here on Crash Course, specifically human animals, because...

尤其是人類這種動物，因為.....

well, because humans... we love talking about ourselves,

因為人類總是喜歡談論自己

and also because animals are just really interesting.

同時也是因為動物們十分有趣

But it's high time that we talked about the rest of the living world.

但是現在是該我們討論世界上其他動物的時候了

Because I hate to break it to ya, but most of the alive things on

我不太想要粉碎你的想像，但事實上地球上大多數的生物

Earth are single-celled organisms.

都是單細胞生物

And by "most of the alive things" I mean that these organisms

關於大多數生物這點，我是指這些生物

make up two of the three taxonomic domains of all life,

佔了三域系統中的三個域

plus one of the four kingdoms.

加上四個界其中一個界

I'm talking about archaea, bacteria and protists.

我指的是古菌、細菌、以及原生生物

With the exception of a few protists, they're all unicellular,

除了少數的原生生物之外，上述生物都是單細胞生物

and they are, by far, the most abundant and diverse organisms on Earth.

而且這些生物，就目前所知，是地球上最繁盛且最多樣的生物

More important, they lay claim to the world's oldest

最重要的是，這些生物有著世界上最古老

and earliest living lineages, dating back to the very first twinkle of life on this planet.

且最早期的血統，可以追溯至這星球的生命起源

So by understanding these three groups,

因此藉由了解這三個域中的生物

you begin to truly understand life on earth, its origins,

你將真正地了解地球上的生命、它的起源

and how everything that came after them, including us, came to be.

以及世間萬物是如何接替出現 － 這也包括了我們

What's more, because their heritage is so ancient,

不僅如此，因為這些生物是如此古老

these organisms often take weird, cool forms

它們的型態千奇百怪

that don't look like life as we think about it,

它們與我們熟知的生物大庭相逕

and they do amazing things.

它們能做到許多神奇的事情

Some not only live but thrive in environments that would kill you, me, and everything we hold dear.

它們之中有些棲息在你我以及我們熟知的一切都無法生存的嚴酷的環境中

And others make their living by invading organisms,

還有些靠著侵襲其他生物營生

including us, and causing disease.

(包括我們在內) 並造成疾病

Then there are those that do the opposite, making life possible by,

還有一部分則使用相反的作法，它們的生存是依靠

fixing nitrogen from the atmosphere and helping animals digest food.

將大氣中的氮氣固定(轉化成含氮化合物)或者協助其他動物消化食物

Members of these groups have names like Sailor's Eyeballs

這些族群中的成員大多數都有著像是"水手的眼球"

and Dog Vomit Slime Mold, and they can take the shape of rods, blobs, corkscrews or coils.

以及"狗嘔吐物似的黏菌"的俗稱，同時他們也具有多種形狀，像是桿狀、泡泡狀、螺旋狀、或是捲曲狀

Kinda like the doddering, eccentric relatives

有點像老態龍鍾、行為怪異的親戚

you're forced to spend some holiday with once a year,

但你每年逢年過節卻還是得要跟它們見一次面。

the archaea, bacteria and protists are our oldest, oddest relatives.

古菌、細菌以及原生生物是我們最老、最怪異的的親戚們

And it's about time you got to know them.

現在正是你好好了解它們的時候

There's no denying it: Every multicellular organism on this planet,

無可否認的是：這星球上所有的多細胞生物

whether it be a mushroom or a vampire bat,

不論是香菇或者吸血蝙蝠

evolved from a single celled organism.

都是由單細胞生物演化而來的

And while some of these single celled organisms evolved to populate

雖然部分的單細胞生物演化成了犀牛或者榕樹

the world as rhinos and strangler figs, others found happiness in the unicellular lifestyle,

並棲息在世界各地，剩下的傢伙們仍然很享受它們的單細胞生活

and they haven't changed much in the past few billion years.

並且它們在過去的數百萬年間都沒有什麼改變

Today, nearly all unicellular organisms are either archaea, bacteria or protists.

直至今日，幾乎所有的單細胞生物都是古菌、細菌或原生生物

Protists, you'll recall, are eukaryotic organisms

如果你還記得的話，原生生物屬於真核生物

that make up the kingdom Protista under the domain Eukarya.

原生生物界位在真核生物域的底下

Bacteria and Archaea, meanwhile, are their own prokaryotic domains.

