生命的奇迹（2013）

所以要解释生命为何如此多样
So it's this molecule that must hold the key
DNA才是关键
to understanding why life today is so diverse.
我们现在明白 要理解
We now know that the answer to the question,
"为何地球上的生命如此多样"
"Why is life on Earth so varied?"
得先理解
is actually the answer to the question,
"为何DNA分子如此多样"
"Why is the DNA molecule itself so varied?"
什么样的自然过程
What are the natural processes
才能让DNA结构发生变化
that cause the structure of DNA to change?
一部分答案无法在这里找到
Well, part of the answer actually doesn't lie on Earth at all.
而要去星空中找寻
It lies up there amongst the stars.
我可以用这个来解释
And I can show you what I mean, using this,
这是一个云室
which is a cloud chamber,
这个装置在物理学史上
a piece of apparatus that has a unique place
有着非凡的意义
in the history of physics.
我现在要用干冰为它降温
I'm going to cool it down using dry ice,
就是冷冻的二氧化碳
frozen carbon dioxide,
零下70多摄氏度
just below -70 degrees Celsius.
把这个放上
I'll put the top on.
听到了吗
Hear that?
是缸底金属骤降至零下70度
That's the metal at the bottom of the tank
发出的声音
cooling down very rapidly to -70.
云室内还要充满过饱和酒精蒸气
The cloud chamber works by having a super-saturated
才能发挥功效
vapour of alcohol inside the chamber.
多洒点
Plenty on there...
现在我要让酒精沸腾
Now, I want to get that alcohol, I want to boil it off,
让酒精蒸汽充满云室
to get the vapour into the chamber.
所以还要在上面放一个热水袋
So I'm going to put a hot water bottle on top.
这就是首个真正的物理离子探测器
This is the first genuine particle physics detector.
正是这个装置首次发现了反物质
It's the piece of apparatus that first saw antimatter.
而其实它只是一个鱼缸
And it really does consist only of a fish tank,
一些酒精 一点纸和一个热水袋
some alcohol, a bit of paper, and a hot water bottle.
看 那里 看到了吗
There, look at that. Do you see that?
云雾化尾迹
Cloud vapour trail.
那是宇宙射线
That's a cosmic ray.
是由一个粒子 很可能是一个质子
That was initiated by a particle, probably a proton,
撞击地球大气层产生的
that hit the Earth's atmosphere.
这些粒子几乎肯定源自太阳系外
It almost certainly originated outside our solar system
受到了银河系磁场的加速
and was accelerated by the magnetic fields of our galaxy.
甚至还可能产生于银河系外
It may even have begun its life beyond our galaxy.
想象一下 如果其中某个粒子
Now, imagine if one of those
击中了某个生物的DNA
hits the DNA of a living thing.
那会令DNA发生突变
What that will do is cause a mutation.
可能是有害的变异
That mutation may be detrimental,
或极少数情况下 也可以是有益的
or, very, very occasionally it might be beneficial.
或许银河系之外的
And I think it's quite wonderful to imagine
一次超新星爆发
that maybe one of the key mutations
产生了这些粒子
that was selected for over the millennia
并撞击某种生物体内的DNA
that led to some trait in ME
造成了有益的突变
was caused by some particle that began its life perhaps
这个关键的突变
in a massive supernova explosion,
经过数千年的自然选择
perhaps outside our galaxy
导致我表现某种性状
and went and hit the DNA of something
这一想法着实奇妙
and caused some kind of beneficial mutation.
我们并不能证实 但总可以幻想一下
We don't know, but you can dream, can't you?
只要生活在地球这样的星球上
Mutations are an inevitable part
变异就不可避免
of living on a planet like Earth.
它们暗示了DNA
They're the first hint at how DNA and the genes
以及编码生命的基因
that code for every living thing
如何在代代相传中改变
change from generation to generation.
变异就是生命
Mutations are the spring
创新的源泉
from which innovation in the living world flows.
但宇宙射线并不是改变DNA的唯一手段
But cosmic rays are not the only way in which DNA can be altered.
其他手段包括岩石发出的天然本底辐射
There's natural background radiation from the rocks,
和化学物质以及自♥由♥基的反应
there's the action of chemicals and free radicals.
遗传密♥码♥翻译过程中也可能会出错
There can be errors when the code is copied.
这些变化都能被性左右
And then all those changes can be shuffled by sex,
整片段的基因
and indeed whole pieces of the code
会在物种间传递
can be transferred from species to species.
