宇宙时空之旅（2014）

Cosmos: A SpaceTime Odyssey S01E02

Part 2 April 25, 2021, 12:39 p.m.

但是它的身体内部正在发生非凡的变化
but something extraordinary is happening inside her.
这种变化会形成新的品种
Something that will give rise to a new species.
为了看到它
In order to see it,
我们必须深入到一个更小的尺度
we'll need to descend down to a much smaller scale,
去到细胞层次
to the cellular level,
探索这头熊的生殖系统
so that we can explore the bear's reproductive system.
我们将从锁骨下动脉穿过心脏
We'll take the subclavian artery through the heart.
快到了
Almost there.
那是它的一些卵子
Those are some of her eggs.
为了明白这其中的奥秘
To see what's going on in one of them,
我们要变得更小一些才行
we'll have to get even smaller.
我们得缩小到分子水平
We'll have to shrink down to the molecular level.
我们的想象号♥飞船现已缩到很小
Our Ship of the Imagination is now so small,
一粒沙就可以装下数百万艘
you could fit a million of them into a grain of sand.
看到那些在梁上大摇大摆走着的家伙了吗
See those guys over there strutting along those girders?
它们是一种叫做驱动蛋白的蛋白质
They are proteins called kinesin.
这些驱动蛋白是运输队的一份子
These kinesin are part of the transport crew
忙于在细胞之间传送货物
that's busy moving cargo around the cell.
它们长得可真古怪
How alien they seem.
然而这些小生物和其他类似的存在
And yet these tiny creatures-- and beings like them--
是每个活着的细胞的一部分
are a part of every living cell,
也存在于你的体内
including the ones inside you.
如果生命也有圣殿
If life has a sanctuary,
那必然是细胞核其中有我们DNA
it's here in the nucleus which contains our DNA...
记录着我们遗传密♥码♥的古老经♥文♥
the ancient scripture of our genetic code.
由所有生命都可阅读的语言谱写
And it's written in a language that all life can read.
DNA分子形似一条扭曲长梯
DNA is a molecule shaped like a long twisted ladder
或双螺旋形
or double helix.
这个长梯的阶梯由
The rungs of the ladder are made
四种更小的分子组成
of four different kinds of smaller molecules.
它们就是基因字母
These are the letters of the genetic alphabet.
基因字母的不同组合拼出了
Particular arrangements of those letters spell out
给所有生命的指令
the instructions for all living things,
告诉它们如何生长移♥动♥ 消化
telling them how to grow, move, digest,
感知环境愈合伤口和繁衍下一代
sense the environment, heal, reproduce.
DNA双螺旋是一台分子机器
The DNA double helix is a molecular machine
由千亿个"原子"部件组成
with about 100 billion parts called "Atoms."
一个DNA分子内的原子数目之多
There are as many atoms in a single molecule of your DNA
可以与一个星系内的恒星数目媲美
as there are stars in a typical galaxy.
狗的DNA也是如此
The same is true for dogs
还有熊
and bears
和其他所有生命
and every living thing.
我们每个生命都是一个小宇宙
We are, each of us, a little universe.
DNA信息从一个细胞传至另一个细胞
The DNA message handed down from cell to cell
从上一代传到下一代
and from generation to generation
都经过精心复♥制♥
is copied with extreme care.
一个新的DNA分子的诞生始于
The birth of a new DNA molecule begins
解链蛋白
when an unwinding protein
解开双螺旋双链
separates the two strands of the double helix,
把阶梯打破
breaking the rungs apart.
在细胞核内的液体中
Inside the liquid of the nucleus,
基因字母分子自♥由♥地漂浮着
the molecular letters of the genetic code float freely.
每条螺旋单链复♥制♥出它丢失的另一半
Each strand of the helix copies its lost partner,
最后得到两个一模一样的DNA分子
resulting in two identical DNA molecules.
这就是生命复♥制♥基因
That's how life reproduces genes
并一代代传递下来
and transmits them from one generation to the next.
当一个活细胞一分为二
When a living cell divides in two,
每一个细胞都带走一份完整的DNA
each one takes away with it a complete copy of the DNA.
有一种特殊的蛋白质校勘这一过程
A specialized protein proofreads to make sure
只有正确的基因字母才能被接受
that only the right letters are accepted
保证每个DNA的准确复♥制♥
so that the DNA is accurately copied.
但没有什么是完美的
But nobody's perfect.
偶尔也会出现一些校对疏漏
Occasionally, a proofreading error slips through,
基因结构因此出现了一个小小的随机改变
making a small, random change in the genetic instructions.
