The aliens among us
我们当中的异类

2020.9

Viruses cause pandemics. They also shape the world
病毒引发大流行病。它们也塑造世界 

 

经济学人


HUMANS THINK of themselves as the world’s apex predators. Hence the silence of sabre-tooth tigers, the absence of moas from New Zealand and the long list of endangered megafauna. But SARS-CoV-2 shows how people can also end up as prey. Viruses have caused a litany of modern pandemics, from covid-19, to HIV/AIDS to the influenza outbreak in 1918-20, which killed many more people than the first world war. Before that, the colonisation of the Americas by Europeans was abetted—and perhaps made possible—by epidemics of smallpox, measles and influenza brought unwittingly by the invaders, which annihilated many of the original inhabitants.
人类自认为是世界上的顶级捕食者。所以剑齿虎湮灭、新西兰恐鸟绝迹,还有许多其他巨型动物濒临灭绝。但此次新冠病毒表明,人类最终也可能成为猎物。病毒在近现代引发了一系列全球大流行病,如新冠肺炎、艾滋病,以及1918年至1920年爆发的致死人数超过一战的大流感等。在此之前,欧洲入侵者无意中带去的让很多原住民丧生的天花、麻疹和流感等区域流行病推动了——或者甚至是促成了——他们对美洲的殖民。
The influence of viruses on life on Earth, though, goes far beyond the past and present tragedies of a single species, however pressing they seem. Though the study of viruses began as an investigation into what appeared to be a strange subset of pathogens, recent research puts them at the heart of an explanation of the strategies of genes, both selfish and otherwise.
然而,病毒对地球生物的影响远远不止单个物种在过去和现在遭遇的灾难,不管这些灾难看起来有多紧迫。尽管最初的病毒研究是在调查一类看似是病原体一个奇怪分支的东西,但近些年的研究已把病毒视为理解基因策略的关键,不管是自私的还是利他的基因。
Viruses are unimaginably varied and ubiquitous. And it is becoming clear just how much they have shaped the evolution of all organisms since the very beginnings of life. In this, they demonstrate the blind, pitiless power of natural selection at its most dramatic. And—for one group of brainy bipedal mammals that viruses helped create—they also present a heady mix of threat and opportunity.
病毒种类繁多又无处不在的程度令人难以想象。人们逐渐认识到,自生命诞生之初,病毒就在很大程度上影响了所有生物的进化。在此过程中,它们以最剧烈的方式展现了自然选择那盲目而无情的力量。而且,对于人类这种在病毒的帮助下形成的有智慧的两足哺乳动物来说,它们令人晕眩地同时带来了“危”与“机”。
Viruses are best thought of as packages of genetic material that exploit another organism’s metabolism in order to reproduce. They are parasites of the purest kind: they borrow everything from the host except the genetic code that makes them what they are. They strip down life itself to the bare essentials of information and its replication. If the abundance of viruses is anything to go by, that is a very successful strategy indeed.
对病毒的最好理解方式是它们是利用另一种有机体的新陈代谢来繁殖的遗传物质组装体。它们是最纯种的寄生生物:除了令它们获得自身特性的遗传密码以外,其他一切都借自宿主。它们将自身生命剥离得只剩下遗传信息及其复制品的最基本要素。从病毒数量之多这一点来看,这确实是非常有效的策略。
The world is teeming with them. One analysis of seawater found 200,000 different viral species, and it was not setting out to be comprehensive. Other research suggests that a single litre of seawater may contain more than 100bn virus particles, and a kilo of dried soil ten times that number. Altogether, according to calculations on the back of a very big envelope, the world might contain 10^31 of the things—that is ten followed by 30 zeros, far outnumbering all other forms of life on the planet.
世界充满了病毒。一项分析在海水中发现了20万种不同病毒,这还不是什么全面的研究。另一项研究表明,一升海水中可能含有超过一千亿个病毒颗粒,而一公斤干燥泥土中有超过一万亿个。根据非常粗略的估算,世界上的病毒总数可能达到10^31个,也就是10后面有30个零,远远超过地球上所有其他生命形式的数量。
As far as anyone can tell, viruses—often of many different sorts—have adapted to attack every organism that exists. One reason they are powerhouses of evolution is that they oversee a relentless and prodigious slaughter, mutating as they do so. This is particularly clear in the oceans, where a fifth of single-celled plankton are killed by viruses every day. Ecologically, this promotes diversity by scything down abundant species, thus making room for rarer ones. The more common an organism, the more likely it is that a local plague of viruses specialised to attack it will develop, and so keep it in check.
就目前所知,病毒——而且往往是很多不同的种类——已经适应了去攻击所有活生物体。它们之所以是进化的推进器,原因之一是它们主导着一场残酷的大规模屠杀,并在此过程中发生突变。这在海洋中尤其明显,每天海洋中有五分之一的单细胞浮游生物被病毒杀死。从生态学的角度来说,这通过大幅缩减一些数量众多的物种的规模,给较稀有的物种腾出生存空间,从而促进了生物多样性。一种生物体越常见,专门攻击它的病毒就越有可能制造一场局部瘟疫,从而控制该生物体的数量扩张。
