生命的进化（1979）

这是地球生命故事中最重要的步骤之一
One of the most crucial steps in the story of life on earth
发生在约3亿5千万年前的一个淡水沼泽里
happened in a freshwater swamp about 350 million years ago.
鱼开始登上陆地
The fish began to haul themselves out onto the land.
陆地那时被最早的植物覆盖着
The land at the time was covered with the first plants.
同今天的红树林很不同 但是它们仍是植物
Very different from these mangrove plants of today, but nonetheless plants.
为了从它们摆脱出来鱼不得不解决两个问题
In order to get out among them, the fish had to solve two problems.
首先它们面临上岸的工具问题
First, they had the mechanical problem of hauling themselves onto land,
然后，它在到达那里时必须能够呼吸
and second, they had to be able to breathe once they got there.
它们解决上岸问题的方法
The way they solved the problem of hauling themselves up onto the land,
我们能从这些生活在 红树林沼泽中的小鱼身上得到答案
we can see from a small fish which lives in these mangrove swamps today.
然而无法同这些早期的鱼类建立密切的联♥系♥
It's in no way closely related to those early fish,
但是它确实给了我们展现了曾经的场景
but it does give us an idea of what that scene must have been like.
这就是弹涂鱼
The mudskipper.
陆地的入侵
它们跳出水面捕食小动物 在泥巴里打滚
They come up out of the water to browse on small creatures swarming on the mud.
它们的前鳍与骨头相连 所以这种鱼能将其当作腿，扭曲前行
Their front fins have jointed bones so the fish can use them as legs to lever itself along.
弹涂鱼不是发展出强壮的鳍的唯一鱼类
The mudskipper is not the only fish to have developed muscular fins like these.
第一批这种鱼的化石已经在岩石中被发现
Fossils of one of the first have been found in rocks
在脊椎动物冒险登上陆地之前， 弹涂鱼冒险一试
laid down just before the time backboned animals ventured onto land.
腔棘鱼
The coelacanth.
这种及其远古的鱼也把鳍当成腿吗？
Did this extremely ancient fish also use its fins as legs?
不幸的是， 没有它们的化石比曾经发现的7千万的更年轻
Unfortunately, no fossils of them younger than 70 million years have ever been found,
在40年前发现的化石
and up to 40 years ago,
科学家得出结论他们不可以回答那问题
scientists concluded that they wouldn't be able to answer that question
很明显这种鱼灭绝了
as the fish was obviously extinct.
而且，在1938年，一个活的一种腔棘鱼被捕捉
And then, in 1938, a living coelacanth was caught
远离南非海岸
off the coast of South Africa.
它是本世纪的科学的轰动
It was the scientific sensation of the century.
在科学家开始调查它的内部以前
Before scientists could get to examine its entrails
看它们如何证实或否认他们曾经的推论
and see how they confirmed or denied the deductions they'd made
从这条非常远古的活化石——腔棘鱼
from the very ancient fossil coelacanths,
已经在腐烂
the fish was already rotting.
它的内脏被未经权衡的丢弃了
Its guts were thrown away unexamined.
所以，为了寻找其他的腔棘鱼 大范围地搜寻被发起
So a huge search was mounted to find another.
鱼的照片被印刷，并给了报酬
Leaflets were printed with pictures of the fish, offering a reward,
被发放到远离非洲海岸的 数不尽的捕鱼村庄之中
and were distributed among the countless fishing villages off the African coast.
但是什么都没有…… 直到14年后第二条腔棘鱼被捕捉
But nothing... until, 14 years later, a second coelacanth was caught.
它来自一个超过1000英里远的地方 与捕到第一条鱼的地方相比
It came from a place over 1,000 miles away from where the first one was landed.
在极小的卡莫洛岛中
Here in the tiny Comoro Islands,
一个小的社团 位于马达加斯加和非洲东海岸的中间
a small group lying midway between Madagascar and the coast of East Africa.
第一条鱼看起来像是一个迷路者
The first one, it seems, was a stray.
这些水域是这条非常稀有的鱼的 真正唯一的家
These waters are the true and only home of this extraordinary rare fish,
且住在那个小村庄人是捕获这种腔棘鱼的专家
and the people who live in that tiny village are the world's experts in catching coelacanths.
