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病毒从哪里来?

Where Did Viruses Come From?

Thanks to Curiosity Stream
感谢Curiosity Stream
for supporting PBS digital studio
向PBS数码工作室提供的支持
The Earth never shook beneath their feet.
它们的脚步从未撼动过地球
We never find their remains in the rocks.
我们从未在化石中找到过它们的遗骸
And by some standards, they’re not even alive.
按某种标准 他们甚至都不是生命
They’re just bits of protein and genetic information
他们仅由蛋白质和基因信息组成
that might give you a sniffle for a couple of days
这些组分可能会让你感冒多天
Or worse.
或病得更严重
But they’re also proof that even the very smallest things
但他们也证实了 即便是最微小的事物
can have an outsize impact on the history of life.
也能极大影响生命的历史
I’m talking, of course, about those tiny genetic burglars
我说的是那些微小的基因窃贼
that you all have been asking about for so long -viruses.
即病毒 你们一直在问关于这些窃贼的事
There’s no fossil record of viruses in the conventional sense.
传统意义上的病毒化石记录并不存在
They’re just too small and fragile to be preserved in rock.
病毒太小又太脆弱 因而很难保存在岩石中
But there are fossils of viruses, of sorts,
但是 某种意义上的病毒化石
preserved in the DNA of the hosts that they’ve infected.
保存在被病毒感染的宿主的DNA里
Including you.
你也是宿主之一
And, yeah, I mean, me too.
我是说 某种程度上
To some extent I guess.
我同样也是宿主
But this molecular fossil trail, can help us understand
这种分子化石踪迹能帮助我们了解
where viruses came from, and how they evolved with the rest of us.
病毒的来源及它们是如何和其他物种一起进化的
And it can even help us tackle the biggest question of all:
它甚至可以帮我们解决最重要的问题:
Are viruses alive?
病毒是有生命的吗?
亿万年
The key to the viruses’ success is their simplicity.
病毒成功的关键在于它们简单的结构
In general, they consist of a bit of genetic information
它们通常由一些基因信息
either DNA or RNA, wrapped in the capsule of protein.
即包裹着蛋白质外壳的DNA或RNA组成
Many are small, of course, of the order of tens of nanometers,
当然 很多病毒都很小 大小约几十纳米
while others are surprisingly big.
有些病毒却大得惊人
But they all rely on infecting some sort of host to reproduce and survive.
但他们都靠感染某些宿主来繁殖和生存
We think that viruses have been around as long as life itself,
我们认为病毒自生命产生以来就一直存在的部分原因
partly because they can infect all forms of life:
是它们可以感染各种形态的生命:
bacteria, archaea, and eukaryotes.
细菌 古生菌以及真核生物
And because they’re so simple, some scientists think that
它们的简单结构使得一些科学家认为
they evolved alongside,
它们和早期细胞共同进化
or even before the earliest cells.
甚至先于早期细胞产生
But without real fossils,
没有真正的病毒化石
how can we know the history of virus?
我们怎样才能了解病毒的历史?
Enter the science of paleovirology.
进入古病毒学领域
This is a young field within paleontology,
这是古生物学中的一个新领域
because it’s built on another emerging field:
因为它们建立在另一个新兴领域
genomics.
——基因组学之上
In order to look for traces of ancient viruses,
为寻找古代病毒的踪迹
experts have to study the genomes of their hosts.
专家们必须研究宿主的基因组
It makes sense when you think about how viruses actually work.
这是了解病毒实际运作方法的有效方法
Viruses have to infect a host cell
病毒必须感染一个宿主细胞
to access the machinery that it uses to replicate its DNA,
来启动它用来复制自身DNA的机制
and then hijack that machinery in order to reproduce.
然后挟持该机制 用以繁殖
Which is, like, when I say it out loud such a scumbag move.
我认为这分明就是种卑鄙无耻的行径
The host cell is forced to manufacture new viruses,
宿主细胞被迫产生新病毒
which then leave and look for new hosts to infect.
它们离开原来宿主去寻找并感染新的宿主
Except…the virus and the host don’t always part ways entirely.
除非 病毒和宿主并未完全分离
Sometimes, the genome of the virus
有时候 病毒的基因组
can become integrated into the DNA of the host.
可能会融入宿主的DNA
And as long as it doesn’t cause a mutation that damages the host cell,
只要这些信息未导致损害宿主细胞的变异产生
