生命的奇迹（2013）

and its surface area is two by two on each side, so that's four,
乘以六面 表面♥积♥为二十四
multiplied by the six faces is 24.
所以表面♥积♥与体积比为二十四比八
So, the surface area to volume ratio is 24 to 8,
也就是三比一
which is 3:1.
再来看看小一点的
Now, look at a smaller thing.
这是一个木块 所以体积为一个单位
This is one block, so its volume is one unit.
边长是一 乘以六面 表面♥积♥为六
Its surface area is one by one by one, six times, so it's six.
表面♥积♥与体积的比为六比一
So, this has a surface area to volume ratio of 6:1.
所以体型由大变小
So, as you go from big to small,
表面♥积♥与体积的比增大
your surface area to volume ratio increases.
小型动物 比如蝙蝠
Small animals, like bats,
对自身体积来说 它们的体表面♥积♥很大
have a huge surface area compared to their volume.
因此 它们的热量自然流失得很快
As a result, they naturally lose heat at a very high rate.
为了弥补 以热量形式
To help offset the cost of losing so much energy
散失的大量能量
in the form of heat,
蝙蝠必须维持较高的新陈代谢率
the bats are forced to maintain a high rate of metabolism.
它们呼吸频率高 心率快
They breathe rapidly, their little heart races,
而且它们必须大量进食
and they have to eat a huge amount.
因此 蝙蝠的体型明显影响了
So, a bat's size clearly affects
它们日常活动的节奏
the speed at which it lives its life.
在自然世界中
Right across the natural world,
体型对新陈代谢率有很大影响
the size you are has a profound effect on your metabolic rate -
或者说"生命的速率"
or your "Speed of Life".
对于澳大利亚小巧的袋鼬来说
For Australia's small marsupial mouse,
即使是休息时间 它的心脏仍急速跳动
even at rest, his heart is racing away.
而狐狸大小的袋獾
For the fox-sized Tasmanian devil,
心跳频率就慢多了
he ticks along at a much slower rate.
而我
And then there's me,
则以每分钟心跳六十次的慵懒节奏生活
living life at a languid 60 beats a minute.
除了心跳频率之外
Looking beyond heart rate,
体型还会影响到身体需要的能量
your size influences the amount of energy you need to consume,
与消耗能量的速率
and the rate at which you need to consume it.
体型较大的动物需要养活更多的细胞
Bigger bodies have more cells to feed.
所以你也许会认为体型增大
So, you might expect that the total amount of energy needed
所需能量也要按相同比例增加
goes up at the same rate as any increase in size.
但事实并非如此
But that's not what happens.
如果你将不同动物消耗的能量
If you plot the amount of energy
与它们的重量画成一张图
an animal uses against its mass,
对于很多不同体型的动物 小至苍蝇
for a huge range of sizes, from animals as small as flies,
或者更小的动物 大至鲸鱼
and even smaller, all the way up to whales,
你确实可以得到一条直线
then you DO get a straight line,
但斜率会小于一
but the slope is less than one.
所以对于每一克体重来说
So, that implies that gramme for gramme,
大型动物比小型动物需要能量少
large animals use less energy than small animals.
新陈代谢与体型之间的关系
This relationship between metabolism and size
极大地影响了大型动物
significantly affects the amount of food
为了维持生存而必需摄入的食物
larger animals have to consume to stay alive.
如果我的新陈代谢率与老鼠完全相同
Now, if my metabolic rate scaled one-to-one with that of a mouse,
我每天就必须吃四千克食物
then I would need to eat about four kilograms of food a day.
用我的话说 是6700万焦耳热量
In my language, that's around 67,000 kilojoules of energy,
更通俗地说 则是1600万卡路里
which more colloquially is 16,000 calories.
是我现在平均每天
That is eight times the amount that I take in
摄入量的八倍
on average on a daily basis.
我身体中每一个细胞所需的能量
Each of the cells in my body requires less energy
都比小型哺乳动物同样细胞所需的能量少
than the equivalent cells in a smaller-sized mammal.
此现象的原因还没有彻底弄清
The reason why this should be so is not fully understood.
我们也并不清楚这条自然定律
It's also not clear whether this rule of nature
给了大型动物优势
gives an advantage to big things,
还是对大型动物的限制
or is actually a constraint placed on larger animals.
以动物的表面♥积♥
Take the relationship between
和体积之间的关系为例
an animal's surface area and its volume.
大型动物相较于小型动物
Big animals have a much smaller
有更小的表面♥积♥与体积比
surface area to volume ratio than small animals,
这也意味着它们热量流失的速率更小
and that means that their rate of heat loss is much smaller.
也就是说大型动物有更多优势
And that means that there's an opportunity there for large animals.
