你是怎么来到这里的？：英语精读讲义

You just clicked on this video, 表達脈絡

你刚刚点开了这个视频，

so you're alive.

所以你还活着。

And interestingly,

有趣的是，

in order to understand exactly where you came from, 語法

要想准确了解你究竟从何而来，

we must first understand what it means to be alive. 語法

我们首先得弄清楚，活着究竟意味着什么。

Life is an organized genetic unit capable of metabolism, 短語搭配

生命是一个有组织的遗传单位，能够进行代谢，

reproduction,

繁殖，

and evolution.

以及进化。

It's important to remember this as we go way back in history to figure out exactly how you got here. 講解

当我们把历史一路倒推，探寻你究竟如何来到这里时，记住这一点非常重要。

Astronomers believe our solar system began to form 4.6 billion years ago when a star exploded and then collapsed to form the sun

天文学家认为，我们的太阳系在46亿年前开始形成：一颗恒星爆炸后坍缩，形成了太阳，

and around 500 smaller planets collided with each other to form the inner planets we know today,

大约500颗较小的行星则相互碰撞，形成了我们今天所知的内行星，

including your home,

其中也包括你的家园——

Earth.

地球。

For about 600 million years,

在大约6亿年间，

Earth was too hot for life. 語法

地球热得无法孕育生命。

Most of the water was evaporating into space,

大部分水都在蒸发到太空中，

and even if some simple chemical reactions began to take place creating life, 講解

即使某些简单的化学反应已经开始孕育生命，

the comets and meteorites hitting Earth at the time

当时撞击地球的彗星和陨石

would have brought enough heat to make the developing oceans boil, 語法

也会带来足以让正在形成的海洋沸腾的热量，

destroying all potential life.

摧毁所有可能出现的生命。

As comets and meteorites subsided,

随着彗星和陨石的撞击逐渐减少，

Earth cooled and it became possible for water to remain on the surface. 語法

地球冷却下来，水也终于可以留在地表。

And so,

于是，

life begins around 3.7 billion years ago.

生命大约在37亿年前诞生。

There are many theories about how exactly it began.

关于生命究竟如何起源，有许多理论。

Some believe simple life arrived from a meteorite, 表達脈絡

有人认为，简单的生命形式是由陨石带到地球上的，

while others think chemical evolution started with compounds reacting to heat,

也有人认为，化学进化始于化合物受热后发生反应，

or perhaps they were struck by lightning.

又或许，是闪电击中了这些化合物。

And while the exact date is difficult to pinpoint, 短語搭配

虽然确切时间很难确定，

a new study claims to have found the oldest fossil ever 語法

但一项新研究声称发现了迄今最古老的化石，

at 3.77 billion years old,

其年代可追溯到37.7亿年前，

an ancient microbe that flourished around a hydrothermal vent on the ocean floor.

那是一种曾繁盛于海底热液喷口周围的远古微生物。

It's around this time that the first simple cells began to evolve on Earth. 語法

大约就在这时，最早的简单细胞开始在地球上进化。

They were able to capture energy,

它们能够捕获能量，

replicate themselves,

自我复制，

and evolve,

并不断进化，

and became the single unit on which all life will be built, 語法

最终成为构建一切生命的基本单位，

including you.

也包括你。

For 2 billion years,

在长达20亿年的时间里，

all organisms on Earth are unicellular,

地球上所有生物都是单细胞生物，

and they likely lived in the oceans shielded from the hard ultraviolet light of the sun,

它们很可能生活在海洋中，借海水抵御太阳强烈的紫外线，

but then something remarkable happened. 表達脈絡

但随后，一件非同寻常的事发生了。

Photosynthesis.

