生命的进化（1979）

Their foot is used to pull them down into the sand
在那里，他们可以安全地不明显地过滤食物
where they can sit and filter food safely and unobtrusively.
扇贝也是滤食者
Scallops are also filter feeders.
它们生活在表面并且不只是有好眼睛 还有一种令人惊讶的移♥动♥方式
They live on the surface and not only have good eyes but a surprising way of moving.
它们中最大的是另一种滤食者 几米长的巨大的蛤
Biggest of all is another filter feeder, the metre-long giant clam.
因为它是如此巨大，所以它不能移♥动♥
So huge, it can't move.
它们的肉体连接着两片贝壳形成一个空腔， 在那里，它们吸取水
Its fleshy mantle joins its two shells, forming a chamber through which water is sucked.
间隔很短， 它们痉挛一样地抖动排出废物
Every so often, it gives a convulsive shudder and gets rid of a little waste.
一些软体动物走向另一个极端 变成自♥由♥游动体
A few molluscs have gone to the other extreme and become free-swimming
通过减小壳的尺寸，直至壳可以隐藏在体内
by reducing their shells to scales concealed within their bodies,
或者是完全不需要壳
or doing without them altogether.
没有了贝壳的保护， 这些软体动物靠污秽的黏液保护自己
Unprotected by a shell, these creatures defend themselves with a nasty-tasting slime.
并且它们鲜艳的颜色 向想要吃它们的动物提出了警告
And their brilliant colours may serve to warn off anything that might contemplate eating them.
假如就是这样， 它们一定是自然界中最可爱的警示
If that's so, they must be among the loveliest warning notices in all nature.
这些动物更复杂并且通常比扁形虫更大
These creatures are more complex and usually larger than flatworms,
并且他们需要特殊的呼吸装置：鳃
and they need special breathing apparatus, the gills.
在一些种类中， 它们在背部暴露出令人心惊胆战的花纹
In some species, they're exposed as a kind of trembling bouquet at the back.
一些种类已经发展出羽毛般柔软的 可以在海面附近漂浮的东西
Several kinds have developed feathery outgrowths for floating near the sea's surface.
在那儿，虽然有很大的噪音 但是它们可以捕食水母
There, extraordinary though it may sound, they hunt for jellyfish.
这个叫海罂粟，并且它已经找到了它的猎物
This one is called glaucus, and it has found its prey.
水母身上的刺并不能起到保护的作用
The stinging cells of the jellyfish are no defence.
甚至一些漂浮的软体动物欢迎它们， 吞食刺细胞
Indeed, some of these floating molluscs welcome them, swallowing the stinging cells
并将它们存储在自己的触角中 以作为二手武器使用
and storing them in their own tentacles to use as second-hand weapons.
这是另一种海罂粟的食物
This is another creature eaten by glaucus.
一种最致命的水母，葡萄牙僧帽水母
One of the most deadly of all jellyfish, a Portuguese man-of-war.
在它拖着的触角下，长满了刺
Beneath it trail its tentacles, loaded with stings.
另一种软体动物也掠食这种动物 而这一次，它有壳
Another mollusc also preys on this creature, and this time, one with a shell.
它对漂浮在海上有一个独特的解决办法
It has a most ingenious solution to the problem of keeping afloat.
它用它勺子状的腿做出特别的动物来 通过黏液获得空气制♥造♥泡沫
It produces bubbles by trapping air in mucus with special movements of its spoon-like foot,
并将它们做成筏，它悬挂在上面
and builds them into a raft, from which it hangs.
当它漂进葡萄牙僧帽水母时它立刻开始进攻
When it drifts into a Portuguese man-of-war, it attacks immediately.
水母的刺细胞，对其他动物是致命的 但是对蜗牛没有作用
The stinging cells of the jellyfish, lethal to other creatures, have no effect on the snail.
它用其余的触角用力咀嚼它们
It munches them with the rest of the tentacles.
一个泡沫筏解决了蜗牛的体重问题 但是对于更大的动物就不起作用了
A raft of bubbles solves this snail's weight problems, but that won't work for bigger creatures.
然而，5亿年前， 一类软体动物发展出另一种方法
500 million years ago, however, a group of molluscs evolved another method.
这个化石贝壳可能看上去 只是一个普通的贝壳种类，虽然非常大
This fossil shell may look perhaps quite an ordinary sort of shell, albeit rather large,
但是在它的里面已经有了很复杂的结构
but inside it has got quite a complicated structure.
这块石头里面有一个贝壳， 石头的外表已经磨损了
Here's one in a boulder where the outside has been worn away
所以我们可以看到它的内部
so that we can see what's inside.
这部分是动物居住的地方， 并且在它的后面，是这些空腔
This part was where the animal lived, and at the back of it, there were these chambers
这里一生中都充满了气体，并作为浮选室
which in life were filled with gas and acted as flotation chambers.
