这是一个有关你 This is a story about you
我 还有你的狗的故事 and me and your dog.
狗出现的时间并不长 There was a time not long ago... before dogs.
之前它们根本不存在 They didn't exist.
现在它们有大有小 有宠物犬 Now there are big ones, small ones, snugglers,
有守卫犬 还有猎犬 guardians, hunters.
任何你想要的犬种 Every kind of dog you could possibly want.
这是怎么发生的 How did that happen?
不仅仅是狗 It's not just dogs.
各种各样的生物都是怎么来的 Where did all the different kinds of living creatures come from?
答案就是转化的力量 这听上去就像 The answer is a transforming power that sounds like something
来自神话传说中的情节 straight out of a fairy tale or myth,
但这并不是神话 but it's no such thing.
■
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翻译 船长 jimmyflower 甜土豆
翻译 ellaxinxin 小十三
校对 OBAFGKM 麦克杜格
时间轴 狱
后期 吉吉 总监 OBAFGKM
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宇宙
时空之旅
让我们回到三万年前 那时狗还未出现 Let's go back across 30,000 years to a time before dogs,
我们的祖先生活在最后一个冰河时期 when our ancestors lived in the endless winter
无尽的冬天里 of the last ice age.
我们的祖先小群聚居 四处流浪 Our ancestors were wanderers living in small bands.
他们露宿在星空下 They slept beneath the stars.
天空就是他们的故事书 日历 The sky was their storybook, calendar,
生活的说明书 an instruction manual for living.
天空告诉他们严寒什么时候到来 It told them when the bitter colds would come,
野生的粮食什么时候成熟 when the wild grains would ripen,
成群的驯鹿和野牛什么时候开始迁徙 when the herds of caribou and bison would be on the move.
他们的家就是整个地球 Their idea of home was Earth itself.
但其他饥饿的生物也让他们提心吊胆 But they lived in fear of other hungry creatures...
山狮和熊 the mountain lions and the bears
它们和人为了同样的猎物竞争 that competed with them for the same prey
而狼则会夺走并捕食 and the wolves that threatened to carry off and devour
他们中最弱小的人类 the most vulnerable among them.
所有的狼都想得到骨头 All the wolves want to get at the bone,
但大部分狼都害怕离人太近 but most of them are too frightened to come close enough.
它们的恐惧起因于血液中 Their fear is due to high levels
高水平的应激激素 of stress hormones in their blood.
这是它们存活的关键 It's a matter of survival.
因为离人太近会致命 Because coming too close to humans can be fatal.
但是一些狼 由于自然变异 But a few wolves-- due to natural variations--
这类激素的水平相对较低 have lower levels of those hormones.
这使得它们不怎么害怕人 This makes them less afraid of humans.
这种狼发现了 This wolf has discovered
它某一枝祖先在15000年前想出的 what a branch of his ancestors figured out some 15,000 years ago...
极好的生存策略 an excellent survival strategy;
人类的驯养 the domestication of humans.
让人们去狩猎 不要威胁他们 Let the humans do the hunting, don't threaten them,
他们就会让你打扫他们的残羹冷炙 and they'll let you scavenge their garbage.
这样进食更规律 也会留下更多后代 You'll eat more regularly, you'll leave more offspring,
那些后代会继承你的性格 and those offspring will inherit your disposition.
这种驯服的选择 This selection for tameness
会一代代逐渐加强 would be reinforced with each generation
直到野狼的这一分支进化成为了 until that line of wild wolves evolves into...
狗 dogs.
你可能会称之为 友好者的幸存 You might call this "Survival of the friendliest."
就像现在一样 这也对人类有利 Then as now, this was a good deal for the humans, too.
这种狗不仅仅能打扫食物 The scavenging dogs weren't just a sanitation squad.
它们还保证人类的安全 They worked security.
随着这种物种间的合作不断深入 As this interspecies partnership continued over time,
狗的外表也在不断变化 the dogs' appearance changed also.
可爱变成了一种选择优势 Cuteness became a selective advantage.
你越可爱 就越有机会 The more adorable you were, the better chance you had
生存和传递基因给下一代 to live and pass on your genes to another generation.
这种临时的合作 What began as an alliance of convenience
变成了日益加深的友谊 became a friendship that deepened over time.
看看接下来会发生什么 To see what happens next,
让我们离开20000年前遥远的祖先 let's leave our distant ancestors of some 20,000 years ago
去更近一些的 to visit the more recent past
冰河世纪的间隙看一看 during an intermission in the Ice Age.
气候发生了变化 推动了进化 This break in the climate starts a revolution.
人们开始定居下来 不再流浪 Instead of wandering, people are settling down.
世界上出现了一些新的东西 聚落 There's something new in the world... villages.
人们仍然打猎 采集 People still hunt and gather,
但是现在他们也会生产食物和衣服 but now they also produce food and clothing...
农业出现了 agriculture.
狼已经用它们的自由 The wolves have traded their freedom
换取了稳定的食物 in exchange for a steady meal.
它们已经放弃了择偶的权利 They've given up their right to choose a mate.
现在人类为它们挑选配偶 Now the humans choose for them.
人们会杀死那些不能被驯化的狗 They consistently kill off the dogs that can't be trained;
那些咬人的狗 the ones that bite the feeding hand.
繁殖那些讨人喜欢的狗 And they breed the dogs that please them.
他们养育那些服从他们命令 They nurture those dogs that do their bidding...
能打猎 放牧 守卫 搬运 hunting, herding, guarding, hauling,
能陪伴他们的狗 and keeping them company.