光合作用。

Around 2.5 billion years ago,

大约25亿年前，

a random mutation occurred that was advantageous to cells,

细胞中发生了一次有利的随机突变，

and they began using the energy of the sun to power their metabolism. 用詞

细胞开始利用太阳能来驱动自身代谢。

And since oxygen or O2 is the product of photosynthesis,

由于氧气（O2）是光合作用的产物，

our atmosphere changed,

我们的大气层随之改变，

eventually creating the ozone layer,

最终形成了臭氧层，

which acted to shield the Earth from the sun's deadly light.

它为地球挡住了太阳致命的光线。

Of course,

当然，

at this point O2 is poisonous to most organisms,

在当时，O2对大多数生物来说都是有毒的，

but over time cells evolved to tolerate it,

但随着时间推移，细胞进化出了耐受它的能力，

and because metabolic reactions using O2 were more efficient,

而且，由于使用O2的代谢反应效率更高，

cells could grow larger.

细胞得以长得更大。

Around 1 billion years later,

大约10亿年后，

cells began to engulf and co-opt smaller cells, 用詞

细胞开始吞噬更小的细胞，并将其收为己用，

increasing their abilities to live in diverse environments.

从而增强了它们在不同环境中生存的能力。

This selective advantage led to cells sticking together in a coordinated manner even after dividing. 語法

这种选择优势使细胞即使在分裂后，也会以协调一致的方式黏在一起。

And these cells eventually began exchanging genetic material,

最终，这些细胞开始交换遗传物质，

aka, 用詞

换句话说，

they had sex.

它们开始有性繁殖了。

Single-celled organisms would divide by mitosis or simple nuclear division,

单细胞生物会进行有丝分裂，或简单的细胞核分裂，

but once meiosis evolved, 語法

但减数分裂一经出现，

genetic reorganization began to occur,

遗传重组便开始发生，

and the rate of evolution increased as offspring were now more genetically variable,

进化速度也随之加快，因为后代之间的遗传差异变得更大，

and some of these offspring were more likely to survive and reproduce. 語法

其中一些后代也更有可能存活并繁殖。

And so,

于是，

the tree of life began to explode. 習語

生命之树开始迅速开枝散叶。

First, 表達脈絡

首先，

there were plants,

植物出现了，

and then fungi,

然后是真菌，

corals,

珊瑚，

and then protostomes like crabs,

接着是螃蟹这样的原口动物，

echinoderms like sea urchins,

海胆这样的棘皮动物，

and then fish like sharks and cod,

然后是鲨鱼和鳕鱼这样的鱼类，

and then tetrapods evolved from fish and began adapting to living outside of the water part-time, 短語搭配

接下来，四足动物从鱼类进化而来，并开始适应偶尔离水生活，

initially gulping air and absorbing oxygen in the gut.

起初，它们通过大口吞入空气，再用肠道吸收氧气。

As time passes,

随着时间推移，

species would evolve lungs separate from the gut for absorbing air,

这些物种进化出了与肠道分离、用来从空气中吸收氧气的肺，

as well as a new way to walk on land.

也进化出了在陆地上行走的新方式。

In come amphibians, 語法

随后登场的是两栖动物，

reptiles,

爬行动物，

dinosaurs,

恐龙，

and finally,

最后还有——

mammals.

哺乳动物。

In fact,

事实上，

our entire ancestry stems from a cute furry-tailed rat-like mammal, 短語搭配

我们的整个祖先谱系都源自一种可爱、长着毛茸茸尾巴、形似老鼠的哺乳动物，

which survived and thrived around 66 million years ago, 短語搭配

这种动物在大约6600万年前幸存下来并繁衍兴盛，

just after an asteroid wiped out the dinosaurs. 短語動詞

那时，一颗小行星刚刚灭绝了恐龙。

And after tens of millions of years of evolution and new species emerging, 短語搭配

经过数千万年的进化，随着新物种不断涌现，

one branch of the Protungulatum family tree evolved into our ape and monkey ancestors.