所以 渐渐地
So, bit by bit,
在代代相传的过程中
in tiny steps from generation to generation,
遗传密♥码♥不停地发生改变
the code is constantly randomly changing.
虽然随机突变能够改变DNA
Now, whilst there's no doubt that random mutation does alter DNA,
进化本身并不是随机的
evolution is anything but random.
不可能是
It can't be,
因为拥有如此复杂DNA的生物
because the chances of something with DNA as complex as this
河马
河马属
是偶然间出现的几乎不可能
appearing by luck alone are vanishingly small.
如果随机改变一个碱基
Imagine you just changed one position in the code at random,
发生随机突变
a random mutation.
因为有ATCG四种碱基
There are four letters, A, T, C and G,
所以就会有四种可能的组合
so there are four possible combinations.
如果基因中有两个位置
If there are two places in the code,
每个又有四种组合 一共就是16种
there are four combinations for each one. So that makes 16.
如果有三个 那就是6♥4♥种可能性
If there are three, then there are 6♥4♥ possibilities.
当一串遗传密♥码♥中有150个字母时
By the time you get to a code with 150 letters in it,
那可能出现的组合方式
then there are more possible combinations in the code
比可观察到的宇宙中的原子还多
than there are atoms in the observable universe.
河马的遗传密♥码♥中有
Now, a hippo has a code
大约三十亿个不同的字母
with around three billion different letters.
以这些字母的组合方式之多
So the number of combinations of those letters,
想要随机产生这串遗传密♥码♥
the chances of producing that code at random,
几乎不可能
are absolutely, infinitesimally small.
就是不可能的
It's impossible.
所以进化一定有一个非随机性的因素
So there must be a non-random element to evolution...
一个自然过程 能够在很大程度上限制
A natural process, which greatly restricts
组合的方式 影响最终的结果
this universe of possibilities, and shapes the outcome.
我们称之为自然选择
We call it natural selection.
为了见证此过程
And to see it in action,
让我们回到旅途的起点
let's return to where we began
马达加斯加岛
on the island of Madagascar.
大约六千五百万年前 一群远洋者
Around 65 million years ago, a group of seafarers were nearing
即将完成横渡印度洋的旅程
the end of a long journey across the Indian Ocean.
这是些偶然踏上旅途的旅行者
These were accidental travellers,
是来自非洲的一群生物
a group of creatures from Africa,
它们被困在天然的筏子上 随波逐流
trapped on a natural raft and carried by the ocean currents.
最终发现了这片全新的绿色大♥陆♥
The land they found was virgin green territory.
这里有植物 昆虫 爬行类和鸟类
Plants, insects, reptiles and birds had established themselves,
但没有它们的同类
but there were none of their own kind.
它们成为了
They were caught up in a saga
地球板块漂移学说的一部分
that tells of the great shifting of Earth's continental plates.
如果不了解地球的板块漂移
It's impossible to understand
是无法理解如今地球上的
the diversity of life on Earth today
物种多样性
without understanding the shifting geography of our planet.
这里有一幅
Here's a map
一亿五千万年前南半球的地图
of Earth's southern hemisphere as it was 150 million years ago,
你可以看到只有一块叫做冈瓦纳的大♥陆♥
and you see it's dominated by a single landmass called Gondwana.
后来 九千万年前
And then, 90 million years ago,
冈瓦纳大♥陆♥分崩离析
Gondwana had begun to break up, to separate,
变成了看似像非洲的大♥陆♥
into something that looks quite recognizably like Africa,
和这两座小岛 马达加斯加岛和印度岛
and these two islands, Madagascar and India.
后来印度岛向北漂移
Now, subsequently India has drifted northwards
和欧亚大♥陆♥碰撞 形成了喜马拉雅山脉
and bumped into Eurasia, raising the Himalayas.
但马达加斯加一直与世隔绝
But, crucially, Madagascar has remained isolated.
九千万年以来
It's been an island
它一直是被海洋包围的孤岛
surrounded by ocean for almost 90 million years.
所以当这些外来者乘着由树木
So, when those seafarers arrived
和枝叶组成的筏子来到这里时
on their raft of trees and twigs and leaves,
它们有了一块广阔的天地 两三个
they had a blank canvas - two, three,
甚至只是一只怀孕的个体
maybe even a single pregnant individual
将整座岛当做栖息地
had a whole island to roam across.