狗每一次产仔 From every litter,
人们就会选择他们最喜欢的小狗 the humans select the puppies they like best.
一代传一代 狗就这样进化了 Over the generations, the dogs evolve.
这种进化被称之为 人工选择 This kind of evolution is called "Artificial selection"
或者 育种 or "Breeding."
把狼变成狗是我们人类第一次 Turning wolves into dogs was the first time
把进化掌握在自己手中 we humans took evolution into our own hands.
从那时起我们就一直这样做 And we've been doing it ever since
以塑造我们赖以生存的植物和动物 to shape all the plants and animals that we depend on.
在宇宙的一瞬间 In a blink of cosmic time,
仅仅过去了15000亦或20000年 just 15,000 or 20,000 years,
我们就把灰狼变成了我们现在爱着的 we turned gray wolves into all the kinds of dogs
各种各样的狗 we love today.
想一想 Think of it.
每一种你所见过的狗 Every breed of dog you've ever seen
都经过人类的雕琢 was sculpted by human hands.
我们最好的朋友 最受欢迎的品种 Many of our best friends-- the most popular breeds--
都是近几个世纪才被创造出来 were created in only the last few centuries.
令人敬畏的进化力量 The awesome power of evolution
把贪婪的狼 transformed the ravenous wolf
变成了忠诚的牧羊犬 into the faithful shepherd...
它们保护着羊群 把狼赶走 ...who protects the herd and drives the wolf away.
人工选择把狼变成了牧羊犬 Artificial selection turned the wolf into the shepherd
把野草变成了小麦和玉米 and the wild grasses into wheat and corn.
事实上 我们现在吃的每种植物和动物 In fact, almost every plant and animal that we eat today
几乎都是由其不太适合食用的野生祖先繁殖而来 was bred from a wild, less-edible ancestor.
如果人工选择能在10000年 If artificial selection can work such profound changes
或15000年里造成如此深远的变化 in only 10,000 or 15,000 years,
自然选择又能在几十亿年里 what can natural selection do
做些什么呢 operating over billions of years?
答案就是美丽多样的生命 The answer is all the beauty and diversity of life.
它是怎样起作用的呢 How does it work?
我们的想象号飞船能带我们去任何空间 Our Ship of the Imagination can take us anywhere in space
任何时间 甚至隐秘的微观世界 and time, even to the hidden microcosmos,
在那里一种生命能被转化成另一种 where one kind of life can be transformed into another.
跟我来 Come with me.
看起来也许不像 May not seem like it,
但我们在过去的二百万年里 but we've been living in an ice age
一直都生活在冰河世纪 for the last two million years.
现在仅仅是其中一个较长的间隔 This just happens to be one of the long intermissions.
这二百万年中的大部分时间 For most of those two million years,
气候都是又干又冷 the climate has been cold and dry.
北极的冰冠跟现在相比 The North Polar ice cap extended much farther south
向南延伸得更远 than it does today.
在某个又长又冷的冰河时期 In one of those long, cold glacial periods
冬天海上的浮冰从北极 when the winter sea ice stretched from the North Pole
一直延伸到现在的洛杉矶 all the way down to what is now Los Angeles,
大熊在爱尔兰的冰原上流浪 great bears roamed the frozen wastes of Ireland.
这可能看上去就像普通的熊 This might look like an ordinary bear,
但是它的身体内部正在发生非凡的变化 but something extraordinary is happening inside her.
这种变化会形成新的品种 Something that will give rise to a new species.
为了看到它 In order to see it,
我们必须深入到一个更小的尺度 we'll need to descend down to a much smaller scale,
去到细胞层次 to the cellular level,
探索这头熊的生殖系统 so that we can explore the bear's reproductive system.
我们将从锁骨下动脉穿过心脏 We'll take the subclavian artery through the heart.
快到了 Almost there.
那是它的一些卵子 Those are some of her eggs.
为了明白这其中的奥秘 To see what's going on in one of them,
我们要变得更小一些才行 we'll have to get even smaller.
我们得缩小到分子水平 We'll have to shrink down to the molecular level.
我们的想象号飞船现已缩到很小 Our Ship of the Imagination is now so small,
一粒沙就可以装下数百万艘 you could fit a million of them into a grain of sand.
看到那些在梁上大摇大摆走着的家伙了吗 See those guys over there strutting along those girders?
它们是一种叫做驱动蛋白的蛋白质 They are proteins called kinesin.
这些驱动蛋白是运输队的一份子 These kinesin are part of the transport crew
忙于在细胞之间传送货物 that's busy moving cargo around the cell.
它们长得可真古怪 How alien they seem.
然而这些小生物和其他类似的存在 And yet these tiny creatures-- and beings like them--
是每个活着的细胞的一部分 are a part of every living cell,
也存在于你的体内 including the ones inside you.
如果生命也有圣殿 If life has a sanctuary,
那必然是细胞核 其中有我们DNA it's here in the nucleus which contains our DNA...
记录着我们遗传密码的古老经文 the ancient scripture of our genetic code.
由所有生命都可阅读的语言谱写 And it's written in a language that all life can read.
DNA分子形似一条扭曲长梯 DNA is a molecule shaped like a long twisted ladder
或双螺旋形 or double helix.
这个长梯的阶梯由 The rungs of the ladder are made
四种更小的分子组成 of four different kinds of smaller molecules.
它们就是基因字母 These are the letters of the genetic alphabet.
