宇宙时空之旅（2014）

Cosmos: A SpaceTime Odyssey S01E02

Part 4 April 25, 2021, 12:39 p.m.

Here's a flatworm's eye view of the world.
这个多细胞生物体
This multi-celled organism
进化出了眼点上的小窝
evolved a dimple in the pigment spot.
碗型的凹窝
The bowl-shaped depression
让它可以区分光线和阴影
allowed the animal to distinguish light from shadow
能从环境中隐约分辨出物体
to crudely make out objects in its vicinity,
包括食物和天敌
including those to eat and those that might eat it.
这是个巨大的优势
A tremendous advantage.
之后视野变得清晰一些了
Later, things became a little clearer.
小窝变深
The dimple deepened
进化出了有小孔的眼窝
and evolved into a socket with a small opening.
几千代之间
Over thousands of generations,
自然选择慢慢地雕刻着眼睛
natural selection was slowly sculpting the eye.
小孔缩小至针孔状
The opening contracted to a pinhole covered
由一层保护性的透明薄膜覆盖
by a protective transparent membrane.
只有很少光线可以通过这个小孔
Only a little light could enter the tiny hole,
但足可以在眼睛敏感的内表面
but it was enough to paint a dim image
形成模糊的图像
on the sensitive inner surface of the eye.
这使焦点更为集中
This sharpened the focus.
较大的开口可以进入更多光线
A larger opening would have let in more light
图像也会更明亮但会脱焦
to make a brighter image but one that was out of focus.
这一发展也引发了视觉上的
This development launched the visual equivalent
演化军备竞赛
of an arms race.
要生存必须在竞争中获胜
The competition needed to keep up to survive.
之后眼睛进化出一个非常棒的新特点
But then a splendid new feature of the eye evolved,
一个既能透光又能精确对焦的透镜
a lens that provided both brightness and sharp focus.
原始鱼类的眼睛中
In the eyes of primitive fish,
针孔附近透明的胶体形成一层透镜
the transparent gel near the pinhole formed into a lens.
同时针孔扩张
At the same time, the pinhole enlarged
让更多的光线进入
to let in more and more light.
现在不论近处还是远处
Fish could now see in high-def,
鱼类都能看到清晰的图像
both close up and far away.
之后可怕的事发生了
And then something terrible happened.
你有注意到从水面看玻璃杯里的吸管
Have you ever noticed that a straw in a glass of water
吸管看起来像是弯曲的吗
looks bent at the surface of the water?
那是因为光线从一种介质进入另一种时会弯曲
That's because light bends when it goes from one medium to another,
比如说从水到空气
say from water to air.
我们的眼睛最初进化出了水中视觉
Our eyes originally evolved to see in water.
眼睛里的水样液体轻松地
The watery fluid in those eyes neatly
消除了弯曲效应带来的变形
eliminated the distortion of that bending effect.
但对陆地动物来说
But for land animals,
承载着图像的光从干燥的空气
the light carries images from dry air
进入它们仍然湿润的眼睛
into their still-watery eyes.
那会使光线弯曲
That bends the light rays,
导致各种各样的失真变形
causing all kinds of distortions.
当我们的两栖祖先离开水到陆地生活
When our amphibious ancestors left the water for the land,
它们为了能在水中看清而精妙进化的眼睛
their eyes, exquisitely evolved to see in water,
在空气里很难看清事物
were lousy for seeing in the air.
自那之后我们的视觉就再没有那么好
Our vision has never been as good since.
我们习惯认为我们的眼睛非常精妙
We like to think of our eyes as state-of-the-art,
但在3亿7千5百万年后
but 375 million years later,
我们仍然无法看清近在鼻端的东西
we still can't see things right in front of our noses
或是像鱼类一样
or discern fine details in near darkness
在黑暗中看清细节
the way fish can.
当我们离开水之后
When we left the water,
为什么自然不重新来过
why didn't nature just start over again
让我们进化出新的眼睛
and evolve us a new set of eyes
最理想的能在空气中看东西的眼睛
that were optimal for seeing in the air?
自然不是这样工作的
Nature doesn't work that way.
进化经过代代更迭来重塑现有结构
Evolution reshapes existing structures over generations,
通过细小的变化优化它们
adapting them with small changes.
它不能就这么回到原点
It can't just go back to the drawing board
从头开始
