在视频的开头 我们将老鼠 狗和大象
Let’s start this video by throwing a mouse, a dog, and an elephant
扔到地面柔软的东西上
from a skyscraper onto something soft.
比如说 一堆床垫
Let’s say, a stack of mattresses.
老鼠着陆后 被吓得愣了一会
The mouse lands and is stunned for a moment,
然后抖了抖身子
before it shakes itself off,
因为受到了这样粗鲁的对待
and walks away pretty annoyed,
而生气地离开了
because that’s a very rude thing to do.
狗则全身骨折
The dog breaks all of its bones
以很普通的方式死去了
and dies in an unspectacular way,
而大象爆裂成一滩红色的骨头和内脏
and the elephant explodes into a red puddle of bones and insides
连生气的机会都没有了
and has no chance to be annoyed.
为什么老鼠能在坠落中活下来
Why does the mouse survive,
而大象和狗却死了呢？
but the elephant and dog don’t?
答案是体型不同
The answer is Size.
体型是最不起眼的生物调控因子
Size is the most underappreciated regulator of living things.
体型决定着我们生物的一切
Size determines everything about our biology,
我们的构成 我们经历 以及我们生存模式和死法
how we are built, how we experience the world, how we live and die.
之所以这样是因为物理法则对于不同体型的动物表现不一
It does so because the physical laws are different for different sized animals.
生物跨越7个数量级 从看不见的细菌到螨虫 蚂蚁
Life spans seven orders of magnitude, from invisible bacteria to mites, ants,
老鼠 狗 人类 大象最后到蓝鲸
mice, dogs, humans, elephants and, blue whales.
每种体型的生物都生活在彼此独殊的世界中
Every size lives in its own unique universe right next to each other,
每个都有自己的规则 有好有坏
each with its own rules, upsides, and downsides.
我们将会在系列节目中探索它们不同的世界
We’ll explore these different worlds in a series of videos.
让我们回到最初的问题 为什么老鼠能在坠落里存活？
Let’s get back to the initial question: Why did our mouse survive the fall?
因为体型差异会让一切都迥然不同 这个道理我们还会多次提及
Because of how scaling size changes everything; a principle that we’ll meet over and over again.
举个例子 非常小的东西实际上对从高处掉落免疫
Very small things, for example, are practically immune to falling from great heights
因为你体型越小你所担心的重力的影响就越小
because the smaller you are the less you care about the effect of gravity.
想象一个理论上的球形动物
Imagine a theoretical spherical animal
跟弹珠那么大 它有3个属性 即长度 表面积
the size of a marble. It has three features: its length, its surface area,
(覆盖有皮肤的区域)还有体积或者里面的所有填充物 像是器官
(which is covered in skin) and its volume, or all the stuff inside it like organs,
肌肉 希望和梦想如果我们将它增长10倍 也就是说
muscles, hopes and dreams. If we make it ten times longer, say the size of a
变成篮球那么大 剩下的属性不止于增加10倍
basketball, the rest of its features don’t just grow ten times. Its skin will
它的外皮表面会增长100倍 而且它的内部(就是体积)增长过1000倍
grow 100 times and it’s inside (so it’s volume) grows by 1000 times.
体积决定重量 或者更准确的说 动物的质量你质量越大
The volume determines the weight, or more accurately, mass of the animal. The more mass you have,
你落地之前的动能就越大 冲击力就越强
the higher your kinetic energy before you hit the ground and the stronger the impact shock.
与体积相关的表面积越大
The more surface area in relation to your volume
或者说质量越大 分散缓和的冲击力就越大
or mass you have, the more the impact gets distributed and softened, and also
使你减速的空气阻力就越大
the more air resistance will slow you down.
大象太大了 以至于比起它的体积 表面积要小得多
An elephant is so big that it has extremely little surface area in ratio to its volume.
所以大量的动能分布在小区域内 且空气并不能让其减速
So a lot of kinetic energy gets distributed over a small space and the air doesn’t slow it down much at all.
这就是大象落地时 被完全摧毁成一堆肉泥的原因
That’s why it’s completely destroyed in an impressive explosion of goo when it hits the ground.
而其他极端的生物 昆虫
The other extreme, insects,
相对于超小的质量而言有着巨大的表面积
have a huge surface area in relation to their tiny mass
所以你可以随便从飞机上扔一只蚂蚁
so you can literally throw an ant from an airplane
它并不会受到很严重的伤害但是在小世界里坠落倒是无关紧要的
and it will not be seriously harmed. But while falling is irrelevant in the small
但有其他的对我们无害却对小玩意们极其危险的外力
world there are other forces for the harmless for us but extremely dangerous for small beings.
像是表面张力 会使水变成对昆虫而言的潜在致命物质
Like surface tension which turns water into a potentially deadly substance for insects.
它是怎么做到的呢？水有粘住自身的倾向
How does it work? Water has the tendency to stick to itself;
水分子通过一种内聚力互相吸引
its molecules are attracted to each other through a force called cohesion
它能在表面造成一种张力 你可以把它想作成一种无形外皮
which creates a tension on its surface that you can imagine as a sort of invisible skin.
