I'm on a fantastic journey to look for the origins of life. 我踏上了生命溯源的奇妙旅程，
I shall be travelling，not only around the world，but back in time， 我即将游历的不仅是世界各的景观，而且让时光倒流，
to try and build a picture 试着完成一幅
of what life was like in that very early period. 最初生命的画面。
Last time I saw how，600 million years ago， 上一次我看见了在6亿年前，
simple cells evolved into the first multi-cellular animals. 单细胞演化为最原始的多细胞动物。
In this programme，I investigate what happened next. 在这一次旅行中，我将探索接下来发生的事。
I will look for evidence in both 我将会用现代生物的证据
fossils and living creatures of what happened in that 或是古老的化石证据
far, distant past, 来证明
when the fundamental features of modern animals 现代动物的基本特征
were being established for the first time. 早在最初的阶段已经建立了。
One group，the arthropods，were the great pioneers。 节肢动物是最主要的先驱物种。
They were the first big predators. 它们是最早的大型食肉动物。
They had eyes 它们具有眼睛
Legs 附肢
And hard external skeletons。 并且具有坚硬的外骨骼。
They were the first to crawl out of water 它们也是最先爬出水面的动物
to conquer the land and the air. 征服了陆地与天空。
600 million years ago，the world was very different 早在6亿年前，
from the planet we know today。 当时的世界与我们现在所熟知的地球非常不同。
The land was entirely without animals or plants. 陆地上毫无动物和植物的踪迹。
But the oceans were teeming with life. 但是在海洋中，却充满了生命。
The first proto-animals were immobile organisms 最初的动物是固生的。
that lived on the sea floor and extracted their nourishment 它们生活在海床上，
from the water flowing around them. 从它们周围的水流中吸取所需的营养物质
But once animals developed mouths 但是一旦这些动物发育出了口，
and the ability move，evolution took off. 并且具有移动的能力，演化的飞跃开始了。
Canada's Rocky Mountains. 在加拿大的落基山脉
Here we can find evidence of a sudden explosion of life 被称为寒武纪的地史时期，
when animals started to evolve with astonishing rapidity. 我们发现动物的演化以惊人的速度启动了，
It happened during a period called the Cambrian. 即爆发式的演化的证据。
And it began 542 million years ago. 距今5.42亿年前，
During the next 10-20 million years, 在随后的1-2千万年间，
animals increased in numbers，diversity and size as never before. 动物的多样性及大小发生了前所未有的增加。
And as they got bigger，so they became more complex. 由于它们变得更大，因此它们变得更加复杂。
And they're preserved to an extraordinary degree of perfection 在我下面的岩石中，
in the rocks right below me. 它们以异乎寻常的完美保存下来了,
The Burgess Shales，where a rich seam of fossils 在布尔吉斯页岩中，有丰富的化石层
documents this Cambrian explosion in astonishing detail. 记载了寒武纪大爆发中让人惊叹的细节。
All this area was once the floor of a shallow sea，teeming with life. 曾经这些地区是浅海海床，生命繁衍生息之处。
As sediment settled down onto the floor，so it became compressed 由于沉积物的沉降使得它们压得扁平
and turned into mudstones and shales that you can see around me here. 并且变为现在我周围的泥岩和页岩。
About a century ago, 大约一个世纪以前，
an American geologist from the Smithsonian Institution 美国Smithsonian研究所的地质学家
was making a survey of this part of the Rockies. 当时他正在考察落基山脉的这个地区。
And he came walking along this particular path. 并且他沿着这条特别的路走着。
And when he got to precisely this spot, 刚好走到这个地方，
he noticed a tiny fossil of a kind he had never seen before. 他发现了一块从未见过的小化石。
He bent down and picked it up and it looked like this. 他就像这样弯着腰捡起来
What sort of a creature could this be? 这是一种什么样的生物呢？
It was only the first of the enigmatic creatures 这仅仅是第一个在布尔吉斯页岩
to come from the Burgess Shales. 现身的神秘生物。
Since then over 65,000 different specimens of now extinct 从那以后，在这个小小的采石场
Cambrian animals have been from this one small quarry. 发现了超过65 000种已灭绝动物的化石。
Many species have never been found elsewhere. 许多种类以前从未被发现。
It seems that the Burgess Shales were deposited in a place 布尔吉斯页岩具有得天独厚的沉积环境
where conditions for fossilisation were uniquely perfect. 这种环境能够让生物体极其完美地保存下来
As a consequence, even bodies of animals that were soft 因此，即使没有硬的组织，
and lacking any hard parts were, nonetheless, preserved. 软体组织也依然能够保存下来。
They survive as thin, almost imperceptible layers, 它们残留为难以察觉的薄层，
that you only see if you get the light just right. 因此你得通过特殊角度的光线去观察。
It's these fossils that have transformed our understanding 正是这些化石
of how animals we know today have come to be the way they are. 改变了我们对现生生物是如何演化的理解。
In some of these specimens we can glimpse shapes and forms 在有些标本中我们能看到它们的形状和构造。
that look faintly familiar. 看起来似曾相识
But many of these bizarre creatures seem like nothing we know of today. 但其中大部分的奇异生物我们似乎从未见过。
This is one of the more mysterious animals from the Shales. 这是布尔吉斯页岩中较神秘的成员之一。
There are two clues as to how this creature might have lived. 这有两条线索可以推测这种生物是如何生活的。
It has flaps along the side of its body, 在它身体的两侧有一排翼状物，
but no legs，and also a broad, flat tail. 但是它却没有附肢，只有扁平宽阔的尾扇。
So it's reasonable to assume that they helped it swim 因此有理由推测尾扇和翼状物是用来游泳的。
and that it lived not crawling along the floor, 它并不是在海底爬行的动物，
but up higher in the water. 而是可以游到较高的海面。
But the really, truly mysterious thing about it is that here 但是非常诡异的是
on its head it had five eyes, 它的头部长着五只眼睛，
each of them like a kind of little mushroom. 每一个眼睛就像是一个小蘑菇。
And beneath that it had a long proboscis 在眼睛的下方还有一个长长的吻
with which it grabbed things. 长吻可以用来捕捉猎物。
It's a truly primitive animal 虽然它是十分原始的动物。
and one that, still, we don't fully understand. 但是，我们并不完全了解它。
It's been named opabinia. 它被命名为“欧巴宾”
And it seems to have been a kind of evolutionary experiment. 似乎它曾经是演化的一种尝试。
It's almost as if an assortment of different body parts 身体的组成就像个大杂烩
had been put together in something of a hurry. 被胡乱组合在一起。
What other animal has five eyes? 还有什么动物具有五个眼睛呢？
And opabinia wasn't the only oddball. 欧巴宾不是唯一的怪物。
Wiwaxia was once thought to be an ancestor of earthworms, 威瓦亚虫曾经被认为是蚯蚓的祖先
but now is considered to be an early snail. 但是现在被列为早期的蜗牛。
Most of the Burgess Shale creatures 布尔吉斯页岩中的大部分生物
are unlike anything ever discovered before. 非常不用于以前的发现。
