from a skyscraper onto something soft.

從摩天大樓到某種軟的東西上

Let's say, a stack of mattresses.

像是⋯⋯床墊好了

The mouse lands and is stunned for a moment,

老鼠著地後愣了一下

before it shakes itself off,

然後會過神來

and walks away pretty annoyed,

不爽地走開了，

because that's a very rude thing to do.

因為這是一件非常粗魯的事情。

The dog breaks all of its bones

狗全身骨折

and dies in an unspectacular way,

悄悄地死去

and the elephant explodes into a red puddle of bones and insides

而大象粉身碎骨，只剩一灘肉泥和內臟

and has no chance to be annoyed.

連生氣的機會都沒有

Why does the mouse survive,

為什麼老鼠活了下來

but the elephant and dog don't?

但大象跟狗則不？

The answer is size.

尺寸是關鍵

Size is the most underappreciated regulator of living things.

尺寸是最被小看的生物特徵。

Size determines everything about our biology,

它決定了生物學上的一切

how we are built, how we experience the world, how we live and die.

從我們由什麼構成，我們如何體驗這世界，到出生、死亡的方式

It does so because the physical laws are different for different sized animals.

原因是，物理定律對不同大小的動物有不同的表現

Life spans seven orders of magnitude, from invisible bacteria to mites, ants,

生命的尺寸橫跨七個等級，從看不見的細菌到塵蟎、螞蟻、

mice, dogs, humans, elephants and, blue whales. Every size lives in its own

老鼠、狗、人類、大象、藍鯨。各種規模的生物在彼此之間

unique universe right next to each other, each with its own rules, upsides, and

獨特的宇宙生存。每一個都有自己的規則、優勢

downsides. We'll explore these different worlds in a series of videos. Let's get

和缺點。我們將在一系列影片中探討這些不同的世界。讓我們

back to the initial question: Why did our mouse survive the fall? Because of how

回到最初的問題：為什麼老鼠可以在下落中生存？因為

scaling size changes everything; a principle that we'll meet over and

尺寸改變了一件事，一個我們會不斷在見到的原則，

over again. Very small things, for example, are practically immune to falling from

非常小的東西從高處掉落實際上是不受傷害的

great heights because the smaller you are the less you care about the effect

因為你越小，受到重力的影響也越低

of gravity. Imagine a theoretical spherical animal

想像一下，一個假想的球形動物

the size of a marble. It has three features: its length, its surface area,

有彈珠的大小。它有三個特徵：長度、表面積（覆蓋在皮膚上）

(which is covered in skin) and its volume, or all the stuff inside it like organs,

和它的體積，或裡面全部的東西例如器官

muscles, hopes and dreams. If we make it ten times longer, say the size of a

肌肉、希望和夢想。如果我們將其增長十倍，如籃球的大小

basketball, the rest of its features don't just grow ten times. Its skin will

它的特徵可不只增長十倍。它的皮膚會

grow 100 times and it's inside (so it's volume) grows by 1000 times. The volume

增加100倍，體積增長1000倍。

determines the weight, or more accurately, mass of the animal. The more mass you

體積決定重量，或者更準確地說，動物的質量。你的質量越大

have, the higher your kinetic energy before you hit the ground and the

你撞到地面前的動能也越高

stronger the impact shock. The more surface area in relation to your volume

衝擊也更強。你的表面積（與體積和質量有關）越大

or mass you have, the more the impact gets distributed and softened, and also

影響越被分散和緩和，也有

the more air resistance will slow you down. An elephant is so big that it has

更多的空氣阻力讓你減速。大象是如此之大，它的

extremely little surface area in ratio to its volume. So a lot of kinetic energy

表面積與體積的比非常小。所以極大的動能

gets distributed over a small space and the air doesn't slow it down much at all.

被分佈在一個狹小的空間且空氣阻力減速程度不高

That's why it's completely destroyed in an impressive explosion of goo when it

這就是為什麼它擊中地面時在爆炸當中被

hits the ground. The other extreme, insects, have a huge surface area in

徹底摧毀。另一個極端的生物，昆蟲，表面積與體積的比

relation to their tiny mass so you can literally throw an ant from an airplane

相對較大，你可以把一隻螞蟻從飛機上丟下

and it will not be seriously harmed. But while falling is irrelevant in the small

而牠得以倖存。雖然墜落在微小世界中無關緊要，

world there are other forces for the harmless for us but extremely dangerous

但有其他力量對我們無害，卻對小生物

for small beings. Like surface tension which turns water into a potentially

特別危險。例如表面張力，把水變成對昆蟲

deadly substance for insects. How does it work? Water has the tendency to stick to