基因字母的不同组合拼出了 Particular arrangements of those letters spell out
给所有生命的指令 the instructions for all living things,
告诉它们如何生长 移动 消化 telling them how to grow, move, digest,
感知环境 愈合伤口和繁衍下一代 sense the environment, heal, reproduce.
DNA双螺旋是一台分子机器 The DNA double helix is a molecular machine
由千亿个"原子"部件组成 with about 100 billion parts called "Atoms."
一个DNA分子内的原子数目之多 There are as many atoms in a single molecule of your DNA
可以与一个星系内的恒星数目媲美 as there are stars in a typical galaxy.
狗的DNA也是如此 The same is true for dogs
还有熊 and bears
和其他所有生命 and every living thing.
我们每个生命都是一个小宇宙 We are, each of us, a little universe.
DNA信息从一个细胞传至另一个细胞 The DNA message handed down from cell to cell
从上一代传到下一代 and from generation to generation
都经过精心复制 is copied with extreme care.
一个新的DNA分子的诞生始于 The birth of a new DNA molecule begins
解链蛋白 when an unwinding protein
解开双螺旋双链 separates the two strands of the double helix,
把阶梯打破 breaking the rungs apart.
在细胞核内的液体中 Inside the liquid of the nucleus,
基因字母分子自由地漂浮着 the molecular letters of the genetic code float freely.
每条螺旋单链复制出它丢失的另一半 Each strand of the helix copies its lost partner,
最后得到两个一模一样的DNA分子 resulting in two identical DNA molecules.
这就是生命复制基因 That's how life reproduces genes
并一代代传递下来 and transmits them from one generation to the next.
当一个活细胞一分为二 When a living cell divides in two,
每一个细胞都带走一份完整的DNA each one takes away with it a complete copy of the DNA.
有一种特殊的蛋白质校勘这一过程 A specialized protein proofreads to make sure
只有正确的基因字母才能被接受 that only the right letters are accepted
保证每个DNA的准确复制 so that the DNA is accurately copied.
但没有什么是完美的 But nobody's perfect.
偶尔也会出现一些校对疏漏 Occasionally, a proofreading error slips through,
基因结构因此出现了一个小小的随机改变 making a small, random change in the genetic instructions.
这头熊的卵细胞出现了基因突变 A mutation has occurred in the bear's egg cell.
一个如此小的随机事件 A random event as tiny as this one
将产生极为深远的影响 can have consequences on a far grander scale.
这个突变改变了控制毛色的基因 That mutation altered the gene that controls fur color.
它将影响这头熊的下一代 It will affect the production of dark pigment
毛发中黑色素的形成 in the fur of the bear's offspring.
大部分突变是无害的 Most mutations are harmless.
有一些是致命的 Some are deadly.
但极少数 只是纯粹偶然 But a few, purely by chance,
能产生有利于生存的关键改变 can give an organism a critical advantage over the competition.
一年过去了 A year has passed.
我们的这头熊已经是一位母亲了 Our bear is now a mother.
因为基因突变的原因 And as a result of that mutation,
她的两只幼崽中有一只天生是白色的 one of her two cubs was born with a white coat.
当幼崽们成长到可以独自探索世界时 When the cubs get old enough to venture out on their own,
哪一只小熊更可能 which bear is more likely
悄悄跟踪猎物不被发现呢 to be able to sneak up on unsuspecting prey?
在雪地里棕熊1.6千米远外就能被发现 The brown bear can be seen against the snow a mile away.
白熊不断繁衍并把它 The white bear prospers and passes on
独特的基因传递下去 its own particular set of genes.
然后不断重复 This happens repeatedly.
经过几代的繁衍之后 Over succeeding generations,
产生白毛的基因已经在 the gene for white fur spreads through
整个北极熊族群中传播开了 the entire population of Arctic bears.
产生深色毛发的基因 The gene for dark fur loses out
在物竞天择中不断失败 in the competition for survival.
基因突变是完全随机且不断出现的 Mutations are entirely random and happen all the time.
但环境更偏爱那些 But the environment rewards those
对生存有利的基因 that increase the chance for survival.
环境自然地选择了那些 It naturally selects the living things
更适于生存的生命形态 that are better suited to survive.
而这一选择过程绝对不是偶然 And that selection is the opposite of random.
这两支熊类族群经过地理隔离 The two populations of bears separated,
和数千年的时间 and over thousands of years,
进化出其他不同的生理特征 evolved other characteristics that set them apart.
它们变成了不同的物种 They became different species.
这就是查尔斯·达尔文的 That's what Charles Darwin meant
《物种起源》想要表达的意思 by "The Origin of Species."
一头熊是无法进化的 An individual bear doesn't evolve;
熊的种群经过数代的繁衍得以进化 the population of bears evolves over generations.
如果北极的冰川因全球变暖不断缩小 If the Arctic ice continues to dwindle due to global warming,
北极熊很可能灭绝 the polar bears may go extinct.
它们将被棕熊所取代 They'll be replaced by brown bears,
因为棕熊更适合如今森林退化的环境 better adapted to the now defrosted environment.
这是一个和狗完全不同的故事 This is a different story from the one about the dogs.
没有饲者干预它们的变化 No breeder guided these changes.
相反 环境自己做出了选择 Instead, the environment itself selects them.
这是通过自然选择的进化 This is evolution by natural selection,
科学史上最颠覆的概念 the most revolutionary concept in the history of science.
1859年达尔文首次提出这一理论的证据 Darwin first presented the evidence for this idea in 1859.
