本文选自《经济学人》8月22日刊文章。这是一篇非常有意思的病毒科普文章，人类自以为是在食物链金字塔的最顶端，但实际上，看不见摸不着的病毒一出动，就能让人类伏尸百万甚至千万。病毒自生命诞生之初就存在，比人类的历史要久远的多，它将生命体精简到极致，只留下必要的信息物质和复制能力。它塑造了世界的多样性，也帮助创造了人类，当一种生物群体的密度过大时，针对这种群体的病毒就会出动，杀死该群体的多余成员，从而为其它稀有物种赢得生存空间。在戴蒙德的《枪炮、病菌与钢铁：人类社会的命运》一书中也讲到，细菌帮助塑造了人类社会，欧洲人之所以能够占领美洲，随欧洲人一起到美洲的病毒功不可没。Richard Dawkins认为进化过程中的自然选择其实是“盲眼钟表匠”，无目的、无意识、无远见。但病毒就像是神秘的上帝之手，在自然界这个复杂而精妙的钟表出现不和谐的时候，出来拨动指针，让自然之钟和谐的转动下去。
选文精讲
The aliens among us 人群中的异类
How viruses shape the worldThey don’t just cause pandemicsAs 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.
- strip down to: 把衣服脱到只剩下...、剥去
- If sb/sth is anything to go by: 如果按某人/某物的标准、经验来看 （It means sb/sth is an example of the point you are trying to make). eg. Presenter A: What percentage of people in the UK has less than 1000 pounds in savings? Is it a) 5%, b) 15%, c) 30%? Presenter B: If I am anything to go by, I'd say c) 30%. A 问:存款少于1000英镑的英国人占多大比例？ a) 5%, b) 15%, c) 30%；B回答：如果按我的情况，我会选c。
正如我们在本周出版的文章中解释的那样，病毒被认为是利用另一种生物的新陈代谢来进行繁殖的遗传物质包。它们是最纯粹的一种寄生虫:它们从寄主那里借用一切，除了遗传密码，正是遗传密码让它们成为病毒。它们剥去生命的冗杂，将生命简化到只剩下必要的物质信息和复制能力。如果按照这些大量的病毒来看，这确实是一个非常成功的策略。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 1031 of the things—that is ten followed by 31 zeros, far outnumbering all other forms of life on the planet.
- back of an envelope: 粗略的快速计算（A calculation or mathematical formulation that is approximated in a quick, informal, and rough manner, as might besketched out on a scrap of paper (such as the back of an envelope).）eg. When it came time to pay the bill, we had to do some back-of-the-envelope calculations to figure out who owed howmuch. 到付帐的时候，我们必须做一些粗略的计算来算出谁欠了多少钱。
世界到处都是病毒。一项对海水的分析发现了20万种不同的病毒种类，这还不是一项全面的研究。其他研究表明，一升海水中可能含有1000亿个病毒体，而一公斤干燥土壤中含有的病毒数可能是这个数字的10倍。总之，根据一个庞大的粗略计算，世界上可能有1031个病毒——也就是10后面有31个零，远远超过地球上所有其他形式的生命。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.
据大家所知，病毒——通常有许多不同种类——已经适应了攻击每一个存在的有机体。它们之所以是进化的动力源，其中一个原因是它们监督着一场无情而大规模的屠杀，并在屠杀过程中变异。这在海洋中尤其明显，每天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，它通过消减密度非常大的物种的数量，为更稀有的物种腾出空间，从而促进多样性。一种生物体越常见，就越有可能发展出一种能够专门攻击它的局部病毒瘟疫，从而约束该生物体数量。
