生命的奇迹（2013）

so it's effectively weightless
这对生活在海洋中的生物来说
and that is extremely important indeed
至关重要
for the animals that live in the ocean.
所有生物的细胞
The cells of all living things
大部分都是由盐水构成的
are predominantly made up of salty water
所以在海洋中 重量根本不重要
so in the ocean, weight is essentially unimportant.
根据阿基米德定律 水的浮力
Because of Archimedes' principle, the supportive nature of water
让生物们免受地球引力的束缚
releases organisms from the constraints of earth's gravity,
得以进化出这些海中巨兽
allowing the evolution of marine leviathans.
但这也需要付出代价
But this comes at a cost.
水的密度是空气的八百倍
Water is 800 times denser than air
所以尽管水能提供浮力
and so whilst it provides support,
但在水中移♥动♥却更费力
it requires a huge amount of effort to move through it.
鲨鱼不仅要在前进时把水划开
Not only does the shark have to push the water out of the way,
还要克服
it also has to overcome drag forces
与水的摩擦接触而带来的阻力
created by the frictional contact with the water itself.
解决办法就藏在鲨鱼的体形中
The solution for the shark lies in its shape.
仔细观察大白鲨
If you look at him, that great white,
它有独特的流线型身材
he's got that distinctive streamlined shape.
它身体的最宽处在身长的三分之一处
His maximum width is about a third of the way down his body,
而且最大宽度是身长的四分之一
and that width itself should be around a quarter of the length.
这样的巨兽只有具有这种比例
That ratio is set by the necessity for something that big
才能在水中高效迅速地游动
to be able to swim effectively and quickly through this medium.
这样的体形能使阻力降到最低
This shape reduces drag forces to a minimum
并使鲨鱼周围 水流达到最优
and optimises the way water flows around the shark's body.
这是在物理定律作用下 进化的成果
It is the result of evolution, shaped by the laws of physics.
太吓人了 就像从《大白鲨》出来的一样
That's cunning! That was straight out of Jaws!
像鲨鱼一样的流线型体形
That streamlined shape of a shark
在大自然随处可见
is something that you see echoed throughout nature.
想想鲸 海豚和金枪鱼
I mean, think of a whale or a dolphin or a tuna,
都是一样的鱼雷状外形
all that same torpedo-like shape,
这是因为它们面对的问题
and that's because they're contending with problems
都源自同样的物理定律
that arise from the same laws of physics
而趋同进化 让它们找到了相同的答案
and convergent evolution has driven them to the same solution.
对于海洋生物 这些巨兽的进化过程
For life in the sea, the evolution of giants is constrained directly
直接被水的物理性质约束
by the physical properties of water.
但在海洋之外
But out of the ocean,
生命需要适应地球的引力作用
life now has to content with the full force of earth's gravity.
正是这种自然力
And it's this force of nature
支配着陆生巨兽的生命
that dominates the lives of giants on land.
新南威尔士布罗肯山以北
This is the hot, dry outback north of Broken Hill
这里炎热而又干燥
in New South Wales.
我来此探究引力
I'm here to explore how gravity,
这种由地球质量决定的力
a force whose strength is governed by the mass of our whole planet,
如何塑造并限制了
moulds, shapes and ultimately limits
陆地上生物的体型
the size of life on land.
我来寻找澳大利亚最具标志性的一种动物
I've come to track down one of Australia's most iconic animals...
红袋鼠
The red kangaroo.
它是澳洲最大的本土陆生哺乳动物
Red kangaroos are Australia's largest native land mammal,
袋鼠科有五十种 它是其中之一
one of 50 species of macropods,
因巨大的脚丫得名
so-called on account of their large feet.
那边 那边
There! There. There. There.
那边不远就有两只[分明是三只]
There's two very close there.
袋鼠是最不同寻常的哺乳动物
Kangaroos are the most remarkable of mammals
因为它们用双脚跳行
because they hop.
没有任何记录 甚至化石记录表明
And there's no record, even in the fossil record,
有其它的大型动物这样行走
of any other large animal that does that,
但这让它们可以快速高效地行进
but it makes them very fast and efficient.
当我的科学偶像约瑟夫·班克斯
When Joseph Banks, who's one of my scientific heroes,
于1770年随库克船长
first arrived here with Captain Cook
乘坐奋进号♥首次来到这里时
on the Endeavour in 1770,
他写到 我们在崎岖多石的地方发现了它们
he wrote that they move so fast over the rocky, rough ground
它们移♥动♥速度非常快 格雷伊猎犬也无法追上
where they're found, even my greyhound couldn't catch them.