因此引起的震动从未平息 The uproar it caused has never subsided.
为什么 Why?
我们都能理解我们和猿猴有同一个祖先 We all understand the twinge of discomfort
这想法给人带来的阵阵不适感 at the thought that we share a common ancestor with the apes.
没有比乱七八糟的亲戚更让人尴尬的了 No one can embarrass you like a relative.
我们的近亲 黑猩猩 Our closest ones, the chimpanzees,
在公众场合的举止总是极其不雅 they frequently behave inappropriately in public.
人类想要与这些亲戚划清界限的想法 There's an understandable human need
是可以理解的 to distance ourselves from them.
传统信仰中的一个核心前提是 A central premise of traditional belief
相对于其他动物 is that we were created separately
人类是被特别创造出来的 from all the other animals.
不难理解这种想法的立足点 It's easy to see why this idea has taken hold.
这让我们感觉 与众不同 It makes us feel... special.
但如果我们和树木也有亲戚关系呢 But what about our kinship with the trees?
这又会让你作何感受呢 How does that make you feel?
这是橡树DNA的一部分 Okay, here's a segment of the oak tree's DNA.
把它看做一个条形码 Think of it like a bar code.
写在这段条形码上的指令 The instructions written in the code of life
告诉树木如何代谢糖分 tell the tree how to metabolize sugar.
现在把它和我的同一段DNA作对比 Now let's compare it with the same section of my own DNA.
DNA不会撒谎 The DNA doesn't lie.
这棵树和我 我们是长久失联的表亲 This tree and me-- we're long-lost cousins.
不仅仅是树木 And it's not just the trees.
如果你回顾得足够远 你会发现 If you go back far enough, you'll find that we share
和我们有共同祖先的还有 a common ancestor with...
蝴蝶 the butterfly,
灰狼 gray wolf,
蘑菇 mushroom,
鲨鱼 shark,
细菌 bacterium,
麻雀 sparrow.
多么神奇的家庭 What a family!
条形码的其他部分因物种而异 Other parts of the bar code vary from species to species.
这是猫头鹰和章鱼之间差异的来源 That's what makes the difference between an owl and an octopus.
除非你有一个同卵双生的兄弟姊妹 Unless you have an identical twin,
宇宙中没有谁 there's no one else in the universe
和你有完全相同的DNA with the exact same DNA as you.
其他的物种内 基因的差别 Within other species, the genetic differences
为自然选择提供了原材料 provide the raw material for natural selection.
环境选择哪些基因能够生存和复制 The environment selects which genes survive and multiply.
谈到基因对生命的 When it comes to the genetic instructions
最基本功能的指导作用 for life's most basic functions,
比如消化糖分 say, digesting sugars,
我们与其他物种几乎无异 we and other species are almost identical.
这是因为这些是生命最基本的功能 That's because those functions are so basic to life,
它们在不同生命形式分化前 they evolved before the various life-forms
就已经进化出现 branched off from each other.
这是我们的生命之树 This is our Tree of Life.
科学让构建这个 Science has made it possible
地球上所有物种的生命之树 for us to construct this family tree
变成可能 for all the species of life on Earth.
有亲近的遗传关系的物种居于同一分支 Close genetic relatives occupy the same branch of the tree,
而相对疏远的则隔得更远 while more distant cousins are farther away.
每个枝杈都代表一个存在的物种 Each twig is a living species.
而树的主干则代表地球上 And the trunk of the tree represents the common ancestors
所有生命的共同先祖 of all life on Earth.
生命的形态无穷多变 The stuff of life is so malleable
当它开始分化时 环境会将其 that once it got started, the environment molded it
塑造成数量惊人的不同形态 into a staggering variety of forms,
比我们能呈现出的要多出上万倍 10,000 times more than we can possibly show here.
单单是甲虫 Biologists have catalogued
生物学家就分出了五十多万种 a half a million different kinds of beetles alone.
更不用说种类不计其数的细菌了 Not to mention the numberless varieties of bacteria.
数以百万计的动物和植物 There are many millions of living species
存在于世 of animals and plants,
大多数还不被科学了解 most of them still unknown to science.
想想 我们目前还未和绝大多数的 Think of that,we have yet to make contact
陆生生物有过接触 with most of the forms of terrestrial life.
单单在这一个小星球上 That's how many kinds of life there are
就有这么多种类的生命 on this tiny planet alone.
生命之树向各方向伸出触角 The Tree of Life extends its feelers in all directions,
探索发现可能的进化 finding and exploiting what works,
为生命的新形式创造新的环境和机会 creating new environments and opportunities for new forms.
生命之树已生长35亿年 The Tree of Life is three and a half billion years old.
它有充裕的时间 That's plenty of time to develop
进化出各式各样的小把戏 an impressive repertoire of tricks.
生物进化让动物可以伪装成植物 Evolution can disguise an animal as a plant...
花费千万代的时间 taking thousands of generations
去获得巧妙的伪装 to contrive an elaborate costume
这样的伪装会迷惑捕食者 that fools predators into looking elsewhere
转而寻找别的猎物 for someone to eat.
或者 植物也可以伪装成动物 Or it can disguise a plant as an animal,
进化的花变成黄蜂的样子 evolving blossoms that take on the appearance of a wasp--
兰花以此吸引真正的黄蜂为其传粉 the orchid's way of fooling real wasps into pollinating it.
这就是自然选择 This is the awesome shape-shifting power
神奇的塑造形态的能力 of natural selection.
