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.人类认为自己站在食物链的顶端，于是剑齿虎灭绝了，新西兰恐鸟消失了，濒危的巨型动物数之不尽。但是，新冠病毒告诉人类，他们自己有一天也会成为猎物。现代的很多传染病都是由病毒引起的，包括新冠肺炎和艾滋病，以及1918年到1920年间暴发的流感，那次流感导致的死亡人数比一战的死亡人数还要多。欧洲人入侵美国时，在不知情的情况下带去了天花、麻疹和流感病毒，导致大量原住民死亡，这可能是欧洲能殖民美洲的一个原因。

　　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. 从古至今，病毒对地球上的生命的影响绝不仅仅只是给单单一个物种带来悲剧。虽然对病毒的研究始于对一组奇怪的病原体所展开的调查，最 新的研究将其置于解释基因策略的核 心位置，这既自私又是不自私的方法。

　　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.病毒的种类多到难以想象，而且无处不在。很明了的是，从生命诞生之初起，病毒越来越多地影响所有微生物的进化。病毒最为显著的方式证明了自然选择盲目性和残酷性。病毒创造了一群聪明的两足哺乳动物——人类，既是威胁，也是机遇，令人捉摸不透。

　　As our essay in this week’s issue explains, 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.正如我们本周刊登的文章所言，对“病毒”最好的解释就是“利用另一种生物的新陈代谢来进行繁殖的遗传物质组合”。它们是一种最纯粹的寄生虫：除了遗传密码外，它们的一切都来自宿主。它们将生命剥离到只剩下赤裸裸的信息及其复制品。如果说种类丰富的病毒们有什么值得学习的地方，那就是它们的生存策略真地非常成功。

　　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 1031 of the things—that is one followed by 31 zeros, far outnumbering all other forms of life on the planet.世界上到处都是病毒。一项针对海水的分析发现,海水里有20万种病毒，而这还不是全部。有一些研究发现，一升海水中可能含有1000亿病毒颗粒，而一千克干燥土壤中的病毒数量可能是这个数字的10倍。据计算，世界上可能有10的31次方个病毒(即1后面有31个零)，远远超过了地球上所有其他生物的总和。

　　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. .众所周知，病毒通常有许多不同的种类，已适应了攻击每一个既有的有机体。病毒之所以是进化的动力源，其中一个原因是它们进行着一场无情的大屠杀，并在屠杀过程中变异——这在海洋中尤 其明显。在海洋中，病毒每天危殆五分之一的单细胞浮游生物。从生态学的角度来说，病毒通过削减物种数量为更稀有的生物腾出空间，促进了物种多样性。一种生物越常见，专门攻击它的病毒就越有可能发展成一场瘟疫，从而控制这种生物。

　　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.病毒引发瘟疫这一倾向促进了生物进化，因为这会促使病毒的猎物作出防御，并时常带来更为广泛的后果。例如，有一种说法，称细胞故意毁灭自己的原因是它的牺牲降低了附近紧密相关细胞的病毒载量。这样，它的基因才得以在邻近细胞中复制，更有可能存活下来。这种无私的自我毁灭是细胞聚集在一起形成复杂生物体(如豌豆植物、蘑菇和人类)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.病毒成为生物进化动力的另一个原因是，它们有基因信息的传输机制。一些病毒的基因组最终融入宿主的细胞之中，然后遗传给宿主的后代。人类基因组里应该有8%-25%来源于病毒。但是，这些病毒基因自身也可能反过来遭宿主劫持，它们的基因也有了新作用。比如，哺乳动物能拥有生育后代的能力，是因为它们体内源自病毒的基因被修改了，这样哺乳动物才能长出胎盘。就连人脑的形成也有一部分要归功于人体内的病毒活动，这些病毒活动在人体内促成了不同种类的神经元。

　　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.进化最吸引人之处在于，生物内部和生物之间持续的、不可调和的、无序的竞争产生复杂结果，令人惊奇。事实上，生物进化让你具备阅读和理解这篇文章文字的能力，在一定程度上是由于成群结队的小小的病毒造成。大约40亿年前，生命首次出现在地球上以来，病毒可能就一直存在。这个原理还在运行着，病毒的行动远没有停止。

　　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.在应对和利用病毒带来的威胁时，人类独 特的，由病毒塑造的意识开辟了新的途径。这要从疫苗这一奇迹说起，疫苗能在病原体发动攻击之前展开防御。天花在20世纪夺走了3亿人的生命，多亏了疫苗才终结了这场瘟疫。小儿麻痹症也有望被消灭。新冠肺炎疫情引发的新研究将增强对病毒的检测能力，提升各机构团体的应对能力，将对病毒的防御提升到一个新的水平。

　　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.人类在应对病毒方面取得的另一个进展是依靠操控生特的工具，而这源于人们了解了病毒及防御手段。早期的生物工程依靠的是限制性内切酶——一种分子剪刀，细菌用这种分子剪刀切断病毒基因序列，而生物技术人员用它们来移动基因。最 新的生物技术利用更为精准的抗病毒机制，可以逐个对基因序列进行编辑，即CRISPR。