The title of this video does not make sense.
这段视频的标题不合情理
There are no single-celled dogs.
没有所谓的单细胞狗
Dogs aren’t just multi-cellular,
狗不仅是多细胞生物
they’re vertebrates,
还是脊椎动物
mammals even.
甚至是哺乳动物
A single celled organism is by definition not a dog.
根据定义 单细胞生物不会是狗
And yet…and yet,
然而……然而
between six and eleven thousand years ago, there was a dog,
距今六千至一万一千年间 有一只狗
I do not know the dog’s name, I do not even know if it was male or female,
虽然我不知道它的名字 甚至不知道它的性别
but we do know quite a bit about it.
但我们的确对它有很多了解
It was black or brown with more than a bit of coyote ancestry,
它是黑色或棕色的 有相当多狼的血统
and it came from an inbred population,
它是近亲繁殖的产物
and also, we know it had cancer.
我们还知道它患有癌症
And to understand what happened next,
要理解接下来发生了什么
and how truly bizarre it is,
并且真的多么不同寻常
you have to understand what cancer actually is.
你得理解癌症到底是什么
And I know what you’re saying,
我知道你会说
“Hank, I know what cancer is.”
“Hank 我知道癌症是什么”
And maybe you think you do,
也许你以为自己知道
you think that cancer is a disease caused by an organism’s cells,
你认为癌症是一种由生物细胞引发的疾病
malfunctioning and reproducing uncontrollably,
这些生物细胞功能失常 无限增殖
and moving to different parts of that organism’s body.
且能转移到身体的不同部位
And that is true, but also, it’s kind of not true.
这是对的 但也不太对
The question is: are the cells malfunctioning, or are they succeeding?
问题是：这些细胞是功能失常还是大获全胜？
And to answer that question, you have to ask another one:
要回答这个问题 你得问另一个问题：
why do malfunctioning cells so often reproduce uncontrollably?!
为什么失常的细胞会如此频繁地无限增殖？
Now it’s convenient to talk about evolution in terms of what it “wants,”
从“需求”的角度来谈论进化很省事
but evolution doesn’t “want” anything.
但进化并不“需要”任何东西
One school of thought proposes that
某学派认为
natural selection is simply
自然选择不过就是
successful traits and their associated genes,
一些生物特性极其相关基因
succeeding and being passed onto future generations.
成功地传承给了后代
And nearly every cell in a dog is trying to help the dog survive,
狗体内几乎每个细胞都在设法帮它活下去
this is what evolution is selecting for at the scale of the dog.
就狗的层面而言 这就是进化选择的目标
Cells work together to keep the animal functioning,
细胞协同工作以维持动物的功能
so that the genetic material can persist in the current dog,
以便遗传物质能在这只狗身上得以维系
but, more than that, in the offspring of the dog.
更重要的是 在它的后代身上延续下去
But sexual reproduction isn’t the only kind of reproduction.
然而有性繁殖并不是唯一的繁殖方式
Single celled organisms often reproduce asexually,
单细胞生物常常采用无性繁殖的方式
and natural selection nontheless still results in evolution in those species,
但自然选择仍会导致这些物种的进化
just more slowly.
只是更慢而已
And we can imagine that, inside of a dog,
我们能想像 在狗体内
natural selection isn’t just selecting on the scale of the dog,
自然选择不仅在狗的层面进行
it is also selecting on the scale of the cell.
也在细胞的层面进行
Natural selection is not a complicated idea.
自然选择并非一个复杂的概念
If something can make more of itself, then there will be more of it.
若某样东西能变得更多 它就会变得更多
If a rat has a gene that allows it to have 1000 babies,
若某只老鼠拥有能生一千个孩子的基因
then that gene will spread throughout the rat population pretty dang fast.
那么该基因就会在老鼠的种群中飞速传播
But if a cell inside an organism has a gene
而若是生物体内的某个细胞拥有某个基因
that allows it to have a hundred thousand or a hundred million copies of itself,
能自我复制出十万或一亿个
that gene will also spread
除非有什么阻止它
through the organism very very rapidly unless something stops it.
否则这个基因也会在该生物中飞速传播
And, when that happens,
当这种情况发生时
when individual cells inside an organism
当生物体内的单个细胞
evolve ways to replicate themselves unchecked,
进化出不受约束的自我复制方式时
we call that cancer.