在生命之树浓密而错综复杂的枝干中 Among the dense, tangled limbs of the vast Tree of Life,
你在这里 you are here.
数不清的枝杈中小小一支 One tiny branch among countless millions.
科学表明 地球上 生命同源 Science reveals that all life on Earth is one.
达尔文揭露了生物进化的机制 Darwin discovered the actual mechanism of evolution.
当时盛行的观点是生命的复杂性与多样性 The prevailing belief was that the complexity and variety of life
一定出自一位聪明的设计师 must be the work of an intelligent designer,
他分别创造了数以百万的物种 who created each of these millions of different species separately.
有人说生命都太复杂了 Living things are just too intricate, it was said,
不可能是无指导进化的结果 to be the result of unguided evolution.
比如说 人眼 Consider the human eye,
复杂性的杰作 a masterpiece of complexity.
它需要角膜 It requires a cornea,
虹膜 晶状体 视网膜 iris, lens, retina,
视神经 肌肉 optic nerves, muscles,
更别说大脑用来理解图像的 let alone the brain's elaborate neural network
复杂的神经网 to interpret images.
它比任何人类智能 It's more complicated than any device
所能设计的设备都要复杂 ever crafted by human intelligence.
因此 结论是 Therefore, it was argued,
人眼不可能是无心进化的结果 the human eye can't be the result of mindless evolution.
为了一探真假 我们需要穿越回 To know if that's true, we need to travel across time
没有眼睛感知世界的时代 to a world before there were eyes to see.
起初 In the beginning,
生物没有视觉 life was blind.
这是我们的世界 This is what our world looked like
四十亿年前的样子 four billion years ago,
没有眼睛来观看世界 before there were any eyes to see.
直到几亿年过去 Until a few hundred million years passed,
忽然 有一天 and then, one day,
一个细菌在DNA复制时 there was a microscopic copying error
发生了错误 in the DNA of a bacterium.
这个随机的突变让那个细菌 This random mutation gave that microbe
有了一个能吸收阳光的蛋白质分子 a protein molecule that absorbed sunlight.
想知道感光细菌看到的世界 Want to know what the world looked like
是什么样子的吗 to a light-sensitive bacterium?
生物视角
看看屏幕的右侧 Take a look at the right side of the screen.
突变持续随机地发生 Mutations continued to occur at random,
就像它在任何生物种群中发生的那样 as they always do in any population of living things.
另一个突变 Another mutation
让嗜暗细菌逃离强光 caused a dark bacterium to flee intense light.
会发生什么呢 What is going on here?
夜晚与白天 Night and day.
这些能够辨别明暗的细菌 Those bacteria that could tell light from dark
相对那些不感光的细菌有决定性的优势 had a decisive advantage over the ones that couldn't.
为什么 Why?
因为白天刺眼的 含紫外线的阳光 Because the daytime brought harsh, ultraviolet light
会损伤DNA that damages DNA.
感光细菌逃离强光 The sensitive bacteria fled the intense light
在黑暗中安全地交换它们的DNA to safely exchange their DNA in the dark.
相对那些呆在水面的细菌 They survived in greater numbers
它们存活的几率更高 than the bacteria that stayed at the surface.
一段时间后 这些感光的蛋白质 Over time, those light-sensitive proteins
在更高等的单细胞有机体上 became concentrated in a pigment spot
逐渐集中为一个眼点 on the more advanced, one-celled organism.
这让找到光成为可能 This made it possible to find the light,
这对那些收集阳光来生产食物的有机体 an overwhelming advantage for an organism
来说是个巨大的优势 that harvests sunlight to make food.
这是扁形虫的视角 Here's a flatworm's eye view of the world.
这个多细胞生物体 This multi-celled organism
进化出了眼点上的小窝 evolved a dimple in the pigment spot.
碗型的凹窝 The bowl-shaped depression
让它可以区分光线和阴影 allowed the animal to distinguish light from shadow
能从环境中隐约分辨出物体 to crudely make out objects in its vicinity,
包括食物和天敌 including those to eat and those that might eat it.
这是个巨大的优势 A tremendous advantage.
之后 视野变得清晰一些了 Later, things became a little clearer.
小窝变深 The dimple deepened
进化出了有小孔的眼窝 and evolved into a socket with a small opening.
几千代之间 Over thousands of generations,
自然选择慢慢地雕刻着眼睛 natural selection was slowly sculpting the eye.
小孔缩小至针孔状 The opening contracted to a pinhole covered
由一层保护性的透明薄膜覆盖 by a protective transparent membrane.
只有很少光线可以通过这个小孔 Only a little light could enter the tiny hole,
但足可以在眼睛敏感的内表面 but it was enough to paint a dim image
形成模糊的图像 on the sensitive inner surface of the eye.
这使焦点更为集中 This sharpened the focus.
较大的开口可以进入更多光线 A larger opening would have let in more light
图像也会更明亮但会脱焦 to make a brighter image but one that was out of focus.
这一发展也引发了视觉上的 This development launched the visual equivalent
演化军备竞赛 of an arms race.
要生存必须在竞争中获胜 The competition needed to keep up to survive.
之后眼睛进化出一个非常棒的新特点 But then a splendid new feature of the eye evolved,
一个既能透光又能精确对焦的透镜 a lens that provided both brightness and sharp focus.
原始鱼类的眼睛中 In the eyes of primitive fish,
针孔附近透明的胶体形成一层透镜 the transparent gel near the pinhole formed into a lens.
同时 针孔扩张 At the same time, the pinhole enlarged
让更多的光线进入 to let in more and more light.
