chapter of The Origin Of Species is | 0:06:12 | 0:06:16 | |
not about the wonders of the natural world, but rather about pigeons. | 0:06:16 | 0:06:22 | |
Understand the pigeon, he is saying, believe the pigeon, | 0:06:22 | 0:06:26 | |
and all the rest follows. | 0:06:26 | 0:06:28 | |
Or does it? | 0:06:31 | 0:06:33 | |
For Darwin had a problem. | 0:06:34 | 0:06:38 | |
Natural selection was the cornerstone of his theory. | 0:06:38 | 0:06:42 | |
It was, for him, the engine of evolution. | 0:06:42 | 0:06:46 | |
And yet it was by no means clear | 0:06:46 | 0:06:50 | |
that natural selection really worked. | 0:06:50 | 0:06:54 | |
There is, he said, a war of nature. | 0:06:57 | 0:07:01 | |
Famine, violence and death are everywhere. | 0:07:05 | 0:07:09 | |
Species and individuals are locked in a struggle for existence. | 0:07:10 | 0:07:15 | |
The strong survive and reproduce... | 0:07:15 | 0:07:18 | |
..while the weak go to the wall. | 0:07:20 | 0:07:23 | |
Given enough variation, this selective pressure | 0:07:25 | 0:07:28 | |
is enough to bring about slow, incremental change. | 0:07:28 | 0:07:32 | |
This was the theory of evolution by natural selection | 0:07:32 | 0:07:37 | |
that Darwin unveiled in The Origin Of Species. | 0:07:37 | 0:07:40 | |
While the idea of evolution was not in itself new, | 0:07:42 | 0:07:46 | |
no-one had argued it more forcefully, | 0:07:46 | 0:07:49 | |
or documented the evidence for it, with greater rigour. | 0:07:49 | 0:07:53 | |
But was it right? | 0:07:53 | 0:07:55 | |
Had Darwin really made his case? | 0:07:55 | 0:07:59 | |
Of course, many religious types hated the very idea of evolution. | 0:08:04 | 0:08:11 | |
But some of Darwin's fellow scientists weren't too keen either. | 0:08:11 | 0:08:16 | |
Notably Richard Owen, who wrote one of the first reviews of The Origin. | 0:08:16 | 0:08:21 | |
Richard Owen, premier palaeontologist, | 0:08:23 | 0:08:26 | |
coined the term 'dinosaur', helped design these things. | 0:08:26 | 0:08:31 | |
Rampaging through a South London park, | 0:08:33 | 0:08:36 | |
these marvellous reconstructions were built in the 1850s. | 0:08:36 | 0:08:41 | |
They are a tableau of dinosaur life based on Owen's research. | 0:08:42 | 0:08:48 | |
Owen had vague evolutionary leanings. | 0:08:49 | 0:08:52 | |
He thought that species change intermittently, | 0:08:52 | 0:08:55 | |
under the influence of some divine law | 0:08:55 | 0:08:59 | |
and that periodically, | 0:08:59 | 0:09:00 | |
they are swept away in some great catastrophe. | 0:09:00 | 0:09:05 | |
He loathed Darwin's godless evolutionism. | 0:09:05 | 0:09:08 | |
Owen was a thoroughly nasty piece of work. | 0:09:10 | 0:09:14 | |
His review of The Origin, rich in malice, dripping with sarcasm, | 0:09:14 | 0:09:18 | |
damns Darwin even as he praises himself. | 0:09:18 | 0:09:22 | |
All anonymously of course. | 0:09:22 | 0:09:24 | |
"Mr Darwin's rash speculations degrade science. | 0:09:24 | 0:09:29 | |
"He's as bad as the French. | 0:09:29 | 0:09:31 | |
"And", continues Owen, "he doesn't know anything about fossils. | 0:09:31 | 0:09:35 | |
"If he did, he would know that | 0:09:35 | 0:09:37 | |
"ichthyosaurs appear in the lower Jurassic, | 0:09:37 | 0:09:40 | |
"stay there pretty much unchanged, and then just disappear - | 0:09:40 | 0:09:44 | |
"no sign of evolution there." | 0:09:44 | 0:09:46 | |
Owen's venom was probably born from mere spite. | 0:09:49 | 0:09:53 | |
Still, he did seem to have the fossil record on his side. | 0:09:53 | 0:09:58 | |
According to Darwin's theory, | 0:09:58 | 0:10:00 | |
gradual change should be visible in the rocks. | 0:10:00 | 0:10:04 | |
But it wasn't. | 0:10:04 | 0:10:07 | |
Instead, species seemed to arrive and depart, | 0:10:07 | 0:10:11 | |
leaving little in between. | 0:10:11 | 0:10:13 | |
Such gaps in the fossil record would haunt Darwin's theory. | 0:10:15 | 0:10:19 | |
The evidence for natural selection simply wasn't there. | 0:10:19 | 0:10:24 | |
Even his friends had their doubts. | 0:10:25 | 0:10:28 | |
Thomas Henry Huxley worked here at Imperial College London, | 0:10:30 | 0:10:35 | |
where I now work. | 0:10:35 | 0:10:36 | |
A firebrand and a populist, they called him Darwin's bulldog. | 0:10:36 | 0:10:42 | |
Huxley also reviewed The Origin. | 0:10:42 | 0:10:45 | |
"It's a magnificent work. | 0:10:45 | 0:10:47 | |
"It makes the case for evolution." | 0:10:47 | 0:10:49 | |
But then he turns to natural selection. | 0:10:49 | 0:10:53 | |
"Yes, it's logical, yes, it's simple, but has Mr Darwin | 0:10:53 | 0:10:58 | |
"actually seen a species originate by natural selection? | 0:10:58 | 0:11:01 | |
"Can he even prove that it really exists?" | 0:11:01 | 0:11:04 | |
" Well, no. It's a hypothesis, | 0:11:04 | 0:11:07 | |
"perhaps even the best one going, but, and I say this as a friend, | 0:11:07 | 0:11:12 | |
"you understand, Mr Darwin really hasn't proved his point." | 0:11:12 | 0:11:17 | |
Huxley said natural selection can't be seen. | 0:11:20 | 0:11:24 | |
Others said it doesn't work. | 0:11:25 | 0:11:28 | |
They claimed that it was logically flawed. | 0:11:29 | 0:11:33 | |
That it was inconsistent with Darwin's account of inheritance, | 0:11:35 | 0:11:40 | |
of how species transmit their features | 0:11:40 | 0:11:43 | |
from one generation to the next. | 0:11:43 | 0:11:46 | |
This is how Darwin thought inheritance works. | 0:11:52 | 0:11:56 | |
Suppose one parent has dark feathers, fur or skin, | 0:11:56 | 0:12:00 | |
the colour of black coffee, while the other is milky white, | 0:12:00 | 0:12:04 | |
their progeny would be a mix of the two. | 0:12:04 | 0:12:08 | |
They would be a blend. | 0:12:10 | 0:12:12 | |
It seems like an innocuous idea. | 0:12:16 | 0:12:19 | |
Quite a reasonable one, too. | 0:12:19 | 0:12:22 | |
After all, isn't this how human skin colour is inherited? | 0:12:22 | 0:12:26 | |
But Darwin had walked into a theoretical trap, | 0:12:28 | 0:12:31 | |
and a Scottish engineer called Fleeming Jenkin sprang it. | 0:12:31 | 0:12:36 | |
This is how Jenkin phrased the argument. | 0:12:38 | 0:12:41 | |
"Imagine that a white man arrives on an island of negroes. | 0:12:44 | 0:12:48 | |
"He would, no doubt make himself king. | 0:12:48 | 0:12:52 | |
"He would take many negro wives and father many mulatto children. | 0:12:52 | 0:12:57 | |
"Yet no matter how successful our hero is, no matter how superior, | 0:12:58 | 0:13:03 | |
"his coffee-coloured descendants would become progressively darker. | 0:13:03 | 0:13:08 | |
"Within a few generations, all trace of his presence would disappear." | 0:13:08 | 0:13:13 | |
Let's ignore, if we can, the casual racism. | 0:13:15 | 0:13:19 | |
This is Scotland in the 1860s, and Jenkin had a point. | 0:13:19 | 0:13:25 | |
Variation is the stuff of evolution, | 0:13:25 | 0:13:28 | |
and if variation blends then it disappears. | 0:13:28 | 0:13:31 | |
And as it disappears, so the power of natural selection ebbs away. | 0:13:31 | 0:13:36 | |
Jenkin's challenge was serious, and Darwin had no response. | 0:13:39 | 0:13:44 | |
How could he? His theory required some system, some law of inheritance | 0:13:46 | 0:13:51 | |
in which variation did not blend, | 0:13:51 | 0:13:53 | |
but remained stable over the generations. | 0:13:53 | 0:13:56 | |
And yet no-one really knew how such a system could work. | 0:13:59 | 0:14:04 | |
The thing is, Darwin knew all this. | 0:14:04 | 0:14:08 | |
And we know that he knew because he told us so. | 0:14:08 | 0:14:12 | |
Perhaps the most wonderful chapter | 0:14:14 | 0:14:16 | |
of The Origin Of Species is Chapter VI. | 0:14:16 | 0:14:20 | |
It's called Difficulties Of The Theory. | 0:14:20 | 0:14:23 | |
Charles Darwin exposes, with unbearable candour, | 0:14:23 | 0:14:26 | |
devastating honesty, all the weaknesses of his theory. | 0:14:26 | 0:14:31 | |
He tells us all the reasons he may be wrong, | 0:14:31 | 0:14:34 | |
the reasons that his critics pointed out, and more, | 0:14:34 | 0:14:37 | |
but then, appeals to future generations of scientists | 0:14:37 | 0:14:41 | |
to draw inspiration from his book, | 0:14:41 | 0:14:43 | |
solve the difficulties with which his theory is riddled. | 0:14:43 | 0:14:49 | |
It's easy to forget that Darwin was not the first evolutionist. | 0:14:53 | 0:14:58 | |
50 years before The Origin Of Species, | 0:14:58 | 0:15:01 | |
a Frenchman had proposed a theory of evolution, | 0:15:01 | 0:15:05 | |
albeit less coherent and comprehensive than Darwin's. | 0:15:05 | 0:15:10 | |
His name - Jean-Baptiste Lamarck. | 0:15:12 | 0:15:15 | |
Lamarck was Professor of Zoology at the Museum d'Histoire Naturelle. | 0:15:17 | 0:15:22 | |
He published his ideas on evolution in the year Darwin was born. | 0:15:22 | 0:15:28 | |
They were, however, very different. | 0:15:28 | 0:15:32 | |
When an animal, any animal, uses an organ, Lamarck argued, | 0:15:34 | 0:15:38 | |
it becomes strengthened and enlarged. | 0:15:38 | 0:15:41 | |
That's fairly obvious. | 0:15:43 | 0:15:45 | |
We all know that exercise modifies the shape of our body. | 0:15:45 | 0:15:48 | |
It's the same for other creatures as well. | 0:15:48 | 0:15:52 | |
But Lamarck went further. | 0:15:52 | 0:15:56 | |