that bit of viral information may stay there indefinitely.
这些病毒信息可能会永久保存在此
And, if this happens in a cell that forms sperm or eggs,
如果这种融入发生在精原或卵原细胞内
then the viral genome can actually be inherited,
那么这种病毒基因实际上会遗传下去
passed on to the host’s offspring with the rest of its genome.
和宿主的其他基因一起传给下一代
So in this way, the viral genome becomes a sort of molecular fossil.
因此 病毒基因是某种意义上的分子化石
And those ancient bits of viral information can also shed light on how old viruses are.
这些古代病毒信息也能透露病毒的年龄
That’s because, ordinarily, viruses change really quickly.
原因在于病毒的变异通常十分迅速
That’s why you have to get a new flu shot every year.
这也是你每年要注射新的流感疫苗的原因
A virus mutates so fast that,
病毒的变异是如此之快
after only a few hundred years, not much of the original genome may be left.
以至于仅仅数百年后原始基因就所剩无几了
However, if that DNA is integrated into its host,
然而 如果病毒DNA和宿主DNA融为一体
then it can only mutate as fast as the host does.
它便只能以宿主变异的速度进行变异
And since hosts reproduce more slowly than viruses,
宿主的繁殖速度低于病毒 因而
their mutation rate is slower too.
它们的突变率同样更慢
All this means that the viral gene will be preserved,
这一切意味着病毒基因会保存下来
though not perfectly.
尽管不是十分完整
for way, way longer than a virus that’s just floating around out there on its own
这样一来这些基因的存在时间远长于独立存在的病毒
Now, scientists can use this to help figure out the age of virus fossils.
现在 科学家们可借此推算出病毒化石的年代
And they do it the same way they study the evolution of other genes:
他们以研究其他物种基因进化的方法
by lining up comparable sequences from different organisms, and comparing them.
即排列和对比不同生物体的相似序列来计算
If a sequence of viral DNA is found in two different animals,
如果在两种动物体内发现同一段病毒DNA序列
then they probably both got it from a common ancestor.
那么这一序列可能是由同一祖先遗传给它们的
And that means the virus has to be at least as old as that ancestor.
这意味着该病毒起码跟这一祖先同样古老
So, for example, circoviruses are a group of viruses
例如 圆环病毒是一类病毒
that are known to cause stomach problems in dogs.
已知它们会引起狗的胃部不适
And scientists once thought that
科学家们曾认为
circoviruses had been around for less than 500 years.
圆环病毒存在年数不到500年
But traces of these viruses have been found in
但此类病毒的踪迹
the genomes of dogs, and also cats, and even pandas.
在狗 猫 甚至熊猫的基因中均有发现
So the viruses must date back to
所以这种病毒定能追溯到
before those mammals last shared a common ancestor,
这些哺乳动物最早的共同祖先之前
which might be as much as 68 million years ago
即约6800万年前的
in the late Cretaceous Period.
白垩纪晚期之前
So, what’s the oldest evidence of viruses?
病毒存在的最古老证据是什么?
Well, one study in 2011 looked at the history of bracoviruses,
2011年有一项针对茧蜂病毒历史的研究
which specifically infect wasps.
这种病毒专门感染黄蜂
And it found evidence to suggest that
该研究找到了支持以下观点的证据:
the group these viruses belong to,
这些病毒所属的族群
could be as old as the insects themselves,
可能和昆虫这一物种一样古老
dating back to the Carboniferous Period,
时间追溯至31亿年前的
310 million years ago.
石炭纪时期
But other research has brought the history of viruses even closer to home.
而其他研究进一步推进了病毒历史的研究
Research in 2009 dated a gene found in mammals, called CGIN1,
2009年一项关于哺乳动物体内CGIN1基因的研究
to the early days of mammal evolution,
将该基因追溯至1.25亿到1.8亿年前
between 125 and 180 million years ago.
这段时间属于哺乳动物进化早期
And that gene is thought to have originally come from a virus,
人们认为 此基因源自一种病毒
because parts of it resemble a type of RNA virus
因为它的某些部分与一种RNA病毒
called a retrovirus.
即逆转录病毒相类似
And guess what. You’re a mammal!
想想 你也是一个哺乳动物!
So, some retrovirus infected
数百万年前 某些逆转录病毒
a sperm or egg cell in one of our mammal ancestors millions of years ago,
感染了我们哺乳动物祖先的一个精子或卵子
and now a gene derived from it is in you.