There were countless bizarre creatures 在寒武纪海洋中，
living in the Cambrian Seas, 生活着有无数的奇异的生物
This unprecedented surge of diversity was something 这种多样性的空前激增
that had never happened before and would never happen again. 是整个地史时期独一无二的。
For many years, scientists excavated and scrutinised the Shales 为了寻找寒武纪爆发的原因
looking for the causes of the Cambrian explosion. 科学家进行了多年来的挖掘与研究。
Their first task was to try and reconstruct 它们的首要任务是
what these strange animals must have looked like when they were alive 试图复原这些奇异生物生活面貌
and that was not at all easy. 这可不是容易的。
This is one of the oddest of the fossils from Burgess Shales. 这是布尔吉斯页岩中最古老的化石。
It seems to have five legs along the bottom, 沿着它的底部好像有五条腿，
and curious kind of lobes along the top, 上部部有奇怪的圆柱状突出物，
which presumably were some devices, which help it to feed. 这大概是有助于进食的设备。
But what kind of animal is that with five walking legs 但是这种五条腿、背部具有进食设备的的动物
and feeding lobes along the top of its back? 究竟是什么种类呢？
It was such an extraordinary thought that the scientist 对于科学家来说这简直是奇幻的生物
who described it thought it was a kind of hallucination, 描述他的人认为它是个荒诞的幻觉
and he called it "hallucigenia". 因此命名为“怪诞虫”。
But since then, more specimens have shown that in fact, 但是，之后更多的化石显示，
this is probably the wrong way up and that it was really like that. 曾经背腹颠倒了，实际是这样的。
The projections at the bottom are, in fact, legs. 底部的实际上是腿
And those along the top are tipped with sharp spines 背部有一系列尖锐的刺
that were presumably, defensive. 这些可能是防御装备。
Perhaps these animals evolved these strange shapes 难道这些动物为了保护自己
because they needed to protect themselves? 因而演化为如此怪异的外形吗？
But if so, from what? 但是，它们要防卫什么呢？
Where were the predators? 天敌在哪里？
No-one could find a likely candidate. 嫌疑犯尚未找到。
And then the answer came from a couple of fossil species 然而，答案就在这两块化石里面。
that they had known almost from the very beginning. 几乎从一开始他们就知道这个答案了。
One of the strangest fossils found here is this. 这是这里找到最奇特的标本之一。
It's also one of the commonest. 也是这最常见的一种。
But what is it? 但是，这是什么呢？
Well, it has what looks like legs, so you might think 可能你觉得它看起来像条腿
it was some kind of caterpillar, or shrimp maybe. 也许是一种毛虫或是虾类？
But the most mysterious thing about it was that 但是最令人费解的是
they never found one with a head. 从未发现过一个带有头部的标本
Then there was another mystery, 之后又有了另一个神秘事件。
not as common as the headlessshrimp, 虽然不如无头虾化石那么普遍
but one that looked like a sort of jellyfish, 有一类具有辐射线的水母状的化石，
with radiating lines out, and this strange hole in the middle. 中间有个奇特的洞。
And about twenty years ago, 大约20年前，古生物学家发现
it was discovered that actually, there is a link between 事实上这两类标本
this and this. 有惊人的联系
This bit is not a separate shrimp, it's actually a claw. 这块不是无头的虾，事实上是个螯肢
And this bit is not a jellyfish, it's a mouth. 并且这块也不是水母，而是个口器。
And in the mouth you can see something 这个口器中，
that looks very significant. 你能看见些至关重要的东西。
Could these be teeth? 这有可能是牙齿吗？
And were these not legs but spikes, used to stab and grab prey? 这些不是腿，而是，用来抓取、刺穿猎物的尖刺。
The two were, in fact, connected. 这两块，实际上是有联系的。
But now we have a most perfect fossil, 但是现在我们有了近乎完整的标本，
which really demonstrates that that is indeed the case. 因此证实了前面两者的联系。
This, you might say, is the Mona Lisa of the Burgess Shales. 你会说，这位是布尔吉斯页中的蒙娜丽莎。
This specimen, at last, gave scientists a picture 这个标本为科学家展现了
of the complete animal. 这个完整的生物。
It had plates along its back, and a tail at the rear end. 它背部具有一系列的片状物，且身体后端具有尾扇。
It was a swimmer. And between those two spiked claws 它是个游泳者，并且在身体前部、两个带刺的螯肢之间，
at the front there was a mouth... 有一个口...
with teeth. 具有齿的口
This was the hunter they had been looking for. 这就是科学家们苦苦寻找的捕食者。
The scientist who discovered the claws called them anomalocaris, 发现它的爪的科学家把它命名为“奇虾”
meaning strange shrimp. 意思是奇怪的虾。
That name is now used for the whole animal. 那个名字现在用来命名这类完整的动物。
With its large tail and flexible plates along its flanks, 奇虾具有宽大的尾扇，沿着侧面柔韧的桨状物
anomalocaris could propel itself through the water at speed. 奇虾可以在水中可以游得飞快
Other specimens show that it could grow to a length of nearly a metre, 其他的标本显示，它几乎可以长到一米。
two feet or so. 或两英尺。
It was, as far as we know, the first big predator on Earth. 这是据我们所知最早的大型捕食性动物。
We can get clues as to what it was like 我们可以得到这样的线索
from an animal that is alive today. 有一种和它很类似的现生的生物。
It's much smaller than anomalocaris, though remarkably similar. 虽然比起奇虾，它显得很小，但是它们非常相似。
And it lives in Australia, here on the Great Barrier Reef. 它们栖息于澳大利亚的大堡礁中。
Professor Justin Marshall has been studying these ferocious Justin Marshall教授致力于
and powerful hunters for over 20 years. 研究那些生猛的肉食动物长达20多年。
You have to very cautious about the way you handle them. 当你抓起它时你必须特别小心。
If you pick them up they can knock the ends off your fingers. 否则它们会切断你的手指。
Fishermen call them thumb splitters because 鱼民称它们是手指刀片
as they handle them they get thumbs and fingers split open. 因为鱼民抓着它们时，手指就被割裂了。
The other, slightly more technical name for them is mantis shrimp. 专业的术语的命名为“螳螂虾”。
They have a very ancient ancestry. 它们有古老的祖先。
Fossils of almost identical creatures have been found 已发现几乎与它们相同的化石
that date back 400 million years. 可追溯到4亿年前。
This animal is almost as ancient as anomalocaris itself. 这种动物几乎与奇虾一样古老。
It lurks in burrows, waiting for its victims 它潜伏在洞穴中等待着它的猎物
to swim within range of its claws. 在它螯肢可以活动的范围内游泳。
Looking at the fossils of anomalocaris 看看奇虾的化石
and comparing them to mantis shrimps, 与螳螂虾对比
one could imagine that these animals are similar. 人们可以想象到它们十分相似。
They both have big raptorial appendages 它们都具有巨大的捕食附肢
that are shot out at the front to grasp prey. 用来对猎物的突然袭击。
You could imagine them lurking behind a rock 你可以想象它们潜伏在石头后面
waiting for unwitting prey to come past. 等待毫无防备的猎物经过。