现在不论近处还是远处 Fish could now see in high-def,
鱼类都能看到清晰的图像 both close up and far away.
之后可怕的事发生了 And then something terrible happened.
你有注意到从水面看玻璃杯里的吸管 Have you ever noticed that a straw in a glass of water
吸管看起来像是弯曲的吗 looks bent at the surface of the water?
那是因为光线从一种介质进入另一种时会弯曲 That's because light bends when it goes from one medium to another,
比如说从水到空气 say from water to air.
我们的眼睛最初进化出了水中视觉 Our eyes originally evolved to see in water.
眼睛里的水样液体轻松地 The watery fluid in those eyes neatly
消除了弯曲效应带来的变形 eliminated the distortion of that bending effect.
但对陆地动物来说 But for land animals,
承载着图像的光从干燥的空气 the light carries images from dry air
进入它们仍然湿润的眼睛 into their still-watery eyes.
那会使光线弯曲 That bends the light rays,
导致各种各样的失真变形 causing all kinds of distortions.
当我们的两栖祖先离开水到陆地生活 When our amphibious ancestors left the water for the land,
它们为了能在水中看清而精妙进化的眼睛 their eyes, exquisitely evolved to see in water,
在空气里很难看清事物 were lousy for seeing in the air.
自那之后我们的视觉就再没有那么好 Our vision has never been as good since.
我们习惯认为我们的眼睛非常精妙 We like to think of our eyes as state-of-the-art,
但在3亿7千5百万年后 but 375 million years later,
我们仍然无法看清近在鼻端的东西 we still can't see things right in front of our noses
或是像鱼类一样 or discern fine details in near darkness
在黑暗中看清细节 the way fish can.
当我们离开水之后 When we left the water,
为什么自然不重新来过 why didn't nature just start over again
让我们进化出新的眼睛 and evolve us a new set of eyes
最理想的能在空气中看东西的眼睛 that were optimal for seeing in the air?
自然不是这样工作的 Nature doesn't work that way.
进化经过代代更迭来重塑现有结构 Evolution reshapes existing structures over generations,
通过细小的变化优化它们 adapting them with small changes.
它不能就这么回到原点 It can't just go back to the drawing board
从头开始 and start from scratch.
在进化的每个阶段 At every stage of its development,
进化中的眼睛都能很好地 the evolving eye functioned well enough
为生存者提供选择优势 to provide a selective advantage for survival.
在现存的动物中 And among animals alive today,
我们找到了在不同发展阶段的眼睛 we find eyes at all these stages of development.
它们都能够发挥作用 And all of them function.
人类眼睛的复杂性并没有 The complexity of the human eye poses
给通过自然选择的进化带来任何挑战 no challenge to evolution by natural selection.
事实上 眼睛以及全部生物离开进化 In fact, the eye and all of biology makes no sense
都将是无意义的 without evolution.
有些人坚持进化只是一个理论 Some claim that evolution is just a theory,
就好像它只是一种观点 as if it were merely an opinion.
进化理论 就像引力理论一样 The theory of evolution, like the theory of gravity,
是科学事实 is a scientific fact.
进化确实在发生 Evolution really happened.
接受我们与地球上所有生物的亲属关系 Accepting our kinship with all life on Earth
不仅仅是严谨科学 is not only solid science.
在我看来这还是令人激动的精神体验 In my view, it's also a soaring spiritual experience.
因为进化是盲目的 Because evolution is blind,
它不能预测或是适应灾难性的事件 it cannot anticipate or adapt to catastrophic events.
生命之树有一些断枝 The Tree of Life has some broken branches.
它们中的大多数都折损于自生命起源后的 Many of them were severed in the five greatest catastrophes
五次大灾变中 that life has ever known.
某个地方 有一个纪念馆 Somewhere, there's a memorial
来纪念众多灭绝的物种 to the multitude of lost species,
灭绝殿堂 the Halls of Extinction.
跟我来 Come with me.
灭绝殿堂
欢迎来到灭绝殿堂 Welcome to the Halls of Extinction.
一个为生命之树上的断枝而建的纪念堂 A monument to the broken branches of the Tree of Life.
对现存的数百万物种中的每一个物种来说 For every single one of the millions of species alive today,
也许有一千种其它的物种已经灭亡 perhaps a thousand others have perished.
它们大多都在与其它生物每天的竞争中 Most of them died out in the everyday competition
逐渐灭亡 with other life-forms.
但也有很多在祸及全球的大灾变中 But many of them were swept away in vast cataclysms
被一扫而空 that overwhelmed the planet.
在过去的五亿年中 In the last 500 million years,
这样的事发生过五次 this has happened five times.
奥陶纪
五次摧毁地球生命的大灭绝 Five mass extinctions that devastated life on Earth.
泥盆纪
三叠纪
最糟糕的一次发生在2亿5千万年前 The worst one of all happened some 250 million years ago,
白垩纪
二叠纪
二叠纪的末期 at the end of an era known as the Permian.
披有甲壳的三叶虫 Trilobites were armored animals that hunted
曾成群的在海底狩猎 in great herds across the seafloor.
它们是第一批进化出 They were among the first animals to evolve
可成像眼睛的动物 image-forming eyes.
三叶虫存活过很长一段时期 Trilobites had a good long run,
大约有2亿7千万年 some 270 million years.
地球曾是三叶虫的天下 Earth was once the planet of the trilobites.
但现在它们都消失了 灭绝了 But now they're all gone, extinct.