and start from scratch.
在进化的每个阶段
At every stage of its development,
进化中的眼睛都能很好地
the evolving eye functioned well enough
为生存者提供选择优势
to provide a selective advantage for survival.
在现存的动物中
And among animals alive today,
我们找到了在不同发展阶段的眼睛
we find eyes at all these stages of development.
它们都能够发挥作用
And all of them function.
人类眼睛的复杂性并没有
The complexity of the human eye poses
给通过自然选择的进化带来任何挑战
no challenge to evolution by natural selection.
事实上眼睛以及全部生物离开进化
In fact, the eye and all of biology makes no sense
都将是无意义的
without evolution.
有些人坚持进化只是一个理论
Some claim that evolution is just a theory,
就好像它只是一种观点
as if it were merely an opinion.
进化理论就像引力理论一样
The theory of evolution, like the theory of gravity,
是科学事实
is a scientific fact.
进化确实在发生
Evolution really happened.
接受我们与地球上所有生物的亲属关系
Accepting our kinship with all life on Earth
不仅仅是严谨科学
is not only solid science.
在我看来这还是令人激动的精神体验
In my view, it's also a soaring spiritual experience.
因为进化是盲目的
Because evolution is blind,
它不能预测或是适应灾难性的事件
it cannot anticipate or adapt to catastrophic events.
生命之树有一些断枝
The Tree of Life has some broken branches.
它们中的大多数都折损于自生命起源后的
Many of them were severed in the five greatest catastrophes
五次大灾变中
that life has ever known.
某个地方有一个纪念馆
Somewhere, there's a memorial
来纪念众多灭绝的物种
to the multitude of lost species,
灭绝殿堂
the Halls of Extinction.
跟我来
Come with me.
灭绝殿堂
欢迎来到灭绝殿堂
Welcome to the Halls of Extinction.
一个为生命之树上的断枝而建的纪念堂
A monument to the broken branches of the Tree of Life.
对现存的数百万物种中的每一个物种来说
For every single one of the millions of species alive today,
也许有一千种其它的物种已经灭亡
perhaps a thousand others have perished.
它们大多都在与其它生物每天的竞争中
Most of them died out in the everyday competition
逐渐灭亡
with other life-forms.
但也有很多在祸及全球的大灾变中
But many of them were swept away in vast cataclysms
被一扫而空
that overwhelmed the planet.
在过去的五亿年中
In the last 500 million years,
奥陶纪
泥盆纪
三叠纪
白垩纪
二叠纪
这样的事发生过五次
this has happened five times.
五次摧毁地球生命的大灭绝
Five mass extinctions that devastated life on Earth.
最糟糕的一次发生在2亿5千万年前
The worst one of all happened some 250 million years ago,
二叠纪的末期
at the end of an era known as the Permian.
披有甲壳的三叶虫
Trilobites were armored animals that hunted
曾成群的在海底狩猎
in great herds across the seafloor.
它们是第一批进化出
They were among the first animals to evolve
可成像眼睛的动物
image-forming eyes.
三叶虫存活过很长一段时期
Trilobites had a good long run,
大约有2亿7千万年
some 270 million years.
地球曾是三叶虫的天下
Earth was once the planet of the trilobites.
但现在它们都消失了灭绝了
But now they're all gone, extinct.
与无数其它物种一起
The last of them were swept from life's stage
它们最后都在
along with countless other species
一场空前的环境灾害中被消灭殆尽
in an unparalleled environmental disaster.
那场浩劫始于现在的西伯利亚
The apocalypse began in what is now Siberia,
火山喷发的规模
with volcanic eruptions on a scale unlike anything
在人类历史中见所未见
in human experience.
那时的地球非常不同
Earth was very different then,
只有一个超级大♥陆♥和一个巨大的海洋
with one single supercontinent and one great ocean.
不间断的炽热熔岩
Relentless floods of fiery lava
吞没了比现在西欧还大的一块区域
engulfed an area larger than Western Europe.
脉冲似的喷发
The pulsing eruptions went on
持续了数十万年
for hundreds of thousands of years.
熔化的岩石点燃了煤藏
The molten rock ignited coal deposits
排出的二氧化碳和其它温室气体污染了空气
and polluted the air with carbon dioxide and other greenhouse gases.
这使地球升温
This heated the Earth
并阻止了洋流的循环
and stopped the ocean currents from circulating.
有毒细菌爆发