不需要吃太多的食物来维持体温
They don't have to eat as much food to stay warm,
因此它们可以拥有更低的新陈代谢率
and therefore they can afford a lower metabolic rate.
这可以解释大型恒温动物的新陈代谢规律
Now this helps explain the lives of large, warm-blooded endotherms,
比如鸟类与哺乳类动物
like birds and mammals,
但这个解释对自然界中的冷血巨人-
but doesn't hold so well for large ectotherms,
大型变温动物们并不适用
life's cold-blooded giants.
现在 也有另一种理论表示
Now, there's another theory that says that
大型动物的新陈代谢速率偏低
it wasn't really an evolutionary opportunity
并不是进化形成的优势
that large animals took to lower their metabolic rate.
而是被迫的 也可以说是限制
It was forced on them. It was a constraint, if you like.
细胞的营养运送管道 毛细血管
The capillaries, the supply network to cells,
其排列方式
branches in such a way
让氧气与营养
that it gets more and more difficult
更容易送到小型动物的细胞中
to get oxygen and nutrients to cells in a big animal
而不是大型动物
than in a small animal.
因此 大型动物的细胞必须更慢地运作
Therefore, those cells must run at a lower rate.
它们必须维持较低的新陈代谢率
They must have a lower metabolic rate.
或者仅仅是因为 体型越大
Or it could just be that as you get bigger,
所需支撑组织的质量比率就会越大
then more of your mass is taken up by the stuff that supports you,
而支撑组织 比如骨头 并不活跃
and support structures, like bones, are relatively inert.
它们不会消耗太多能量
They don't use much energy.
但不管原因如何 必须得说
But whatever the reason, it's certainly true to say
大型动物们能在地球上生存的唯一方法
that the only way that large animals can exist on planet earth
就是保持较低的新陈代谢率
is to operate at a reduced metabolic rate.
若非如此
If this wasn't the case,
体型最大的恒温动物 例如你我
the maximum size of a warm-blooded endotherm like me or you
将和山羊一般大小
would be around that of a goat.
而冷血动物或者说变温动物 比如恐龙
And cold-blooded animals, or ectotherms like dinosaurs,
将只和矮种马一样大
could only get as big as a pony.
任何更大的生物都会体温过高
Any bigger, and giants would simply overheat.
与体型有关的规律导致的最后一个结果
Now, there's one last consequence of all these scaling laws
我认为你一定非常关心
that I suspect you'll care about more than anything else,
细胞的有效新陈代谢率
and it's this - there's a strong correlation
与生物的生命周期
between the effective cellular metabolic rate of an animal
有非常紧密的联♥系♥
and its lifespan.
也就是说 体型越大 寿命越长
In other words, as things get bigger, they tend to live longer.
为了研究体型与寿命的关系
To explore this connection between size and longevity,
我离开内陆 到了行程的终点
I've left the mainland behind, for my final destination,
澳大利亚最偏远的村落
I've come to one of Australia's remotest outposts.
这是圣诞岛
Named Christmas Island
因为在16♥4♥3年的圣诞节被发现而得名
when it was spotted on Christmas Day in 16♥4♥3,
这座印度洋中与世隔绝岩石小岛
this isolated lump of rock in the Indian Ocean
就是螃蟹的天堂
is a land of crabs.
而它们中隐藏着自然界的奇迹
And in their midst lurks a giant wonder of the natural world.
这是一只圣诞岛强盗蟹
This is a Christmas Island robber crab,
地球上最大的陆地蟹
the largest land crab anywhere on the planet.
它们可以长到五十厘米长
And these things can grow to around 50 centimetres in length,
四千克重
they can weigh over four kilograms,
成年蟹很好地适应了岛上的生活
and they are supremely adapted as an adult to life on land.
它们甚至能够爬树
They can even climb trees.
在近几年间 这些螃蟹已经
Over the years, the crabs have become
相当适应与人类共处了
well adapted to human co-habitation.
它们之所以被叫做强盗蟹
These things are called robber crabs
就是因为它们旺盛的好奇心
because they have a reputation
以及偷窃行为 让它们臭名远扬
for curiosity and for stealing things,
任何没有被固定好的东西
anything that isn't bolted down.
食物 相机
They'll steal food and cameras
它们只要有机会就偷走
if they can get half a chance.
这些巨型螃蟹以种子和水果为食
These giants live on a diet of seeds and fruit,
也偶尔吃一些小型螃蟹
and occasionally other small crabs.
大而有力的螯钳
Their large, powerful claws
能帮它们砸开掉落的椰子
mean they can also rip open fallen coconuts.
作为螃蟹来说 它们还真是危险生物
They're really quite a menacing animal, actually, for a crab!
这些螃蟹最神奇之处
What's wonderful about these crabs
在于它们会经历不同的体型
is that they live through a range of scales.
在它们生命中的不同时期