我们称其为癌症
One way of thinking about cancer is
对癌症的一种看法是
that it is simply the result of evolution acting on the cells of a multi-cellular organism
它是进化作用于多细胞生物体内细胞的结果
rather than the organism itself.
而非进化作用于生物本身的结果
And this is kind of a hot take,
这是个有点热门的观点
but it’s one that makes sense according to what we know.
而据我们所知 这个观点也说的通
Cancer cells are evolutionarily successful,
癌细胞在进化上是成功的
not for the organism, of course, but for the cell.
当然 不是对生物而是对细胞而言
Seen through this lens,
从这个角度看
cancer is not an organism’s cells malfunctioning,
癌症并非生物细胞的功能失常
it is kind of a return to a single celled lifestyle.
而有点像是回归到单细胞的生存方式
A step, at least.
至少是回归了一步
They still require you as a host organism,
它们仍需要你作为宿主
and since they usually hurt the host you in the process,
因为在此过程中它们经常会伤害你这个宿主
it’s not a great step.
所以这一步并不妙
Still, your cells have become more like a pathogen.
不过 你的细胞已变得更像一种病原体
They have human DNA,
它们拥有人类的DNA
but they have started living for themselves instead of for you,
但它们开始为自己而不是为你而活
metabolizing, replicating, and evolving.
自我代谢 复制和进化
So one way to look at cancer is that
因此有一种看待癌症的观点是
it is a single-celled organism with a multi-cellular organism’s DNA.
它是一种拥有多细胞生物DNA的单细胞生物
Now evolutionary pressure on the organism level encourages lots of systems
生物层面的进化压力激发很多机体系统
for preventing individual cells from growing unchecked,
阻止单个细胞不受约束地生长
because when that happens,
因为这种情况一旦发生
the organism can no longer pass on its genes because of how it is dead.
生物死亡了 就再也不能传递其基因
But evolution at the level of the cell is hard to overcome.
但细胞层面的进化难以战胜
Natural selection is always selecting, genes are always mutating.
自然选择一直在进行 基因一直在变异
It only takes one cell being really good at evading the immune system
只要有一个细胞擅于免疫逃逸
and selfishly replicating itself perpetually
自私地不停自我复制
for the whole organism to crash.
整个生物就会崩溃
Great, Hank, thanks! Wonderful!
很好 Hank 谢谢！太精彩了！
That’s all very terrifying and upsetting.
这一切都太可怕了 让人不安
Cancer is the most natural thing ever,
癌症从来都是最自然不过的事
and despite the fact that our bodies have evolved
尽管我们的身体已进化出
a tremendous arsenal of tools to prevent it from killing us,
大量阻止癌症杀死我们的武器
it nonetheless remains an extremely common cause of death.
但它仍是一种极其常见的死因
But, for the most part, all of this is just semantic line shifting.
而多数情况下 所有这些都只是文字游戏
Is cancer a kind of single-celled organism?
癌症是一种单细胞生物吗？
Is a hot dog a sandwich?
热狗是三明治吗？
It doesn’t really matter.
这并不重要
It’s a deadly disease
它是一种致死的疾病
and it’s not like it’s going to jump off of the sick person and go live on its own.
癌细胞不可能脱离病体独自存活
Unless it does exactly that.
除非它确实能这样做
Remember that dog that died thousands of years ago?
还记得那只几千年前死去的狗吗？
Well, before it died, its cancer managed to spread to at least one other dog,
在它死前 成功地将癌症传给了至少另一只狗
potentially through sexual contact.
有可能是通过性行为传播的
These cancerous cells were now a contagious pathogen,
这些癌细胞此时成了传染性病原体
that for thousands of years, have been successfully living the single-celled lifestyle.
数千年来 它们一直成功地以单细胞的形式存活了下来
This disease is called Canine Transmissible Venereal Tumor or CTVT.
这种疾病被称为犬传染性性病肿瘤 简称为CTVT
And you really cannot say
你的确无法断言
that the cells that cause it aren’t alive.
引起这种疾病的细胞不是生命体
Because they grow, they reproduce, they metabolize, and they evolve.
因为它们在生长 增殖 代谢和进化
A dog with CTVT does not have a cancer made of its own cells,
患有CTVT的狗并非因其自身细胞致癌
it has a disease made of cells that are descended from a dog
而是因为一只早已死了几千年的狗
that has been dead for thousands of years.
