The game-changing amniotic egg - April Tucker

改變遊戲規則的羊膜卵 - 艾普麗爾·塔克 (April Tucker)

譯者: Ning Zhang 審譯者: Sophie Wang

Would you believe that walruses,

你相信海象、

rattlesnakes,

響尾蛇

and parakeets

和鹦鹉

all once lived in the same house?

牠們曾經都生活在同一个屋檐下吗？

Let's go back about 350 million years.

讓我們回到3.5億年前。

Look around.

看

Steamy swamps and rain forests of horsetails and ferns

潮濕的沼澤，馬尾草的熱帶雨林和各種蕨類植物

cover the region.

遍佈地面。

Amphibians are the dominant land vertebrates.

兩棲動物在陸地上佔主導地位。

They range in size from newts

牠們從最小的蠑螈

to crocodiles.

到碩大的鱷魚。

And all require water to do their egg laying.

牠們所有的都依賴水來產卵。

If they don't go to the water,

如果牠們不依靠水，

their shell-less, jelly-like eggs will dry out.

牠們無殼的，像果凍一樣的卵會變乾。

Because of this hazard,

因為這個危險，

they spend most of their time

牠們大部份時間都要

住在或靠新鮮的水域而生。

living in or near fresh water.

That is, until a breakthrough

也就是說，直到一個變革性的突破

in evolution changes everything:

改變了一切：

the amniotic egg.

羊膜卵。

The amniotic egg is shelled,

羊膜卵是有外殼的，

waterproof,

防水的，

and can be laid on dry land.

而且能夠被產在乾燥的陸地上。

It is produced by the amniotes,

羊膜卵是由羊膜動物生產的，

a new group of animals named after their revolutionary egg.

一種新的動物族群因其革命性的卵而得名。

The first amniote is a tetrapod,

第一個羊膜動物是四足動物（tetrapod），

a four-legged animal,

一種四條腿的動物，

resembling a small lizard.

類似小的蜥蜴。

While some amphibians can walk around on land

雖然一些兩棲動物可以在陸地上行走

and bury their eggs in wet soil or highly humid areas,

以及將牠們的卵埋在 濕土裡或極度潮濕的區域，

nothing before the amniotes has the ability

在羊膜動物之前，牠們沒有能力

to lay its eggs on completely dry land.

將卵產在完全乾燥的陸地上。

Because of this evolved egg,

因為這個進化的卵，

the amniotes are the first animals

羊膜動物是第一種動物

with the ability to live a fully terrestrial life.

完全具備陸地生活能力的動物。

But, despite their move inland,

但是，儘管牠們向陸地進軍，

the amniotes have not abandoned

羊膜動物沒有拋棄

their pond-dwelling upbringing.

牠們池塘生活的習性。

In fact, the amniotic egg brings the pond with them

事實上，羊膜卵用牠們的外殼

by enclosing the aquatic environment within its shell.

把池塘的水生環境給包裹了起來。

This is achieved by four main upgrades

這是通過四個主要的升級而實現的

that are unique to amniotic eggs.

這些也是羊膜卵的獨特之處。

Let's take a closer look.

讓我們仔細看看。

The first development is the most obvious:

第一個進化是最明顯的：

the egg's protective shell.

卵的保護外殼。

It's tough but flexible,

外殼堅硬但靈活，

and has a leathery surface,

還由貌似皮毛狀的外表，

still seen in reptile eggs today.

至今仍然可以在爬行類動物的卵上發現。

The shell protects the eggs from predators,

外殼保護卵免於捕食者，

細菌，

bacteria,

damage,

損壞，

and drying out.

和乾燥。

But, unlike the walls of a fish tank,

但，不同於魚缸壁是不透氣的，

the shell of the amniotic egg is porous,

羊膜卵的外殼有很多細小的透氣孔，

allowing oxygen to pass through

這樣氧氣可以透過這些小孔

so that the growing amniote inside doesn't suffocate.