致命的潛在陷阱。為何？水有相吸的特性

itself; its molecules are attracted to each other through a force called

水分子會藉由凝聚力彼此吸引

cohesion which creates a tension on its surface that you can imagine as a sort

在其表面形成一股張力，可以想像成一層

of invisible skin. For us this skin is so weak that we don't even notice it

隱形皮膚。對我們而言這層皮膚很無力，甚至平常不會注意到。

normally. If you get wet about 800 grams of water or about one percent of your

當你全身溼透，約800公克(或體重1%)的水

body weight sticks to you. A wet mouse has about 3 grams of water sticking to

會黏在你身上。一隻溼透的老鼠則約有3公克的水

it, which is more than 10% of its body weight. Imagine having eight full water

附著在牠身上，超過其體重的10%。想像一下有八瓶裝滿的

bottle sticking to you when you leave the shower. But for an insect the force

寶特瓶，在你洗完澡後綁在你身上。但對於昆蟲，

of water surface tension is so strong that getting wet is a question of life

水的表面張力是如此強，讓碰水變成一個攸關生死

and death. If we were to shrink you to the size of

的問題。如果我們把你縮小到螞蟻

an ant and you touch water it would be like you were reaching into glue. It

的大小，再讓你碰水，那就像碰到一團黏膠。

would quickly engulf you, its surface tension too hard for you to break and

它會很快把你吞進去，由於表面張力太難打破

you'd drown. So insects evolved to be water repellent. For one their exoskeleton is

你會被淹死。所以昆蟲演化出防水功能，其中之一是牠們的外骨骼

covered with a thin layer of wax just like a car. This makes their surface at

包覆著一層薄臘，就像車子，讓牠們的體表

least partly water repellent because it can't stick to it very well. Many insects

至少部分防水，因為它無法完美黏附體表。許多昆蟲

are also covered with tiny hairs that serve as a barrier. They vastly increase

也覆蓋著細毛當作阻擋。大大增加了

their surface area and prevent the droplets from touching their exoskeleton

它們的表面積及防止水滴觸碰自己的外骨骼

and make it easier to get rid of droplets. To make use of surface tension

並更容易擺脫它。為了利用表面張力

evolution cracked nanotechnology billions of years before us. Some insects

演化搶先我們數十億年破解奈米科技。有些昆蟲

have evolved a surface covered by a short and extremely dense coat of water

已經演化成擁有由密集短毛構成的

repelling hair. Some have more than a million hairs per square millimeter when

防水外套，有些光是每平方毫米就有上百萬根毛。當

the insect dives under water air stays inside their fur and forms a coat of air.

昆蟲潛水時，空氣停留在短毛內並形成空氣的外膜。

Water can't enter it because their hairs are too tiny to break its surface tension.

水無法進入，因為牠們的毛髮太細密了，無法打破水的表面張力。

But it gets even better, as the oxygen of the air bubble runs out, new oxygen

但不只如此，外膜中的氧氣用完時，新的氧氣

diffuses into the bubble from the water around, it while the carbon dioxide

從周圍的水擴散到膜內，而二氧化碳

diffuses outwards into the water. And so the insect carries its own outside lung

向外擴散到水中。所以昆蟲能到處帶著自己的外肺

around and can basically breathe underwater thanks to surface tension.

並基本上能在水下呼吸。一切受惠於表面張力

This is the same principle that enables pond skaters to walk on water by the way,

順道一提，水黽能在水面上行走也是靠相同的道理

tiny anti-water hairs. The smaller you get the weirder the environment becomes. At

防水細毛。你體型越小，環境也變得越怪異。在

some point even air becomes more and more solid. Let's now zoom down to the

某些時候甚至連空氣變得越來越更加黏稠。現在，讓我們放大來到

smallest insects known, about half the size of a grain of salt,

已知最小的昆蟲，大約有一粒鹽一半大小

only 0.15 millimeters long: the Fairy Fly. They live in a world even weirder than

僅有0.15毫米長：纓小蜂。他們生活的世界，甚至比其他昆蟲

another insects. For them air itself is like thin jello, a syrup-like mass

都還來的怪異。對牠們來說，空氣本身就像果凍，糖漿般的物質

surrounding them at all times. Movement through it is not easy. Flying

時時圍繞他們，在其中活動相當不容易。飛行

on this level is not like elegant gliding; they have to kind of grab and

在這個尺度上可不像優雅地滑翔，牠們必須像攀附在

hold onto air. So their wings look like big hairy arms rather than proper insect

空氣上。因此牠們的翅膀就像長毛的手臂，而非普通昆蟲的翅膀。

wings. They literally swim through the air, like a tiny gross alien through

牠們確實是「游」過空氣，就像奇異的長毛外星人

syrup. Things only become stranger from here on

游過糖漿。當我們探索更多不同尺度，

as we explore more universes of different sizes. The physical rules are

事情只會變得更奇怪。物理法則在每個地方

so different for each size that evolution had to engineer around them

的不同，讓演化必須不斷解決這些問題

over and over as life grew in size in the last billion years. So why are there

讓生命數十億年來持續繁盛。所以為什麼

no ants the size of horses? Why are no elephants the size of amoeba? Why?

沒有像馬那麼大的螞蟻？為什麼沒有像阿米巴原蟲尺寸的大象？為何？

We'll discuss this in the next part.

我們將在下一部影片討論這個問題。

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我們現在有每月電子報了！

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