种外皮对我们来说太脆弱了 让我们经常忽略了它的存在
For us this skin is so weak that we don’t even notice it normally.
如果淋了大约800克的水或者你体重的1％附在你身上
If you get wet about 800 grams of water or about one percent of your body weight sticks to you.
一只淋湿的老鼠大约有5克的水粘在身上
A wet mouse has about 3 grams of water sticking to it,
超过了它体重的10％
which is more than 10% of its body weight.
想象一下在你淋浴之后有8瓶装满水的瓶子挂在你身上
Imagine having eight full water bottle sticking to you when you leave the shower.
但是对于昆虫 水的表面张力很强
But for an insect the force of water surface tension is so strong
被打湿就要面临生存还是毁灭的问题
that getting wet is a question of life and death.
如果我们将你缩小成蚂蚁般大小
If we were to shrink you to the size of an ant
你碰到水就像走进胶水一样
and you touch water it would be like you were reaching into glue. It
水会很快吞噬你 它的表面张力强到让你无法挣脱
would quickly engulf you, its surface tension too hard for you to break and
并且会溺水窒息 昆虫因此而进化出防水措施
you’d drown. So insects evolved to be water repellent.
它们的外骨骼包被一层蜡 就像车子一样
For one their exoskeleton is covered with a thin layer of wax just like a car.
这让它的表面至少能在一定程度上防水 因为它黏着性不好了
This makes their surface at least partly water repellent because it can’t stick to it very well.
许多昆虫也覆盖有起屏障作用的细小毛发
Many insects are also covered with tiny hairs that serve as a barrier.
大大增加了它的表面积
They vastly increase their surface area
还能阻止液滴触碰到他们的外骨骼
and prevent the droplets from touching their exoskeleton
使“清除液滴”变得更加简单
and make it easier to get rid of droplets.
为了利用表面张力
To make use of surface tension
生物演变早在我们亿万年前就破解了纳米技术
evolution cracked nanotechnology billions of years before us.
有的昆虫进化出覆盖表面的短且极其致密的防水毛
Some insects have evolved a surface covered by a short and extremely dense coat of water repelling hair.
有的每平方毫米过不止100万个
Some have more than a million hairs per square millimeter when
当昆虫跳进水里时 它们皮毛内部保留有空气 形成了空气套
the insect dives under water air stays inside their fur and forms a coat of air.
水进不去 因为它们的防水毛很细小 不能打破它的表面张力
Water can’t enter it because their hairs are too tiny to break its surface tension.
但是更棒的是 当气泡中的空气耗尽时 新的空气
But it gets even better, as the oxygen of the air bubble runs out, new oxygen
散布进水周围的气泡里 而二氧化碳
diffuses into the bubble from the water around, it while the carbon dioxide
向外散布到水中 所以昆虫外置自己的肺
diffuses outwards into the water. And so the insect carries its own outside lung
而且由于表面张力能使其主要进行水下呼吸
around and can basically breathe underwater thanks to surface tension.
这和滑冰者在池塘上行走是一样的道理
This is the same principle that enables pond skaters to walk on water by the way,
细小防水毛 你越小 你所存在的环境就越怪诞
tiny anti-water hairs. The smaller you get the weirder the environment becomes. At
在某个时间 空气也会变得越来越立体 让我们缩小
some point even air becomes more and more solid. Let’s now zoom down to the
到我们所知的最小昆虫吧 大约有一颗盐粒那么大
smallest insects known, about half the size of a grain of salt,
只有0.15毫米长:苍蝇仙子 它们生活的地方比
only 0.15 millimeters long: the Fairy Fly. They live in a world even weirder than
其他昆虫更加怪诞 对他们来说空气本身像薄薄的果冻 糖浆状物质
another insects. For them air itself is like thin jello, a syrup-like mass
一直环绕在周围 想要穿过它运动并不简单
surrounding them at all times. Movement through it is not easy. Flying
在这种水平的空气中飞行并不能很优雅 它们不得不夺取
on this level is not like elegant gliding; they have to kind of grab and
并紧紧抓住空气 所以它们的翅膀看起来就像毛茸茸的手臂 而不是昆虫合适的翅膀
hold onto air. So their wings look like big hairy arms rather than proper insect wings.
它们能随意在空气中游泳 就像糖浆里渺小的外星人
They literally swim through the air, like a tiny gross alien through syrup.
随着我们探索不同体型生物的多样性 事情至此变得越发奇怪了
Things only become stranger from here on as we explore more diversity of different sizes.
物理法则对于不同体型生物表现不同 生物周围有进化指导方向
The physical rules are so different for each size that evolution had to engineer around them
周而复始 且随着生物规模的增长有上十亿年了
over and over as life grew in size in the last billion years.
为什么没有像马一样大的蚂蚁？
So why are there no ants the size of horses?
为什么没有大象像变形虫那么小？为这些是什么呢？
Why are no elephants the size of amoeba? Why?
这个话题我们将会在下一期里进行讨论
We’ll discuss this in the next part.
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