And bang! Suddenly that's dinner. 啪！速来的美味。
The mantis shrimp illustrates the essential characteristics 螳螂虾具有
of this brand new predator class of animals. 肉食性动物的基本的特征
Superb vision, great speed and superior size. 极佳的视力，游速快以及较大的体格。
Like anomalocaris, it's considerably larger than its victims. 像奇虾一样，它比猎物大很多。
It also has extremely acute vision, 它具有敏锐的视力，
with 12 different types of colour receptors in its eyes. 在它的眼中具有十二种原色接收器。
We have just three. 而我们人类却只能看见三种原色。
And it's one of the fastest animals alive, 它是现存游得最快的动物。
some species striking with the speed of a pellet from a gun. 有些种类具有子弹的速度。
It's unlikely anomalocaris was as fast, or that it saw its prey 奇虾的运动不会比它的猎物更慢，
so clearly, but nonetheless, it was a formidable predator, 显然，它是个强大的猎食者，
just as the mantis shrimp is today. 正如现生的螳螂虾一样凶猛。
Even a glimpse of a finger through glass is enough 即使瞥见隔着玻璃的手指，
to make this animal strike, 足以激起这个动物的攻击。
and with alarming force. 它具有惊人的攻击性。
So why did the mantis shrimp evolve in this way? 那么，为何螳螂虾演化为这种形式？
Well, obviously... 显然，
in order that it could 它为了能够抓住猎物
outfox and outmanoeuvre, and eventually catch its prey. 从而采取以智取胜的策略。
It's become very fast, very powerful, 它变得很快，非常强大，
and capable of great patience. 并且具有极大的耐心。
And those are characteristics of predators everywhere. 这些都是肉食动物的基本特征。
So the fossilised remains of anomalocaris 因此，奇虾化石的证据证明
are evidence that hunting had begun in the Cambrian. 在寒武纪初期，就有了猎食行为。
And as predators became bigger, faster and stronger, 作为肉食者，它们变得更大，更加凶猛。
so their prey had to develop increasingly elaborate defences. 因此，不想成为它们的猎物就必须开发出一系列的防御措施。
Opabinia's five eyes helped it spot trouble. 欧巴宾的五只眼睛，帮助他尽快发现危险。
And Hallucigenia protected itself with those spines along its back. 怪诞虫用背部的刺来保护自己。
One of the world's leading experts on the Burgess Shales, 作为世界领先的布尔吉斯页岩的研究专家，
Dr Jean-Bernard Caron, believes that it was the arrival Jean-Bernard Caron先生认为，
of predators like anomalocaris that stimulated the great 像奇虾这样的猎食者的出现，
Cambrian explosion of diversity. 激发了寒武纪爆发的多样性。
It is during the Cambrian 在寒武纪时期
that we can start seeing animals with legs, eyes, swimming. 我们可以看到动物具有附肢、眼睛并且它们可以四处游动。
This didn't exist before and this evolved very, very quickly 在寒武纪早期，
at the beginning of the Cambrian. 这些前所未有生物就以惊人的速度演化了。
But once you have a big predator, presumably the rest of life, 但是一旦你的天敌出现了，那么你的余生
which it was feeding on, 很有可能成为它们的食物，
had to evolve quite fast to develop some sort of defences. 那么就必须发展某种防御措施。
Would that be true? 那是真的吗？
Well, we think that this evolution occurred relatively quickly because, 我们认为演化事件发生得迅速
in a place like the Burgess Shale you find organisms 因为，在布尔吉斯页岩发现的众多生物中
that may have had some kind of defensive mechanism, 它们都有各种防御装备。
which is thought to be a response to higher predatory levels. 这些可以认为是对高等的天敌的反应。
Arms race, if you want, between predators and prey. 捕食者与猎物之间展开了一场军备竞赛。
One result of this duel between predators and prey 竞赛的结果是
was the development of armour. 它们都发展了盔甲。
Animals everywhere were absorbing calcium carbonate 动物无时不刻地吸收着
and other inorganic substances from the seawater 海水中碳酸钙及各种无机物质
and mineralising their bodies. 从而加固着它们的身体。
Many of them, like wiwaxia, that early mollusc, 它们中间，像威瓦亚虫早期的软体动物
and ancestors of the squid, ammonites, 以及章鱼、菊石的祖先，
developed protective shells. 都发展出具保护作用的外壳。
But one group, the arthropods, which had jointed legs, 像具有关节的附肢的节肢动物，
encased their entire bodies with hard armour plating. 它们的身体包裹在坚硬的盔甲内。
And what began as defensive armour, necessary for survival, “防御装甲是生存的必需品 ”的时代开始了。
brought with it another great advantage. 此外，带来了意想不到的好处。
Hard parts can be used not only to give protection, 坚硬的部分不仅仅用来防御，
but to provide support for a body. 而是用来支撑身体。
Ha-ha! 哈哈！
This spider crab is a crustacean. 这是个甲壳纲的蜘蛛蟹。
And it secretes chitin from its body, 它的身体的外骨骼
which it then strengthens with calcium carbonate. 由几丁质与碳酸钙结合起来形成的。
And a whole range of creatures 有一系列的生物
have skeletons like this, based on chitin. 有像这样几丁质骨骼
Arthropods today include shrimps, lobsters and crabs, 包括现生的节肢动物包括小虾、龙虾、蟹，
as well as land-living creatures, 当然还有陆生的生物，
such as millipedes, scorpions and insects. 比如蜈蚣、蝎子和昆虫。
But the ancestors of all of them first appeared in the Cambrian Seas. 但是它们的祖先最早出现在寒武纪的海洋中。
Over 50% of fossils in the Burgess Shales 在布尔吉斯页岩中，
are arthropods of one kind or another. 节肢动物的化石的种类占所有种类的50%。
But one family was particularly abundant and varied. 一个科的的多样性就十分丰富。
Just across the valley from the quarry, 对面山谷的采石场
near the summit of Mount Stephen, 在斯提芬山脉的顶端的附近
almost every rock you turn over contains their remains. 几乎随便翻开一块石头都能找到化石。
Here, they are found all over the place. 这里遍地都是这种化石。
They're called trilobites. 它们被称为三叶虫，
Trilobites because their bodies were in three sections. 之所以叫它们三叶虫是因为它们的身体分为三个部分。
Here on this slab there are several of them. 在这块标本上有好几个三叶虫。
That's the head. 这是头甲。
There's the middle bit. And there's the tail. 这是胸甲这是尾甲。
One, two, three trilobites. 一、二、三个三叶虫。
Trilobites, at this particular time, 三叶虫，在这个特别的时期，
right at the beginning of the Cambrian, 就在寒武纪之初
began to proliferate into all sorts of forms. 开始辐射为各种形态。
These creatures, for the next 250 million years, 在接下来的2.5亿年，
were probably the most advanced forms of life on this planet. 三叶虫很可能以最先进的形式生活在这个星球上。
To see how advanced the trilobites eventually became, 三叶虫的巅峰时期是怎样的情形呢？
I'm going to North Africa. 我即将到非洲北部。
In Morocco, on the southern flanks of the Atlas Mountains, 在摩洛哥Atlas山脉南翼，
the hills contain an amazing variety of them. 山上保存着成千上万的三叶虫。 They were only discovered a few years ago, 它们仅在几年前刚被发现
but now the demand for them is so great 但现在的需求量是如此之大