He argued that these changes, | 0:15:56 | 0:15:58 | |
acquired in one's lifetime, were passed on. | 0:15:58 | 0:16:01 | |
And it is this, the inheritance of acquired characteristics, | 0:16:04 | 0:16:08 | |
as it came to be known, that's the engine of evolution. | 0:16:08 | 0:16:12 | |
The icon of Lamarckism is the giraffe. | 0:16:15 | 0:16:20 | |
According to Lamarck, some ancestral giraffe had stretched its neck | 0:16:20 | 0:16:25 | |
reaching for leaves on the highest branches. | 0:16:25 | 0:16:28 | |
That stretched neck had been passed on to its offspring, who, in turn, | 0:16:28 | 0:16:33 | |
had stretched their necks even further, | 0:16:33 | 0:16:37 | |
so that now all giraffes have long necks. | 0:16:37 | 0:16:40 | |
There is a seductive, intuitive, quality to Lamarck's logic, | 0:16:43 | 0:16:48 | |
one that Darwin, confronting the inadequacies of his own theory, | 0:16:48 | 0:16:52 | |
found increasingly hard to resist. | 0:16:52 | 0:16:55 | |
The giraffe's neck is a cliche. | 0:17:01 | 0:17:03 | |
It's in every textbook that explains the difference | 0:17:03 | 0:17:06 | |
between Darwinian and Lamarckian evolution. | 0:17:06 | 0:17:10 | |
But if you actually read what Darwin says about the giraffe | 0:17:10 | 0:17:14 | |
in the sixth and final edition of The Origin, | 0:17:14 | 0:17:18 | |
what you find is something rather different. | 0:17:18 | 0:17:22 | |
First he talks about natural selection. | 0:17:23 | 0:17:26 | |
That's what gives you the giraffe's neck. | 0:17:26 | 0:17:28 | |
But then he adds another line | 0:17:28 | 0:17:30 | |
about the inherited effects of the increased use of parts. | 0:17:30 | 0:17:34 | |
Together, they give you the giraffe's neck. | 0:17:34 | 0:17:37 | |
"Increased use of parts"? | 0:17:37 | 0:17:40 | |
What's going on here? | 0:17:40 | 0:17:41 | |
That's pure Lamarck. | 0:17:41 | 0:17:43 | |
Can it be that Darwin, in his dotage, is becoming less Darwinian? | 0:17:43 | 0:17:49 | |
Well, yes. | 0:17:51 | 0:17:53 | |
Perhaps natural selection is not as powerful as once he had thought. | 0:17:53 | 0:17:59 | |
A recantation? No. | 0:18:01 | 0:18:04 | |
Just the candour of an old man | 0:18:04 | 0:18:07 | |
who had spent his life trying to understand the world. | 0:18:07 | 0:18:11 | |
Darwin died in April 1882. | 0:18:11 | 0:18:14 | |
He had wanted to be buried quietly near his house in Kent, | 0:18:18 | 0:18:22 | |
but his supporters arranged a funeral here at Westminster Abbey. | 0:18:22 | 0:18:28 | |
They turned the agnostic into a saint | 0:18:28 | 0:18:31 | |
of the new secular materialist age. | 0:18:31 | 0:18:35 | |
It was the apotheosis of Charles Robert Darwin. | 0:18:35 | 0:18:40 | |
He had become a great Briton. | 0:18:42 | 0:18:46 | |
But the eulogies rang hollow. | 0:18:47 | 0:18:51 | |
Darwin had shown that life on earth was the result of natural laws. | 0:18:51 | 0:18:56 | |
But what were those laws? | 0:18:56 | 0:18:58 | |
Everyone - everyone, that is, who mattered - | 0:18:58 | 0:19:02 | |
agreed that evolution was a fact. | 0:19:02 | 0:19:05 | |
But natural selection? | 0:19:05 | 0:19:08 | |
No thanks. | 0:19:08 | 0:19:09 | |
Even as Darwin lay in state, | 0:19:15 | 0:19:18 | |
some Darwinians were breaking ranks. | 0:19:18 | 0:19:21 | |
Chief among them, Dutch botanist, Hugo De Vries. | 0:19:24 | 0:19:27 | |
Inspired by Darwin, he was searching for a suitable organism | 0:19:31 | 0:19:34 | |
with which to investigate the workings of inheritance... | 0:19:34 | 0:19:38 | |
and found one. | 0:19:38 | 0:19:40 | |
He chose a plant called Oenothera lamarckiana. | 0:19:40 | 0:19:46 | |
Gardeners will know it as the evening primrose | 0:19:48 | 0:19:52 | |
for it blooms at dusk. | 0:19:52 | 0:19:54 | |
It is found throughout the dunes that protect Holland from the sea. | 0:19:54 | 0:19:59 | |
And it's really just a weed. | 0:19:59 | 0:20:01 | |
Though lovely for all that. | 0:20:01 | 0:20:06 | |
De Vries discovered that Oenothera lamarckiana | 0:20:08 | 0:20:12 | |
occasionally produces progeny that looked very different from itself, | 0:20:12 | 0:20:18 | |
that have different stems, leaves, flowers. | 0:20:18 | 0:20:23 | |
These new variants he found did not blend | 0:20:23 | 0:20:28 | |
but were stable, as stable as new species. | 0:20:28 | 0:20:32 | |
Coining a term, De Vries called these dramatic variations mutations. | 0:20:33 | 0:20:39 | |
Following his discovery, | 0:20:43 | 0:20:45 | |
De Vries was made director of the botanical gardens in Amsterdam. | 0:20:45 | 0:20:49 | |
He bred and crossbred more Oenotheras, 53,000 of them. | 0:20:53 | 0:20:58 | |
It seems like a lot, but then again, he was Dutch. | 0:21:00 | 0:21:04 | |
This is the palm house that Amsterdam built for De Vries. | 0:21:08 | 0:21:11 | |
And these are some of his flowers pressed for posterity. | 0:21:11 | 0:21:16 | |
They are ancient and desiccated | 0:21:16 | 0:21:18 | |
but you can still see the differences in growth and form. | 0:21:18 | 0:21:24 | |
Mutation, it seemed, could produce radically new plants. | 0:21:24 | 0:21:28 | |
It could even, said De Vries, produce new species. | 0:21:28 | 0:21:33 | |
This was all very unDarwinian. | 0:21:35 | 0:21:38 | |
What of the vertiginous time scales, the infinity of incremental steps, | 0:21:42 | 0:21:48 | |
the grandeur of Darwin's view of life? | 0:21:48 | 0:21:52 | |
Irrelevant, said De Vries. | 0:21:52 | 0:21:55 | |
The origin of species requires only one thing: mutation. | 0:21:58 | 0:22:04 | |
He called it his Mutation Theory. | 0:22:04 | 0:22:07 | |
It made him famous. | 0:22:07 | 0:22:09 | |
For Lamarck, he said, the origin of species was a natural phenomenon. | 0:22:09 | 0:22:14 | |
For Darwin, the object of scientific investigation, | 0:22:14 | 0:22:18 | |
for De Vries, he liked to talk of himself in the third person, | 0:22:18 | 0:22:21 | |
it was the object of experimental enquiry. | 0:22:21 | 0:22:24 | |
Lamarck, Darwin, De Vries. | 0:22:24 | 0:22:28 | |
No doubts about HIS place in the pantheon, then. | 0:22:28 | 0:22:31 | |
What De Vries or no-one else realised at the time | 0:22:34 | 0:22:37 | |
was that Oenothera lamarckiana was a genetic freak. | 0:22:37 | 0:22:42 | |
Few other organisms mutate so spectacularly. | 0:22:42 | 0:22:47 | |
He had based his entire theory on one, very peculiar, species. | 0:22:47 | 0:22:54 | |
That, however, didn't stop the rise of mutationism. | 0:22:54 | 0:22:59 | |
Others began to investigate the oddities of nature. | 0:23:02 | 0:23:05 | |
In Britain, a Cambridge biologist, William Bateson, | 0:23:07 | 0:23:11 | |
published materials for the study of variation. | 0:23:11 | 0:23:14 | |
A collection of two-headed turtles, | 0:23:14 | 0:23:17 | |
girls with four ears, | 0:23:17 | 0:23:21 | |
and eight-fingered hands. | 0:23:21 | 0:23:23 | |
It was a medieval monsters and marvels book, | 0:23:23 | 0:23:27 | |
reworked for the evolutionary age. | 0:23:27 | 0:23:30 | |
Mutation was the real creative force behind evolution | 0:23:33 | 0:23:37 | |
and natural selection, said the mutationists, just wasn't needed. | 0:23:37 | 0:23:43 | |
London 1909. | 0:23:49 | 0:23:51 | |
Darwin is long dead, and his theory is 50 years old. | 0:23:55 | 0:23:59 | |
The British Museum of Natural History celebrates | 0:24:03 | 0:24:06 | |
with an exhibition of Darwiniana: | 0:24:06 | 0:24:08 | |
specimens, letters, manuscripts. | 0:24:08 | 0:24:13 | |
It's a magnificent celebration, | 0:24:13 | 0:24:15 | |
a worthy commemoration of the man who gave us evolution. | 0:24:15 | 0:24:20 | |
But something is missing, | 0:24:21 | 0:24:23 | |
something upon which the organisers refuse to be drawn. | 0:24:23 | 0:24:27 | |
Natural selection. | 0:24:27 | 0:24:29 | |
You might have expected that the South Kensington museum, | 0:24:31 | 0:24:35 | |
now a temple of evolutionism, | 0:24:35 | 0:24:37 | |
would have wanted to tell the public about Darwin's theory. | 0:24:37 | 0:24:41 | |
But no, that's all too controversial for the keepers and curators who'd | 0:24:41 | 0:24:45 | |
much rather not commit themselves in the great evolution debate. | 0:24:45 | 0:24:50 | |
Hardly courageous, but understandable. | 0:24:50 | 0:24:54 | |
By 1909 scientific consensus had shifted against Darwin's theory. | 0:24:54 | 0:25:00 | |
Evolution by natural selection was almost extinct. | 0:25:02 | 0:25:06 | |
Just as Darwinism was at its nadir, a revival was underway. | 0:25:18 | 0:25:24 | |
For Darwin's critics were, themselves, coming under attack. | 0:25:24 | 0:25:27 | |
And leading the vanguard was a German scientist, August Weismann. | 0:25:27 | 0:25:34 | |
Weismann was a doctor, a biologist and above all a great Darwinian. | 0:25:35 | 0:25:42 | |
He would revive the case for natural selection. | 0:25:42 | 0:25:46 | |
His key exhibit, an insect called Papilio dardanus. | 0:25:46 | 0:25:51 | |
Papilo dardanus is a butterfly that lives throughout Africa, | 0:25:54 | 0:25:59 | |
and the females of the species are mimics. | 0:25:59 | 0:26:05 | |
This female Papilo dardanus here | 0:26:07 | 0:26:09 | |
mimics this altogether unrelated species. | 0:26:09 | 0:26:13 | |
