外星人长啥模样？来谈谈进化论给我们的洞见 [英国媒体]

Aliens could be everywhere. There are at least 100bn planets in our galaxy alone, and at least 20% of them could be habitable. Even if a tiny fraction of those planets – less than 1% of 1% – evolved life, there would still be tens of thousands of planets with aliens in our vicinity. But if we want to figure out where to start looking for these neighbours, we need to understand what they might be like and where they might thrive.

很有可能哪儿都有外星人的存在。仅仅我们一个银河系，就有至少1000亿颗行星，并且它们中至少有20%是宜居的。哪怕那些行星中少于万分之一的极少部分存在生命，在我们附近就仍会有成千上万个行星上存在外星生命。但如果我们想弄明白要从哪里开始寻找这些邻居们，我们就需要明白它们是什么样子的，以及它们可能会在哪里繁衍兴盛。

Ultimately, we want to understand as much as possible about an extraterrestrial species before we encounter it. Yet making predictions about aliens is hard because we have only one example – life on Earth – to extrapolate from. Just because eyes and limbs have evolved many times on Earth doesn’t mean they will appear even once elsewhere. Just because we are made of carbon and coded by DNA doesn’t mean aliens will be – they could be silicon based and coded by “XNA”.

我们终究还是想在不期而遇前尽可能多地了解天外物种。但是对外星生命做出预测是很难的，因为我们手头只有地球生命这一个例子可以用来推断。就因为眼睛和四肢在地球上演化出了很多次，并不意味着它们就会出现在别处哪怕一次。就因为我们是碳基的并由脱氧核糖核酸（DNA）编码,并不意味着外星生命也是如此，可能它们是硅基的并且由“XNA”编码。

However, as my colleagues and I argue in our new study, published in the International Journal of Astrobiology, there is another approach to making predictions about aliens that gets around this problem: using evolutionary theory as a guiding principle. The theory of natural selection allows us to make predictions that don’t depend on the details of Earth and will hold even for eyeless, nitrogen-breathing aliens.

然而，正如我和同事们发表于国际天体生物学期刊的新研究中主张的那样，为解开这个问题存在着另一种对外星生命作出预测的方法：
以进化论作为指导原则。自然选择理论允许我们不依赖地球上的案例来做出预测，甚至对那些无眼、呼吸氮气的外星生命也能成立。

Darwin formulated his theory of natural selection long before we knew what DNA was, how mutations appeared, or even how traits were passed on. It is remarkably simple and requires just a few ingredients to work: variation (some giraffes have longer necks than others), heritability of that variation (long-necked giraffes have long-necked babies) and differential success linked to the variation (long-necked giraffes eat more leaves and have more babies).

远在我们知道DNA是什么东西、基因突变如何产生甚至性状如何传代之前，达尔文就推演出了他的自然选择理论。这套理论非常得简洁，只需要一些构成要素就能成立：变异（一部分长颈鹿比其他个体拥有更长的脖子）、变异的遗传力（脖子更长的长颈鹿会生出脖子长的幼崽）以及变异带来的差异化成功（脖子更长的长颈鹿能吃到更多树叶进而能够繁衍出更多幼崽）。

In our paper, we use evolutionary theory to make a number of predictions about aliens. We argue that aliens will undergo natural selection. This is something often taken for granted or assumed to be an unknown. We show that there are firm theoretical grounds for believing that aliens will undergo (or have undergone) natural selection.

在我们的论文中，我们运用进化论作出了一系列关于外星生命的预测。我们主张外星生命将会经历（或已经历过）自然选择。



This is because “apparent design” is what sets life apart from non-life – such as a single-celled organism from inert rocks. Living things have many intricate parts that are fine-tuned for the common purpose of replicating the organism. The only way to achieve this apparent design, or adaptedness, the only way to get life, is through natural selection.

这是因为系“显见的设计”让生命出脱于非生命，如同一个单细胞微生物出脱于不活泼的石块。生物拥有许多旨在复制机体而被妥善调制的复杂部件。唯一能够达到这种显见设计、完成自适应、得到生命的途径就是通过自然选择。

So, as aliens are highly likely to undergo natural selection, we can make some predictions about what they will be like. In particular, our predictions are about complex aliens. By complexity we mean anything more complex than, say, a virus.

所以，因为外星生命极有可能经历自然选择过程，关于它们长成什么样子我们能够做出一些预测了。我们的预测特别针对外星复杂生命，谈到复杂我们指的是，比如，任何比病毒复杂的生命。

Even a bacterial cell has intricate parts that work together to achieve goals, like moving and eating. In other words, most aliens we would be interested in finding, or be able to find, are complex. That’s because the only things so simple that they could have arisen without natural selection would be molecules, which are physically hard to detect or to distinguish from the background of inert molecules. They would also be transient: without natural selection making them fitter they would disappear. Even if we did find them, we probably wouldn’t even classify them as life.