細菌以及古菌，都屬於原核生物並各成一域

And I hope you haven't forgotten this, the big difference

我希望你還沒忘記

between prokaryotes and eukaryotes is that eukaryotic organisms,

原核生物以及真核生物之間有很大的不同

including you and the plants, and fungi and animals that you know,

真核生物包括你、你熟知的植物、真菌以及動物

have cells with a nucleus that hold their genetic information,

都具有細胞核，並把基因訊息都儲存在細胞核中

while prokaryotic cells don't have a nucleus or any organelles to speak of.

而原核生物則沒有細胞核和膜狀胞器

These two groups do have some important things in common,

這兩個類群還是有共通點的

like having plasma membranes that are filled with cytoplasm,

像是都具有細胞膜，膜裡面充滿著細胞質

and ribosomes that contain RNA and synthesize proteins.

以及具有包含著RNA並負責製造蛋白質的核醣體

And they both have DNA that carries the instructions for operating the cell.

而且這兩個類群都具有DNA，調控著整個細胞的生理運作

But eukaryotic DNA comes in strands in the form of chromosomes,

但真核生物的DNA會束在一起，纏繞成為染色體

while prokaryotic DNA is found in rings called plasmids.

而原核生物的DNA則為在環狀的質體上 (實際上是散落在細胞質中，質體只是一部分DNA)

So, again, and this time with feeling:

再來整理一次，這次要放入感情：

Protists are mostly single-celled eukaryotic organisms.

原生生物大多數是單細胞的真核生物

Archaea and bacteria are single-celled prokaryotic organisms.

古菌以及細菌是單細胞的原核生物

The word "prokaryote" actually means before the nucleus,

原核指的是在核出現之前

which is a clue that prokaryotes are an older form of life.

這暗示著原核生物的起源更為古早

And we literally cannot find anything older than Archaea.

我們也確實沒發現有比古菌更早的生物

The first Archaea fossils date back 3.5 billion years ago

最早的古菌化石可以追朔到三十五億年前

I'm talking just a billion years after the Earth formed

而這只是地球形成的十億年之後

and was still bombarded by comets and meteors,

當時仍受到小行星以及隕石的轟炸

not to mention fried by UV radiation.

更不用說受到UV的無情照射

But in the midst of all that, archaea were just chillaxing.

而在這樣的環境中，古菌卻是怡然自得

Earth's climate has calmed down since then, so today

之後，地球的環境逐漸冷卻穩定，到了今天

archaea are found in some of the world's most extreme environments:

古菌僅生存於地球上最極端的環境中

In underwater hydrothermal vents, oil wells, volcanic hot springs,

例如海底熱泉、石油井、火山熱泉

even acidic mine drainage.

甚至是酸性的採礦廢水中

Archaea were probably the earliest living things,

古菌很可能是最早的生命形式

and their adaptability is probably what allowed them

它們的適應能力使它們得以

to take root in Earth's early, kind of grody environment.

於地球早期生存，當時的環境較為惡劣

One key group of the archaea are the methanogens.

古菌中的一大類別是甲烷生成菌

These guys prefer more moderate environments, like mud,

這些傢伙偏好相較溫和的環境，像是泥地、

swamps and your intestines, but they derive their energy from hydrogen gas and carbon dioxide,

沼澤以及你的腸道。它們利用氫氣和二氧化碳來獲得能量

which is pretty cool and they emit methane as their waste product.

這相當特別，另外在這過程中它們會排出副產物甲烷

Methanogens, methane generators.

甲烷生成菌是甲烷的製造者

We know that waste as swamp gas, and also, other kinds of gas.

我們都知道那個副產物甲烷就是沼氣，同時也可以算是瓦斯

The other groups are extremophiles, which not only tolerate

另一個類別是嗜極端菌，它們不僅是忍耐力超強

but prefer really wicked surroundings.

而是根本就喜歡住在險惡的環境中

The most famous of these are the thermophiles,

它們之中最有名的是嗜熱菌

which live in temperatures that would melt your face off.

他生活的環境溫度可以融掉你的臉

I mean, serious: Pyrolobus fumarii, a species of archaea

我沒在開玩笑，Pyrolobus fumarii 是古菌的一種，

discovered in the late 1990's in a hydrothermal vent,

1990年代晚期在海底熱泉中發現

live at temperatures around 113 degrees celsius.