And this one over here mimics something completely different. | 0:26:13 | 0:26:19 | |
And it does so in every detail. | 0:26:19 | 0:26:23 | |
Over many generations, Papilio dardanus females have evolved. | 0:26:27 | 0:26:33 | |
The shapes and colours of their wings have transformed... | 0:26:33 | 0:26:36 | |
..and the reason why is very obvious. | 0:26:39 | 0:26:42 | |
Birds eat butterflies, | 0:26:45 | 0:26:47 | |
so many butterflies have evolved offensive chemicals | 0:26:47 | 0:26:51 | |
that make them taste repugnant. | 0:26:51 | 0:26:53 | |
Papilio dardanus doesn't, | 0:26:54 | 0:26:57 | |
but by mimicking those that do, they can fool the birds. | 0:26:57 | 0:27:01 | |
They are the cardboard tanks in the battle of nature. | 0:27:02 | 0:27:06 | |
Here, said Weismann, is evidence that Darwin was right. | 0:27:09 | 0:27:14 | |
Only natural selection, that slow and subtle craftsman, | 0:27:14 | 0:27:18 | |
working in infinitesimally small steps, | 0:27:18 | 0:27:22 | |
could make two unrelated butterfly species so very much alike. | 0:27:22 | 0:27:27 | |
Hugo De Vries and his fellow mutationists had argued that species | 0:27:32 | 0:27:37 | |
originate instantaneously by single dramatic mutations. | 0:27:37 | 0:27:42 | |
No, said Weismann, they evolve gradually | 0:27:47 | 0:27:51 | |
by the accumulation of a great many tiny mutations. | 0:27:51 | 0:27:55 | |
Natural selection is a subtle force - | 0:27:55 | 0:27:58 | |
as subtle as the markings on the wings of a butterfly. | 0:27:58 | 0:28:03 | |
But Weissman's real ire was reserved | 0:28:06 | 0:28:09 | |
for that other great anti-Darwinian theory, Lamarckism. | 0:28:09 | 0:28:14 | |
He knew that sperm and eggs carry the material of inheritance. | 0:28:16 | 0:28:22 | |
But where, he asked, do they come from? | 0:28:22 | 0:28:25 | |
By tracing the origin and fate of the cells in the embryo, | 0:28:27 | 0:28:30 | |
Weismann realised that the cells that give rise to sperm and eggs | 0:28:30 | 0:28:35 | |
were quickly isolated from the rest of the body's cells. | 0:28:35 | 0:28:38 | |
That they formed a separate lineage. | 0:28:38 | 0:28:42 | |
That, said Weissman, is why acquired characteristics | 0:28:45 | 0:28:48 | |
could not be passed on to future generations, | 0:28:48 | 0:28:52 | |
why Lamarck was wrong, and why the giraffe stretches its neck in vain. | 0:28:52 | 0:28:59 | |
A body could strive, suffer, stretch and sacrifice | 0:29:01 | 0:29:06 | |
and none of it would matter. | 0:29:06 | 0:29:08 | |
All bodies must die was Weismann's message, | 0:29:08 | 0:29:13 | |
only your eggs and sperm have even a shot at immortality. | 0:29:13 | 0:29:17 | |
But Weissman did more. | 0:29:19 | 0:29:22 | |
He reasoned that the material of inheritance | 0:29:22 | 0:29:25 | |
was something physical in the nucleus of each sperm and egg cell. | 0:29:25 | 0:29:29 | |
He called this material germ plasm. | 0:29:29 | 0:29:32 | |
Looking closer, his contemporaries saw distinct particles | 0:29:34 | 0:29:38 | |
within the germ plasm - chromosomes. | 0:29:38 | 0:29:41 | |
With reproduction, chromosomes mix, mingle, and recombine, | 0:29:44 | 0:29:49 | |
but they never blend. | 0:29:49 | 0:29:51 | |
They are always passed on intact. | 0:29:53 | 0:29:57 | |
This dance of the chromosomes | 0:29:58 | 0:30:00 | |
confirmed what an Augustinian monk has supposed three decades earlier. | 0:30:00 | 0:30:07 | |
Gregor Mendel, he's the archetypal scientific hero: | 0:30:09 | 0:30:14 | |
works away breeding peas in a Moravian monastery, | 0:30:14 | 0:30:17 | |
publishes two luminous papers in an obscure journal that no-one reads, | 0:30:17 | 0:30:24 | |
give up science and becomes, | 0:30:24 | 0:30:27 | |
like so many great scientists, an administrator. | 0:30:27 | 0:30:30 | |
Mendel was appointed abbot of Brno monastery. | 0:30:34 | 0:30:38 | |
He abandoned his experiments; his publications were forgotten | 0:30:38 | 0:30:43 | |
for 34 years, and when he died his papers were burned. | 0:30:43 | 0:30:48 | |
When, in 1900, his experiments were rediscovered and republished, | 0:30:48 | 0:30:53 | |
they became, however, the stuff of scientific legend. | 0:30:53 | 0:30:57 | |
Think about it, you're breeding peas, | 0:31:03 | 0:31:06 | |
green peas, yellow peas, wrinkly peas, smooth peas. | 0:31:06 | 0:31:11 | |
You count the numbers of peas in each generation, | 0:31:11 | 0:31:17 | |
calculate a few ratios, and you discover what everyone else, | 0:31:17 | 0:31:22 | |
what Darwin himself had missed. | 0:31:22 | 0:31:25 | |
The laws that rule the inheritance of nearly every living thing. | 0:31:25 | 0:31:31 | |
Here, among Mendel's peas, were mathematical laws | 0:31:32 | 0:31:36 | |
that explained how traits are passed down the generations. | 0:31:36 | 0:31:41 | |
And, rather wonderfully, these laws, mere statistical abstractions, | 0:31:41 | 0:31:48 | |
were the very system of inheritance that natural selection needed. | 0:31:48 | 0:31:53 | |
They gave natural selection | 0:31:53 | 0:31:56 | |
the supply of heritable variation that it needed to work. | 0:31:56 | 0:32:00 | |
Rothamsted Agricultural Station in Hertfordshire | 0:32:10 | 0:32:13 | |
is an unlikely landmark in the history of evolutionary biology. | 0:32:13 | 0:32:19 | |
What it's really famous for is an experiment aimed at estimating | 0:32:19 | 0:32:23 | |
the effects of fertilizers on crop yields. | 0:32:23 | 0:32:26 | |
The experiment had begun in the 1840s. | 0:32:28 | 0:32:31 | |
Every year, samples had been collected and stored | 0:32:31 | 0:32:34 | |
and there they lay. | 0:32:34 | 0:32:35 | |
Until 1919 when they hired a young Cambridge mathematician | 0:32:35 | 0:32:41 | |
to analyse them. | 0:32:41 | 0:32:42 | |
His name was Ronald Aylmer Fisher. | 0:32:42 | 0:32:47 | |
Fisher was a prodigy. | 0:32:49 | 0:32:51 | |
Profoundly myopic, | 0:32:51 | 0:32:53 | |
he had learnt to visualize mathematical problems in his head. | 0:32:53 | 0:32:58 | |
You wouldn't think that such a clever man | 0:33:02 | 0:33:05 | |
would be happy calculating agricultural yields. | 0:33:05 | 0:33:09 | |
But he liked it. | 0:33:10 | 0:33:12 | |
There were lots of numbers to crunch, | 0:33:14 | 0:33:17 | |
and no-one knew how to do it. | 0:33:17 | 0:33:19 | |
No problem, said Fisher, | 0:33:19 | 0:33:22 | |
and invented some new statistics. | 0:33:22 | 0:33:24 | |
Some new statistics? | 0:33:29 | 0:33:30 | |
Fisher invented just about every statistical test I've ever used. | 0:33:30 | 0:33:35 | |
And not just the tests. When Fisher wanted to solve a problem, | 0:33:35 | 0:33:39 | |
he would invent a whole new branch of mathematics. | 0:33:39 | 0:33:43 | |
But Fisher was interested in more than crop yields. | 0:33:45 | 0:33:50 | |
He was also rather keen on eugenics. | 0:33:50 | 0:33:54 | |
NARRATOR: In institutions such as this all over the country, | 0:33:54 | 0:33:57 | |
mental defectives are cared for. | 0:33:57 | 0:33:59 | |
But it would have been better by far, | 0:33:59 | 0:34:02 | |
for them and for the rest of the community, | 0:34:02 | 0:34:04 | |
if they had never been born. | 0:34:04 | 0:34:06 | |
Fisher was worried that the British were becoming thick. | 0:34:06 | 0:34:11 | |
That the poor, feckless and stupid | 0:34:11 | 0:34:14 | |
were outbreeding the rich, thrifty and smart. | 0:34:14 | 0:34:18 | |
So you see, that in a mere matter of four generations | 0:34:18 | 0:34:21 | |
individuals below the average | 0:34:21 | 0:34:23 | |
have become more than five times as abundant as those above it. | 0:34:23 | 0:34:26 | |
And so if we want to maintain the race at a high level, | 0:34:27 | 0:34:31 | |
everybody sound in body and mind should marry | 0:34:31 | 0:34:34 | |
and have enough children to perpetuate their stock | 0:34:34 | 0:34:37 | |
and carry on the race. | 0:34:37 | 0:34:39 | |
Fisher fathered eight children himself - | 0:34:39 | 0:34:42 | |
his own personal eugenics programme. | 0:34:42 | 0:34:46 | |
It was, of course, absurd. | 0:34:48 | 0:34:50 | |
There's no evidence that the nation's collective IQ | 0:34:50 | 0:34:54 | |
was in terminal decline. | 0:34:54 | 0:34:56 | |
Yet out of Fisher's eugenical obsessions came something wonderful. | 0:34:56 | 0:35:00 | |
For in the evenings between calculating correlation coefficients | 0:35:00 | 0:35:04 | |
and fathering children, he thought about natural selection. | 0:35:04 | 0:35:09 | |
For Fisher, natural selection was a force | 0:35:14 | 0:35:17 | |
rather like the waves that beat against a beach. | 0:35:17 | 0:35:20 | |
Just as they may at times pound the shore without relent | 0:35:22 | 0:35:27 | |
and at other times lap gently, | 0:35:27 | 0:35:30 | |
so too natural selection may gust or whisper, but it never disappears. | 0:35:30 | 0:35:35 | |
And just as the waves winnow, sift and sort the pebbles on this beach, | 0:35:39 | 0:35:44 | |
so natural selection winnows, sifts and sorts | 0:35:44 | 0:35:47 | |
the variation within species. | 0:35:47 | 0:35:49 | |
And it is this sorting that is evolution itself. | 0:35:51 | 0:35:55 | |
All this Fisher described with a single equation. | 0:35:59 | 0:36:04 | |
He called it his Fundamental Theorem of Natural Selection, | 0:36:04 | 0:36:10 | |