that digging them out has become a major industry. 以至于挖掘化石成了这里的主要产业。
These rocks, which were laid down about 150 million years after 这些岩石，比布尔吉斯页岩年轻1.5亿年
the Burgess Shale, also contain trilobites. 也含有三叶虫
The trouble is, the rock is very hard 岩石非常坚硬
and the trilobites are quite rare. 三叶虫是十分罕见的。
But when these people find them, 但是当人们发现它们，
their specimens are absolutely extraordinary. 它们的种类绝对特别。
Some species have features that are so delicate 一些种类具有非常脆弱的特征
that it can take days, sometimes weeks, 需要几天，甚至几个星期
to fully prepare a specimen. 来完成化石修理的准备工作。
Skilled technicians use dentists' drills 训练有素的人员用牙科钻头去修理
to get down to the finest detail. 以完成最细致入微的作品。
Every particle of rock must be carefully removed, 要非常小心地移除每一个岩屑
with enormous patience and absolute precision. 这需要巨大的耐心和缜密的精确性。
The end results reveal that trilobites 最后，三叶虫展现出来了
moulded their external skeletons 它们外骨骼的构型
into an almost unbelievable variety of shapes. 显示出难以置信的多样性。
And that enabled them to colonise a great variety of habitats, 这使得它们能够占领各种栖息地。
just as modern arthropods still do today. 正如现生的节肢动物一样。
There were about 50,000 different trilobite species that we know of, 据我们所知，这里的三叶虫具有50000个种
and doubtless there are still many more to be discovered. 毫无疑问，还有很多种类还没有被发现
Their hard exoskeletons 坚硬的外骨骼
not only ensured their abundance in the fossil record, 不仅保证了丰富的化石记录
they also tell us a lot about their owners' lives. 也告诉我们许多它们的生活
Many of the trilobites that are found in these cliffs 这个悬崖上发现很多三叶虫，
are curled up like this one. 像这个一样卷曲着，
Sometimes even more tightly than this is, 有些甚至卷曲得比它更加紧
with their tail tucked underneath their heads. 它们头尾蜷缩在一起。
And it's clear that this was some kind of protective posture, 这显然是一种防御姿势。
just as it is for some kinds of woodlice 这种行为与如今我们花园里
that you find in the garden today. 潮虫科的窃虫（俗称西瓜虫）非常类似。
That protected them against their enemies. 这种行为保护它们免受天敌的攻击。
But there are so many that are curled in these deposits, 但是这里保存了如此多蜷曲一团的的三叶虫
together with others that have their backs arched upwards 它们的背部都向上拱起，
and others in other strange postures, 也有些其他的奇特姿势。
that it seems that they are the victim of some kind of catastrophe. 这些似乎看来它们是一次大灾难的遇难者。
The sea floor, it seems, was quite steep. 海底看来很陡峭，
And the mud that accumulated on 在上部的泥质不断地积累，
the bottom slipped down 时不时地滑下来
in a submarine avalanche, 类似发生在在海底的泥石流，
carrying the animals that lived in it and on it, 泥质带着那些动物，
higgledy-piggeldy, and burying them alive. 滚得乱七八糟，就这样把它们活埋了。
Moroccan trilobites are big business these days. 摩洛哥的三叶虫成为当今的一大产业，
Particularly rare species sell for thousands of pounds. 尤其是某些稀有的品种，以数千英镑的价值销售。
The world's leading trilobite experts, 世界三叶虫研究的首席专家，
such as Professor Richard Fortey, 比如说，Richard Fortey教授，
come here to study these extraordinary animals. 来到这里致力于这些奇特生物的研究。
He believes that their external skeleton 他认为三叶虫的外骨骼
was the key to their success. 是它们成功的关键。
The trilobites did almost everything 所有的三叶虫都有外骨骼
you possibly can do with an exoskeleton. 所以研究它的外骨骼可能会有收获。
I think that skeleton was what gave them an advantage. 我认为外骨骼为它们提供了极大的好处。
They were protected. They could do all kinds of interesting things. 为它们提供保护并能做各种有趣的事情。
They could grow spines. 它们可以长出刺。
They could get flat, like pancakes. 它们可以变得扁平，像个烙饼。
They could protect themselves by getting thick exoskeleton 它们通过较厚的外骨骼保护自己
with pobbles all over it. 具有各种袖珍的突起。
It was a great advantage to them, just as it is to crabs and lobsters 对于它们是很大的进步，
living today, which of course weren't around 正如现生的龙虾与螃蟹一般，
at the time of the trilobites. 虾蟹们在三叶虫时代并不存在的。
So they utilised the virtues of having a tough exoskeleton, 因此三叶虫利用它们有坚硬的外骨骼的优势
to radiate into all kinds of ecological niches. 占领了所有不同的生态位。
You can see one of the most comprehensive collections 你看这个最复杂的
of trilobite fossils 三叶虫化石
just a few miles from where they're quarried, at Erfoud Museum. 它采集于离采石场几英里的地方，现在的伊尔福德博物馆。
The collection here reveals just how varied 这里的收藏品展示了它们
the trilobite skeleton could be. 形态各异的外骨骼。
There is no question that an exoskeleton 毫无疑问，
gave the trilobites protection. 外骨骼为三叶虫提供了保护。
But it also gave them something else of great value. 但也给它们带来了意想不到的好处。
There must have been many reasons why trilobites were so successful. 三叶虫的成功因素是多方面的。
But one of them, unquestionably, was their power of sight. 其中之一是它们视力极佳。
They had eyes. 它们具有眼睛。
not just eyespots that could tell the difference 眼点不仅能够分别明暗
between light and dark, 复眼的形成，
but complex eyes that could form detailed pictures 完成了生命史上
of their surroundings, for the first time in the history of life. 最先对周围环境的细节的感知。
Eyes like these. 即这样的眼睛。
Most animals on Earth today have eyes of one kind of another. 然而，现生的大部分动物拥有另一种眼睛。
Most are made of soft tissue, as ours our. 和我们的眼睛一样，大部分由软组织形成。
But trilobite eyes are unique. 但是三叶虫的眼睛十分独特。
Their lenses are derived from their mineralised external skeleton. 它们的镜头（小眼）是矿化的外骨骼的衍生而来的。
They're made of rock. 它们是由岩石制成的。
Each one of these little dots is a lens. 每一个这样的小眼是一个镜头。
And each is made from calcite, 每个镜头是由
a crystalline form of chalk. 柱状的方解石晶体形成的。
Trilobites were the only organisms 三叶虫是唯一利用这种材料
ever really to use this stuff as their lens material. 作为它们的视觉镜头的生物。
And in doing so they evolved very sophisticated vision indeed. 它们一定以这种方式演化出精密的视觉。
For example, these sorts of trilobites had very large lenses. 比如说这种三叶虫有非常大的视觉镜头。
And each lens is readily visible with the naked eye 并且我们可以用肉眼看见每个镜片（小眼）
and each one is biconvex. 每个都是是双凸的镜片。
And it's been proven that individual lenses have little bowls inside them 并且单独的镜片内部有一个小的碗状物，
to help them focus more precisely. 可以帮助它们更好的聚焦。
These creatures were among the first, 这些生物是首批能够聚焦