哪怕是一个细菌细胞都拥有能够互相协同达成目的的复杂部件，比如运动和进食。换句话说，大多数我们有兴趣找或者说有能力找到的外星生命，实是复杂生命。那是因为，唯一的简单到无需经历自然选择就能出现的东西是分子，而这些分子在物理上要么难以被探测到，要么在惰性分子组成的背景中难以被辨别出来。它们的存在也可以是极其短暂的：没有自然选择来保证它们发挥效用它们就会消失。哪怕我们确实发现了它们，我们甚至很可能无法将其归类为生命。

Complexity on Earth has arisen through a handful of “major transitions in individuality”. These occur when independent organisms come together to form a new type of individual. On Earth, genes came together to form genomes, single-celled organisms formed multicellular organisms, like us. In some rare cases, multicellular organisms, like insects, have formed societies that act as “super organisms”. These events are rare, and require extreme evolutionary conditions.

地球上的复杂生命是经由“个体的重大异变进程”一手出现的。当独立的有机体聚合并化生出一个新品种的个体时，复杂生命就出现了。地球上的基因经由聚合形成基因组，单细胞有机物组成像我们人类一样的多细胞有机物。而在一些罕见的案例中，如昆虫的多细胞有机物组成社群，如同“超级有机物”那样运作。这种情况非常少见，它需要极端的演化环境（来促成）。

We argue that complex aliens will have undergone major transitions too, as this is probably the only way to advance beyond a simple replicating molecule. The conditions for major transitions to occur are rare, and are quite well understood from an evolutionary perspective, allowing us to say something about the makeup of aliens.

我们主张外星复杂生命也将会经历重大异变，因为这很可能是唯一一种途径，来超越单纯的分子自我复制。能催生重大异变发生的环境是非常少见的，以演化的观点来考察它们就能够透彻理解，这也使得我们能够谈论外星生命的组成。


  
In particular, just as you and I are made up of cells, which are made up of nuclei and mitochondria (the breathing engine of the cell), which are made up of genes, aliens will be a similar nested hierarchy of units. Aliens might not be made of cells as we think of them, but they will be made up of parts that were once free living, and those parts will be too – all the way down to aliens’ hereditary material (whatever it is). Our parts have mechanisms in place that keep all the parts working together to make an organism.

尤其是鉴于你和我都是由细胞组成的，细胞由细胞核和线粒体（细胞的呼吸器）组成的，而这二者又由基因组成，因此外星生命也会拥有相似的嵌套化单元。外星生命可能并非如我们所想的由细胞组成，但它们会是由曾经自主生活的部件们组成，而那些部件们也曾经是自主生活的，如此便可以一路下溯到外星生命的遗传物质（无论它们具体是什么）。我们人类的部件拥有恰如其分的机制来保证所有的部件协同工作以组成一个有机体。

For example, our cells start as one single cell (the zygote). This means that all our cells are clones, which is why they cooperate to make us. Aliens will have similar ways of enforcing cooperation between their internal parts at each level of units.

举例来说，我们人的那些细胞是从一个单细胞（受精卵）开始的。这意味着我们所有的细胞都是复制出来的，这也是为什么它们会彼此协作来造就我们。外星生命会拥有相似的途径来加强它们内部部件在同一级上的单元协作。

Aliens might not have two legs, or any legs, but their structure, from an evolutionary standpoint, will be much more familiar than we might think. I don’t mean superficially familiar. They might look wildly different from anything on Earth, but they will be similar on a more fundamental level: their bodies will be constructed in the same way (formerly free-living parts within formerly free-living parts), and they will have undergone a similar evolutionary history (independent organisms cooperating to form new, higher-level organisms).

外星生命可能没有两条腿，或者根本没有腿，但从演化角度考察，它们的结构会比我们想象得还要令人熟悉。我说的并非表面上的熟悉。可能它们看上去会极突兀地不同于任何地球生命，但它们会在更加根本的层面上与地球生命相像，它们的肢体可能由同样的方式构建（由曾自主生活的部件组成的曾自主生活的部件），并且它们将会经历相似的演化史（独立的有机物互相协作来组成新的更高级的有机物）。

There is much more work to be done to understand what aliens might be like and where we might find them. And the tantalising question – Are we alone? – remains unanswered. But, as we have shown, if we are not alone, perhaps we understand more about the makeup of our neighbours than science fiction would have us believe.

为了弄明白外星生命可能长啥样以及能在哪里找到它们，还有更多的工作要做。而摄人心魄的那个问题，“我们是仅存的吗？”，仍旧悬而未决。但如同我们已经展示给各位的，如果我们不是（宇宙间）仅有的存在，也许懂得更多我们这些邻居是由什么组成的，会比科幻小说要更能令我们保有这份相信。

（译者注：本文作者Samuel Levin是牛津大学动物学系的一名PhD candidate）



Robert Fantozzi
I think a more realistic claim is that it was only in the last 4.5B years that earth developed the right environment for homo sapiens. The universe has been going fro around 13B year. The chances of another world where intelligent life might have evolved long before we did is high.

