生命的进化（1979）

世界上有百万种动物和植物
There are four million different kinds of animals and plants in the world.
有四百万种不同的生存方法
Four million different solutions to the problems of staying alive.
这里就有一些它们的生存方法的故事
This is the story of how a few of them came to be as they are.
生物多样性
南美洲的雨林
The South American rainforest.
世界上最多种多样的生物大聚集
The richest and most varied assemblage of life in the world.
在上面的那些是大声尖叫的猴子
Those are howler monkeys up there.
有这些森林之中有大约50种不同的猴子
There are around 50 different kinds of monkeys in these forests.
这里最美丽的生物就是蜂鸟了
Some of the most beautiful creatures here are hummingbirds.
在几英里的范围内就有54个不同的种类
54 different kinds have been found within a few miles of here,
而整个南美洲可以找到300多种
and over 300 have been found in South America as a whole.
没有人知道这里到底有多少种动物
Nobody knows how many kinds of animals there are here.
眼睛之所及，全都是生命
Wherever you look, there's life.
已被命名的昆虫就达几十万种
There are several hundred thousand insects that have been named,
毫无疑问地，更多的还没有命名
and, without doubt, many more that haven't.
全部这些生命和植物组成了一个复杂的体系
All these creatures and plants form one complex mosaic.
兰花需要蜜蜂为它们授粉
The orchid needs the bee to pollinate it.
食蚁动物是因为有了蚂蚁才能生存
The anteater couldn't have existed before the ants.
所以，除非整个复杂的体系是在一瞬间完成的
So unless the whole complex came about in a flash of instant creation,
否则不同的生物群体一定是在不同时期出现的
different organisms must have appeared at different times.
但是哪些是最先出现的呢 为什么会显得如此多样的种类呢？
But which came first, and why should there be such an immense variety?
这种问题迷住了一个24岁的英国年轻人
Such questions obsessed a young 24-year-old Englishman
他在1832年来到了这里
who came here in 1832.
他的名字叫查尔斯·达尔文
His name was Charles Darwin
他在这里发现了丰富的生命 整个人都被吸引住了
and he was enthralled to the point of ecstasy by the richness of life he found here.
一天之内，在一个小小的区域里 他就发现了69种不同的甲虫
In one day, in a small area, he discovered 69 different species of beetle.
当他写日记的时候
As he wrote in his journal,
他写道：“这足以打破昆虫学家心里的平静，
"It's enough to disturb the composure of the entomologist's mind
足以令人构想完整的物种数目在将来会有多大。”
"to contemplate the future dimension of a complete catalogue."
当时传统的观念是
The conventional view of the time
每种动物和植物都是由上帝创造的
was that every species of animal and plant had been individually created by God.
而达尔文也是这样相信的
And Darwin was no atheist.
在以后的三年里贝格尔号♥走遍了整个南美洲
During the next three years, the Beagle sailed round South America
一直到太平洋地区
and up into the Pacific.
厄爪多尔向西600英里
600 miles west of Ecuador,
他们来到了偏僻的加拉帕戈斯群岛
they came to the lonely Galapagos islands.
就在这里，在这些火山岛屿上
It was here, on these volcanic islands,
达尔文关于物种的起源的怀疑又复苏了
that Darwin's doubts about the creation of species were reawakened.
到处达尔文都发现跟他在内地看到的生物
Everywhere, Darwin found creatures that bore a general resemblance
大体相像的群体
to those he had seen on the mainland.
但是几乎所有的都存在着小小的差异
But nearly all were slightly different.
例如，这里有鹧鹳
These, for example, were cormorants
就跟他在巴西河流看到的差不多
similar to those he had seen flying along Brazilian rivers.
但在加拉帕戈斯群岛上， 那些鹧鶸的翅膀很小，还有没发育好的羽毛
But in the Galapagos, their wings were so small, with such stunted feathers,
他们已经丧失了飞翔的能力
that the birds had lost their powers of flight.
还有明显的鬣蜥
And these were clearly iguanas.