and said that it was supreme among the laws of biological science. | 0:36:10 | 0:36:16 | |
He even compared it in its scope and power and generality | 0:36:16 | 0:36:21 | |
to the Second Law of Thermodynamics. | 0:36:21 | 0:36:24 | |
Fisher turned natural selection into a formula. | 0:36:28 | 0:36:32 | |
But a formula without data isn't much good. | 0:36:32 | 0:36:37 | |
You have to show that it actually works - | 0:36:37 | 0:36:39 | |
that it says something useful | 0:36:39 | 0:36:41 | |
about living, breathing, copulating creatures. | 0:36:41 | 0:36:45 | |
Which brings us to a rather dull-looking moth. | 0:36:47 | 0:36:51 | |
Here is a story of natural selection in action. | 0:36:54 | 0:36:58 | |
The story of Biston bestularia - the peppered moth. | 0:36:58 | 0:37:03 | |
Once upon a time, it was the colour of speckled ivory. | 0:37:05 | 0:37:09 | |
This colour was an adaptation, | 0:37:09 | 0:37:12 | |
camouflaging the moth as it rested on woodland lichens, | 0:37:12 | 0:37:16 | |
protecting it from the birds that would prey on it. | 0:37:16 | 0:37:19 | |
But then came the Industrial Revolution. | 0:37:19 | 0:37:23 | |
Soot killed the lichens and turned the trees black. | 0:37:23 | 0:37:27 | |
The moths were no longer camouflaged, | 0:37:29 | 0:37:32 | |
they were exposed and vulnerable to attack. | 0:37:32 | 0:37:35 | |
So they began to evolve - fast. | 0:37:37 | 0:37:41 | |
A new, dark, form of the moth spread. | 0:37:41 | 0:37:44 | |
By the 1950s it was found across Britain. | 0:37:44 | 0:37:48 | |
In the woods, biologist Bernard Kettlewell conducted experiments, | 0:37:51 | 0:37:56 | |
calculated the rate of change and the strength of natural selection, | 0:37:56 | 0:38:02 | |
and he found that the equations worked. | 0:38:02 | 0:38:07 | |
Every character, in every species of insects, plant and man himself, | 0:38:07 | 0:38:13 | |
is constantly under collective pressure. | 0:38:13 | 0:38:17 | |
We have shown if the pressure is high enough within 50 generations | 0:38:17 | 0:38:23 | |
one character can nearly entirely substitute another. | 0:38:23 | 0:38:28 | |
It is due to such changes in many characters | 0:38:28 | 0:38:32 | |
that new species are gradually evolving. | 0:38:32 | 0:38:36 | |
And the moths have continued to evolve. | 0:38:41 | 0:38:44 | |
In 1956 the Clean Air Act scrubbed the soot from the nation's skies, | 0:38:44 | 0:38:49 | |
and from the bark of the nation's trees. | 0:38:49 | 0:38:51 | |
The dark moths began to disappear, | 0:38:53 | 0:38:55 | |
and the light moths returned. | 0:38:55 | 0:38:57 | |
Evolution went into reverse. | 0:38:59 | 0:39:01 | |
Natural selection not only existed, it was far more powerful, | 0:39:04 | 0:39:09 | |
and evolution far swifter, than Darwin had ever imagined. | 0:39:09 | 0:39:14 | |
But if there is a place of which Darwinians dream, it is Lake Malawi. | 0:39:19 | 0:39:25 | |
One of the three great lakes of Africa, | 0:39:32 | 0:39:36 | |
it was discovered by David Livingstone | 0:39:36 | 0:39:38 | |
just as The Origin of Species was going to press. | 0:39:38 | 0:39:41 | |
But it took the best part of a century before we realised | 0:39:47 | 0:39:51 | |
just how remarkable are the fish in these waters. | 0:39:51 | 0:39:55 | |
They are, quite simply, | 0:39:57 | 0:39:59 | |
the most beautiful vindication of Darwin's theory. | 0:39:59 | 0:40:03 | |
Dive among them, and the first thing you notice | 0:40:04 | 0:40:07 | |
is how astonishingly various are these fish. | 0:40:07 | 0:40:12 | |
They differ from each other | 0:40:12 | 0:40:13 | |
in the shapes of their bodies, their mouth and teeth - | 0:40:13 | 0:40:17 | |
in their colours and their breeding habits, | 0:40:17 | 0:40:21 | |
and yet they are all members of the same family. | 0:40:22 | 0:40:27 | |
They are all cichlids. | 0:40:27 | 0:40:29 | |
Two million years ago | 0:40:33 | 0:40:35 | |
a cichlid must have entered the lake and multiplied. | 0:40:35 | 0:40:40 | |
Over time it seems the lake levels rose and fell, | 0:40:40 | 0:40:44 | |
creating a universe of different habitats, | 0:40:44 | 0:40:47 | |
each with its own resources to exploit, | 0:40:47 | 0:40:49 | |
and each evolving its own set of cichlids. | 0:40:49 | 0:40:53 | |
And now there are 400, 500, maybe 600 species here - | 0:41:01 | 0:41:07 | |
more than all the species of fish | 0:41:07 | 0:41:10 | |
in all the lakes and rivers of Europe or America. | 0:41:10 | 0:41:15 | |
It's not just that this lake has so many species of cichlids, | 0:41:27 | 0:41:31 | |
it's how diverse they, | 0:41:31 | 0:41:33 | |
how many different ways in which they make a living. | 0:41:33 | 0:41:36 | |
This fish over here is Pseudotropheus elongatus and | 0:41:36 | 0:41:40 | |
it makes a living by scraping algae off rocks and combing through it. | 0:41:40 | 0:41:45 | |
This one does the same except it has an even more elaborate mouth. | 0:41:45 | 0:41:50 | |
It has its teeth arranged rather like a rasp | 0:41:50 | 0:41:54 | |
with lots of little teeth with which it files away | 0:41:54 | 0:41:57 | |
and scrapes the algae off the rocks. | 0:41:57 | 0:41:59 | |
This...this fish here buries it head in the sand, opens its mouth | 0:41:59 | 0:42:05 | |
and gobbles up little Chironomid midges that are living there. | 0:42:05 | 0:42:10 | |
And this thing is the most remarkable cichlid of all, | 0:42:10 | 0:42:14 | |
Rhamphochromis. | 0:42:14 | 0:42:15 | |
It is the uber-predator, the Tyrannosaurus of the lake, | 0:42:15 | 0:42:20 | |
gobbling anything that it can with those formidable sharp teeth. | 0:42:20 | 0:42:25 | |
What's so most amazing about these fish is that they're all descended | 0:42:28 | 0:42:33 | |
from one cichlid that entered this lake about two million years ago. | 0:42:33 | 0:42:38 | |
0 to 600 fish in about two million years. | 0:42:38 | 0:42:43 | |
It is one of the most astonishing evolutionary events | 0:42:43 | 0:42:46 | |
that has ever happened on this planet. | 0:42:46 | 0:42:49 | |
By the end of the 1950s evolution had a new formula. | 0:42:53 | 0:42:58 | |
A combination of natural selection, | 0:42:58 | 0:43:01 | |
isolation, Mendelian inheritance, and mathematical theory. | 0:43:01 | 0:43:06 | |
It was called the neo-Darwinian synthesis. | 0:43:08 | 0:43:11 | |
The formula wasn't entirely Darwinian, but that didn't matter. | 0:43:14 | 0:43:19 | |
On the centenary of The Origin of Species, | 0:43:19 | 0:43:22 | |
everyone agreed that Darwin's vision had triumphed. | 0:43:22 | 0:43:25 | |
Everyone was a Darwinian. | 0:43:25 | 0:43:28 | |
You could almost say that they were more Darwinian than Darwin himself. | 0:43:28 | 0:43:32 | |
And yet, as Darwinism entered its second century, | 0:43:37 | 0:43:41 | |
some anomalies remained. | 0:43:41 | 0:43:43 | |
Natural selection may have triumphed, | 0:43:44 | 0:43:47 | |
yet some animal behaviours were still hard to explain | 0:43:47 | 0:43:51 | |
in terms of natural selection. | 0:43:51 | 0:43:53 | |
Such as altruism. | 0:43:58 | 0:44:01 | |
In a world driven by competition, | 0:44:05 | 0:44:08 | |
why are some animals altruistic? | 0:44:08 | 0:44:12 | |
Termites, for instance, | 0:44:13 | 0:44:15 | |
cooperate relentlessly building vast mounds on the African plain. | 0:44:15 | 0:44:20 | |
A termite mound is filled with millions of altruists, | 0:44:21 | 0:44:25 | |
the soldiers and workers | 0:44:25 | 0:44:33 | |
whose lives | 0:44:33 | 0:44:35 | |
are devoted to defending and feeding the queen. | 0:44:35 | 0:44:40 | |
They are the eunuchs of the termite state | 0:44:43 | 0:44:47 | |
and their existence is surprisingly hard to explain. | 0:44:47 | 0:44:52 | |
According to Darwinian logic, creatures are engineered | 0:44:55 | 0:44:59 | |
by natural selection to increase their chances of reproduction. | 0:44:59 | 0:45:03 | |
Yet most termites are sterile, they don't reproduce at all. | 0:45:09 | 0:45:13 | |
They work for the colony, apparently without reward. | 0:45:13 | 0:45:17 | |
Why? | 0:45:19 | 0:45:21 | |
In 1964 zoologist, Bill Hamilton, | 0:45:21 | 0:45:25 | |
proposed a solution to the problem of altruism. | 0:45:25 | 0:45:28 | |
One that explained the existence of social insects. | 0:45:28 | 0:45:33 | |
This highly regimented move by hundreds of thousands of individuals | 0:45:33 | 0:45:37 | |
is a typically impressive achievement of the social insects. | 0:45:37 | 0:45:40 | |
Hamilton realised that the members of any colony | 0:45:40 | 0:45:44 | |
are very closely related. | 0:45:44 | 0:45:45 | |
And, as such, they share genes. | 0:45:47 | 0:45:50 | |
The queen alone is replicating the genes of the colony on its behalf. | 0:45:50 | 0:45:55 | |
That, said Hamilton, is the key. | 0:45:56 | 0:45:58 | |
If your altruistic act benefits a relative then you may pay a cost. | 0:46:01 | 0:46:06 | |
But at least some of your genes will reap the benefit. | 0:46:06 | 0:46:10 | |
Natural selection does not count the fates of individuals, | 0:46:14 | 0:46:19 | |
it counts the fates of genes. | 0:46:19 | 0:46:21 | |
Termite soldiers sacrifice themselves for their queen | 0:46:27 | 0:46:31 | |
because she shares many of their genes. | 0:46:31 | 0:46:34 | |