这头熊的卵细胞出现了基因突变
A mutation has occurred in the bear's egg cell.
一个如此小的随机事件
A random event as tiny as this one
将产生极为深远的影响
can have consequences on a far grander scale.
这个突变改变了控制毛色的基因
That mutation altered the gene that controls fur color.
它将影响这头熊的下一代
It will affect the production of dark pigment
毛发中黑色素的形成
in the fur of the bear's offspring.
大部分突变是无害的
Most mutations are harmless.
有一些是致命的
Some are deadly.
但极少数只是纯粹偶然
But a few, purely by chance,
能产生有利于生存的关键改变
can give an organism a critical advantage over the competition.
一年过去了
A year has passed.
我们的这头熊已经是一位母亲了
Our bear is now a mother.
因为基因突变的原因
And as a result of that mutation,
她的两只幼崽中有一只天生是白色的
one of her two cubs was born with a white coat.
当幼崽们成长到可以独自探索世界时
When the cubs get old enough to venture out on their own,
哪一只小熊更可能
which bear is more likely
悄悄跟踪猎物不被发现呢
to be able to sneak up on unsuspecting prey?
在雪地里棕熊1.6千米远外就能被发现
The brown bear can be seen against the snow a mile away.
白熊不断繁衍并把它
The white bear prospers and passes on
独特的基因传递下去
its own particular set of genes.
然后不断重复
This happens repeatedly.
经过几代的繁衍之后
Over succeeding generations,
产生白毛的基因已经在
the gene for white fur spreads through
整个北极熊族群中传播开了
the entire population of Arctic bears.
产生深色毛发的基因
The gene for dark fur loses out
在物竞天择中不断失败
in the competition for survival.
基因突变是完全随机且不断出现的
Mutations are entirely random and happen all the time.
但环境更偏爱那些
But the environment rewards those
对生存有利的基因
that increase the chance for survival.
环境自然地选择了那些
It naturally selects the living things
更适于生存的生命形态
that are better suited to survive.
而这一选择过程绝对不是偶然
And that selection is the opposite of random.
这两支熊类族群经过地理隔离
The two populations of bears separated,
和数千年的时间
and over thousands of years,
进化出其他不同的生理特征
evolved other characteristics that set them apart.
它们变成了不同的物种
They became different species.
这就是查尔斯·达尔文的
That's what Charles Darwin meant
《物种起源》想要表达的意思
by "The Origin of Species."
一头熊是无法进化的
An individual bear doesn't evolve;
熊的种群经过数代的繁衍得以进化
the population of bears evolves over generations.
如果北极的冰川因全球变暖不断缩小
If the Arctic ice continues to dwindle due to global warming,
北极熊很可能灭绝
the polar bears may go extinct.
它们将被棕熊所取代
They'll be replaced by brown bears,
因为棕熊更适合如今森林退化的环境
better adapted to the now defrosted environment.
这是一个和狗完全不同的故事
This is a different story from the one about the dogs.
没有饲者干预它们的变化
No breeder guided these changes.
相反环境自己做出了选择
Instead, the environment itself selects them.
这是通过自然选择的进化
This is evolution by natural selection,
科学史上最颠覆的概念
the most revolutionary concept in the history of science.
1859年达尔文首次提出这一理论的证据
Darwin first presented the evidence for this idea in 1859.
因此引起的震动从未平息
The uproar it caused has never subsided.
为什么
Why?
我们都能理解我们和猿猴有同一个祖先
We all understand the twinge of discomfort
这想法给人带来的阵阵不适感
at the thought that we share a common ancestor with the apes.
没有比乱七八糟的亲戚更让人尴尬的了
No one can embarrass you like a relative.
我们的近亲黑猩猩
Our closest ones, the chimpanzees,
在公众场合的举止总是极其不雅
they frequently behave inappropriately in public.
人类想要与这些亲戚划清界限的想法
There's an understandable human need
是可以理解的
to distance ourselves from them.
传统信仰中的一个核心前提是
A central premise of traditional belief
相对于其他动物
is that we were created separately
人类是被特别创造出来的
from all the other animals.
不难理解这种想法的立足点
It's easy to see why this idea has taken hold.
这让我们感觉与众不同
It makes us feel... special.
但如果我们和树木也有亲戚关系呢
But what about our kinship with the trees?
这又会让你作何感受呢
How does that make you feel?