Viruses--The aliens among us（part-2）

Viruses cause pandemics. They also shape the world

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.

powerhouse n. ??/?pa??ha?s/??1.a group or an organization that has a lot of power 強大的集團（或組織）?2.a person who is very strong and full of energy 精力充沛的人；身強力壯的人

Relentless??adj. /r??lentl?s/ ?

1.not stopping or getting less strong 不停的；持續(xù)強烈的；不減弱的??her relentless pursuit of perfection 她對完美的不懈追求

2.refusing to give up or be less strict or severe 不放棄的；嚴格的；苛刻的；無情的??a relentless enemy 殘酷的敵人

prodigious ?adj. /pr??d?d??s/ ?( formal ) very large or powerful and causing surprise or admiration 巨大的；偉大的

Slaughter???/?sl??t?(r)/ ?n. 屠宰；大屠殺；（非正式）徹底擊敗; v. 屠宰（動物）；（尤指大量）屠殺（人、動物）；（非正式）徹底擊?。▽κ郑?/span>

Mutate ?v. /mju??te?t/ ?

1.to develop or make sth develop a new form or structure, because of a genetic change （使）變異，突變 ?mutated genes 發(fā)生變異的基因

2. to change into a new form 轉變；轉換 ?Rhythm and blues mutated into rock and roll. 節(jié)奏布魯斯演變成為搖滾樂

plankton ?/?pl??kt?n/ ?浮游生物? ? ? ??scythe /sa?e/ n. 長柄大鐮刀；釤刀 vt. 用大鐮刀割

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.

Propensity??/pr??pens?ti/ ?

~ (for sth)~ (for doing sth)~ (to do sth) ( formal ) a tendency to a particular kind of behaviour （行為方面的）傾向；習性 ? He showed a propensity for violence. 他表現(xiàn)出暴力傾向。

evolutionary stimulus :?進化刺激

Altruistic?/??ltru???st?k/ 利他的? ? ? ??altruistic suicide 利他性自殺

prerequisite ?n. /?pri??rekw?z?t/ ?

~ (for/of/to sth) ( formal ) something that must exist or happen before sth else can happen or be done 先決條件；前提；必備條件

pea plants：豌豆植物

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.

這段話的大意是：例如，一種解釋細胞為何自毀？細胞的自毀會降低周邊細胞的病毒載量。從而提升其被臨近細胞復制基因的存活率。

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.

genome n. ??/?d?i?n??m/ ?( biology 生 ) 基因組；染色體組

Descendant ?/d??send?nt/ ?n. 后裔，子孫；（由過去類似物發(fā)展來的）派生物；（機器等）后繼型產(chǎn)品?adj. 下降的；祖?zhèn)鞯?/span>

in turn?be?hijacked：反過來被挾持?

hijack ?/?ha?d??k/ vt. 搶劫；揩油vi. 攔路搶劫?n. 劫持；威逼；敲詐

placenta ?n. /pl??sent?/ 胎盤? ???neuron n. ?/?nj??r?n/ 神經(jīng)元

the ability of mammals to bear live young is a consequence of a viral gene being modified to permit the formation of placentas.大意是哺乳動物能夠生育幼崽是病毒基因被宿主修改，從而允許胎盤形成的結果。

原文：經(jīng)濟學人9月刊