他曾经在南美的森林里看到过它们爬树
He'd seen them climbing trees in the South American forests,
但是在加拉帕戈斯群岛上只有稀少的植被
but on the Galapagos, with its sparse vegetation,
那些鬣蜥吃的是海草而它们长得了不一样
these iguanas fed on seaweed, and they were not the same.
它们比较小，比较黑，通常有着长长的爪子来
Smaller, darker and with unusually long claws to help them keep a foothold
保证他们可以在容易掉下去的暗礁上可以立足
among the crashing breakers.
它们也有一些不寻常的习惯
They also had extraordinary habits,
它们会勇敢地游到海里潜到海底去找东西吃
swimming fearlessly out to sea and diving deep to graze on the sea bed.
加拉帕戈斯群岛这个名字是因为 它们的上面有着海龟群
The Galapagos Islands got their name from the herds of tortoises that live on them,
几个世纪以来，水手们吃着这些海龟
which sailors for centuries had slaughtered for food.
但是这些海龟与内地的海龟有着很明显的不同
But these too were obviously different from mainland tortoises.
它们大了好几倍
They were many times bigger.
岛上的英国的副官告诉达尔文
The English vice-governor of the islands told Darwin
他可以从外形看出那些海龟来自哪个岛屿
that he could tell which island a tortoise came from by its shape.
比如，这个，它有着拱的圆壳
This one, for example, with its deep, rounded shell,
是从一个被水围绕着的岛屿来的 它在那里是以地上的植物为食的
comes from a well-watered island where it can feed on vegetation on the ground.
这个壳有尖，可以使它的脖子向前伸长的
This one has a peak to the front of its shell that enables it to stretch its long neck upwards.
是从一个干旱的岛屿来的
It comes from an arid island,
那里的海龟都要伸长它们的脖子 以便可以够得着唯一的食物
where the tortoises have to crane up to reach the only food there,
树枝和仙人掌
the branches of trees and cactus.
达尔文怀疑生物的种类不是自始至终的存在的
The suspicion grew in Darwin's mind that species were not fixed for ever.
有可能所有的海龟都是来自共同的祖先
Perhaps the tortoises were all descended from common ancestors
但是为了适应各自的小岛而改变了
and had changed to suit their particular islands.
达尔文在加拉帕戈斯群岛上 注意到的动物之间的区别
The differences Darwin noticed among these Galapagos animals
当然，是很微小的
were, of course, tiny.
但是如果这些区别继续发展下去的话， 几千几百万年以来
But if they could develop them, wasn't it possible that over the thousands or millions of years,
一系列化的区别不就构成了 一个进化性的改变了吗？
a whole series of such differences might add up to one revolutionary change?
难说没有可能，也许
Was it not possible, perhaps,
以前的两栖动物的皮肤变得致密 然后就成了爬行类？
that in the past amphibians had developed watertight skins and so turned into reptiles?
或者一个像蜥蜴的爬行动物 已经发展成了一种羽毛的水平
Or that a lizard-like reptile had developed a feathery kind of scale
然后就成了鸟类呢？
and become a bird?
而人类自己甚至也有可能是 从一群在树上荡秋千的猿猴发展而来的呢？
And even that man himself might be descended from a group of tree-swinging apes?
事实上，这不是一种新的想法了
In truth, the idea was not a new one.
在达尔文之前的人曾认为 世上所有的生命有可能都有着同一个祖先
Others before Darwin suggested that all life on earth might have a common ancestry,
但是达尔文研究得更加深入
but Darwin went further.
他通过提供一个机制
He gave the idea irresistible force
来让这种想法难以抗拒
by suggesting a mechanism which might have brought that about.
他把这种机制叫做自然选择
He called the mechanism natural selection.
简单的说，他的说法是这样的
Put briefly, his argument was this.
相同种类中的个体并不是完全相同的
Individuals of the same species are not absolutely identical.
这种大海龟的幼儿中有一些从出生之时
Some of these giant tortoise hatchlings may have, from birth,
就有着比其他长一点点的脖子
slightly longer necks than others.
在干旱的时候，它们可以够得着树叶， 然后就生存了下来
In times of drought, they will reach leaves and live,
而那些有着短脖子的够不着就死了
while the shorter-necked ones die.
