生命的奇迹（2013）

a specific evolutionary niche.
赤眼蜂体型虽小 用处却很大
The Trichogramma wasps may be small, but they're very useful.
澳洲坚果蛀果螟以坚果为食
They're natural parasites of an insect pest species
而赤眼蜂专门寄生在这种害虫身上
called the nut borer moth which attacks the macadamia nuts.
这些微型蜂类在螟蛾的卵中产卵
The micro-wasps lay their eggs inside the eggs of the moths,
杀死正在发育的幼虫
killing the developing moth larvae.
这是澳洲坚果的表面
What you're seeing here is the surface of the macadamia nut
这里有一小串螟蛾的卵 在那里
and here's a small cluster of moth eggs and there,
你可以看见赤眼蜂在卵上爬行
you see the wasp is walking over the eggs.
它们在用步伐测量卵的大小
They're almost pacing out the size to see
来看看是否适合把自己的卵产在里面
whether the eggs are suitable for their eggs to be laid inside.
如果我们够幸运 好了 你看
And if we're lucky, there you go, you see that...
那里
That...
开始了
There we go.
赤眼蜂幼虫仅用九天就完全发育为成虫
The wasps emerge just nine days later as full-grown adults.
拥有这样小的体型 它们的世界是"粘糊糊"的
At this scale, they live in a very sticky world,
强大的分子作用力占据着主导作用
dominated by strong intermolecular forces.
对它们来说 甚至连空气都像粘稠的液体
To them, even the air is a thick fluid
它们其实是在用桨一样的翅膀游泳
through which they essentially swim, using paddle-like wings.
难以置信的是 这些微小的动物
Incredibly, these tiny animals
能在几棵树之间飞来飞去
can move about across several trees,
寻找螟蛾卵
seeking out the moth eggs.
不过让我觉得更不同寻常的是
But what I find more remarkable
它们仅凭非常有限的脑力
is that they do all this
完成这一切
operating with very restricted brain power.
决定昆虫最小尺寸的
One of the limiting factors
限制因素之一
that determines the minimum size of insects
就是它们中枢神经系统的容量
is the volume of their central nervous system.
换句话说 就是能塞进它们身体的
In other words, the processing power you can fit
处理能力
inside their bodies
而这些小黄蜂基本已到达极限了
and these little wasps are pretty much at their limit.
它们的整个神经系统只有不到一万个神经元
They've less than 10,000 neurons in their whole nervous system.
与之相比
To put it into perspective,
多数小型昆虫的神经元数量是它们的一百倍
most tiny insects have 100 times that many,
不过这已经足够
but that's still enough to allow them
让它们做出复杂的行为了
to exhibit quite complex behaviour.
这些微小的蜂类
These micro-wasps exist
几乎是多细胞动物能达到的最小体型
at almost the minimum possible size for multicellular animals.
但是地球上生命的尺寸还可以小得多
But the scale of life on our planet gets much, much smaller.
对于地球上体型最小的生命来说
The wasps are giants compared to life
赤眼蜂就是巨兽
at the very limit of size on earth.
地球上最小的生物 同时也是最古老
The smallest organisms on our planet are also our oldest
最丰富的生命形式
and most abundant type of lifeforms.
在珀斯之南 克利夫顿湖浅滩
These weird, rocky blobs in the shallows of Lake Clifton,
这些奇形怪状的石块 是由细菌构成
just south of Perth, are made by bacteria.
这些石堆因为它们凝块式的结构
These mounds are called thrombolites,
被称为凝块石
on account of their clotted structure,
数百年间
and they're built up over centuries
它们由极小的细菌细胞堆积而成
by colonies of microscopic bacterial cells.
虽然现在这种菌落很罕见 但从各个方面说
Now although these colonies are rare, by most definitions,
细菌都是我们星球上最主要的生命形式
bacteria are the dominant form of life on our planet.
每一寸土地上 都有细菌的身影
On every surface across every landscape, you find bacteria.
单从数字上来看 在人体表和体内的细菌
In fact, numerically speaking, then there are more bacteria
比人体细胞还要多
living on and inside my body than there are human cells.
细菌以多种形状和形式存在
Bacteria come in many shapes and forms
也并不属于动物或植物
and are not actually animals or plants,
在分类学上 它们有专属的世界
instead sitting in their own unique taxonomic kingdom.
与构成人体的细胞相比
Compared to the cells we're made of,
细菌在结构上要简单得多 也小得多
bacteria are structurally much simpler and far, far smaller.
典型的细菌一般长约两微米
Bacteria are typically around two microns in size.