你体内某个基因正好源自于它
And again, yeah probably me too
当然 我体内很可能也有
Scientists don’t think this gene has much of a function,
科学家认为这个基因不起太大作用
but they do think it’s just one of many examples of
但他们确实认为 这是那些能说明
how viruses have left their mark on our own DNA.
病毒如何对我们DNA产生影响的例子之一
In fact, it’s been estimated that 8 percent of the human genome
实际上 据估算8%的人类基因中
includes sequences that originally came from viruses.
含有最初来源于病毒的序列组
So paleovirology has helped us date the evolution of virus
古病毒学帮助我们将病毒的进化史
back hundreds of millions of years.
追溯到了数亿年前
But that doesn’t bring us much closer to when we think viruses first originated,
但这无法让我们与病毒起源的时间(数十亿年前)
billions of years ago.
更为接近
Now, there are a few different models for where viruses came from,
当前 有一些探究病毒来源的不同模型
and they’re still hotly debated by scientists.
科学家们激烈地讨论着它们
So, just be prepared if you pick a side,
你在支持某个模型前要做好准备
One model is known as the virus-first model,
一个模型叫“病毒优先模型”
and it holds that,
该模型提出
since viruses are so much simpler than cellular life,
由于病毒比细胞生命体简单太多
they must have evolved first.
他们必须早早地进化
This would mean that viruses are older than the oldest single-celled organisms.
这意味着病毒先于最古老的单细胞生物产生
They’d be relics of a time when all life was made up of
它们是这样一个时代的遗物:
simple, self-replicating units, probably made of RNA,
所有生命体由简单自我复制单元(可能由RNA组成) 构成
which preyed on more complex life forms as they evolved.
它们在进化过程中捕食更复杂的生命体
But there’s also what’s known as the escape hypothesis.
但也有一个模型叫“脱离假说”
This model suggests that viruses evolved after cells did,
此模型提出 病毒自身基因的进化
from within their own genes.
要晚于细胞基因进行
See, our genomes contain pieces that can actually copy and paste themselves
其实 我们基因组的某一部分可以自我复制
from one part of our DNA to another.
并粘贴至DNA的另一部分
So, some experts think
因此 一些专家认为
that if one of those pieces became able to make itself a nice coat of protein,
如果其中一个部分能为自己裹上美妙的蛋白质外衣
it could easily escape the cell and become a virus.
它便很容易脱离细胞成为一个病毒
The third model hinges on the discovery of so-called giant viruses.
第三种模型的提出得益于巨型病毒的发现
The first one, discovered in 2003, was named Mimivirus
发现于2003年的第一个巨型病毒被命名为米米病毒
— short for mimicking microbe.
——模拟微生物的简称
And these things are huge by virus standards, around 750 nanometers across.
它们宽约750纳米 远超病毒标准大小
That’s bigger than some bacteria.
这比一些细菌还大
Now fortunately, they only infect amoebas,
幸运的是 他们只感染单细胞生物
so you don’t have to worry about them. At least yet.
所以你无须担心他们 至少现在不必
Now, Mimiviruses have way more genes than normal viruses do,
如今 米米病毒比普通病毒拥有更多的基因
including some genes that can be used to make protein
包括那些可以用来生成蛋白质的基因
which viruses are not supposed to be able to do.
普通病毒则不可能拥有这些基因
But Mimiviruses still depend on their hosts to reproduce,
但米米病毒的繁殖仍依赖于宿主
so what are all those genes doing in there?
那么这些基因在这儿做些什么呢?
Some scientists think those genes are leftovers from a time
一些科学家认为这些基因是一些病毒
when some groups of viruses were bigger, more complex, and more like cellular life.
处于更大 更复杂 更接近细胞生命体时期的残留物
This model suggests that viruses were once free-living
该模型指出 病毒曾独立生活
and then developed a symbiotic relationship with another organism.
后来与另一种生物构建起共生关系
And then over time that relationship became parasitic.
渐渐地 共生关系变成了寄生关系
Which sometimes happens
这种情况时有发生
The more dependent they became on their hosts to replicate,
繁殖时 病毒越依赖它们的宿主
the more complexity the viruses lost.
病毒的结构就越复杂
Or at least, so the thinking goes.
至少 此模型是这么说的
But recent research has cast doubt on this idea, known as the regressive model,