certainly, to actually focus a picture, weren't they? 真正的聚焦成像，不是吗？
It wasn't just a question of telling light from dark, 这不仅仅分辨明暗，
they could do better than that? 或是比分别明暗稍好点？
On no, these, these had really sophisticated vision. 哦，不！这些可是十分精密的视觉系统。
The kind of trilobites that have these eyes were probably hunters. 具有这种眼的三叶虫很可能是捕食者。
Some people have claimed that they could form stereoscopic images, 也有人认为这种眼睛可以辨认出立体形状。
using both eyes, so they could really home in on the prey. 用两只眼睛，因此它们可以轻而易举地捕食。
May predators today, including ourselves, 包括我们在内的肉食性动物，
have 3D, or stereoscopic vision. 具有三维或者立体视觉。
It makes it possible for a hunter to accurately judge the distance 这种视觉有助于猎食者准确判断
between itself and its prey. 自己和猎物之间的距离。
But not all trilobites were predators. 但是并不是所有的三叶虫都是猎食者。
Some were inoffensive creatures that lived by munching mud. 许多长得相貌平平的家伙以嚼泥为生。
But sight must have been valuable 但是视力也是很必要的，对它们来说，
for them too, enabling them to spot enemies in time to escape. 视力让它们及时地逃跑。
There are trilobite eyes with more than 5,000 lenses. 这只三叶虫具有5000只小眼。
5,000? More than 5,000 lenses. 5000？也许更多。
Now each of those, does it have an image? 那么，每一个小眼都能成像吗？
Each doesn't have an image, but if they go for lots of tiny lenses, 单个小眼并不能成像，但是许多小眼可以成像
they're particularly sensitive to movement, 它们对运动特别敏感。
i.e. something changing between one lens and the next. 例如，一有动静，小眼就会接二连三地察觉到。
This trilobite's eyes are so big they extend right round its head 这只三叶虫的眼睛十分大，围绕着头部
and meet in the middle. 在中间连接起来。
And that suggests that the animal swam high above the sea floor 这说明这种动物生活距在海底较高的水域
and had a 360-degree view of the scene below. 对下面的景象视角达到360°。
With each lens capable of detecting movement 每个小眼能够察觉移动。
its owner must have been able to see an enemy coming from any direction. 物主能够从任何角度察觉到敌人行动方向。
But the shape of a trilobite's eyes can reveal more than the 但是三叶虫的眼睛的形态展现了
kind of image they produced. 比视觉识别更重要的东西。
Eyes can tell us a surprising amount about how and where an animal lived. 眼睛可以告诉我们生物生活的大量的信息，比如它在什么地方、怎样生活。
This one with its eyes on turrets probably lived in the sea where it 这只具有塔楼式的复眼，很可能它生活在
was gloomy, but nonetheless there was enough light for the animal to 昏暗的光线下，尽管如此，
be able to see on either side of it. 这里对于三叶虫来说可以看见任何一方。
This one, on the other hand, has eyes also on turrets, but at the top 这只三叶虫，也可以认为是塔楼式的眼睛，
it has flanges, like sun shades. 但是它眼睛顶部有一个凸檐用来档住阳光。
So it's, er, likely that it lived in the shallow, sunlit sea 因此，这只似乎生活在充满阳光的浅水区。
and valued shades above its eyes so it didn't get dazzled. 这种形式的眼，功能在于不会受到炫目的阳光的影响。
This one, however, has very reduced eyes, and it may well be 这只，却有非常少的小眼，
that it skated along the mud along the bottom, 这样它可以沿着底部的泥前进
where it was gloomy anyway and there wasn't much to see, 反正生活在阴暗的地方，视觉并没有多大用处
so like an animal living in a cave, it slowly lost the use of its eyes. 所以像生活在洞穴中的动物一样，它的视觉慢慢地退化了，
And finally there's this creature, 最后就成了这个样子了。
and this is the one I think is particularly delightful. 我认为这个让我觉得十分新奇。
This one has its eyes on stalks. 这只三叶虫具有带柄的眼睛。
And probably lived under the mud, 它很可能生活在泥质底之下
gobbling up food there with its, just its eyes 它在埋头大吃时，伸出两只长长的眼睛
peeking out of the top, to see whether there was danger around. 去窥探上方是否有危险。
So trilobites were the first animals to see clearly. 所以三叶虫是最早能看清的动物了。
But they had other senses as well, perhaps some 但是它们具有其他的感官，
we don't even know about. 可能并不为我们所知。
Take this species with this bizarre trident structure on its nose. 就这个种类的头部具有奇特的三叉戟。
What was it for? Some kind of motion sensor? 这是用来做什么的？某种动力传感器？
Prehistoric radar, perhaps? 或许是史前的雷达？
Trilobites were, without question, 毫无疑问，
the most successful animals of their time. 在那段时间，三叶虫是最成功的类群。
They flourished in all parts of the ocean. 它们在整个海洋中相当繁盛。
Indeed, they could be counted as one 事实上，它们可以算是整个生命史上
of the most successful kinds of animals in the entire history of life. 最成功的类群。
Most trilobites are quite small, rather like beetles are today. 大部分的三叶虫相当小，和现在的甲虫差不多。
But the biggest living beetle is about that big, the goliath beetle. 但是现生最大的歌利亚甲虫有这么大，
Trilobites, on the other hand, grew very big indeed. Like this one. 三叶虫能够长到很大，就像这个。
And this is by no means the biggest. 这绝不是最大的三叶虫了。
The biggest known is nearly a metre, nearly three feet long. 已知最大的将近一米长，几乎三英尺。
And it's thought that these really big ones grew to this size 这么大的算比较大的了，
because they lived in cold waters, and that's a tendency of animals 因为它们生活在冷水域，
in cold, to grow large. 这是个冷水动物的生长趋势。
And at the time that these rocks were laid down, Africa, 这些岩石发现于现在在非洲，
where we are now, and where these are found, 在当时还没有沉积下来，
was down by the South Pole. 当时这里却在南极地区。
Spectacular though these are, 虽然这些非常壮观，
they were by no means the largest arthropods in the ocean at the time. 它们在当时海洋中绝不是最大的节肢动物。
The trilobites had remote cousins, also arthropods, that had grown 三叶虫有同样也是节肢动物门的远亲，
into monsters. 它能够长成个巨型怪物。
Their remains are much rarer, and often fragmentary, 它们的化石非常罕见，并且很不完整。
but some of the most complete have been found in Scotland. 但是最完整的化石在苏格兰发现了。
ALARM SOUNDS 警报声
One of the best is held in the vaults 它被存放在最好的储藏室
of Edinburgh's National Museum. 即爱丁堡国家博物馆。
Gosh! 天哪！
Well, this is a magnificent example of just how big an animal can grow 那么，如果它具有外骨骼的话
if it has an external skeleton. 这是一个绝佳的证据证明这种动物能长到多大。
This is a creature called the Eurypterid, or a sea scorpion. 这种生物被称为“广翅鲎”或海蝎。
And it was a hunter. 它也是肉食类。
It had a pair of powerful pincers at the top, just behind its head. 它头部后面与身体前部之间具有一对强壮的钳状螯枝，
It was obviously a monster, a terror of the seas. 它是神秘海洋中的一个巨怪
And this is by no means the biggest of the eurypterids. 这绝不是板足鲎类中最大的