那是一米的百万分之二 很难描述
That's two millionths of a metre, which is very hard to picture
不过你可以将五十万个细菌
but it means that you could fit around half a million of them
放在针尖上 或换句话说
on the head of a pin or, to look at it another way,
如果我将一个细菌 将它放大成
if I took a single bacterium and scaled it up
这个硬币的大小 那么我就有25千米高
to the size of this coin, then I would be 25 kilometres high.
细菌 这种微生物是地球上最先出现的生命
Bacterial-type organisms were the first life on earth
此后它们一直主宰着这颗星球
and they've dominated our planet ever since.
除了病毒
Excluding viruses,
因为它们几乎不能算做生命
which by most definitions are not alive,
细菌是已知最小的 能独♥立♥生存的生命形式
bacteria are the smallest free-living lifeforms we know of.
但到底是什么 决定了生命的最小尺寸
But what ultimately puts the limit on the smallest size of life?
单细胞生物要足够大
Single-cell life needs to be big enough
才能容纳生命必需的细胞器
to accommodate all the molecular machinery of life
这一尺寸最终由基本的物理法则决定
and that size ultimately depends on the basic laws of physics.
取决于分子的大小
It depends on the size of molecules
分子又取决于原子的大小
which depends on the size of atoms
原子又取决于宇宙的基本属性
which depends on fundamental properties of the universe
比如电磁力的大小
like the strength of the force of electromagnetism
还有电子的质量
and the mass of an electron.
经过计算后
And when you do those calculations,
你会发现 一个可自主生活的生命
you find out that the minimum size of a free-living organism
最小的体型约为两百纳米
should be around 200 nanometres
约五百万分之一米
which is around 200 billionths of a metre.
放之宇宙皆是如此
And that should be universal,
不仅适用于地球上的生命
it shouldn't only apply to life on earth
也适用于宇宙任何地方的
but it should apply to any carbon-based life
碳基生命
anywhere in the universe
因为它取决于宇宙的基本属性
because it depends on fundamental properties of the universe.
从最小的细菌到最大的树
From the smallest bacterium to the largest tree,
是你的体型决定了
it's your size that determines
物理法则如何控制你的生活
how the laws of physics govern your life.
体型大者受重力的影响
Gravity imposes itself on the large,
而微观世界则由分子作用力掌控
and the electromagnetic force rules the world of the small.
不过地球上生物的大小
But the consequences of scale for life on earth
不止决定了
extend beyond dictating the relationship
你与周围环境的关系
you have with the world around you.
你的体型也会影响
Your size also influences
能量在你体内流动的方式
how energy itself flows through your body.
这是南方长翼蝠
These are southern bent-wing bats...
澳大利亚最稀有的蝙蝠之一
One of the rarest bat species in Australia.
每晚 它们成百上千地
Every evening, they emerge in their thousands
从洞穴里飞出 寻找食物
from this cave, in order to feed.
这些蝙蝠成年后也仅有5.5厘米长
When fully grown, these bats are just 5.5cm long,
约18克重
and weigh around 18 grams.
因为它们如此之小
Because of their size,
必须一直顽强地与生命抗争
they face a constant struggle to stay alive.
我们在用热感摄像机拍摄蝙蝠
Now we're using a thermal camera here to look at the bats,
它们在空中飞过 留下了一道道身影
and you can see that they appear as streaks across the sky.
它们看起来和我一样亮
They appear as brightly as me -
因为它们与我的体温大致相等
that's because they're roughly the same temperature as me.
它们是恒温动物
They're known as endotherms -
即能维持自己体温的动物
they're animals that maintain their body temperature.
那得付出很大努力
And that takes a lot of effort.
这些蝙蝠每晚得吃
And these bats have to eat something like
相当于自己体重四分之三的食物
three-quarters of their own body weight every night,
很大一部分能量都用于维持体温
and a lot of that energy goes into maintaining their temperature.
和所有生物一样
As with all living things,
这些蝙蝠靠进食为新陈代谢提供能量
the bats eat to provide energy to power their metabolism.
虽然和我们一样
Although, like us,
它们运动时体温会变高
they have a high body temperature when they're active,
但考虑到它们的体型
keeping warm is a considerable challenge,
保持温度是相当大的挑战
on account of their size.
这些蝙蝠的热量大多从体表散失
The bats lose heat mostly through the surface of their bodies.
但是由于体表面♥积♥
But because of simple laws governing the relationship
和体积之间的对应关系
between the surface area of a body and its volume,
小体型带来一个问题
being small creates a problem.
再来看看我们的木块
So, let's look at our blocks again,
这次用来计算表面♥积♥和体积间的关系
but this time for surface area to volume.
看这个大家伙
Here's a big thing -
它由八个木块组成 所以体积为八个单位
it's made of eight blocks so its volume is eight units,
它的边长为二 侧面♥积♥即四