And by devoting their lives to her, | 0:46:34 | 0:46:36 | |
more of her genes, and hence their genes, | 0:46:36 | 0:46:39 | |
are passed on than they could possibly achieve by themselves. | 0:46:39 | 0:46:43 | |
This was a radical extension of Darwinism | 0:46:47 | 0:46:50 | |
and it spawned a new science. | 0:46:50 | 0:46:52 | |
At Harvard E O Wilson gave it a name - sociobiology. | 0:46:52 | 0:46:56 | |
At Oxford, Richard Dawkins gave it a slogan - The Selfish Gene. | 0:46:56 | 0:47:02 | |
Wherever sociobiologists looked, they explained | 0:47:04 | 0:47:07 | |
all the strange things animals do as the product of natural selection, | 0:47:07 | 0:47:12 | |
not on individuals, but on their genes. | 0:47:12 | 0:47:16 | |
Each individual is just obeying its own genes. | 0:47:16 | 0:47:19 | |
And humans, they said, are no different. | 0:47:19 | 0:47:23 | |
Our behaviours too, can be explained by genetic programmes | 0:47:25 | 0:47:28 | |
shaped by natural selection. | 0:47:28 | 0:47:31 | |
This is the fundamental principle of sociobiology. | 0:47:31 | 0:47:34 | |
The genes for particular social behaviour exist. | 0:47:34 | 0:47:38 | |
Applied to humans, sociobiology seems excessively reductive. | 0:47:38 | 0:47:44 | |
But there's no doubt that as an explanation of animal behaviour, | 0:47:45 | 0:47:49 | |
it triumphed. | 0:47:49 | 0:47:52 | |
And sociobiology's triumph was the triumph of natural selection. | 0:47:52 | 0:47:57 | |
A force, that in Darwin's time, seemed weak and ephemeral, | 0:48:02 | 0:48:07 | |
was now omnipotent and omnipresent. | 0:48:07 | 0:48:10 | |
Yet Darwin gave us more than natural selection, | 0:48:15 | 0:48:18 | |
more than a mechanism of evolution. | 0:48:18 | 0:48:21 | |
He also gave us a new narrative, or at least the promise of one. | 0:48:23 | 0:48:28 | |
He told us that the history of life was a tale of epic forces and scales | 0:48:28 | 0:48:35 | |
and that it was ours to discover. | 0:48:35 | 0:48:39 | |
If there is an icon of Darwin's theory, it is this. | 0:48:48 | 0:48:52 | |
A metaphor for all evolutionary history. | 0:48:54 | 0:48:59 | |
A tree. | 0:48:59 | 0:49:00 | |
The twigs, Darwin said, were species. | 0:49:04 | 0:49:07 | |
And they were connected to their ancestors by branches, | 0:49:07 | 0:49:10 | |
and those ancestors to theirs, reaching deep into the past. | 0:49:10 | 0:49:15 | |
So that the whole history of life | 0:49:15 | 0:49:17 | |
could be represented as a great tree. | 0:49:17 | 0:49:21 | |
Darwin first conceived this image in 1837. | 0:49:24 | 0:49:29 | |
He sketched a simple tree-like diagram to show how lineages | 0:49:29 | 0:49:34 | |
could originate from a single source and then diverge and proliferate. | 0:49:34 | 0:49:39 | |
Above it he scribbled the words, "I think". | 0:49:39 | 0:49:43 | |
22 years later, in The Origin, | 0:49:46 | 0:49:49 | |
he confidently asserts that just such a tree | 0:49:49 | 0:49:53 | |
could be constructed for any group of creatures. | 0:49:53 | 0:49:57 | |
Easy to say, hard to do, and Darwin didn't even try. | 0:50:00 | 0:50:05 | |
Why did Darwin, so bold and so visionary, | 0:50:11 | 0:50:14 | |
not give us the history of life that his theory implied? | 0:50:14 | 0:50:18 | |
Perhaps because he was so acutely aware | 0:50:20 | 0:50:24 | |
of the deficiencies of the fossil record. | 0:50:24 | 0:50:28 | |
The rocks ought to bear mute testimony to titanic conflicts | 0:50:28 | 0:50:33 | |
playing out over eons of time. | 0:50:33 | 0:50:36 | |
But, as Richard Owen had so cruelly exposed, | 0:50:37 | 0:50:41 | |
the reality was rather different. | 0:50:41 | 0:50:44 | |
Animal fossils were abundant, but there were also huge gaps. | 0:50:46 | 0:50:50 | |
And nowhere was the gap greater than at the base of the Cambrian. | 0:50:50 | 0:50:55 | |
That's when an explosion of animal life seems to have occurred. | 0:50:57 | 0:51:02 | |
New species, entire faunas emerged as if from nowhere, | 0:51:02 | 0:51:07 | |
their ancestors absent. | 0:51:07 | 0:51:10 | |
Those rocks over there are Cambrian. | 0:51:14 | 0:51:17 | |
That makes them around 525 million years old. | 0:51:17 | 0:51:21 | |
And they contain animal life, wonderful creatures such as | 0:51:21 | 0:51:25 | |
brachiopods, ostracods and trilobites. | 0:51:25 | 0:51:29 | |
These rocks are Precambrian, they're only about 30 million years older. | 0:51:29 | 0:51:36 | |
And yet they are empty. | 0:51:36 | 0:51:39 | |
There are no animal remains in them whatsoever. | 0:51:39 | 0:51:42 | |
But how could this be? | 0:51:44 | 0:51:46 | |
If these Precambrian rocks didn't have any fossils in them, | 0:51:46 | 0:51:50 | |
where did the animals come from? | 0:51:50 | 0:51:52 | |
Characteristically, Darwin did not shirk the problem. | 0:51:52 | 0:51:55 | |
"During these vast, and unknown periods of time", he wrote, | 0:51:55 | 0:52:00 | |
"the world must have swarmed with living creatures." | 0:52:00 | 0:52:04 | |
That he couldn't produce them was, he admitted, a grave difficulty. | 0:52:04 | 0:52:10 | |
Darwin despaired of being able to reconstruct the history of life. | 0:52:11 | 0:52:15 | |
Yet he did not doubt that his successors would do just that. | 0:52:15 | 0:52:21 | |
And so they have. | 0:52:21 | 0:52:23 | |
Enter one of Darwin's most ardent disciples - | 0:52:29 | 0:52:32 | |
a young German scientist, Ernst Haeckel. | 0:52:34 | 0:52:37 | |
Of all the scientists who followed Darwin, | 0:52:41 | 0:52:44 | |
Haeckel was the most protean. | 0:52:44 | 0:52:47 | |
A gifted artist who could reveal nature's exquisite geometries | 0:52:49 | 0:52:52 | |
with the stroke of a pen, | 0:52:52 | 0:52:55 | |
he was also a brilliant anatomist, | 0:52:55 | 0:52:57 | |
devoting months to the study of obscure sea creatures. | 0:52:57 | 0:53:02 | |
And he was a romantic, | 0:53:05 | 0:53:06 | |
of the sentimental, nature-loving Goethe-worshipping German kind. | 0:53:06 | 0:53:11 | |
For Haeckel loved his cousin, Anna. | 0:53:14 | 0:53:17 | |
She had golden hair and blue eyes. | 0:53:17 | 0:53:20 | |
He described her as "a true German child of the forest." | 0:53:20 | 0:53:25 | |
Haeckel was besotted with her and married her. | 0:53:28 | 0:53:32 | |
What bliss! | 0:53:32 | 0:53:34 | |
But for only a few months, | 0:53:34 | 0:53:37 | |
and then she died. | 0:53:37 | 0:53:38 | |
Anna's death left Haeckel unhinged. | 0:53:44 | 0:53:46 | |
He contemplated suicide. | 0:53:46 | 0:53:49 | |
But then he found religion. | 0:53:49 | 0:53:51 | |
Not the false consolations of Christianity, | 0:53:51 | 0:53:54 | |
but the harsh, godless clarity of Der Darwinismus. | 0:53:54 | 0:53:58 | |
He would become its greatest apostle. | 0:53:58 | 0:54:01 | |
He would take the good book to the German masses, | 0:54:01 | 0:54:05 | |
he would preach the truth and he would do what Darwin had | 0:54:05 | 0:54:08 | |
so conspicuously failed to do - he would re-write the history of life. | 0:54:08 | 0:54:15 | |
But how? | 0:54:17 | 0:54:18 | |
Haeckel needed a way of reconstructing the evolutionary past | 0:54:18 | 0:54:23 | |
that did not rely on fossils. | 0:54:23 | 0:54:25 | |
The answer, he said, was to look at the embryo. | 0:54:25 | 0:54:29 | |
The embryo of an animal contains, is, | 0:54:31 | 0:54:34 | |
a record of its evolutionary past. | 0:54:34 | 0:54:37 | |
The earlier in development you look, | 0:54:37 | 0:54:40 | |
the further back into their past you can see. | 0:54:40 | 0:54:42 | |
The embryo, Haeckel said, | 0:54:42 | 0:54:46 | |
is Ariadne's thread. | 0:54:46 | 0:54:48 | |
He began by comparing vertebrate embryos. | 0:54:53 | 0:54:57 | |
Just before birth they seem very different, as you'd expect. | 0:54:58 | 0:55:04 | |
But follow the embryos back in time, to when they are younger, | 0:55:04 | 0:55:07 | |
and less developed, they look remarkably alike. | 0:55:07 | 0:55:11 | |
They have the same dorsal nerve cords, the same pharyngeal slits. | 0:55:11 | 0:55:18 | |
But Haeckel looked further, deeper into the embryo, | 0:55:22 | 0:55:26 | |
earlier into its development. | 0:55:26 | 0:55:28 | |
Before the limbs appear, | 0:55:28 | 0:55:31 | |
before there's a head or a tail, and further yet, | 0:55:31 | 0:55:35 | |
to when it is but a ball of cells with the beginnings of a gut. | 0:55:35 | 0:55:40 | |
This is a stage of development called "gastrulation". | 0:55:40 | 0:55:44 | |
And here he thought he found something wonderful - | 0:55:44 | 0:55:48 | |
the ancestor of us all. | 0:55:48 | 0:55:52 | |
Here, said Haeckel, is a remembrance, a recollection, | 0:55:55 | 0:55:59 | |
a recapitulation of the very first animal. | 0:55:59 | 0:56:03 | |
A creature, no more than a ball of flagellated cells, | 0:56:03 | 0:56:07 | |
that had once whirled through the Precambrian seas. | 0:56:07 | 0:56:11 | |
He called it the gastrea | 0:56:11 | 0:56:13 | |
and said that it was his most important discovery. | 0:56:13 | 0:56:17 | |
Others said it was his most outrageous invention. | 0:56:17 | 0:56:22 | |
Haeckel used embryos to produce evolutionary trees. | 0:56:24 | 0:56:28 | |
Lots of them. | 0:56:28 | 0:56:29 | |
They look a bit like Darwin's tree, but they are not abstract metaphors, | 0:56:31 | 0:56:36 | |