他带着格雷伊猎犬做什么
What was he doing with a greyhound?
袋鼠是食草动物
Kangaroos are herbivorous
以草为生
and scratch out a living feeding on grasses.
觅食时 它们用一种不甚优雅的姿势移♥动♥
While foraging, they move in an ungainly fashion,
用它们粗壮的尾巴当作第五条腿
using their large, muscular tail like a fifth leg.
但如果它们愿意
But when they want to,
这些大型有袋目哺乳动物可以飞速移♥动♥
these large marsupials can cover ground at considerable speeds.
每跳一步
To take a leap,
袋鼠就要与地球
kangaroos have to work against
向下的引力抗争
the downward pull of earth's gravity.
这需要很多能量
This takes a lot of energy.
动物移♥动♥得越快 消耗的能量越多
As animals go faster, they tend to use more energy.
但袋鼠却不这样
Not so with the kangaroos.
袋鼠移♥动♥得越快
As the roos go faster,
消耗的能量反而降低
their energy consumption actually decreases.
之后保持不变
It then stays constant,
即使它们保持每小时四十公里的速度前进
even at sustained speeds of up to 40 kilometres per hour.
这种大型袋鼠的惊人效率
This incredibly efficiency for such a large animal
与它的生理结构直接相关
comes directly from the kangaroos' anatomy.
袋鼠移♥动♥得如此高效
Kangaroos move so efficiently
是因为它们有绝妙的能量存储机制
because they have an ingenious energy storage mechanism.
当一样东西从高处落下
See, when something hits the ground
撞向地面
after falling from some height,
它的能量需要被消耗掉
then it has energy that it needs to dissipate.
如果是一块石头
If you're a rock...
能量就转化成声音和一点热量
That energy is dissipated as sound and a little bit of heat,
但如果是个网球
but if you're a tennis ball...
一些能量被再次利用
Then some of that energy is reused
因为网球有弹性
because a tennis ball is elastic,
它可以变形 再复原
it can deform, spring back,
用这些能量
and use some of that energy
把自己弹回到空中
to throw itself back into the air again.
袋鼠与此相似
Well, a kangaroo is very similar.
它腿上有弹性极强的腱
It has very elastic tendons in its legs,
尤其是它的跟踺
particularly its Achilles tendon
以及尾巴上的腱
and also the tendons in its tail,
它们可储存能量 然后释放出来
and they store energy and then they release it,
为肌肉提供力量
supplementing the power of the muscles
让袋鼠在空中弹跳
to bounce the kangaroo through the air.
一只成年袋鼠有85到90公斤
Now, an adult kangaroo is 85, 90 kilos,
比我还重
which is heavier than me,
当它全速前进时
and when it's going at full speed,
可以跳九米远
it can jump around nine metres.
这是我和那部车之间的距离
That's the distance from me to that car.
演化出跳行能力
The evolution of the ability to hop
为袋鼠提供了低消耗且高效率的前进方式
gives kangaroos a cheap and efficient way to move around.
但不是所有动物都可以像袋鼠这样移♥动♥
But not everything can move like a kangaroo.
红袋鼠是世界上最大的
The red kangaroo is the largest animal in the world
靠此种独特方式移♥动♥的动物
that moves in this unique way,
即在陆地上高速跳行
hopping across the landscape at high speed,
不存在巨大的跳行大象或恐龙
and there are reasons why there aren't giant
是有原因的
hopping elephants or dinosaurs,
不是生物学的原因
and they're not really biological,
不是由于进化论中
it's not down to the details of evolution
自然选择或环境压力造成的结果
by natural selection or environmental pressures.
动物体型越大
The larger an animal gets,
它身体的形态和移♥动♥方式
the more severe the restrictions
所受限制就越多
on its body shape and its movement.
为了了解原因
To understand why this is the case,
我要研究在体型变大时
I want to explore what happens to the mass of a body
身体的质量发生了什么
when that body increases in size.
看看这个木块
Take a look at this block.
规定它宽为一
Let's say it has width - one,
长为一 高为一
length - one, and height - one,
它的体积即为一乘一乘一
then its volume is one multiplied by one multiplied by one,
也就是一立方
which is one cubic...
随便什么单位
things, whatever the measurement is.
它的质量与体积成正比