那裏的溫度高達攝氏113度

Not fahrenheit, celsius!

這可不是華氏，是攝氏!

Significantly above the boiling point of water!

很明顯地已經高出了水的沸點!

Most organisms can't take heat like that,

大多數的生物根本無法忍受這樣的高溫

because it causes their DNA to unwind and their proteins to denature

因為這會使得生物的DNA解旋，並使得蛋白質變性

or permanently change shape.

或者永久地改變構型

But thermophiles have evolved adaptations that keep them stable

但嗜熱菌演化出了適應方式來保持DNA和蛋白質的穩定

at these screamin' hot temperatures.

以生存在這嚇死人的高溫當中

There are also halophiles, or salt lovers, which live in places

另外還有所謂的嗜鹽菌，或稱鹽類偏好生物，它們住在

like the Dead Sea or the Great Salt Lake, and probably Daniel Tosh's mouth.

像是死海或者大鹽湖之類的地方，又或者是Daniel Tosh的嘴中

Most halophiles breathe oxygen and are heterotrophic,

多數的嗜鹽菌呼吸氧氣並且是異營生物

but there are some bizarro outliers, like species that use sunlight

但總有特例，像是有些種類會利用陽光

to make energy, but not like plants do

來產生能量，但用的方式卻跟植物不同

they have light-harvesting pigments in their membranes

它們的細胞膜上具有能吸收光的色素

that react with light and enable the cell to make ATP for energy.

可以與光進行反應使得細胞能獲得ATP作為能量

I know, it's crazy!

我知道這聽起來很瘋狂

But despite their alien-sounding ways of life,

但即使它們生活的方式簡直像是外星生物

archaea really aren't all that different from bacteria,

古菌與細菌其實仍有些許相似

which are also prokaryotes.

兩者都是原核生物

In fact, archaea and bacteria were classified together for much of the 20th century.

事實上，在二十世紀時，它們常常被歸為同一類，

It was only when scientists realized that they had some important genetic differences,

直到科學家們發現兩者之間存在著很大的基因差異

like, in the sequence of their ribosomal DNA and the makeup of their RNA,

像是核醣體DNA的序列以及RNA的組成

that they were separated into two domains.

都可以將它們劃分成為兩個不同的域

Bacteria are nearly as ancient as archaea.

細菌跟古菌幾乎一樣古老

Fossils show that they were widespread about 1.5 billion years ago,

化石證據顯示它們在十五億年前時廣為分布

but there's evidence that they've been around for more than 3 billion years.

不僅如此，還有證據顯示它們已經存在至少三十億年

Today, they make up the vast majority of prokaryotes on Earth,

截至今日，地球上的原核生物絕大多數都是細菌

and they're super slick when it comes to adapting quickly.

它們千錘百鍊，能夠快速適應任何環境

Many bacteria are parasitic.

許多種細菌是寄生性的

Think strep throat, your staph infection,

想想鏈球菌咽喉炎以及你的葡萄球狀菌感染

anything you've ever taken an antibiotic for.

或是任何需要用到抗生素的疾病治療過程

But bacteria can fend off antibiotics,

不過細菌有辦法避開抗生素

and the ninjas in your immune system,

它們就像躲在你免疫系統內的忍者一樣

by garbling up their DNA from one generation to another.

藉由不同世代之間彼此交換DNA

They can randomly turn genes on and off,

它們可以隨機的開啟或者關閉基因

creating unique genetic combination as its population multiplies,

隨著族群數量的增加創造出更多獨特的基因組合

keeping its host's immune system, and drug-makers, on their toes.

使其宿主的免疫系統以及各大藥廠疲於奔命

Like archaea, bacteria don't reproduce sexually,

如同古菌一樣，細菌並不進行有性生殖

but bacteria have devised a way to pass their genetic material to their buddies,

但是細菌能以獨到的方法來交換彼此的基因物質

a little trick called horizontal gene transfer.

一種被稱做基因水平轉移的小把戲

For example: you've heard of antibiotic resistance, right?

舉例而言，你應該聽過抗藥性吧?

Well, horizontal gene transfer is one reason for it.

恩，基因水平轉移就是抗藥性的原因之一

A strain of bacteria that has genetic resistance to an antibiotic

某一株細菌具有可以抵抗某種抗生素的基因

can pass some of its DNA, and that drug resistance,

而這株細菌可以將自身部分的DNA，包括抗藥性的那部分

to another strain, which is why we're always in

交給另一株細菌(使另一株細菌也有抗藥性)。這就是為什麼

kind of an arms race with the bacteria of the world.