they are the first attempt to put every living thing | 0:56:36 | 0:56:40 | |
in its evolutionary place. | 0:56:40 | 0:56:42 | |
All the animals are there, in more or less the right order, | 0:56:44 | 0:56:48 | |
and somewhere near the base of the trunk | 0:56:48 | 0:56:51 | |
leading to all the other animals is the gastrea - | 0:56:51 | 0:56:55 | |
Haeckel's hypothetical ancestral beast. | 0:56:55 | 0:56:58 | |
Haeckel's speculations were, no doubt, too bold. | 0:57:01 | 0:57:05 | |
The embryo does not contain a simple picture of the history of life. | 0:57:05 | 0:57:09 | |
And yet, there's no doubt that his guesses were, | 0:57:09 | 0:57:13 | |
more often than not, inspired. | 0:57:13 | 0:57:16 | |
Since the 1950s, a trickle of animal fossils | 0:57:20 | 0:57:25 | |
has been emerging from Precambrian rocks. | 0:57:25 | 0:57:28 | |
Some are little more than imprints, others are minute. | 0:57:29 | 0:57:34 | |
But by using Computed Tomography Imaging, | 0:57:36 | 0:57:39 | |
even individual cells can be seen. | 0:57:39 | 0:57:41 | |
And, what's more, some of these proto-creatures | 0:57:42 | 0:57:46 | |
are not so very different from Haeckel's gastrea. | 0:57:46 | 0:57:50 | |
But there's another reason to think that animals lived | 0:57:54 | 0:57:57 | |
long before the Cambrian and that's because DNA tells us so. | 0:57:57 | 0:58:01 | |
When Watson and Crick elucidated the structure of DNA they unified life. | 0:58:10 | 0:58:16 | |
The DNA story is without doubt one of the greatest success stories | 0:58:16 | 0:58:20 | |
in the history of science. | 0:58:20 | 0:58:22 | |
Because it can't be often that two newcomers to a field | 0:58:22 | 0:58:25 | |
make such a major discovery so quickly. | 0:58:25 | 0:58:28 | |
Nearly all living things use DNA as the stuff of inheritance. | 0:58:30 | 0:58:35 | |
So they must all be related, | 0:58:35 | 0:58:37 | |
and descend, much as Darwin had supposed, from a single ancestor. | 0:58:37 | 0:58:44 | |
But now we can go further. | 0:58:47 | 0:58:49 | |
We can sequence the genome of any living thing | 0:58:49 | 0:58:54 | |
and read it as if we were reading a book. | 0:58:54 | 0:58:58 | |
Genomes are documents written in billion of letters. | 0:59:00 | 0:59:05 | |
They are palimpsests, endlessly augmented, erased, | 0:59:05 | 0:59:09 | |
and rewritten by the hand of evolution. | 0:59:09 | 0:59:13 | |
And if you can read them | 0:59:13 | 0:59:15 | |
you can read the history of life. | 0:59:15 | 0:59:19 | |
By sequencing genomes we can now date | 0:59:20 | 0:59:23 | |
the origin of animals in the tree of life. | 0:59:23 | 0:59:27 | |
Some of them turn out to be astonishingly ancient. | 0:59:27 | 0:59:31 | |
Perhaps the simplest of all animals | 0:59:34 | 0:59:37 | |
is a microscopic creature called Trichoplax. | 0:59:37 | 0:59:40 | |
It doesn't have a gut, a mouth, a brain, or even sense organs. | 0:59:40 | 0:59:46 | |
Its genome suggests that its ancestors departed | 0:59:46 | 0:59:49 | |
from the main trunk of animal evolution, | 0:59:49 | 0:59:52 | |
perhaps a billion years old. | 0:59:52 | 0:59:54 | |
Just as Darwin had supposed, | 0:59:56 | 0:59:58 | |
there must have been animals in the Precambrian seas. | 0:59:58 | 1:00:02 | |
The sequencing machines are revealing new branches | 1:00:04 | 1:00:07 | |
on the tree of life. | 1:00:07 | 1:00:08 | |
They are giving us a new historical narrative. | 1:00:08 | 1:00:13 | |
But, we are also discovering new fossils. | 1:00:14 | 1:00:17 | |
And often, the story they tell is the same. | 1:00:17 | 1:00:22 | |
Consider the whale. | 1:00:24 | 1:00:27 | |
Whales obviously evolved from some land mammal but, if so, | 1:00:27 | 1:00:31 | |
where were the fossil half-whales? | 1:00:31 | 1:00:34 | |
Where were the whales with legs? | 1:00:34 | 1:00:36 | |
By Darwin's logic, they must have existed and they must have been big. | 1:00:36 | 1:00:41 | |
So where were they? | 1:00:41 | 1:00:43 | |
For years, the origin of whales was shrouded in obscurity. | 1:00:46 | 1:00:51 | |
Not any more. | 1:00:51 | 1:00:53 | |
In recent decades, the fossil record has become wonderfully complete. | 1:00:54 | 1:00:59 | |
Just as Darwin had predicted, just as Darwin had hoped, | 1:01:02 | 1:01:06 | |
we now have an astonishing array of fossils that show how a land mammal | 1:01:06 | 1:01:10 | |
makes a transition to one that lives in the sea. | 1:01:10 | 1:01:13 | |
They show how front limbs evolved into flippers, | 1:01:13 | 1:01:18 | |
and how hind limbs just wither away, | 1:01:18 | 1:01:22 | |
and how a whale comes to breathe | 1:01:22 | 1:01:24 | |
not through their nostrils in the tips of its snout | 1:01:24 | 1:01:27 | |
but rather a blowhole in the back of its head. | 1:01:27 | 1:01:30 | |
And they show us one more thing. | 1:01:30 | 1:01:33 | |
They tell us about the place of whales in the tree of life. | 1:01:33 | 1:01:39 | |
The evidence hinges, literally, on an ankle bone. | 1:01:41 | 1:01:45 | |
For primitive whales, it turns out, have ankle bones | 1:01:45 | 1:01:49 | |
that are remarkably similar to those of modern ungulates, | 1:01:49 | 1:01:52 | |
such as cows, sheep and pigs. | 1:01:52 | 1:01:55 | |
Yet we don't have to rely on fossilised bones | 1:01:56 | 1:01:59 | |
to tell us about the ancestry of whales. | 1:01:59 | 1:02:01 | |
We can use DNA too. | 1:02:04 | 1:02:07 | |
And to do that we have to go to Africa. | 1:02:09 | 1:02:13 | |
Compare the DNA of a cetacean to that of any other mammal | 1:02:17 | 1:02:21 | |
and something surprising emerges. | 1:02:21 | 1:02:24 | |
Their closest living relation is this, a hippo. | 1:02:24 | 1:02:29 | |
It's not that whales evolved from hippos, | 1:02:38 | 1:02:41 | |
or that hippos evolved from whales. | 1:02:41 | 1:02:45 | |
Rather, it is simply that hippos and cetaceans are, as it were, cousins. | 1:02:45 | 1:02:51 | |
They are descended from a common ancestor that lived, perhaps, | 1:02:51 | 1:02:55 | |
55 million years ago. | 1:02:55 | 1:02:57 | |
It is precisely this sort of agreement | 1:03:05 | 1:03:08 | |
between DNA and fossil evidence | 1:03:08 | 1:03:11 | |
that makes the case for evolution so utterly compelling. | 1:03:11 | 1:03:15 | |
And so, to the evolution of the one species | 1:03:19 | 1:03:23 | |
we care about more than any other. | 1:03:23 | 1:03:26 | |
One might have expected Darwin to say something about human evolution. | 1:03:29 | 1:03:34 | |
And, in The Origin Of Species, he does. | 1:03:36 | 1:03:40 | |
After 400 pages of ants and agoutis, bats and barnacles, | 1:03:44 | 1:03:50 | |
the whole bestiary, in fact, right through to zebras, | 1:03:50 | 1:03:53 | |
he settles down to consider humanity. | 1:03:53 | 1:03:57 | |
And what he says is this. | 1:03:57 | 1:04:00 | |
"Light will be thrown on the origin of Man and his history." | 1:04:04 | 1:04:10 | |
And that's it. | 1:04:19 | 1:04:21 | |
Well, thanks for that, Charles. | 1:04:21 | 1:04:24 | |
Darwin, of course, knew we were descended from apes, | 1:04:27 | 1:04:30 | |
but left others to spell it out. | 1:04:30 | 1:04:33 | |
Among them, Ernst Haeckel. | 1:04:35 | 1:04:38 | |
With a characteristic flourish, | 1:04:42 | 1:04:44 | |
he imagined humanity like Botticelli's Venus, | 1:04:44 | 1:04:48 | |
rising gloriously from the brutes that surround her. | 1:04:48 | 1:04:52 | |
At the time, there were no fossils linking man to apes. | 1:04:55 | 1:04:59 | |
And so he set to imagining what lay between. | 1:05:01 | 1:05:05 | |
No human fossils, no problem. | 1:05:07 | 1:05:11 | |
Let's just invent one. | 1:05:11 | 1:05:13 | |
Something between an ape and a man. | 1:05:13 | 1:05:16 | |
Let's give it a name. Ape man. | 1:05:16 | 1:05:20 | |
Let's give it a real, proper, Latin name, Pithecanthropus. | 1:05:20 | 1:05:25 | |
Like the gastrea, Pithecanthropus was an invention, | 1:05:28 | 1:05:33 | |
a hypothetical ancestor. | 1:05:33 | 1:05:36 | |
Yet Haeckel's reasoning was sound. | 1:05:36 | 1:05:38 | |
If we were descended from apes, | 1:05:40 | 1:05:43 | |
then sooner or later intermediates would be found. | 1:05:43 | 1:05:47 | |
In 1891, a Dutch physician, Eugene Dubois, | 1:05:50 | 1:05:54 | |
digging in the banks of the Solo River in Java | 1:05:54 | 1:05:57 | |
discovered this skullcap. | 1:05:57 | 1:05:59 | |
It wasn't human, it wasn't ape, it was an ape man. | 1:05:59 | 1:06:04 | |
In homage to Haeckel, Dubois called it Pithecanthropus. | 1:06:04 | 1:06:10 | |
In the centuries since, | 1:06:16 | 1:06:18 | |
Pithecanthropus has acquired a new name, Homo erectus, | 1:06:18 | 1:06:23 | |
and has been joined by a collection of other fossils, | 1:06:23 | 1:06:26 | |
some, apish humans, | 1:06:26 | 1:06:30 | |
others, human apes. | 1:06:30 | 1:06:33 | |
The family tree of humanity can now be richly filled with species | 1:06:35 | 1:06:40 | |
and there's a clear and unambiguous line | 1:06:40 | 1:06:43 | |
between the earliest apes and us, Homo sapiens. | 1:06:43 | 1:06:49 | |
But which of the great apes now alive is our closest relation? | 1:06:54 | 1:06:58 | |
That question, endlessly debated since Darwin's time, | 1:07:00 | 1:07:04 | |