Sea scorpions were the top predators of their day. 在当时，海蝎是肉食动物
As far as we know, they were the biggest arthropod 据我们所知，它们是最大的节肢动物
that has ever existed. 它们前所未有的。
The discovery of a large fossilised claw suggests 它的最大的前螯肢化石表明
that they could grow up to two and a half metres, eight feet in length. 它们可以长到将近2.5m，长达八英尺。
So arthropods of one kind or another 所以，各式各样的节肢动物
were certainly dominant 420 million years ago. 它们曾经主宰着4.2亿年前的海洋世界。
The seas were full of life. 海洋孕育着各类生物。
From huge complex animals like this sea scorpion 从巨大且复杂的海蝎
creeping along the bottom, 到在爬行于海底的小生物
to simple creatures, like jellyfish, floating on the surface waters. 到漂浮在海面上的水母。
But the land was barren and without animals of any kind. 但是当时的陆地是贫瘠的，没有任何动物的踪迹。
But there was food up there, simple plants, 但是，在那里有食物--低等植物，
and that tempted some animals to venture out of the water. 这些美味诱惑着动物们离开水面。
Surviving on land, however, was a problem for them. 对它们来说到陆地上生活，却存在一个问题。
Coming from the sea, they had to evolve ways 从海洋里出来后，
of preventing their bodies from drying out. 它们必须防止身体脱水。
And even more difficult, they had to develop a method of breathing air. 而更加困难是，它们得设法呼吸空气。
The very first animals had simply absorbed 最初的动物
dissolved oxygen from the water 可以直接吸收水中的游离氧。
through the skins of their soft bodies. 这是通过皮肤软组织的渗透来完成的。
As they began to move and grow bigger, they needed more energy, 一旦它们开始运动、生长，
more quickly. 它们需要更快地补充能量。
And that meant 这就意味着
they had to improve their method of collecting dissolved oxygen. 它们得改进方法收集到更多的溶解氧。
Bigger, more complex animals, 对于更大、更复杂的动物，
like for example, this lobster, 比如说龙虾。
have to have specialised devices, 必须有专门的设备获取氧
Here in the lobster they are these flaps underneath its abdomen, 在这只龙虾的腹部有很多桨状物。
which is flaps forwards 当它们来回划动时，
and backwards to increase the flow of oxygenated water over them. 增加了含氧水的流量
But the trouble with gills is that they only work when they're wet. 然而，问题是腮只能在潮湿的环境下工作。
In the dry, they do not absorb oxygen. 在干燥的地方，它们不能够吸收氧气。
So if animals are to live on land, 因此，如果动物想要生活在陆地上，
they had have to have a new way of breathing. 它们必须具有全新的呼吸方式。
The Burgess Shales, 在布尔吉斯页岩中，
that astonishingly rich treasury of Cambrian fossils, 保存了异常丰富的寒武纪生物。
contain the remains of just one 有一类十分稀有的化石，
particularly rare species that may well have been the very first animal 这种生物被认为是最先
to make that move onto land. 移居到陆地上的生物。
It was not, as you might think, an amphibian, it was not even 你可别以为是两栖动物，
a true arthropod, but one of their far distant cousins. 也不是真正的节肢动物，而是与节肢动物门较远的姐妹类群。
This little creature, 这个小家伙，被称为“埃谢栉蚕”
from the Burgess Shale seas, is thought to be the ancestor 在布尔吉斯页岩中发现的海洋生物，
of the very first creature that went on to land. It's called Aysheaia. 被认为是最早登陆物种的祖先。
And we don't have to imagine what it was like in life, 我们没必要联想有什么和它相似的现生生物，
because there's a creature, that seems to be almost identical, 因为现生有和它长得几乎完全相同的生物
that is alive today. 它们还活着。
It lives in many parts of the tropics, including the rainforest, 热带地区很常见，尤其是雨林中。
here in Queensland, Australia. 这里是澳大利亚的昆士兰州。
It's nocturnal and seldom seen. 这是一种罕见的夜行动物。
It spends most of its time hidden away inside rotten logs. 它爱在腐木中度过大半的时光。
Ah, it's nice and wet! 哈，这里很好，很湿！
Certainly, er, perfect for what we're looking for. 当然，呃，这里是找到它的绝佳之地。
You need local expertise to find one. 你需要个当地专家帮忙才能找到它。
I generally find that it's just from the outside 我通常在枯树干中
of the, er, core of the tree. 能发现它。
All nice and... Oh! What is that? Ooh, look at that. 非常漂亮 啊！那是什么？呵，看那个。
And this enchanting little creature 这个讨人喜欢的小家伙
is what we were looking for. 就是我们一直在寻找的。
Sometimes called a velvet worm, 俗名：天鹅绒虫，
or to give it its scientific name, Peripatus. 学名：栉蚕
If there is such a thing as a living fossil, 如果要找活化石的话，
this surely must be one of them. 它显然是其中之一。
Because it seems to be almost identical 因为它与布尔吉斯的埃谢栉蚕相比
with that fossil, Aysheaia, which we saw in the Burgess Shales. 几乎完全相同。
It looks at first sight like a worm. 猛地一瞅很像个蠕虫，
But of course no worm has legs. In fact, 但是，世上没有带腿的蠕虫。
it seems to be halfway 它似乎是
between a worm 处于节肢动物与蠕形动物之间的
and an insect. 过渡类群。
Aysheaia, of course, lived in the sea. 当然，埃谢栉蚕生活在海洋中，
But this little creature lives on land. 然而，这只小家伙生活在陆地上。
And it has one further attribute, 并且它具有更加先进的功能
which Aysheaia could not have had. 而埃谢栉蚕却没有的
It has tiny little holes all along its flanks, 那就是，沿着它的侧面具有一系列的小孔，
which enable it to breathe air. 它们是用来呼吸空气的。
So this is one of the first creatures 因此，
that moved on to land, 这是5.4亿年前，
540 million years ago. 最初登陆的成员之一。
Velvet worms may have been the first animals to set foot on land, 天鹅绒虫曾经很可能是最早踏上陆地的生物。
but they have hardly changed during the following half-billion years. 然而几亿年来它们几乎没有什么变化。
Why? 为什么？
Well, unlike true arthropods, their bodies are covered, 然而，不同于真节肢动物，它们没有外骨骼
not by an exoskeleton, but by soft, permeable skin. 而是覆盖着一层柔软、可渗透的皮肤。
That lack of an external skeleton means that their bodies, 外骨骼的缺乏，意味着它们的身体是由水来支撑的，
unsupported by water, can't grow any bigger. 没有水的支撑，长不了多大大。
It also means that in order to prevent themselves from drying out, 因此，为了不让它们自己晒伤，
they have to stay in damp environments. 它们不得不呆在潮湿的环境中。
True arthropods, like this scorpion, 对于巨型海蝎的后代-蝎子这类真节肢动物来说
a descendent of those giant sea scorpions, were not so restricted. 可没有那么多的生存限制。
They had external skeletons. 它们具有外骨骼，
That meant that not only were their bodies protected from drying out, 这意味着，不仅能够防止身体脱水，
but they were strong and rigid enough to allow them to grow bigger 并且它们很强壮可以把自己养得更大
and get around without the support of water. 它们并不需要水支持身体形状。
So how and when did true arthropods with exoskeletons 那么，这些具有外骨骼的真节肢动物