与无数其它物种一起 The last of them were swept from life's stage
它们最后都在 along with countless other species
一场空前的环境灾害中被消灭殆尽 in an unparalleled environmental disaster.
那场浩劫始于现在的西伯利亚 The apocalypse began in what is now Siberia,
火山喷发的规模 with volcanic eruptions on a scale unlike anything
在人类历史中见所未见 in human experience.
那时的地球非常不同 Earth was very different then,
只有一个超级大陆和一个巨大的海洋 with one single supercontinent and one great ocean.
不间断的炽热熔岩 Relentless floods of fiery lava
吞没了比现在西欧还大的一块区域 engulfed an area larger than Western Europe.
脉冲似的喷发 The pulsing eruptions went on
持续了数十万年 for hundreds of thousands of years.
熔化的岩石 点燃了煤藏 The molten rock ignited coal deposits
排出的二氧化碳和其它温室气体污染了空气 and polluted the air with carbon dioxide and other greenhouse gases.
这使地球升温 This heated the Earth
并阻止了洋流的循环 and stopped the ocean currents from circulating.
有毒细菌爆发 Noxious bacteria bloomed,
海洋里几乎所有其他生命都死去了 but nearly everything else in the seas died.
污浊的水域向空气中释放出致命的硫化氢气体 The stagnant waters belched deadly hydrogen sulfide gas into the air,
使大多数陆地动物窒息而死 which suffocated most of the land animals.
地球上百分之九十的物种都灭绝了 Nine in ten of all species on the planet went extinct.
我们称之为 We call it...
大灭绝 The Great Dying.
地球上的生物几乎被消灭殆尽 Life on Earth came so near to being wiped out
经历了一千万年才恢复过来 that it took more than ten million years to recover.
但新的生命形态在缓慢进化 But new life-forms slowly evolved
来填补二叠纪大灭绝留下的空白 to fill the openings left by the Permian holocaust.
这中间最大的赢家就是恐龙 Among the biggest winners were the dinosaurs.
现在地球是它们的了 Now the Earth was their planet.
它们的时代持续了1亿5千多万年 Their reign continued for over 150 million years.
直到在另一场大灭绝中被摧毁 Until it, too, came crashing down in another mass extinction.
地球上的生命在跨越万古的过程中历尽艰辛 Life on Earth has taken quite a beating over the eons.
并仍然存活下来 And yet it's still there.
生命坚韧得令人难以置信 The tenacity of life is mind-boggling.
我们总在意想不到的地方发现它 We keep finding it where no one thought it could be.
至于那道未命名的走廊 That nameless corridor?
是留给以后的 That's for another day.
我知道有一种动物可以生活在沸水中 I know an animal that can live in boiling water
或在坚冰中 or in solid ice.
可以十年不喝水 It can go ten years without a drop of water.
可以裸露在寒冷真空 It can travel naked in the cold vacuum
且充满强辐射的宇宙中 and intense radiation of space
并毫发无损地归来 and will return unscathed.
缓步类动物 或称水熊虫 The tardigrade, or water bear.
无论在最高的山顶 It's equally at home atop the tallest mountains
还是在最深的海沟 它都同样自在 and in the deepest trenches of the sea.
在我们的后院 它们大量聚集 And in our own backyards, where they live among the moss
在苔藓间生活 in countless numbers.
大概你从未察觉过它们 You've probably never noticed them
因为它们太小了 because they're so small.
像针尖那么小 About the size of a pinpoint.
但它们很顽强 But they're tough.
缓步类动物躲过了五场大灭绝 The tardigrades have survived all five mass extinctions.
已存在五亿年之久 They've been in business for a half a billion years.
我们曾认为生命很挑剔 We used to think that life was finicky,
只能生根于 that it would only take hold where it was
不太热 不太冷 not too hot, not too cold,
不太暗 不咸 不酸 无辐射的地方 not too dark or salty or acidic or radioactive.
还有 不管怎样 都不能没有水 And whatever you do, don't forget to add water.
可是我们错了 We were wrong.
顽强的缓步类动物告诉我们 As the hardy tardigrade demonstrates,
生命可以忍耐 life can endure conditions
人类不能承受的恶劣环境 that would mean certain death for us humans.
但地球上极端环境里的生物 But differences between us and life found
和我们之间的区别 in even the most extreme environments on our planet
就像相同主旋律上的变奏 are only variations on a single theme,
同种语言中的不同方言 dialects of a single language.
即地球生物的遗传密码 The genetic code of Earth life.
其他星球上的生物是什么样的呢 But what would life be like on other worlds?
有着与地球截然不同的历史 Worlds with a completely different history,
化学成分和演化的星球 chemistry and evolution from our planet?
我想带你们去一个遥远的世界 There's a distant world I want to take you to--
一个与我们的世界大相径庭 a world far different from our own,
但可能孕育生命的世界 but one that may harbor life.
如果这是真的 它的样子 If it does, it promises to be unlike anything
一定是我们见所未见的 we've ever seen before.
云雾遮盖土卫六的整个表面 Clouds and haze completely hide the surface of Titan,
它是土星的巨大卫星 Saturn's giant moon.
土卫六有种家的感觉 Titan reminds me a little bit of home.
像地球一样 它的大气主要由氮气构成 Like Earth, it has an atmosphere that's mostly nitrogen.
却是地球大气密度的四倍 But it's four times denser.
土卫六的空气中没有氧气 Titan's air has no oxygen at all.
比地球上任何一个地方都寒冷 And it's far colder than anywhere on Earth.