我们是怎样这么确定的呢？
How can we be so sure?
好，因为这是另一个幸存的 实际上没有改变的动物
Well, because this is another of those creatures that have survived virtually unchanged
在数亿年间
for hundreds of millions of years.
这是一个鹦鹉螺， 现在仍有鹦鹉螺生活在海洋中
This is a nautilus, and there are nautilus swimming in the seas today.
它们生活在南太平洋 但是很少人曾见过活着的鹦鹉螺
They live in the South Pacific, but few people ever see them alive,
因为它们大部分时间花在500米深的海底
for they spend most of their time in depths of up to 500 metres.
它们可以游到任何深度 通过抽吸体腔和外面的流动的水
They can swim at any depth, by pumping fluid in and out of their chambers,
并这样控制浮力
and so controlling their buoyancy.
为了成为这样的运动物体 它们需要好的感觉器官
Being so mobile, they need good sense organs,
它们的眼睛，虽然没有晶状体 却是我们目前所看到的动物中最好的
and their eyes, although they have no lenses, are the best of any creature we've seen so far.
它们的身体已经改进成成打的触角
Their bodies have become modified into dozens of tentacles.
一些带有感觉器官用来发现食物，一些被用来繁殖
Some carry sense organs to detect food, some are used in reproduction
其他的被用来和它们的食物搏斗 这些食物通常是腐肉，龙虾或者螃蟹
and others to grapple with their prey, which is usually carrion, or lobsters or crabs.
这被证实是非常成功的设计
This proved to be an immensely successful design.
并且由它演化成另一种巨大的 软体动物种类，菊石
And from it came another great group of molluscs, the ammonites.
菊石在接下来的2亿年中支配着世界上的海洋
The ammonites were to dominate the seas of the world for the next 200 million years.
它们生活在岩石的后面， 特别是生活在英格兰南部的莱姆里吉斯
They left behind in the rocks, particularly here in Lyme Regis in southern England,
菊石化石在我看来是最有趣的化石中的一些
fossils that to my mind are some of the loveliest fossils of all.
就像鹦鹉螺一样， 菊石在生长的时候增加了一些新的浮选室
Like the nautilus, the ammonites added new flotation chambers as they grew,
而它们的身体只是占用了外面的一个
while their bodies occupied only the outer one.
菊石是如此众多， 并且它们的化石是如此完好
Ammonites were so numerous and their shells fossilised so well,
所以我们知道很多 关于它们在2亿年的时间内发展的情形
so we know a great deal about the way they developed over a period of 200 million years.
但是它们的历史充满了谜
But their history is full of puzzles.
例如，为什么一些种类发展了展开的种类
Why, for example, did some groups develop uncoiled species
然后，经过数代之后，又慢慢地向上盘绕？
and then, over generations, slowly coil up again?
为什么浮选室之间的连接
Why did the junctions between the flotation chambers,
最先是简单的曲线
which originally had been simple curves,
逐渐变得精细复杂，最终变得华丽？
become increasingly elaborate and intricate, and eventually florid?
小的菊石也许曾经生活在底部的浅水区
Small ones may have lived in shallow water near the bottom,
但是其他的长成极大的尺寸
but others grew to an immense size
并可能像帆船一样在史前的海面上航行
and probably sailed the upper waters of the prehistoric seas like galleons.
并且有一个最终的奥秘。 为什么，五千万年前，它们全都灭绝了
And there is one final mystery. Why, 50 million years ago, did they all die out?
今天，没有一个活着的菊石
There is not one surviving ammonite today.
但是这些极薄的贝壳看上去像它们
But these paper-thin shells look like them.
在非常少有的场合， 在新西兰偏僻的海滩，它们被冲上来
On very rare occasions, they are washed up on lonely beaches in New Zealand.
它们既不属于菊石，也不属于鹦鹉螺 但是它们有亲缘关系
They belong neither to an ammonite nor a nautilus but a relative,
一种叫舡鱼的章鱼， 有时，舡鱼和菊石及鹦鹉螺关系让人进退两难
a kind of octopus called the argonaut, which is sometimes stranded with them.
这种动物不在壳中生活
The animal doesn't live in the shell.
它用一只臂中分泌壳，并在壳里面产卵
It secretes it from one of its arms and then lays its eggs in it.
很少有人曾经看到那种情况发生
Few people have ever seen that happen.
只有一次偶然机会，风暴袭击了繁殖中的群体
Just once in a while, a storm catches the breeding shoals
并把这些脆弱的摇篮打到岸上 它们中的一些仍然怀着卵
and drives these delicate cradles ashore, some of them still holding their eggs.
在生命中的大多数时候，舡鱼， 像所有其他的章鱼一样，是完全没有壳的
For most of its life, the argonaut, like all other octopus, is totally without a shell.