hasn't been answered by fossils. | 1:07:04 | 1:07:07 | |
It required DNA. | 1:07:07 | 1:07:09 | |
By comparing DNA sequences from each of the great apes, | 1:07:13 | 1:07:16 | |
the order of evolutionary descent has become clear. | 1:07:16 | 1:07:20 | |
We're genetically closest to chimpanzees and bonobos. | 1:07:23 | 1:07:27 | |
Five to six million years ago our ancestor was theirs. | 1:07:27 | 1:07:33 | |
Seven million years ago, we shared an ancestor with the gorilla. | 1:07:36 | 1:07:40 | |
12 million years ago, with an orang-utan. | 1:07:43 | 1:07:46 | |
And so on back to the very beginning of life. | 1:07:48 | 1:07:53 | |
"Who do you think you are?" asked Haeckel. | 1:07:58 | 1:08:01 | |
And answered, | 1:08:01 | 1:08:02 | |
"You are an ape, a mammal, a reptile, a fish, | 1:08:02 | 1:08:08 | |
"a worm, a ball of cells and finally a single cell | 1:08:08 | 1:08:13 | |
"floating in the saline womb of the primordial seas." | 1:08:13 | 1:08:18 | |
150 years ago, Darwin spoke of a time | 1:08:19 | 1:08:23 | |
when the tree of life would be more than a metaphor, | 1:08:23 | 1:08:26 | |
when it would be an accurate historical record. | 1:08:26 | 1:08:31 | |
That time has come. | 1:08:31 | 1:08:33 | |
The tree of life stands before us, | 1:08:33 | 1:08:36 | |
its branches becoming clearer with every fossil and DNA sequence, | 1:08:36 | 1:08:42 | |
and our species is but a leaf on a twig, | 1:08:42 | 1:08:46 | |
buried within in its vast and ramifying canopy. | 1:08:46 | 1:08:51 | |
When we look at living things it is the differences that we first see, | 1:09:04 | 1:09:10 | |
the astonishing variety of form, colour and behaviour. | 1:09:10 | 1:09:16 | |
And yet, beneath this diversity runs a deep, unifying plan. | 1:09:16 | 1:09:23 | |
For most animals have much the same geometry, | 1:09:23 | 1:09:27 | |
the same basic body plan. | 1:09:27 | 1:09:30 | |
For Darwin, this paradox of unity within diversity | 1:09:32 | 1:09:37 | |
was the gift of the tree of life, | 1:09:37 | 1:09:39 | |
the consequence of species giving rise to species, | 1:09:39 | 1:09:44 | |
endlessly adapting over countless generations. | 1:09:44 | 1:09:49 | |
But what Darwin could never have imagined | 1:09:56 | 1:09:58 | |
is that such unity within diversity can be found in every cell, | 1:09:58 | 1:10:04 | |
every molecule and every gene of every living thing. | 1:10:04 | 1:10:09 | |
Well done, where's that? | 1:10:09 | 1:10:11 | |
Can you look at the light? Where's my light? | 1:10:11 | 1:10:14 | |
Where's that? | 1:10:14 | 1:10:16 | |
Ellie is a patient at Moorfields Hospital in London. | 1:10:16 | 1:10:20 | |
She was born without irises. | 1:10:20 | 1:10:23 | |
Her pupils are enormous for they cannot contract, | 1:10:23 | 1:10:27 | |
and she can barely see. | 1:10:27 | 1:10:29 | |
Where's it gone now? Where's it gone now? | 1:10:29 | 1:10:32 | |
The disorder is called Aniridia | 1:10:32 | 1:10:35 | |
and it's caused by a mutation that she inherited from her mother. | 1:10:35 | 1:10:39 | |
Well done, oh, you get a lovely view of your eye. | 1:10:39 | 1:10:42 | |
She's such a good girl. | 1:10:42 | 1:10:43 | |
Good, well done. | 1:10:43 | 1:10:45 | |
In 1992, geneticists identified the mutant gene. | 1:10:45 | 1:10:49 | |
Now that one... Good, good, good, good. | 1:10:50 | 1:10:53 | |
Located on chromosome 11, it's called PAX6. | 1:10:53 | 1:10:57 | |
Well done, well done. You're such a good girl. | 1:10:57 | 1:11:00 | |
PAX6 is a very special kind of gene. | 1:11:00 | 1:11:04 | |
It's a molecular switch, a gene that turns other genes on and off, | 1:11:04 | 1:11:09 | |
and this particular molecular switch | 1:11:09 | 1:11:12 | |
is needed in the construction of the human eye. | 1:11:12 | 1:11:16 | |
The really interesting bit, however, is what happens next. | 1:11:16 | 1:11:21 | |
In 1994, geneticists were studying fruit flies, | 1:11:27 | 1:11:31 | |
searching for the genes that make its different organs. | 1:11:31 | 1:11:35 | |
They screened thousands of flies for mutations that cause abnormality. | 1:11:37 | 1:11:44 | |
Some of the mutant flies were blind. | 1:11:47 | 1:11:49 | |
They had a mutation called eyeless. | 1:11:51 | 1:11:54 | |
Normal flies have large, red, compound eyes. | 1:11:57 | 1:12:01 | |
Eyeless flies have none. | 1:12:01 | 1:12:05 | |
Analysing the DNA of eyeless flies, they identified the mutant gene. | 1:12:06 | 1:12:13 | |
It was PAX6 - | 1:12:13 | 1:12:15 | |
the same gene, or at least its fly version, | 1:12:15 | 1:12:19 | |
that causes aniridia in humans. | 1:12:19 | 1:12:22 | |
I remember how amazed we all were when we heard about this result. | 1:12:25 | 1:12:29 | |
Everyone just knew that human eyes and fly eyes | 1:12:29 | 1:12:33 | |
had evolved independently. | 1:12:33 | 1:12:35 | |
How could it be otherwise - they just looked so very different? | 1:12:35 | 1:12:40 | |
But the discovery that they shared a gene | 1:12:40 | 1:12:43 | |
told us that they shared an evolutionary history. | 1:12:43 | 1:12:47 | |
Geneticists started looking into the eyes of other animals | 1:12:54 | 1:12:57 | |
and wherever they looked, they found the same thing. | 1:12:58 | 1:13:04 | |
The molecular circuit of which PAX6 is a part | 1:13:04 | 1:13:06 | |
is universal. | 1:13:06 | 1:13:08 | |
Eyes are so ubiquitous, so useful and so various in their design, | 1:13:10 | 1:13:16 | |
that for most of the 20th century, | 1:13:16 | 1:13:17 | |
zoologists had argued that they must have evolved many times. | 1:13:17 | 1:13:21 | |
This, however, must be wrong. | 1:13:23 | 1:13:25 | |
Eyes have evolved only once. | 1:13:26 | 1:13:29 | |
All the eyes, belonging to all the animals on earth, | 1:13:31 | 1:13:36 | |
can trace their origin to one very simple eye | 1:13:36 | 1:13:40 | |
that belonged to one, doubtless, very simple creature that lived, | 1:13:40 | 1:13:44 | |
perhaps, one billion years ago. | 1:13:44 | 1:13:47 | |
Here is another mutant fruit fly. | 1:13:50 | 1:13:53 | |
Its eyes are quite normal, | 1:13:55 | 1:13:57 | |
but it has an extra pair of legs where its antennae should be. | 1:13:57 | 1:14:02 | |
And here's a different mutant. | 1:14:05 | 1:14:08 | |
Instead of the usual two wings, it has four. | 1:14:10 | 1:14:14 | |
True, they're a little deformed, | 1:14:14 | 1:14:16 | |
but they're definitely an extra set of wings. | 1:14:16 | 1:14:19 | |
These flies have mutations in their Hox genes. | 1:14:21 | 1:14:25 | |
Like PAX6, Hox genes are molecular switches | 1:14:29 | 1:14:32 | |
that turn other genes on and off. | 1:14:32 | 1:14:35 | |
They determine a fly's basic geometry, the number and position | 1:14:35 | 1:14:40 | |
of its segments, limbs and wings. | 1:14:40 | 1:14:43 | |
And like PAX6, Hox genes are universal. | 1:14:44 | 1:14:48 | |
They can be found in all animals, including us. | 1:14:48 | 1:14:52 | |
Animal bodies seem so very different from each other. | 1:14:55 | 1:14:59 | |
And yet they are not. | 1:14:59 | 1:15:02 | |
A fly has wings and segments, we have arms and vertebrae. | 1:15:02 | 1:15:09 | |
A facile comparison, you may think, until you look at the embryo. | 1:15:09 | 1:15:15 | |
This is a fruit fly embryo. | 1:15:18 | 1:15:21 | |
And here, one by one, the Hox genes are being expressed. | 1:15:21 | 1:15:26 | |
They ensure that every segment, head to tail, | 1:15:26 | 1:15:30 | |
knows what structure to make. | 1:15:30 | 1:15:32 | |
They work with the exquisite Boolean logic of a computer programme, | 1:15:32 | 1:15:36 | |
directing cells to their fates. | 1:15:36 | 1:15:39 | |
And this is a human embryo. | 1:15:42 | 1:15:45 | |
Again the Hox genes are activated along the head-to-tail axis | 1:15:45 | 1:15:49 | |
ensuring that our parts are arranged in the right order | 1:15:49 | 1:15:53 | |
and end up in the right place. | 1:15:53 | 1:15:55 | |
The circuitry is more complex than a fruit fly's, | 1:15:57 | 1:16:00 | |
but the logic is the same. | 1:16:00 | 1:16:02 | |
The discovery that many important genes | 1:16:07 | 1:16:10 | |
are shared across the animal kingdom was thrilling. | 1:16:10 | 1:16:14 | |
A new science was born - | 1:16:16 | 1:16:18 | |
Evolutionary Developmental Biology, | 1:16:18 | 1:16:21 | |
Evo-Devo, for short. | 1:16:21 | 1:16:24 | |
Like Haeckel, | 1:16:29 | 1:16:30 | |
we would delve into the embryo to unravel our evolutionary past. | 1:16:30 | 1:16:35 | |
But now, instead of working out what our ancestors looked like, | 1:16:36 | 1:16:41 | |
we'd work out the genetic programmes that made them. | 1:16:41 | 1:16:44 | |
Evo-Devo would explain how organic structures can be, at once, | 1:16:47 | 1:16:51 | |
so similar and conservative and, yet, so promiscuously different. | 1:16:51 | 1:16:58 | |
There is a paradoxical quality to genes. | 1:17:01 | 1:17:04 | |
Look at any animal and you can see many of the same genes | 1:17:04 | 1:17:07 | |
doing much the same thing. | 1:17:07 | 1:17:09 | |
And yet, look at them closely, look at them working in the embryo, | 1:17:09 | 1:17:15 | |
and you can see the origins of all diversity. | 1:17:15 | 1:17:19 | |
This is the embryo of a tetrapod. | 1:17:22 | 1:17:25 | |