但最近的研究向所谓的“回归模型” 提出质疑
at least where Mimivirus is concerned.
至少是向有关米米病毒的部分
Some scientists argue that the extra genes in Mimivirus are just random leftovers that
一些科学家提出 米米病毒中的多余基因
it picked up from its hosts over the eons.
只是远古以来宿主的随机遗留物
Now, these different models all put different spins on the big question:
这些模型对这个关键问题提出了不同看法:
Are viruses alive?
病毒具有生命吗?
Now I said at the beginning
正如我刚开始说的
that paleovirology can help us tackle this question.
古病毒学能帮助我们解决这个问题
And it can.
它确实能
But the answer depends a lot on who you ask.
但答案很大程度上依赖于你问是的谁
Many scientists are content to just put viruses in a sort of gray area of semi-living things.
许多科学家情愿将病毒放入某种半生物灰色领域
But others are determined to figure out
其他科学家则决心去研究
whether they have a place on the tree of life.
生命树上是否有它们的位置
And if so, where?
如果有 在哪?
To answer the question of whether viruses are alive,
为了回答病毒是否有生命的问题
we need to agree on a definition of life.
我们需要在生命的定义上达成一致
It’s generally agreed that life can reproduce,
我们普遍认为生命体可以自我繁殖
make energy for itself, maintain a stable environment within its cells,
给自己提供能量 维持细胞内的稳定环境
and can evolve, among other things
还可以进化 等等
Viruses can reproduce, but not on their own.
病毒虽繁殖 但不能独立完成繁殖
And we’ve already talked about how viruses can evolve.
我们已讨论过病毒如何进化的问题
But they have no way to produce energy.
但是它们无法产生能量
And they can’t control their internal environment.
无法控制自身的内部环境
And that’s why they occupy such a gray area,
这是他们被放在灰色区域的原因
because the answer to some questions is yes,
因为有些问题的答案是肯定的
and others no.
有些则不是
It has been suggested that, while viruses don’t occupy their own branch of the tree of life,
有人提出 尽管生命树上没有病毒的分支
they might be thought of as vines that wrap around it
但病毒可被视作在生命树周围缠绕的藤蔓
Which is an elegant image.
真是一幅美丽的图景
If also maybe a little creepy one
或许还有点吓人
But either way, viruses are here.
但是无论哪种方法 病毒都在
They’re in our DNA.
他们在我们的DNA中
They make us sick, sometimes very badly.
他们让我们生病 有时还十分严重
So there’s no denying that
无可否认的是
they have a place in the greater picture of what life on Earth is like.
病毒在地球宏大的生命图景中拥有一席之地
For good or for ill.
无论有利还是有害
Thanks for joining me today,
感谢您收看我们的栏目
and you’re welcome for not making a joke about going viral or whatever.
也希望您不要开有关病毒传播之类的玩笑
And thanks also to Curiosity Stream for continuing to support PBS Digital Studios.
感谢Curiosity Stream对PBS数字工作室的不断支持
With Curiosity Stream you can stream documentary films,
您可以在Curiosity Stream上浏览纪录片
and programs about science, nature, and history,
以及有关科学 自然和历史的节目
including Curiosity Stream originals!
还有Curiosity Stream的原创剧集
One show you might like:
您可能会喜欢这个节目:
Rapidly Evolving Human,
“快速进化的人类”
which explores how changes to our genetic code have made us who we are today,
该节目探索人类基因密码如何改变 从而变成现在的我们
and why we continue to evolve.
以及我们为什么持续进化
You can learn more at curiositystream.com/eons,
您可以在curiositystream.com/eons网站上了解更多信息
and when you sign up, use the code:EONS.
注册时请使用这个密码:EONS
Now, what do you want to learn about?
现在 你们想了解什么?
And you know we read these comments.
我们会读这些评论
because that’s where this episode came from.
因为这正是本视频的灵感来源
So leave a comment below,
请在下方留下你们的评论
and if you haven’t already, go to youtube.com/eons and subscribe.
如果您还没有关注我们 请前往youtube.com/eons并订阅吧

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视频概述

病毒的来源,病毒的发展历史,病毒来源的三种假说

听录译者

收集自网络

翻译译者

Clio

审核员

审核员SR

视频来源

https://www.youtube.com/watch?v=X31g5TB-MRo

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