我认为更符合现实的断言是，直到45亿年前地球才发展出适合智人的合适环境，而宇宙已经在那里运转了130亿年。远在我们出现以前另一个拥有智慧生命星球的存在可能性是很高的。

Garry Sharp
The efficient functioning of our universe is better explained by creation.

我们宇宙符合效率要求的功能性运转，要比什么神创论靠谱得多了。

Geoffrey Watson
Of course they “could be silicon based” - except that being carbon based is one of the few things that we do know about possibel alien life. Using facts (mechanistic methods) rather than theory, chemists (they only have 92 elements to work through, not millions of planets) have determined that silicon just won’t work as a basis for any complex life form.
Reduced to a take-home message, the one important point of this article is that any alien more complex than an amoeba is likely to multicellular.

当然它们可以是硅基的，只是碳基才是我们仅有且确切知道的潜在外星生命的存在方式。拿事实（机械方法）而不是理论来看，化学家（他们只有92种元素可以用来摸索而不是数百万个行星）已经确认了：对任何复杂生命形式来说，以硅为基根本行不通。
如果把全文拿来提炼启示，全文其中重要的一点是：任何比阿米巴原虫复杂的外星生命很可能是以多细胞形式存在。

Auraboy  Winstons1
No species capable of interplanetary travel would produce anything like Gove. Except maybe as a waste byproduct...

任何能够做到星际旅行的物种都不会制造出像戈夫这样的东西。除非可能是作为下脚料。
（译者注：调侃某英国下议院议员）

Bobjob21  ccwalker 
Hope you never try trading with, or otherwise co-operating with aliens if that is your attitude to our own species, even the closer parts of it with very similar cultures. You would quickly find yourself on the wrong end of their high energy particle beams.

希望你们这些人绝不要去和外星人搞贸易或者搞合作，如果这是你们对我们自己种族所持的态度，哪怕是和那些与我们文化相近的。你会很快发现自己处在它们高能粒子束武器的对敌一端。

Rchrd Hrrcks  Tintenfische 
You're basing an entire universe on the (dubious) record of one species on one planet?

您这是要以一个行星上一个物种无甚把握的记录来作为考察一整个宇宙的基础吗？

bf_silvertown 
I thought all of this was absolutly obvious, but it probably does no harm that an actual scientist says it in his own words. Evolution is such an obvious mechanism at work in every aspect of life that it takes a complete nutter or idiot to even question it as a theory.

我认为所有这些给出的说辞都是非常显见的，不过这可能不会妨碍一个真正的科学家用他自己的言语娓娓道来。进化是如此显见的一个机制，它作用在生命的每个方面，以至于这让一个彻底的疯子或白痴都会去质疑这个理论。

Tintenfische  Rchrd Hrrcks 
Because our big brains were supported by eating meat, cooked meat more specifically. In order to get said meat you need to be able to hunt and that requires a whole lot more brain power than fight or flight and is an inherently violent way to obtain food. The assumption is that like us aliens will have started their evolutionary life as hunters as it seems that hunting is the driving force behind animal intelligence.

因为我们是用吃肉支持着我们硕大的大脑，确切说是熟的肉。为了得到肉你得有能力狩猎，而狩猎需要用到的脑力远远多于打斗或飞翔，这是一种天性中带来的的暴力取得食物的方式。这个假设是，如同我们一样外星人也会作为猎手来开启它们的演化生涯，因为看上去狩猎是动物发展智能背后的驱动力。

MrMouse
One could say that bacteria are the most advanced lifeform if we are to believe endosymbiotic theory. These amazing creatures built a cellular body armour around themselves and set up huge megastructures called humans.

有人会说细菌是最先进的生命形式如果我们打算相信内共生起源理论。这些神奇的生灵给自己造了个细胞做的盔甲然后待在里头，并最终建起了这个叫做人类的巨型建筑。

packick 
"Surest sign that intelligent life exists elsewhere in the universe is that none of it has tried to contact us" Calvin and Hobbes.

“智慧生命在宇宙别处存在最有力的信号就是：它们没有一个试图联系我们。”===Calvin and Hobbes.（译者注：来自漫画《Calvin and Hobbes》的一句自嘲话，也是点赞最高的一条评论）

answerthis  HereIsNoTelephone 
If we do go to other planets and they didn't want to let us stay, would we call them racist?
It would probably be the smartest move they ever made.

如果我们去到另一个行星，而对方不让我们留下，我们会不会指责它们种族主义？而这可能是它们最高明的做法。（译者注：自嘲）

hardmoney  Richard Thorton 
Why are earthlings only able to think within their own biological box?

为什么地球人只能够在他们自己的生物箱体内思考？

Chriswr  TheOverload 
Either possibility would be astonishing. We remain unastonished only because we don't know which one to be astonished by.

任一一种可能性（外星人不存在和外星人存在）都会是令人惊叹的，而我们还没有被惊叹到只是因为我们不知道到底会被其中的哪一种惊叹到而已。