使得發育中的胚胎不會在卵裡窒息。

The next two developments are two separate membranes

接下來的兩個進化是有兩個單獨的膜

that work together like a pair of lungs.

牠們能像肺協同工作。

They bring oxygen into the embryo

牠們將氧氣帶入胚胎

while removing carbon dioxide.

同時又清除二氧化碳。

The first is the chorion,

第一個是絨毛膜，

which is the protective layer that oxygen passes through

這是一層保護膜，

after entering the shell's tiny pores.

能令氧氣進入外殼的 細小毛孔之後順利通過。

You may recognize the chorion

你可以將絨毛膜看成

as the thin skin you peel away on a hard boiled egg.

一個煮雞蛋剝掉外殼之後 剩下的那層薄薄的皮。

Think of this waterproof membrane

可以將這層防水膜想像成

as the in and out doors of the egg.

一個卵的氣體交換的大門。

It's the entrance for oxygen

它是氧氣的進口

and exit for carbon dioxide.

同時又是二氧化碳的出口。

The membrane working with the chorion

與絨毛膜協同工作的

is the allantois.

是尿膜。

If the chorion is the doors,

如果絨毛膜是大門，

then the allantois is essentially the lobby of the building.

那麼尿膜就是這座建築的大堂。

It directs the oxygen and carbon dioxide

它為氧氣和二氧化碳指明方向

while simultaneously storing

同時儲存

unneeded waste from the embryo.

胚胎不需要的廢物。

The chorion and the allantois make sure the embryo

絨毛膜和尿膜確保胚胎

has everything it needs

獲得一切所需

and gets rid of anything it doesn't.

並且也為其清除一切廢物。

The last and perhaps the most important development

最後一個可能也是最重要的進化是羊膜

is the amnion, the membrane for which the egg is named.

羊膜卵就是以其命名的。

The amnion is also contained within the chroion

羊膜也包裹在絨毛膜內

and holds the fluid in which the embryo floats.

使得胚胎能在液態環境中漂浮。

Because it has left the watery world of the amphibians,

因為它已經離開了 兩棲動物生活的水底世界，

the amnion is necessary for preventing

所以羊膜對防止胚胎乾燥

the embryo from drying out.

是必不可少的保護。

It is the transportable pond

它是一個可移動的池塘

that allows the amniote to lay the egg on dry land.

使得羊膜動物可將卵產在乾燥的陸地上。

Its fluid also protects the embryo

它的液體也保護胚胎

from any collisions or rough landings,

免於碰撞或生硬著陸，

like a shock absorber on your bike or car.

就像你的自行車或汽車的減震器

Together, the shell and these four membranes

外殼和這些膜共同

create a safe, watery environment

為胚胎的發育和成長

for the embryo to grow and develop.

提供了一個安全的水生環境。

The new amniote offspring will continue

新的羊膜動物的後代將繼續

the process of vertebrate evolution

推進脊椎動物的進化過程

as it explores new land away from the water.

離開水域去探索新大陸。

They will spend the next million years

牠們將用接下來的幾百萬年

splitting into two distinct groups:

分化成兩個不同的組：

the synapsids and sauropsids.

下孔類和蜥行類。

Synapsida is the group of animals

下孔類動物包括

that contain mammals,

哺乳類動物，

while sauropsida is the group that contains

蜥行類動物包括

reptiles,

爬行動物、

birds,

鳥

and dinosaurs.

和恐龍。

These two amniotic groups collectively contain

這兩個羊膜動物的組包括

the walruses,

rattlesnakes,

海象、

響尾蛇

and parakeets we know today.

和我們今天所熟知的鸚鵡。

Like a family reunion,

就像一個家庭團聚一樣，

with relatives of every shape and size,

雖然形態體格各異，

coming together from different corners of the Earth,

來自地球的不同角落，

these animals can all call one place home:

這些動物都有一個共同的家：

the amniotic egg.

羊膜卵。