我們總是在跟世界上的細菌進行軍備競賽的原因

And of course bacteria are incredibly diverse,

當然，細菌有著難以置信的多樣性

with too many phyla to name, more than two dozen.

有太多門細菌需要命名，超過兩打

But one way of classifying them is by their different kinds of cell membranes,

但其中一種方式是依據它們細胞膜的不同來分類

which react differently to a staining technique

不同的細胞膜會對同種染色方式產生不同的反應

scientists use called Gram staining.

科學家們使用的方法稱為革蘭氏染色

Gram positive bacteria have thick cell membranes,

革蘭氏陽性菌具有較厚的細胞膜

and they're a huge group that includes species that live individually like staphlococcus and streptococcus,

它們是一大類群，其中包括了葡萄球菌屬以及鏈球菌屬

as well as some colonial bacteria that are responsible for diseases like leprosy and tuberculosis.

以及會造成痲瘋或是肺結核的部分菌屬

There are lots of groups of Gram-negative bacteria too,

革蘭氏陰性菌也有不少成員

which have thinner membranes.

它們的細胞膜較薄

The biggest group here are Proteobacteria,

其中最大的族群要屬變形菌門

named after Proteus because they take so many forms.

用變形作為命名是因為它們有許多型態

These include bacteria that make our lives possible

這裡面有些細胞對我們的生存是不可或缺的

by converting nitrogen in the atmosphere into compounds available to plants,

它們會將大氣中的氮轉化為植物可以利用的氮化合物

as well as others that cause stuff like food poisoning and Legionnaire's disease.

還有一些種類可能會造成像是食物中毒或是退伍軍人症

Cyanobacteria, meanwhile, are the only prokaryotes

在這之中，藍菌門是唯一的原核生物

that use photosynthesis to make their food,

進行光合作用來生產自己的食物

and they're some of the most important members of aquatic food webs,

它們也是水生食物網中最重要的部分之一

providing microscopic forage for all kinds of freshwater and marine ecosystems.

提供顯微鏡尺度的食糧給各式淡水以及海洋生態系

Spirochetes are the corkscrew-shaped bacteria

螺旋體門是螺旋狀的細菌

that you've no doubt heard of most are harmless,

你耳聞的螺旋體門大多為無害的

but a couple of parasitic species are the culprits behind illnesses like Lyme disease and syphilis.

但其中有些寄生性的種類是造成萊姆病以及梅毒的元兇

And speaking of sexually transmitted diseases,

說到性傳染病

the last major group of bacteria worth mentioning are Chlamydias,

值得一提的最後一類細菌便是衣原體屬

which are strictly parasitic and live only in animal cells.

它們是專性寄生菌，只有寄生在動物細胞中才能生存

They're scumbags, obviously, and are the leading infectious cause of blindness in the world,

他們明顯是一群陰險小人，還導致世人得到眼疾而目盲

as well as that eponymous infection of the urethra

以及造成惡名昭彰的尿道感染

that makes me kind of want to, cross my legs, just thinking about it.

我一想到這點就覺得想要夾起自己的腿

So, Archaea have managed to make a nice,

古菌成功地

multi-billion-year living by surviving in weird, out of the way places,

在各種怪異、不尋常的環境中存活了百萬年

and bacteria have developed ways

而細菌則發展出了

to pass their DNA without sexual reproduction.

不用透過有性繁殖即能交換DNA的方法

But you know who's a hot freakin' mess? Protists.

但你知道誰才是這群怪咖中的明星嗎? 答案是原生生物

Evolutionarily, they're the youngest of the three,

演化上來看，原生生物是三個類群中最年輕的

having evolved from bacteria around 1.7 billion years ago,

它們的祖先在約17億年前由細菌演化而來

and in a lot of ways they're more sophisticated.

在許多方面來看原生生物都有更好的適應能力

For starters, they're eukaryotic, but also, some are multicellular,

首先，他們是真核生物也是多細胞生物

and a few kinds can even reproduce sexually.

少數幾種甚至能進行有性生殖

But their domain is a big crap circus, because some protists

但原生生物就像一個大馬戲團，因為

seem to be more closely related to plants or animals or fungi than other protists.