尽管如此 我还是想去 But still... I want to go there.
我们必须穿过 We have to descend
几百千米的烟雾 through a couple hundred kilometers of smog
才能看到它的表面 before we can even see the surface.
掩藏在下面的是熟悉到奇怪的地貌 But hidden beneath lies a weirdly familiar landscape.
在太阳系中 只有地球和土卫六上 Titan is the only other world in the solar system
存在降雨 where it ever rains.
它拥有河流和海岸线 It has rivers and coastlines.
和数以百计的湖泊 Titan has hundreds of lakes.
其中一个比北美的苏必利尔湖更大 One of them larger than Lake Superior in North America.
湖水蒸发 Vapor rising from the lakes
冷凝后又变成雨水 condenses and falls again as rain.
雨水落入河流 The rain feeds rivers,
冲刷出山谷的地貌 which carve valleys into the landscape,
就像在地球上一样 just like on Earth.
但有一个重大的不同 But with one big difference.
在土卫六上 所有的海洋和雨水 On Titan, the seas and the rain
不是水 而是甲烷和乙烷 are made not of water but of methane and ethane.
在地球上 这些分子组成天然气 On Earth, those molecules form natural gas.
而在寒冷的土卫六上 On frigid Titan,
它们以液态存在 they're liquid.
土卫六上有很多水 Titan has lots of water,
但全部结成坚冰 but all of it is frozen hard as rock.
事实上 它的地形和山脉 In fact, the landscape and mountains
主要由水冰构成 are made mainly of water ice.
土卫六的温度为零下二百度左右 At hundreds of degrees below zero,
水不可能以液态存在 Titan is far too cold for water to ever be liquid.
卡尔·萨根之后的天体生物学家都想知道 Astrobiologists since Carl Sagan have wondered
土卫六充满碳氢化合物的湖泊中有无生命 if life might swim in Titan's hydrocarbon lakes.
这种生命的化学基础 The chemical basis for such life
一定会颠覆我们已有的认知 would have to be entirely different from anything we know.
地球上所有生命都依赖于液态水 All life on Earth depends on liquid water.
而土卫六的表面不满足这个条件 And Titan's surface has none of that.
但我们可以想象其他类型的生命 But we can imagine other kinds of life.
它们可能吸入氮气 There might be creatures that inhale hydrogen
而非氧气 instead of oxygen.
呼出甲烷 而非二氧化碳 And exhale methane instead of carbon dioxide.
用乙炔代替糖类作为能量来源 They might use acetylene instead of sugar as an energy source.
我们如何得知在黑色波浪下 How could we find out if such creatures
是否有生命统治这个隐秘的帝国呢 rule a hidden empire beneath the oil-dark waves?
我们潜入克拉肯海的深处 We're diving down deep into the Kraken Sea,
它是以神话中的挪威海怪命名的 named for the mythic Norse sea monster.
即便里面真的有海怪 Even if there is one of those down there,
我们也八成看不到 we probably couldn't see it.
太暗了 It's so dark.
地球上所有石油和天然气加起来 If you took all the oil and natural gas on Earth,
也只是土卫六油气储备的一小部分 it would amount to but a tiny fraction of Titan's reserves.
让我们开几盏灯 Let's turn on some lights.
此刻我们处于两百米深 We're now 200 meters beneath the surface.
你看到什么东西了吗 Did you see something?
在那边 喷发口旁边 Over there, by that vent.
可能是我自己想象的 Maybe it was just my imagination.
如果想确切查证 I guess we'll have to come back
我们得改日再来 if we want to find out for sure.
我还想再讲最后一个故事 There's one last story I want to tell you.
科学史上最伟大的故事 And it's the greatest story science has ever told.
这是关于地球上生命的故事 It's the story of life on our world.
欢迎来到四十亿年前的地球 Welcome to the Earth of four billion years ago.
这是生命诞生前的地球 This was our planet before life.
没人知道生命是如何诞生的 Nobody knows how life got started.
那个时代留下的线索 Most of the evidence from that time
大多已被撞击和侵蚀销毁 was destroyed by impact and erosion.
科学在知识与无知的边界探索 Science works on the frontier between knowledge and ignorance.
我们不怕承认自己不知道 We're not afraid to admit what we don't know.
不必对此感到羞愧 There's no shame in that.
假装掌握一切答案才是唯一的羞愧 The only shame is to pretend that we have all the answers.
或许此片的某位观众 Maybe someone watching this
会是第一个破解 will be the first to solve the mystery
地球生命诞生之谜的人 of how life on Earth began.
通过研究微生物我们得知 The evidence from living microbes
它们最早的祖先 suggest that their earliest ancestors
偏爱高温环境 preferred high temperatures.
地球上最早的生命可能起源于 Life on Earth may have arisen in hot water
海底火山口附近的热水 around submerged volcanic vents.
在卡尔·萨根的原版《宇宙》系列中 In Carl Sagan's original Cosmos series,
他描绘了一条完整的时间线 he traced the unbroken thread that stretches
从将近四十亿年前的 directly from the one-celled organisms
单细胞生物开始 of nearly four billion years ago...
一直到你 to you.
将四十亿年用四十秒呈现 Four billion years in 40 seconds.
从尚分不清昼夜的生物 From creatures who had yet to discern day from night
到探索宇宙的生物 to beings who are exploring the cosmos.
这就是被给予了四十亿年进化时间后 Those are some of the things that molecules do
分子所做到的一些事 given four billion years of evolution.