因从它身上传下来的细胞而患病
As the authors of a 2014 paper put it,
正如2014年一篇论文的作者所言
“It is remarkable that a somatic genome
引人注目的是 在狗的一生中
whose DNA would normally have survived for no more than 15 years during the life of one dog
一种通常活不了15年的体细胞基因组DNA
has continued to exist for several millennia
以一种寄生体的形式
as a parasitic life form.
持续存在了数千年
CTVT’s survival and global dominance
CTVT留存至今 并分布全球
is a testament to the ability of the mammalian somatic cell genome
证明了 哺乳动物的体细胞基因组
to adapt and persist in a new ecological niche.
能在新生态环境中适应和延续
In other words, this cancer, if you look at it a certain way,
换言之 如果从某种角度看
is a single-celled dog.
这种癌症是一只单细胞的狗
Now the success of CTVT is very weird and unusual.
CTVT的成功是非常怪异且不同寻常的
Cancer cells evolve to succeed inside a very particular environment:
癌细胞的进化成功是在一个非常特殊的环境：
the body they are a part of.
它们作为组成部分的这个身体
And they evolve to evade the immune system of that one organism.
它们靠进化逃避这个生物的免疫系统
That’s why cancer: jumping from one organism to another is extremely rare.
这就是为什么癌症在生物间的传播极其罕见
Now, we’re not entirely sure how CTVT did this,
现在 我们还不能完全确定CTVT是如何做到这一点的
but other transmissible cancers have occurred in species that were in population bottlenecks,
但在种群瓶颈生物中 出现过其他可传播的肿瘤
which just means that their population shrank a lot,
种群瓶颈是指某个种群的数量大幅减少
and the individuals in that group wound up being severely inbred.
其中的个体近亲繁殖的情况很严重
It isn’t difficult to imagine this happening to a population of early dogs.
不难想像 在古代的狗群中 有过这种情况
In a situation like this, CTVT would be able to jump from dog to dog
在这种情况下 CTVT能在狗群中转移
because their low genetic diversity
因为其较低的遗传多样性
might have made it less likely that their immune systems would notice that those cells belonged to somebody else.
使免疫系统 不太可能分辨出这些细胞属于别的狗
Given the new evolutionary pressure not just to grow in one organism,
鉴于新的进化压力 CTVT不仅要在一种生物中生长
but to be transmissible and survive in other organisms,
更要在别的生物中传播和生存
CTVT continued to evolve,
CTVT在不断进化
and it can now infect not just most dogs,
如今它不仅能感染绝大多数的狗
but also related animals like jackals and coyotes!
还能感染它的近亲 如豺狼和丛林狼！
The fact that there is a line of pathogenic cells, reproducing asexually,
一系列无性繁殖的病原细胞
descended from an ancient dog that has persisted for millenia
从一只古老的狗身上传下来 存续了数千年
is one of the weirdest things that I have ever found out about biology,
这是我在生物学上发现的最奇怪的事情之一
and it only makes sense to me
在我看来
if you view cancer not as a malfunction,
癌症不是功能失常
but as a kind of terrible evolutionary success.
而是了不得的进化成功 这才说得通
Cancer through this lense, is a kind of biological inevitability
从这个角度看 癌症是一种生物必然性
and so we need to see it as a thing
因此我们要把癌症看作是
that our bodies have developed systems to control
身体已发展出一些机制能加以控制的疾病
and that we can help our bodies control.
并且我们也能协助身体来控制这种疾病
Evolution allows these selfish cells to evade both our bodies systems for destroying them,
进化让这些自私的细胞 躲过了能摧毁它们的身体机制
and our technologies for destroying them.
躲过了能摧毁它们的技术
We are in a race,
我们与疾病赛跑
but it is one that we are winning more now than we ever have before.
但在当今 我们距离成功 比以往任何时候都近
And if you want to learn more about this,
如果你想了解更多
let me suggest “The Cheating Cell” a fantastic book,
我推荐一本很棒的书《欺骗的细胞》
which is how I found out about this single celled dog,
从书中我发现了这只单细胞狗
at once the smallest, and the oldest dog on Earth.
同时是地球上最小的也是最古老的狗
And if you wanna learn more about how you can help SciShow continue
如果你想了解如何帮助《科学秀》
making free science content for everyone,
继续为大家呈现免费的科普内容
let me also suggest patreon.com/scishow,
我推荐你关注patreon.com/scishow
where you can learn more about becoming a SciShow patron,
在这你能了解更多成为《科学秀》赞助者的信息
and all of the cool perks that go along with that.
和随之而来的所有酷炫福利