宇宙时空之旅（2014）

Cosmos: A SpaceTime Odyssey S01E02

Part 3 April 25, 2021, 12:39 p.m.

这是橡树DNA的一部分
Okay, here's a segment of the oak tree's DNA.
把它看做一个条形码
Think of it like a bar code.
写在这段条形码上的指令
The instructions written in the code of life
告诉树木如何代谢糖分
tell the tree how to metabolize sugar.
现在把它和我的同一段DNA作对比
Now let's compare it with the same section of my own DNA.
DNA不会撒谎
The DNA doesn't lie.
这棵树和我我们是长久失联的表亲
This tree and me-- we're long-lost cousins.
不仅仅是树木
And it's not just the trees.
如果你回顾得足够远你会发现
If you go back far enough, you'll find that we share
和我们有共同祖先的还有
a common ancestor with...
蝴蝶
the butterfly,
灰狼
gray wolf,
蘑菇
mushroom,
鲨鱼
shark,
细菌
bacterium,
麻雀
sparrow.
多么神奇的家庭
What a family!
条形码的其他部分因物种而异
Other parts of the bar code vary from species to species.
这是猫头鹰和章鱼之间差异的来源
That's what makes the difference between an owl and an octopus.
除非你有一个同卵双生的兄弟姊妹
Unless you have an identical twin,
宇宙中没有谁
there's no one else in the universe
和你有完全相同的DNA
with the exact same DNA as you.
其他的物种内基因的差别
Within other species, the genetic differences
为自然选择提供了原材料
provide the raw material for natural selection.
环境选择哪些基因能够生存和复♥制♥
The environment selects which genes survive and multiply.
谈到基因对生命的
When it comes to the genetic instructions
最基本功能的指导作用
for life's most basic functions,
比如消化糖分
say, digesting sugars,
我们与其他物种几乎无异
we and other species are almost identical.
这是因为这些是生命最基本的功能
That's because those functions are so basic to life,
它们在不同生命形式分化前
they evolved before the various life-forms
就已经进化出现
branched off from each other.
这是我们的生命之树
This is our Tree of Life.
科学让构建这个
Science has made it possible
地球上所有物种的生命之树
for us to construct this family tree
变成可能
for all the species of life on Earth.
有亲近的遗传关系的物种居于同一分支
Close genetic relatives occupy the same branch of the tree,
而相对疏远的则隔得更远
while more distant cousins are farther away.
每个枝杈都代表一个存在的物种
Each twig is a living species.
而树的主干则代表地球上
And the trunk of the tree represents the common ancestors
所有生命的共同先祖
of all life on Earth.
生命的形态无穷多变
The stuff of life is so malleable
当它开始分化时环境会将其
that once it got started, the environment molded it
塑造成数量惊人的不同形态
into a staggering variety of forms,
比我们能呈现出的要多出上万倍
10,000 times more than we can possibly show here.
单单是甲虫
Biologists have catalogued
生物学家就分出了五十多万种
a half a million different kinds of beetles alone.
更不用说种类不计其数的细菌了
Not to mention the numberless varieties of bacteria.
数以百万计的动物和植物
There are many millions of living species
存在于世
of animals and plants,
大多数还不被科学了解
most of them still unknown to science.
想想我们目前还未和绝大多数的
Think of that,we have yet to make contact
陆生生物有过接触
with most of the forms of terrestrial life.
单单在这一个小星球上
That's how many kinds of life there are
就有这么多种类的生命
on this tiny planet alone.
生命之树向各方向伸出触角
The Tree of Life extends its feelers in all directions,
探索发现可能的进化
finding and exploiting what works,
为生命的新形式创造新的环境和机会
creating new environments and opportunities for new forms.
生命之树已生长35亿年
The Tree of Life is three and a half billion years old.
它有充裕的时间
That's plenty of time to develop
进化出各式各样的小把戏
an impressive repertoire of tricks.
生物进化让动物可以伪装成植物
Evolution can disguise an animal as a plant...
花费千万代的时间
taking thousands of generations
去获得巧妙的伪装