所以这些能够很好适应环境的
So those best fitted for the environment
就把它们的特点传给了后代
will transmit their characteristics to their offspring.
代代相传，在干旱岛屿上的海龟
After many generations, tortoises on arid islands
就会有着比在有水围绕的岛屿上的 海龟更长的脖子
will have longer necks than those on well-watered ones.
所以同一个种类会带来另外一个
And so one species will have given rise to another.
在这些节目里，我们会调查
In these programmes, we're going to survey
由自然选择而来的无数动物相异之处
the unmeasurable variety of animals produced by natural selection,
不是把它们当成独♥立♥的怪异来看
and look at them not as isolated oddities,
而是看从10亿年以来它们是怎样发展的
but as elements in a long and continuing story that began 1,000 million years ago,
而今天仍在继续发展下去
and is still continuing today.
有些生物，如哺乳动物
Some creatures, the mammals,
像海狮和我自己， 都是在这一幕上有联♥系♥地发展到现在的产物
such as these sea lions and myself, are relatively recent arrivals on the scene.
其他的，像鸟类、爬行类、两栖类、鱼类 它们在这个世界上的存在比我们早得多
Others: birds, reptiles, amphibians, fish, have been here much longer than we have.
在很长的时间里，有些地方的条件保持不变
In places where conditions have remained unchanged over immense periods of time,
那里仍然聚居着这一些与
there are still creatures living which resemble very closely
它们的祖先非常相像的生物
their early ancestors.
它们可以说明很多
They can tell us a lot.
但是为了解开这个故事 我们仍然要从化石上找证据
But to disentangle the story, we shall also have to look for evidence in the rocks.
动物的尸体掉进了古代的海洋和沼泽里
The bodies of animals fall into the bottom of ancient seas and swamps,
有时候被埋到了沉积层下
sometimes get entombed in the accumulating sediment.
而，当几百万年后这些沉积层变成了岩石
When, after millions of years, those sediments turn to rock,
而动物的骨头也就成了化石而存在
those remains of animals and plants survive as fossils.
自从射线发现以来
Since the discovery of radioactivity,
科学家们发展出了可以测量石头年龄的技术
scientists have developed techniques of measuring the age of rocks
这种技术是基于化学元素衰减的程度的
based on the rates at which some chemical elements decay.
所以化石可以被追朔到几百万年前
So fossils can be dated to within a few million years.
但是还有一些更加简单的测定方法， 人人都可以用
But there are much simpler ways of establishing the ages of rocks that anyone can use,
而在美国西部的大峡谷是最好的方法了
and there is no more dramatic place to do so than in the Grand Canyon in the American west.
伴随着风和雨的科罗拉多河
The Colorado river, aided by wind and rain,
在亚利桑那州的沙岩和石灰石上 冲蚀了一个巨大的断面
has cut a gigantic section through the sandstones and limestones of Arizona.
那些岩层大部分还没改变
The layers still lie largely undisturbed,
所以很明显地， 底下的岩层比上面的出现得要早
so obviously the lower ones were deposited before the upper ones.
如果我们想生命的始祖的话
So if we want to trace the ancestry of life back to its beginnings here,
我们就要层层深入到石灰石层里去
we have to go deeper and deeper into the canyon.
这个是在地球表面存在的最大的裂缝
This is the greatest gash that exists in the surface of the earth.
从边缘上到底下的河是一段很大的垂直距离
From the rim to the river at the bottom is a vertical mile.
去到下面的方法有很多最常用的就是骑骡下去
There are a number of trails down. The usual way is on the back of a mule.
现在，我们已到了离大峡谷缘下面 大约500英里的地方
Here, we're about 500 feet below the lip of the canyon.
这里的岩石已经有两千万年了
Already the rocks are about 200 million years old.
这里还没有哺乳动物 但是已经有了一些四脚的陆地动物
There are no mammal fossils here, but there are some four-legged land animals.
简单的爬行动物一种像小蜥蜴的生物
Small reptiles: a little lizard-like creature
沿途都在过去是沙丘的表面上留下了它的痕迹