它們有些比較像植物或動物、有些像真菌卻不像其他原生生物

So scientists tend to talk about them based on what else they resemble.

因此科學家們通常會以其相似體來談論它們

There are Protozoa, which are kinda animal-like,

原生動物，原生生物中比較像動物的一群

Algae, which are kinda plant-like,

藻類，比較像植物的一群

and fungus-like ones, including the tastefully-named Slime Molds.

以及比較像真菌的一群 -黏菌，它們有著看似美味的名字

The one thing all of these have in common

這些生物都具有一個共通點

is they need to live somewhere wet:

就是它們都需要生長在潮濕的環境

in a bog, or in your body, or in a snow bank, wherever.

像是沼澤、你的體內、雪堆中之類的

Protozoa are actually really cool because they're like tiny animals.

原生動物相當酷，他們就像是迷你的動物一樣

Like us, they're heterotrophs,

如同你我，它們是異營性生物

so they have to eat other stuff in order to live.

需要靠著吃東西來維生

And because they need to eat, they've got mouthparts,

既然它們需要吃，它們就得要具有口器

or at least mouth-part sorts of things,

或者是類似口器的東西

and they can move around by using all kinds of really cool structures.

而且藉由一些獨特的構造，它們可以到處移動

Some have flagella, the whip-like tails, to propel them through the water,

有一些具有細長尾狀的鞭毛，來驅動它們在水中前進

or cilia, little hair-like structures

或是纖毛，細小的毛髮狀構造

that work like oars, and some move around with a kind of blobby amoeba-like motion.

功用就像槳一樣。最後的一些則像阿米巴原蟲一樣運動

I say amoeba-like because the protozoans

我會提到像阿米巴原蟲一樣是因為

that move this way are amoebas.

原生動物中這樣運動的就正是阿米巴原蟲

And speaking of amoebas, some protozoans are parasitic.

說到阿米巴原蟲，有一些原生動物是寄生性的

You've probably heard of amoebic dysentery: that's caused by amoebas.

你可能聽過阿米巴性痢疾：由阿米巴原蟲造成的一種疾病

Malaria is caused by this little guy,

而瘧疾則是由另一個小傢伙造成

a protozoan called Plasmodium vivax.

一種稱為瘧原蟲的生物 (Plasmodium vivax 間日瘧原蟲，四種瘧原蟲中的一種)

While African Sleeping Sickness is caused by Trypanosoma brucei, this guy here.

還有非洲昏睡病是由布氏錐蟲造成

Moving on to the plant-like protists, which are algae.

現在我們來談談像植物的原生生物，也就是藻類

All algae photosynthesize like plants,

所有的藻類都能像植物一樣行光合作用

even though they're not plants,

即使這樣它們仍不算植物

because they use different kinds of chlorophyll molecules.

因為兩者使用的葉綠素分子不同

Some are unicellular, like tiny diatoms,

有些藻類是單細胞生物，像是矽藻

which have a hard shell made of of silica.

具有二氧化矽做成的硬殼

But the amazing thing about single-celled algae

單細胞藻類還有一件神奇的事蹟

is that they can get really honkin' huge.

就是它們可以長到非常巨大

For example, ladies and gentlemen, cast your gaze

舉例來說，各位先生女士們，讓我為你們呈現

upon the Sailor's Eyeball, thought to be the biggest

"水手的眼球"，也是目前已知

single-celled organism on the planet.

地球上最大的單細胞生物

Also known as "bubble algae," it lives on the sea floor in tropical oceans

又名氣泡藻，它生長在熱帶地區的海床上

and can grow up to 5 centimeters across.

可以長到超過五公分大

How is that thing one cell?

而這居然只是一個細胞!?

Anyway, you already know multicellular types of algae,

想必你已經聽過藻類的多細胞型態了

aka seaweed. They're closely related to land plants,

那就是海藻，它們與陸地上的植物非常相近

as you can tell by looking at them,

你一看就能明白這點

and they're generally grouped in to red, green and brown varieties,

它們被大致上分類為紅藻、綠藻以及褐藻

although these all have their unicellular forms as well.

雖然它們也有單細胞的型態

The green algae are probably what gave rise to land plants about 475 million years ago.

綠藻大約在4億7千5百萬年前出現

They're the most abundant and diverse,

它們是最豐富且多樣的一群