to contrive an elaborate costume
这样的伪装会迷惑捕食者
that fools predators into looking elsewhere
转而寻找别的猎物
for someone to eat.
或者植物也可以伪装成动物
Or it can disguise a plant as an animal,
进化的花变成黄蜂的样子
evolving blossoms that take on the appearance of a wasp--
兰花以此吸引真正的黄蜂为其传粉
the orchid's way of fooling real wasps into pollinating it.
这就是自然选择
This is the awesome shape-shifting power
神奇的塑造形态的能力
of natural selection.
在生命之树浓密而错综复杂的枝干中
Among the dense, tangled limbs of the vast Tree of Life,
你在这里
you are here.
数不清的枝杈中小小一支
One tiny branch among countless millions.
科学表明地球上生命同源
Science reveals that all life on Earth is one.
达尔文揭露了生物进化的机制
Darwin discovered the actual mechanism of evolution.
当时盛行的观点是生命的复杂性与多样性
The prevailing belief was that the complexity and variety of life
一定出自一位聪明的设计师
must be the work of an intelligent designer,
他分别创造了数以百万的物种
who created each of these millions of different species separately.
有人说生命都太复杂了
Living things are just too intricate, it was said,
不可能是无指导进化的结果
to be the result of unguided evolution.
比如说人眼
Consider the human eye,
复杂性的杰作
a masterpiece of complexity.
它需要角膜
It requires a cornea,
虹膜晶状体视网膜
iris, lens, retina,
视神经肌肉
optic nerves, muscles,
更别说大脑用来理解图像的
let alone the brain's elaborate neural network
复杂的神经网
to interpret images.
它比任何人类智能
It's more complicated than any device
所能设计的设备都要复杂
ever crafted by human intelligence.
因此结论是
Therefore, it was argued,
人眼不可能是无心进化的结果
the human eye can't be the result of mindless evolution.
为了一探真假我们需要穿越回
To know if that's true, we need to travel across time
没有眼睛感知世界的时代
to a world before there were eyes to see.
起初
In the beginning,
生物没有视觉
life was blind.
这是我们的世界
This is what our world looked like
四十亿年前的样子
four billion years ago,
没有眼睛来观看世界
before there were any eyes to see.
直到几亿年过去
Until a few hundred million years passed,
忽然有一天
and then, one day,
一个细菌在DNA复♥制♥时
there was a microscopic copying error
发生了错误
in the DNA of a bacterium.
这个随机的突变让那个细菌
This random mutation gave that microbe
有了一个能吸收阳光的蛋白质分子
a protein molecule that absorbed sunlight.
想知道感光细菌看到的世界
Want to know what the world looked like
是什么样子的吗
to a light-sensitive bacterium?
生物视角
看看屏幕的右侧
Take a look at the right side of the screen.
突变持续随机地发生
Mutations continued to occur at random,
就像它在任何生物种群中发生的那样
as they always do in any population of living things.
另一个突变
Another mutation
让嗜暗细菌逃离强光
caused a dark bacterium to flee intense light.
会发生什么呢
What is going on here?
夜晚与白天
Night and day.
这些能够辨别明暗的细菌
Those bacteria that could tell light from dark
相对那些不感光的细菌有决定性的优势
had a decisive advantage over the ones that couldn't.
为什么
Why?
因为白天刺眼的含紫外线的阳光
Because the daytime brought harsh, ultraviolet light
会损伤DNA
that damages DNA.
感光细菌逃离强光
The sensitive bacteria fled the intense light
在黑暗中安全地交换它们的DNA
to safely exchange their DNA in the dark.
相对那些呆在水面的细菌
They survived in greater numbers
它们存活的几率更高
than the bacteria that stayed at the surface.
一段时间后这些感光的蛋白质
Over time, those light-sensitive proteins
在更高等的单细胞有机体上
became concentrated in a pigment spot
逐渐集中为一个眼点
on the more advanced, one-celled organism.
这让找到光成为可能
This made it possible to find the light,
这对那些收集阳光来生产食物的有机体
an overwhelming advantage for an organism
来说是个巨大的优势
that harvests sunlight to make food.
这是扁形虫的视角