一个村民仍然有一些干的腔棘鱼 让我看过
A villager still had a dried coelacanth which he let me see.
从现在还生存着的不是很多的腔棘鱼 了解它们的生活习惯
From what we know of the habits of the living coelacanth, which is not much,
看起来，这些后鳍是用来游泳的
it seems that these rear fins are used for swimming
但是前面的鳍是用来
but the front ones are used for manoeuvring
帮助鱼在它们居住的岩石的底部攀爬
and for helping the fish to clamber about along the rocky bottom where it lives.
它们所有的鳍有肌肉的根基
All the fins have fleshy bases to them.
在晚上，渔夫在约300公尺的深度捕捉它们
The fishermen catch them at night from depths of 300 metres or so.
一旦钩住，鱼猛烈地挣扎 而且整整一晚只钓上一条
Once hooked, the fish fight valiantly, and it may take all night to haul one up.
因此在得到它时，它通常是死的
So it's usually dead on arrival.
科学家仍不能够观察一条活着的
Scientists have still not been able to observe one alive.
然后，当我们在科摩罗的时候，捕捉了一条
Then, while we were in the Comoros, one was caught.
虽然它很虚弱， 但是当照相机到来的时候，它仍然活着
Although it was weak, it was still alive when the cameras arrived.
在3亿5千万年以前，有像这一样的鳍的鱼
350 million years ago, fish with fins like these
正遨游于世界的海洋
were cruising the seas of the world.
一些生活在浅水的鱼生产了后裔
Some living in shallow waters produced descendants
最后爬上陆地
which eventually clambered onto the land,
而这个祖先还在没有变化过的深度
while this creature's ancestors moved down to the unchanging depths,
自己也没有变化
there to remain unchanged themselves.
科摩罗人每年捕捉一或二条这种腔棘鱼
The Comorians catch one or two coelacanths a year.
它们通常不值很多钱，因为它们的肉不好吃
They used not to value them much, for their flesh isn't good to eat.
然而，现在科学机构给予很多的报酬
Now, however, big rewards are offered by scientific institutions,
捕捉这一条鱼的老人将会很快变富
so the old man who caught this one will soon be rich.
一些研究员在几个星期之内 将会专注于研究这个鳍
Some researcher in a few weeks' time will be absorbed in examining this fin
科学家同意一定非常像四肢
which scientists agree must resemble closely those limbs
四肢首次把脊骨动物带到了陆地上
that first took backboned animals onto the land.
那么，那个第二的问题怎么样解决？ 在陆地上面的呼吸的问题
But how about that second problem? The problem of breathing up on land.
当在水中游泳的时候， 鳃非常出色地为它们服务
The gills, which had served them well while swimming in water,
吸取溶解的氧 但在空气中不起作用
extracting dissolved oxygen, wouldn't work in the air.
鱼如何解决那一个问题？
How did the fish solve that problem?
好吧，这里是东非 现在是干季节的顶峰期
Well, this is East Africa and it's the height of the dry season.
在这片炎热的地形上没有一滴水被发现
There is not a drop of water to be found in this parched landscape.
然而，靠近我的这里 有鱼以能在空气中生存和呼吸
And yet, here, close by me, there are fish that are living and breathing in air.
如果只有我能找它们
If only I can find them.
在六个月以前这是一个好几尺深的池塘
Six months ago, this was a pond several feet deep in water.
但是旱季来临，水蒸干了
But as the dry season progressed, the water evaporated
池塘里的鱼挖洞到达这里， 雨季有着软的液体的泥浆
and the fish in it burrowed down into this, which was soft liquid mud
但现在像砖块一样硬
and is now brick-hard.
它们在某处作茧
And there, somewhere, they cocoon.
而且……看起来像……鼻子
And that... That looks like...the nose of one.
挖开泥土
Poking out from the mud, there.
现在，如果我把它拿走， 放到一个有水的水箱子中
Now, if I take this and drop it in a tank of water,
看起来好像雨来早了，这条鱼应会活过来
it should seem as though the rains have come early, and the fish should come to life.
当水渗入泥土，它变得柔软，松落
As the water soaks in, the mud softens and falls away,
暴露了一个干燥黏液的很薄的茧
exposing a papery cocoon of dried mucus.
这个特别的动物有能在空气和水中呼吸的咽
And there is the throat of this extraordinary creature that can breathe in air and water.