只有在这个时候如此鲜明地 证明了它和鹦鹉螺目软体动物的亲缘关系
Only on this one occasion does it demonstrate its relationship with the nautilus so vividly.
有时很难记起章鱼是一种软体动物
It's difficult to remember at times that the octopus is a mollusc
而且它的大多数同类拖着重壳，
and that most of its relations are weighed down with shells
快速移♥动♥和聪明要走很长的距离
and a long way from being quick-moving or intelligent.
它的软体动物触角 已经变成有吸盘的重装甲
Its molluscan tentacles have become heavily armoured with suckers.
被蛤用来过滤食物的虹吸管 提供了一个喷射推进的喷嘴
The siphon used by the clams for filter feeding serves as a nozzle for jet propulsion.
它的视力是极好的， 并且它有灵活的头脑和快速的反应
Its eyesight is excellent and it has a lively brain and quick reactions.
鱿鱼和它很类似
The squid is very similar.
它比章鱼还多两条触角 并且是一个更积极的游泳者
It has two more arms than the octopus and is a very much more active swimmer.
鱿鱼仍然在身体中 保留了一个祖传的贝壳的最后遗迹
Squids still keep within their bodies a last relic of their ancestral shell.
一个角状的剑形结构帮助它们支撑长长的身体
A horny, sword-shaped structure that helps to support their long body.
游动的时候它们让触角水平伸出
As they swim, they hold their tentacles out horizontally.
它们靠喷射推进来产生速度
They use jet propulsion for speed
也可以闲散地沿着任何方向 挥动身上的鳍状物
but can also idle along in either direction by waving fin-like extensions of their mantle.
鱿鱼和章鱼是软体动物中最积极和最有智慧的
The squids and octopuses are the most active and intelligent of molluscs,
能解决复杂的问题
able to solve complicated problems.
它们也是最大的
They're also the largest.
这只在挪威搁浅的巨型鱿鱼有9米长
This giant squid that ran aground in Norway was nine metres long,
并且还有比它大两倍的鱿鱼的报导
and there are reports of others twice the size.
它们都是从6亿年前生活在海中的 像扁虫一样的祖先进化而来
They all developed from ancestors like flatworms that lived in the seas of 600 million years ago.
但是来自远古岩石中的第二种动物又如何呢？
But what about the second group of creatures from these ancient rocks?
它们被这种放射状对称的像花一样的化石重现
The ones represented by this flower-like fossil with a radial symmetry.
那么，在接下来的几百万年中
Well, within the next few million years,
它们发展成数目众多的最美丽的形式， 叫做海百合，
these developed into a multitude of most beautiful forms called sea lilies
或者海百合类
or crinoids.
它是一个合理的猜测， 它们也是从蠕虫类动物进化来的，
It's a reasonable guess that these too evolved from worm-like creatures
有片状板加强和保护它们自己
that developed limey plates to strengthen and protect themselves.
这些大约3亿年了
These are about 300 million years old,
并且很少有像它们这样的种类 仍在海洋深处生存
and a very few species like them still survive in the ocean depths.
但是在大堡礁一些近亲依然繁盛：
But on the Barrier Reef some close relatives still flourish in great numbers:
海羊齿
feather stars.
它们很像海百合，但是没有柄 除非在十分小的时候
These are just like crinoids, but without stems, except when very young.
它们成熟的时候可以自♥由♥地游动 大多数时候是晚上，寻找进食的场所
These adults swim freely around, mostly at night, in search of feeding places
在那里，它们可以粘在岩石上 并用它们的触角收集漂浮的食物颗粒
where they can cling to rocks and collect floating particles with their arms.
它们的近亲，海星， 清楚地显示这个族群的另一个特征
Their relatives, the starfish, show clearly another characteristic of this group.
它们的身体有五重对称性
Their bodies have a five-fold symmetry.
嘴在中♥央♥的下面
The mouth is underneath, at the centre.
它们用管足移♥动♥ 这是另一个独特的特征
They move on tube feet, another unique feature.
每条腿的末端都有一个很小的吸垫
Each foot has a tiny suction pad at the end,
它们通过水起作用
and the many thousands of them are worked by hydraulics,
因为它们都连接着装满水的贯穿身体的导管
for they are all connected to water-filled vessels that run through the body.
它们的兄弟姐妹， 海蛇尾，在这一族群中是速度最快的动物
Their cousins, the brittle stars, are much the speediest creatures in the group.
海胆更典型
Sea urchins are more typical.
它们也有管足 但是它们主要靠它们的刺状脊骨移♥动♥
They too have tube feet, but they move largely with the help of their spines.
一些管足专门用于移走嘴周围的残骸
Some of the tube feet are specialised for jobs such as moving debris from around the mouth,
就像海星的管足一样，它的管足身体的下方
which, like that of the starfish, is on the underside of the animal.
海胆靠慢慢地划过海藻进食