As it grows, Hox genes switch on and off in a kaleidoscopic pattern. | 1:17:25 | 1:17:31 | |
Molecular signals sweep across the limb buds, telling each cell | 1:17:31 | 1:17:34 | |
what it is and what it must become. | 1:17:34 | 1:17:37 | |
The cells of the limb condense into the outline of bones | 1:17:38 | 1:17:42 | |
and so a mole grows a paw. | 1:17:42 | 1:17:46 | |
Another embryo and the same thing happens... | 1:17:48 | 1:17:51 | |
..at least to begin with. | 1:17:51 | 1:17:53 | |
But there's far more bone growth signal in this embryo. | 1:17:53 | 1:17:56 | |
The bones of the limb grow longer and the cells between the fingers | 1:17:56 | 1:18:00 | |
do not die, they become webbing. | 1:18:00 | 1:18:03 | |
And so a bat grows a wing. | 1:18:03 | 1:18:06 | |
Two embryos that start their lives in much the way, but with just | 1:18:08 | 1:18:12 | |
a subtle shift in gene activity, become two very different creatures. | 1:18:12 | 1:18:18 | |
I could tell many such stories about the evolution of beaks and feathers, | 1:18:21 | 1:18:28 | |
scales and spots and snouts. | 1:18:28 | 1:18:31 | |
But is it enough? | 1:18:31 | 1:18:33 | |
Surely the point of science is not merely to tell stories, | 1:18:33 | 1:18:37 | |
but rather to reveal the laws of nature. | 1:18:37 | 1:18:42 | |
Haeckel believed that the symmetries shown by living things | 1:18:44 | 1:18:48 | |
were caused by simple laws, | 1:18:48 | 1:18:50 | |
not very different from those that explained | 1:18:50 | 1:18:54 | |
the symmetries of crystals. | 1:18:54 | 1:18:56 | |
Living things are, of course, much more complex than crystals, | 1:18:58 | 1:19:02 | |
yet they do have a geometry. | 1:19:02 | 1:19:06 | |
An internal one composed of vast and intricate networks | 1:19:06 | 1:19:12 | |
of genes, proteins and molecules, all working together to give life. | 1:19:12 | 1:19:18 | |
Perhaps then, the war of nature is not simply | 1:19:20 | 1:19:24 | |
a struggle among individuals, or even genes, | 1:19:24 | 1:19:28 | |
but a struggle among different ways of organising life. | 1:19:28 | 1:19:33 | |
A struggle among systems. | 1:19:33 | 1:19:36 | |
In the short run, success depends on being robust. | 1:19:38 | 1:19:42 | |
On being able to weather the vicissitudes of existence | 1:19:42 | 1:19:46 | |
and then reproduce. | 1:19:46 | 1:19:47 | |
In the long run, however, in the evolutionary long run, | 1:19:48 | 1:19:52 | |
success needs something else, it needs flexibility. | 1:19:52 | 1:19:56 | |
On being able to respond to a mutable and contingent world. | 1:19:56 | 1:20:02 | |
Let me put it another way - | 1:20:02 | 1:20:04 | |
in the short run, creatures evolve. | 1:20:04 | 1:20:07 | |
In the long run, they evolve evolvability. | 1:20:07 | 1:20:12 | |
About a billion years ago, a creature, | 1:20:14 | 1:20:17 | |
something like Trichoplax, crawled out of the pre-Cambrian ooze. | 1:20:17 | 1:20:21 | |
Superficially, it may have been unremarkable. | 1:20:24 | 1:20:28 | |
But it seems that there was something new and rather special | 1:20:28 | 1:20:32 | |
about its genetic network. | 1:20:32 | 1:20:34 | |
It had a structure that was robust enough to be strong, | 1:20:35 | 1:20:39 | |
yet flexible enough to change. | 1:20:39 | 1:20:42 | |
Over time, this way of organising life was copied | 1:20:45 | 1:20:49 | |
and modified countless times. | 1:20:49 | 1:20:51 | |
Parts could added, even rearranged, | 1:20:56 | 1:20:58 | |
and yet the system as a whole would continue to work. | 1:20:58 | 1:21:03 | |
It was an engine of innovation | 1:21:03 | 1:21:08 | |
and it went on to conquer the world. | 1:21:08 | 1:21:10 | |
The theory of evolution by natural selection | 1:21:40 | 1:21:43 | |
is one of the most beautiful products of science. | 1:21:43 | 1:21:47 | |
It provided an answer, the only rational one we have, | 1:21:47 | 1:21:50 | |
as to why living things bear the hallmarks of design. | 1:21:50 | 1:21:55 | |
It is so beguilingly simple, so powerful and so manifestly true, | 1:21:58 | 1:22:05 | |
that it is easy to forget just how inadequate it is. | 1:22:05 | 1:22:10 | |
There are so many questions that we can't answer... | 1:22:10 | 1:22:14 | |
Why are there 600 species of cichlid in this lake and not 60 or 6,000? | 1:22:14 | 1:22:21 | |
Why are there no anglerfish cichlids, or flying fish cichlids? | 1:22:21 | 1:22:25 | |
Or, cichlid sharks? What, in short, are the limits to evolution? | 1:22:25 | 1:22:33 | |
The theory is inadequate because it is not predictive. | 1:22:35 | 1:22:39 | |
It explains what has evolved, but not what will. | 1:22:39 | 1:22:44 | |
There are simply too many possible streams | 1:22:46 | 1:22:50 | |
and there's no saying which one will be chosen. | 1:22:50 | 1:22:53 | |
We can only follow the journey and reconstruct the route | 1:22:57 | 1:23:01 | |
once it is done. But must it always be so? | 1:23:01 | 1:23:06 | |
Compare Darwin's theory of evolution | 1:23:09 | 1:23:12 | |
to Newton's account of the planetary motions. | 1:23:12 | 1:23:15 | |
Newton, after all, gave us celestial mechanics - | 1:23:19 | 1:23:24 | |
a mathematical theory that enables us | 1:23:24 | 1:23:27 | |
to make predictions far into the future. | 1:23:27 | 1:23:30 | |
Darwin did nothing of the kind, | 1:23:32 | 1:23:35 | |
but can we, perhaps, make a predictive theory of evolution? | 1:23:35 | 1:23:39 | |
Can we compute | 1:23:39 | 1:23:41 | |
the future of life? | 1:23:41 | 1:23:43 | |
Many would say no. | 1:23:45 | 1:23:48 | |
The evolution of life, they say, is ruled by chaos and contingency. | 1:23:48 | 1:23:53 | |
Perhaps evolution is like the weather. | 1:23:57 | 1:24:00 | |
Given enough data and computing power, | 1:24:03 | 1:24:06 | |
forecasters can tell us whether or not it will rain at the weekend. | 1:24:06 | 1:24:09 | |
But ask them about a month of Sundays and their predictions | 1:24:11 | 1:24:14 | |
fall apart - defeated by imperfect data | 1:24:14 | 1:24:20 | |
and the chaos concealed in their own equations. | 1:24:20 | 1:24:23 | |
And yet, I still think | 1:24:37 | 1:24:39 | |
a predictive theory of evolution might be possible. | 1:24:39 | 1:24:42 | |
And the reason I do is because of the fish in Lake Malawi. | 1:24:42 | 1:24:48 | |
Two million years of evolution have produced 600 species of cichlid here | 1:24:49 | 1:24:54 | |
and an astonishing diversity of form. | 1:24:54 | 1:24:57 | |
But what's even more remarkable | 1:24:59 | 1:25:02 | |
is that this great evolutionary experiment is not unique. | 1:25:02 | 1:25:06 | |
Follow the African rift north-west for just a few hundred miles | 1:25:13 | 1:25:17 | |
and you come to Lake Tanganyika. | 1:25:17 | 1:25:19 | |
There, too, a cichlid arrived a few million years ago | 1:25:22 | 1:25:26 | |
and there, too, it multiplied and evolved | 1:25:26 | 1:25:29 | |
into hundreds of different species. | 1:25:29 | 1:25:32 | |
The fish in both lakes are only remotely related, | 1:25:34 | 1:25:37 | |
but they have similar colours, fins, teeth, diets, habits and habitats. | 1:25:37 | 1:25:44 | |
You can hardly tell some of them apart without DNA. | 1:25:47 | 1:25:51 | |
In other words, the tape of cichlid evolution has been run twice | 1:25:55 | 1:26:00 | |
and both times the outcome has been much the same. | 1:26:00 | 1:26:05 | |
It's this repeatability that makes me think | 1:26:05 | 1:26:09 | |
that much of evolution is indeed predictable. | 1:26:09 | 1:26:12 | |
Perhaps then evolution does not so much resemble the weather | 1:26:16 | 1:26:19 | |
as it does our climate. | 1:26:19 | 1:26:21 | |
At the grandest scales of space and time, the atmosphere is not chaotic. | 1:26:23 | 1:26:28 | |
The physics of our planet imposes order and, thus, | 1:26:28 | 1:26:32 | |
predictability upon it. | 1:26:32 | 1:26:35 | |
So, although we can scarcely tell what the weather will be | 1:26:37 | 1:26:40 | |
three weeks from now, we can predict, at least | 1:26:40 | 1:26:43 | |
probabilistically, what the climate will be three centuries hence. | 1:26:43 | 1:26:48 | |
I think evolution is like that. | 1:26:52 | 1:26:56 | |
As we explore the internal geometry of living things, | 1:26:56 | 1:26:59 | |
I think we'll discover that there are deterministic laws | 1:26:59 | 1:27:03 | |
that impose order upon the capricious designs | 1:27:03 | 1:27:07 | |
of natural selection and that limit the paths of evolution. | 1:27:07 | 1:27:12 | |
And when we discover those laws, we'll be able to construct | 1:27:14 | 1:27:18 | |
a predictive theory of evolution. | 1:27:18 | 1:27:21 | |
We'll be able to complete Darwin's great project. | 1:27:22 | 1:27:26 | |
We'll explain life itself. | 1:27:27 | 1:27:31 | |
"There is grandeur in this view of life, with its several powers | 1:27:36 | 1:27:41 | |
"having been originally breathed into a few forms, or into one. | 1:27:41 | 1:27:46 | |
"From so simple a beginning, endless forms most beautiful | 1:27:46 | 1:27:51 | |
"and most wonderful have and are being evolved." | 1:27:51 | 1:27:57 | |
That is how The Origin ends. | 1:27:57 | 1:28:02 | |
And it is how our science begins. | 1:28:02 | 1:28:05 | |
Subtitles by Red Bee Media Ltd | 1:28:13 | 1:28:16 | |
E-mail [email protected] | 1:28:16 | 1:28:19 |