它是一个肺鱼
It's a lungfish.
虽然它的水中呼吸器官，鳃，再一次工作了
While its water-breathing apparatus, the gills, are getting working again,
但是，它攫取了空气的额外的气体
it snatches another gulp of air.
它能够呼吸空气因为它有来自腹部的开放的
It's able to breathe air because it has, opening from its gut,
一个沿血管排列的长的气囊
a long pouch lined with blood vessels,
而且它们通过它的潮湿衬里能吸收气体的氧
and they can absorb gaseous oxygen through its moist lining.
腔棘鱼没有肺，但已经有了一个简单的腿
The coelacanth has no lung but it has got a simple leg,
鳍以肌肉为基础 并由骨头支撑
that fin with a fleshy base to it, supported by bones.
因此，既不是腔棘鱼也不是肺鱼
Neither it nor the lungfish, therefore,
是接近第一批登陆的创造者
can be close to the creature that first moved to land.
但是如果两种决定性的因素 要在一只动物身上发生
But if those two crucial elements were to occur in one animal,
那么它会是强大的候选人
then such a creature would be a strong candidate.
而且的确，它们是
And indeed, they do.
这一个化石鱼，来自4亿5千万岁的岩石， 具有这两个因素
This fossil fish, from rocks 450 million years old, has them both.
它叫做eusthenopteron 当它的鳍的周围的岩石和尺寸被移♥动♥的时候
It's called eusthenopteron. When the rock and scales around its fin are removed,
你能看见骨头：一块靠近身体， 其余是成群的小骨头
you can see the bones: one close to the body, then two, then a group of small ones.
的确，在所有的陆地脊椎动物的四肢中 发现了这样的模式
Exactly the pattern found in the limb of all land vertebrates.
具有冒险精神的祖先可能非常像这个
And that adventurous ancestor may have been very like this.
但是为什么它登上陆地？也许它迫于干旱
But why should it have climbed onto the land? Perhaps it was forced out by droughts.
也许它被食物诱惑，动物涌向陆地
Maybe it was tempted by food, the creatures that swarmed on the mud.
无论什么原因， 它的后裔来在陆地上花费更多的时间
Whatever the reason, its descendants came to spend more of their time on land.
而且数百万年以来， 它们进化了更适合在陆地上的生活的身体
And over millions of years they evolved bodies more suited to life on land
而且变成第一批两栖动物
and became the first amphibians.
这个时间的植物不同于今天的植物
The vegetation of the time was different from that of today.
没有开花植物，而且最常见的之一是一种马尾
There were no flowering plants, and one of the commonest was a kind of horsetail,
很像这些生长的在英国北部的马尾
rather like these growing in the north of England,
除马尾外，在3亿年以前长到约50或60尺高的
except the horsetails then, 300 million years ago, grew to about 50 or 60 feet tall
生长在沼泽中的茂密的森林
and formed dense forests growing in swamps.
当它们死的时候， 马尾树干落入水中，形成一种泥煤
When they died, the horsetail trunks fell into the water and formed a kind of peat.
很多年以来，淹没沼泽的海平面时有变化
Over the years, there were variations in the sea level which flooded these swamps
把泥煤埋藏到了沙子的沉积物之下
and buried the peat beneath deposits of sand.
在这些沉积物的重量作用之下
Under the accumulating weight of these sediments,
泥煤变成了煤
the peat then turned to coal.
而且在矿中，你能看见变成了石头的沙子
And in the mine, you can see the sand that's been turned to stone
而且在沙子之下，植物被压缩的残余物
and beneath it, the compressed remains of the plants.
而且在这个特别的地层中已经发现了骨骼
And in this particular seam have been found the bones
一些动物在那些远古的沼泽中爬行
of some of the animals that crawled in those ancient swamps.
这是最生龙活虎的骨骼之一
This is one of the most dramatic of them.
头盖骨 这是它的巨大牙齿
It's a skull. Here are its huge teeth,
是简单的牙齿，而不像鱼有钉一样的牙齿
which are simple teeth, rather like the peg-like teeth of the fish then.
我们知道这个动物有一只桨形的尾部
We know that this creature had a paddle-shaped tail
以及非常好的四肢
and also four very good limbs.
因此它的确是真正的两栖动物