This propensity to cause plagues is also a powerful evolutionary stimulus for prey to develop defences, and these defences sometimes have wider consequences. For example, one explanation for why a cell may deliberately destroy itself is if its sacrifice lowers the viral load on closely related cells nearby. That way, its genes, copied in neighbouring cells, are more likely to survive. It so happens that such altruistic suicide is a prerequisite for cells to come together and form complex organisms, such as pea plants, mushrooms and human beings.
病毒引发瘟疫的这种特性也强有力地促进了猎物自身防御能力的进化,而这些防御能力有时会产生更广泛的影响。例如,为什么细胞会故意自我毁灭?一种解释是,当一个细胞自我毁灭后,与它密切相关的邻近细胞上的病毒载量就会减少。这样,它在邻近细胞中复制的基因存活下来的几率就更大。巧合的是,这种利他性自杀正是促使细胞聚集并形成豌豆苗、蘑菇和人类等复杂生物体的先决条件。
The other reason viruses are engines of evolution is that they are transport mechanisms for genetic information. Some viral genomes end up integrated into the cells of their hosts, where they can be passed down to those organisms’ descendants. Between 8% and 25% of the human genome seems to have such viral origins. But the viruses themselves can in turn be hijacked, and their genes turned to new uses. For example, the ability of mammals to bear live young is a consequence of a viral gene being modified to permit the formation of placentas. And even human brains may owe their development in part to the movement within them of virus-like elements that create genetic differences between neurons within a single organism.
病毒成为进化引擎的另一个原因是它们充当了基因信息的传输机制。一些病毒基因组最终被整合到其宿主的细胞中,从而可以遗传给那些生物体的后代。8%到25%的人类基因组似乎具有这种病毒起源。但反过来病毒自己也可能被“劫持”,它们的基因被改作新用途。比如,哺乳动物能够生育幼仔,就是一种病毒基因被修改而使胎盘得以形成的结果。甚至人类大脑的发育在一定程度上可能也要归功于类病毒元素在大脑内部的运动,这些元素制造了单个生物体中的神经元之间的遗传差异。
Evolution’s most enthralling insight is that breathtaking complexity can emerge from the sustained, implacable and nihilistic competition within and between organisms. The fact that the blind watchmaker has equipped you with the capacity to read and understand these words is in part a response to the actions of swarms of tiny, attacking replicators that have been going on, probably, since life first emerged on Earth around 4bn years ago. It is a startling example of that principle in action—and viruses have not finished yet.
关于进化,最让人着迷的见解是,在生物体内部以及生物体之间持续的、不可调和的、破坏性的竞争会产生令人叹为观止的复杂性。自然选择这一“盲眼钟表匠”之所以让你拥有阅读和理解本文的能力,一定程度上是对成群结队微小的病毒复制基因的攻击做出的反应,这些攻击可能自大约40亿年前地球上刚出现生命起就一直在发生着。这是自然选择法则在起作用的惊人例子——而病毒的历程尚未完结。
Humanity’s unique, virus-chiselled consciousness opens up new avenues to deal with the viral threat and to exploit it. This starts with the miracle of vaccination, which defends against a pathogenic attack before it is launched. Thanks to vaccines, smallpox is no more, having taken some 300m lives in the 20th century. Polio will one day surely follow. New research prompted by the covid-19 pandemic will enhance the power to examine the viral realm and the best responses to it that bodies can muster—taking the defence against viruses to a new level.
人类独特的、由病毒雕琢而成的意识为应对和利用病毒威胁开辟了多种新途径。首先是疫苗接种这一奇迹,它能在病毒发起致病攻击之前做出防御。因为有了疫苗,上世纪夺走约三亿人性命的天花得以绝迹。总有一天,小儿麻痹症也会被消灭。此次新冠疫情推动的新研究将提高对病毒族群的研判能力,加强人体能够调集起的最佳响应,从而把病毒防御提升到一个新水平。
Another avenue for progress lies in the tools for manipulating organisms that will come from an understanding of viruses and the defences against them. Early versions of genetic engineering relied on restriction enzymes—molecular scissors with which bacteria cut up viral genes and which biotechnologists employ to move genes around. The latest iteration of biotechnology, gene editing letter by letter, which is known as CRISPR, makes use of a more precise antiviral mechanism.
另一条进步途径存在于操纵生物体的工具中。创造这类工具的基础是对病毒以及病毒防御的了解。早期的基因工程依赖限制性内切酶,细菌用这把“分子剪刀”切断病毒基因,生物技术学家用它来四处移动基因的位置。最新的生物技术被称为CRISPR,可以逐个对碱基加以编辑,利用了一种更精确的抗病毒机制。
From the smallest beginnings 从最小处入手 The natural world is not kind. A virus-free existence is an impossibility so deeply unachievable that its desirability is meaningless. In any case, the marvellous diversity of life rests on viruses which, as much as they are a source of death, are also a source of richness and of change. Marvellous, too, is the prospect of a world where viruses become a source of new understanding for humans—and kill fewer of them than ever before.
自然界并不友好。要想生存在一个没有病毒的世界里是不可能的,也根本做不到,因此追求这一点毫无意义。无论如何,生命妙不可言的多样性有赖于病毒——它们不仅是死亡之源,同样也是丰富性和变化之源。同样妙不可言的是未来会出现这样一个世界——在这里,病毒成为人类新认知的来源,而它们的致死人数低于以往任何时候。