draw their first breath of air? 是何时、怎样第一次呼吸的？
The answer can be found in this. 这里可以找到答案。
It is perhaps the smallest and most fragmentary fossil I've seen so far, 这是我见过的最小的化石碎片，
but don't be fooled by appearances. 可别被它的外表骗了。
It's almost certainly one of the most significant. 它的意义极其重大。
This specimen was collected in Cowie Harbour, here in Scotland, in 2004. 这块标本于2004年发现于苏根兰的考伊港口。
Even though it's so small, under the microscope you can see 虽然很小，但是我们可以在显微镜下
extraordinary detail. 观察到非凡的的细节。
This is the main body of the animal with its segments. 这是它的身体和体节，
And here are its legs. 这是它的腿。
But above each there is a tiny hole. 但是在每个腿的上部有一个极小的洞。
That is a spiracle, through which the animal was able to breathe air 这是个气孔，这个生物通过过这个气孔呼吸
just as insects do today. 就像现生的许多昆虫一样。
And since it breathed air, if it had gone into the water 那么，既然它可以呼吸空气，
it would have drowned. 如果把它放在水里，会淹死的。
So this is a truly land-living animal and what is more, 所以，这是一个真正的陆生动物，
it's the first and oldest that we know. 这是我们所知道最早的登陆者，
It's 428 million years old. 距今4.28亿年。
But what kind of creatures were these early land-dwelling arthropods? 但是最早的陆生节肢动物是什么种类呢？
Animals very like them are still quite common 在世界的很多地方，
in many parts of the world. 像这样的动物随处可见。
There are certainly plenty of them in those Australian rainforests. 在澳大利亚的热带雨林中有很多这样的动物。
One sort are millipedes, 其中一类是马陆。
which today grow as long as that and live on vegetation 它们生存与植被丰盛且含有枯枝烂叶的环境中。
and rotting wood, harmless vegetarians. 它们是温柔的的草食动物。
But there's also another multi-leg creature, which is a much more 但是，这还有个多腿的
difficult customer. 但却不好惹的家伙。
This is one of them. 这是条蜈蚣
A centipede. A very formidable hunter, with a powerful bite, 它是个强悍的肉食动物，具有有力的大颚
and some centipedes have bites that are lethal to human beings. 有些种类的蜈蚣甚至会伤人致命的。
What kind of a bite this one has, 被这个家伙咬一口会是怎样，
I don't know. 我不知道。
But when I let him out I shall do so 但是放他出去的时候我得非常小心。
very carefully, because I don't propose to find out. 我可不打算知道答案。
Come on. 去吧。
So multi-legged arthropods invaded the land and became 多足类节肢动物侵占陆地后，
more successful than ever. 它们变得更加成功。
Back in Scotland, 让我们回到苏格兰，
there is impressive evidence of just how successful they became. 我们来看看究竟它们变得有多成功。
This is a small fishing village 这是个小渔村，
on the East Coast of Scotland called Crail. 苏格兰南部海岸线的克雷尔。
Nothing particularly strange about it, you might think... 你可能认为这里没什么特别的
until, that is, you go down to the shore. 直到你来到这个岸边
And then you can see something that is really extraordinary. 那么你会发现些非常奇特的东西。
Standing here and there on the beach are fossils, 在海岸保存的化石中，
not of animals, but of plants. 保存的不是动物而是植物。
This huge circular stump looks just like the base of a tree. 这个大的圆柱形很像个树桩。
And indeed that is what it is, or rather, 更确切地说
what it was, 335 million years ago. 但是它并不是我们现在意义上的树。
But it wasn't a tree like trees we know today. 远在3.3亿年前，
It was related 它们与现生的一种小型植物
to the small plants that are alive today called horsetails. 木贼类有关，
But this tree grew to 90 feet. 但是这棵树长到90英尺高。
It was immense. 如此硕大，
When they were alive, during a period called the Carboniferous, 它们生活在"石炭纪"
long after the Cambrian, 在寒武纪之后的很长一段时期，
this whole area was very different 当时的那片地区
from the windswept coastline of today. 不同于今天这个疾风拍岸的景象，
This was a time when the continents of the world were grouped together 当时形成了联合大陆，
and forests were widespread. 有广袤的森林。
So much plant life was pumping out oxygen 由于植物制造了大量的氧气。
that the composition of the atmosphere began to change. 因此大气的成分开始发生变化。
This had a profound effect on animal life. 从而对动物的生活产生深远的影响。
In the forest that was growing near Crail, the ancient trees。 这棵古树生长在克雷尔附近。
were rooted in a sandy swamp. 它2根植于一个沙地沼泽。
And on the expanses of sand that stretched between those huge trees, 这些沙子使这些巨树能够固定住。
sand that's now turned to this sandstone, 现在那些沙子成了现在的砂岩。
there are tracks. 这些是爬痕
Tracks that come in pairs, there's one pair that goes up there. 爬痕是成对的附肢留下的，一处在那儿。
There's another pair that goes up here. 这是另一处爬痕
And when you look at them in detail, you can see, 当你观察细节时，你能发现，
particularly on this pair, that each track has a number of dimples in it. 特别是这个，爬痕有许多凹坑。
And those are the imprints of individual feet. 这是每一个附肢留下的足迹。
So this animal had a lot of feet. 因此，这种动物有很多的附肢。
It's thought to have been a giant millipede. 被认为是巨大的百足虫留下的。
It was about... 它大约有...
four and a half feet long, one and a half metres. 0.5-1米
And it had 26 or 28 segments. 并且大约有26-28个体节。
A magnificent beast. 一个巨型怪物
Arthropleura. 节胸属的
A giant millipede, 巨大的百足虫，
probably the biggest terrestrial arthropod that has ever existed. 它们可能是史上最大的陆生节肢动物。
The largest specimen discovered so far was nearly as long as a car... 最大的标本有将近一辆卡车那么大...
two and a half metres. 长达2.5米
The Carboniferous was the golden age for the arthropods, 石炭纪是节肢动物的鼎盛时期,
for the air was now particularly rich in oxygen. 因当时空气中的氧气异常地高。
Today the atmosphere contains around 21% oxygen. 我们现在的空气中含氧量仅为21%。
Back in the Carboniferous, 然而，追溯到石炭纪，
it was around 35% and that enabled animals to grow very big indeed. 高达35%的含氧量使得动物长得如此硕大。
But growing large was not their only success. 但是它们的成功之处不仅在于长得大，
Some other arthropods in these carboniferous rainforests 在石炭纪雨林中的许多其他节肢动物
were evolving in a different way. 以截然不同的方式演化。
Instead of becoming huge and ponderous, 它们并不是变得巨大而笨重，
they became agile and speedy. 而是灵活而敏捷。
To do that it's better to be short rather than long, and some 因此它们通过减少体节来使身体变短
reduced their segments and ran around on just three pairs of legs, 并且只有三对腿，
as silverfish and bristletails do today. 正如今天的蠹虫无翼昆虫。
These early insects then made another dramatic move... 这些早期昆虫的又一戏剧性事件是...