原蹄兽属谱系中的一个分支进化成了我们的猿猴祖先。

And nearly 4 million years ago,

而在将近400万年前，

one of the first human-like creatures arrives,

最早的类人生物之一出现了，

Australopithecus afarensis,

它就是阿法南方古猿，

the most famous discovered remains being that of Lucy,

其中最著名的出土遗骸就是露西，

who stood upright.

她能够直立行走。

100,000 generations later,

十万代之后，

or 2 to 3 million years ago,

也就是距今200万到300万年前，

the species group Homo began,

人属这一类群出现了，

which had a bigger brain and started using their hands for more complex activities like creating and wielding tools.

他们的脑容量更大，并开始用双手从事更复杂的活动，比如制作和使用工具。

This was the first step of transforming our environment to improve our lives.

这是我们改造环境、改善生活迈出的第一步。

It was also a catalyst to switch from a vegetarian diet to one containing meat, 講解

这也推动我们从素食转向包含肉类的饮食，

which is a more concentrated form of nutrition and less affected by seasonal shortages.

肉类能提供更集中的营养，也较少受到季节性食物短缺的影响。

These simple stone tools allowed us to rip through meat and would become the tool of choice for 2 million years. 講解

这些简单的石器让我们能够撕开肉类，并成为此后200万年间的首选工具。

And around 1.8 million years ago,

大约180万年前，

Homo erectus emerged,

直立人出现了，

the direct ancestor to our species.

他们是我们这一物种的直系祖先。

Finally,

终于，

a few hundred thousand years ago,

在几十万年前，

modern humans or Homo sapiens step into the light, 習語

现代人类，也就是智人，登上了历史舞台，

larger,

他们体型更高大，

smarter,

更加聪明，

and more capable than their predecessors.

能力也比前辈更强。

Interestingly,

有趣的是，

we almost didn't make it. 習語

我们差点就没能挺过来。

A climate change event around 140,000 years ago plummeted the human population to only hundreds of people,

大约14万年前的一次气候变化事件，使人类总人口骤降到只有几百人，

an endangered species.

人类就此成了濒危物种。

But we survived.

但我们活了下来。

As recently as 60,000 years ago,

甚至直到距今6万年前，

three different species of the family Homo coexisted:

人属的三个不同物种仍然共存：

Homo neanderthalensis,

尼安德特人，

Homo denisova,

丹尼索瓦人，

and we Homo sapiens,

以及我们——智人，

which all lived on this planet together.

这三个物种共同生活在这个星球上。

In fact,

事实上，

sapiens and neanderthals mated quite often,

智人和尼安德特人经常交配，

which is why most contemporary humans, 語法

这就是为什么大多数当代人类，

including you,

包括你，

have neanderthal DNA.

体内都有尼安德特人的DNA。

The neanderthals died out around 30,000 years ago when Homo sapiens were arriving in what is now Europe. 講解

尼安德特人大约在3万年前灭绝，当时智人正进入今天的欧洲地区。

And from this point on,

从此以后，

the Homo sapiens were the only living humans left on Earth.

智人便成了地球上仅存的人类。

Unlike our primate relatives, 語法

与我们的灵长类近亲不同，

whose evolution favored strength,

它们的进化更偏向力量，

ours chose brain power.

我们的进化则选择了脑力。

In fact,

事实上，

your brain weighs 2% of your body weight, 表達脈絡

你的大脑重量只占体重的2%，

but uses 20% of your caloric intake.

却要消耗你摄入热量的20%。

And this brain power allowed us to survive in a variety of environments as we began to migrate around the entire world.

这种脑力让我们在开始向全球迁徙时，能够在各种环境中生存下来。

Where we started as small wandering groups of less than 100,

起初，我们只是人数不足100人的小型迁徙群体，

we began to settle in groups of thousands,

后来，我们开始形成数千人的定居群体，

then millions, 表達脈絡

随后发展到数百万人，

and now billions.

如今则有数十亿人。

You were born a Homo sapiens,

你生而为智人，

and that is how you got here. 表達脈絡

这就是你来到这里的历程。