they developed wings and became the first animals of any kind to fly. 它们演化出了翅，成为最早飞翔在天空的动物。
Truly the invertebrates had colonised 真正的无脊椎动物不仅占领了陆地，
not only the land, but the air. 还称霸了天空。
And in an atmosphere so rich in oxygen, 大气中丰富的氧含量使得
they did so in a truly dramatic way. 它们形成了如此生动多样的生存方式。
This giant dragonfly, 这个巨大的蜻蜓，
the biggest flying insect that has ever existed, is called Meganeura. 是有史以来最大的类型，被命名为“古蜻蜓”。
Its wings were nearly three feet across. 它的翅膀将近3英尺长，
But the golden age of the giant arthropods was not to last. 但是巨型节肢动物的黄金时代并没有持续多长时间。
The rainforest died back, and oxygen in the atmosphere dropped. 热带雨林衰退后，氧气含量下降。
Giant insects are no longer alive today and that may be 巨大的昆虫现在已经不复存在，
because the proportion of oxygen in the atmosphere is very much lower. 很可能是因为大气中的氧含量变得非常稀薄。
But nonetheless, insects have managed to find a way 即使这样，昆虫总是有办法适应
of overcoming the problems of size. 克服大小的问题
They've become colonial. 它们组成社会性群体。
Just as in the far distant, remote past, 正如很久很久以前，
individual cells clubbed together to form a larger organism, 单个细胞聚集起来成为大型的有机体，
such as a sponge, 例如海绵，
so hundreds of thousands of individual insects, termites, 这些成千上万单独的昆虫，例如白蚁，
have cooperated to build this nest. 它们合作建成这样的巢。
And a colony like this can crop as much vegetation 蚁群能够联合起来形成羚羊群般的破坏力，
from the surroundings as a bigger animal like an antelope. 它们割下周围环境中的植物。
So by living in vast colonies like this, 通过这样巨大的群居生活，
arthropods can still dominate their surroundings. 节肢动物仍然可以主宰它们周围的环境。
They've become super-organisms... 它们变成超有机体（社会性动物的集合体）
hundreds of thousands of individuals all descended from the same female, 数以千计的后代都出于同一个母亲，
working and behaving as one. 它们具有万众一心的工作效率
So arthropods remain 所以节肢动物仍然是
one of the most successful groups of animals on the planet. 这个星球动物中最成功的。
They've spread to all its corners. 它们蔓延到世界的每个角落。
Insects alone make up at least 80% of all animal species. 仅昆虫纲就占了所有动物种类的80%。
But arthropods weren't the only ones to make this move on to land. 但是节肢动物不是唯一登上陆地的动物。
The Burgess Shales - 在布尔吉斯页岩中-
the place where the beginnings of all this proliferation of life 无比精细地展现了寒武纪时期的
in the Cambrian period are recorded in unparalleled detail. 所有后生动物的起源。
Among the ancestors of all the insects, 与昆虫的祖先在一起生活的生物还有：
spiders, the scorpions, the shellfish, the crustaceans, 蜘蛛、蝎子、双壳类、甲壳类动物
the shrimps, the sponges, 虾、海绵等。
there's just one tiny little creature, very insignificant, 这是一个非常小的生物，但是意义重大
which we human beings might think is perhaps the most important of all. 我们人类之所以认为它如此重要，
Because this... 是因为...
is the first creature to have the sign of a backbone, 这是最早具有脊索的生物，
and thus, therefore, is probably the ancestor of us all. 因此，这很有可能是我们的祖先。
It's a tiny, worm-like creature called Pikaia. 它很小，蠕虫般的形态，名叫皮卡虫。
It was not a fearsome hunter. 他并不是凶猛的捕食者。
It had no teeth for attack and no external skeleton for defence. 它既无爪牙以袭击，也无盔甲以御敌。
But Pikaia did have something new. 但是皮卡虫具有它独特的之处。
Instead of an external skeleton, 虽然没有外骨骼，
it had an internal one, a thin gristly rod... 它的内部具有一个杆状的软骨。
the beginnings of a backbone. 是脊锥的雏形
It, or something very like it, was the ancestor of all vertebrates. 它看起来像是所有脊椎动物的祖先。
From such a creature as this, the first fish evolved. 正如这样的生物，第一条鱼演化出来了。
Some of them, living in swamps, started to gulp air and wriggled up 它们中的一些种类，生活在沼泽中，
onto the land. They gave rise to moist-skinned amphibians. 开始大口吸气，并且它们在向陆地蠕动着，它们使那些皮肤湿润的两栖类崛起了。
Some of them developed scaly, impermeable skins that enabled them 它们中的一些类群发展出了鳞片，
to colonise the driest places... 防水的皮肤使它们可以向陆地进军了...
they were the reptiles. 它们是爬行动物。
And from them came the birds. 它们又变成了鸟类。
And the mammals. 哺乳类，
Today mammals, like this rhinoceros, 今天的哺乳类比如说犀牛
are the biggest of all living animals. 已成为现生动物中最大的类群了。
Hello, old boy. How are you? 嗨，你好，小伙子，你好吗？
How are you? 你好吗？
All mammals, including ourselves, extract oxygen from the air with 包括我们在内的所有哺乳动物，
the end of internal lungs, and distribute it through our bodies 都用肺来吸收空气中的氧气
in our blood. 并且通过血液循环至全身。
There we are. There's a good lad. 我们在这儿，你是个好小伙。
But we also owe our success, and our size, 但是我们也有我们的成就，
to the nature of our skeletons. 我们的大小取决于我们骨骼的特质。
Animals with an internal skeleton, like this rhinoceros, 这只犀牛具有内骨骼，
have a huge advantage over animals whose skeleton is external. 这类动物比具有外骨骼的动物更加具有优势，
A white rhinoceros, like this, 像这样的白犀牛，
is one of the biggest land animals alive today. 是现生的陆生动物中较大的一类。
Compare him 与它相比
with him... a rhinoceros beetle. 一只独角仙
Its skeleton is external. 它具有外部的骨骼。
It's very powerful. 它非常强悍。
It can carry 850 times its own weight. 它能够举起它体重的850倍的重物，
But it can't grow much bigger. Because the only way it can grow is 但是它不能长得更大。因为它之所以长到现在这么大
by shedding its skeleton and growing a new one. 是因为每一次蜕皮之后再长出新的外骨骼。
And while its skeleton is not there, its body is unsupported. 当它的骨骼不存在时，它的身体就无法支撑。
And after a certain size, the body will collapse under its own weight. 长到一定程度，外骨骼会因无法支撑体重的而崩溃。
Here. 这儿。
Here we are, come on boy. Come on boy. 我们在这儿，过来小伙子，过来小伙子。
Despite these differences, it's no coincidence that 虽然有这么多差异，但是并非巧合使得
backboned animals evolved many of the same features as the arthropods. 脊椎动物与节肢动物一样演化为许多共同的特征，
Teeth. 牙齿
Legs. 腿
Shells. Eyes. 骨骼、眼睛
And wings. 翅
Any animal group needs such things if they are to colonise 因为对于任何要征服世界各种环境的动物类群来说
all the Earth's varied habitats. 这些特殊的装备是很必要的。
A journey that began for me near my boyhood home in Charnwood Forest 旅行的起点从童年故乡的Charnwood森林开始
has taken me around the world and through 600 million years 之后，我环游世界，
of evolutionary history. 并且追溯6亿年的生命演化史，
I've seen evidence of how single-celled life dominated the planet for billions of years, 我见证了单细胞生物，曾主宰地球长达十亿年的证据。 750
until a global ice age triggered the emergence of the first animals. 直到全球性的冰期启动时，最早的动物才诞生，
Many animal groups lasted millions of years. 虽然许多动物类群历经了数百万年，
But eventually their time ran out and they disappeared. 但是最终它们生命耗尽，永远地消失了。
But others endured. 但是其他能够坚持下来的，
And between them they evolved 其中一些类群
into the wondrous variety of life that inhabits this planet today. 演化为现在生活在这个星球的纷繁多样的生物，
Life originated in the oceans. 生命起源于海洋。
After an immense period of time, some creatures managed to crawl up 经过非常漫长的一段时期，
onto the land. 一些种类设法爬上了陆地。
Those animals may seem to us to be very remote, 对我们来说，这些动物似乎离我们非常遥远，
strange, even fantastic. 它们奇形怪状、荒诞离谱，
But all of us alive today owe our very existence to them. 然而，今天我们能活着，归功于它们的存在。