劍橋雅思10Test4Passage3閱讀原文翻譯 When evolution runs backwards

劍橋雅思10Test4Passage3閱讀原文翻譯 When evolution runs backwards

劍橋雅思10 Test4 Passage3閱讀原文翻譯

第1段

The description of any animal as an ‘evolutionary throwback’ is controversial. For the better part of a century, most biologists have been reluctant to use those words, mindful of a principle of evolution that says ‘evolution cannot run backwards’. But as more and more examples come to light and modern genetics enters the scene, that principle is having to be rewritten. Not only are evolutionary throwbacks possible, they sometimes play an important role in the forward march of evolution.

將任何動(dòng)物描述為“進(jìn)化倒退”是有爭(zhēng)議的。該世紀(jì)的大部分時(shí)間里，大多數(shù)生物學(xué)家一直不愿意使用這些詞匯。他們謹(jǐn)記著進(jìn)化的一條基礎(chǔ)原則，“進(jìn)化不能后退”。但隨著越來(lái)越多的例子出現(xiàn)，以及現(xiàn)代基因科學(xué)的誕生，這條規(guī)則不得不被改寫(xiě)。進(jìn)化的倒退不僅是可能的，它們還在向前的進(jìn)化中起著重要作用。

第2段

The technical term for an evolutionary throwback is an ‘a(chǎn)tavism’, from the Latin atavus, meaning forefather. The word has ugly connotations thanks largely to Cesare Lombroso, a 19th-century Italian medic who argued that criminals were born not made and could be identified by certain physical features that were throwbacks to a primitive, sub-human state.

用于描述進(jìn)化后退的技術(shù)詞匯是“返祖現(xiàn)象”，它來(lái)自于拉丁語(yǔ)atavus，意思是祖先。該詞具有一定的丑陋含義。這在很大程度上要?dú)w功于19世紀(jì)意大利醫(yī)務(wù)人員Cesare Lombroso。他認(rèn)為犯罪分子是天生的，而不是后期造成的。并且可以根據(jù)特定的身體特征來(lái)進(jìn)行識(shí)別。而這些特征可以追溯到原始的亞人類(lèi)狀態(tài)。

第3段

While Lombroso was measuring criminals, a Belgian palaeontologist called Louis Dollo was studying fossil records and coming to the opposite conclusion. In 1890 he proposed that evolution was irreversible: that ‘a(chǎn)n organism is unable to return, even partially, to a previous stage already realised in the ranks of its ancestors’. Early 20th-century biologists came to a similar conclusion, though they qualified it in terms of probability, stating that there is no reason why evolution cannot run backwards—it is just very unlikely. And so the idea of irreversibility in evolution stuck and came to be known as ‘Dollo’s law’.

Lombroso在描述罪犯時(shí)，一名叫做Louis Dollo的比利時(shí)古生物學(xué)家正在研究化石記錄，并得出相反的結(jié)論。1890年，他提出進(jìn)化是不可逆的，“一種生物無(wú)法回到其祖先在進(jìn)化序列中已經(jīng)完成的任何先前階段，即使是部分回歸也不可能”。二十世紀(jì)早期的生物學(xué)家得出了相似的結(jié)論，盡管他們?cè)诟怕噬蠈?duì)其進(jìn)行了限定，認(rèn)為并沒(méi)有任何理由支持進(jìn)化無(wú)法后退，它僅僅是不太可能。因此，這種進(jìn)化不可逆的觀(guān)念扎根下來(lái)，并被稱(chēng)為“Dollo定律”。

第4段

If Dollo’s law is right, atavisms should occur only very rarely, if at all. Yet almost since the idea took root, exceptions have been cropping up. In 1919, for example, a humpback whale with a pair of leg-like appendages over a metre long, complete with a full set of limb bones, was caught off Vancouver Island in Canada. Explorer Roy Chapman Andrews argued at the time that the whale must be a throwback to a land-living ancestor. ‘I can see no other explanation,’ he wrote in 1921.

如果Dollo定律是正確的，那么返祖現(xiàn)象哪怕確實(shí)存在，也應(yīng)該十分少見(jiàn)。然而，幾乎從這一概念扎根以來(lái)，例外就一直出現(xiàn)。例如，1919年，加拿大溫哥華島上捕獲了一頭座頭鯨。它有一雙類(lèi)似于腿的、一米多長(zhǎng)的附屬物，并擁有完整的四肢骨骼。探險(xiǎn)家Roy Chapman Andrews那時(shí)認(rèn)為這頭鯨魚(yú)一定退化成了其生活在陸地上的祖先狀態(tài)。他于1921年寫(xiě)到，“我找不到任何其他解釋”。

第5段

Since then, so many other examples have been discovered that it no longer makes sense to say that evolution is as good as irreversible. And this poses a puzzle: how can characteristics that disappeared millions of years ago suddenly reappear? In 1994, Rudolf Raff and colleagues at Indiana University in the USA decided to use genetics to put a number on the probability of evolution going into reverse. They reasoned that while some evolutionary changes involve the loss of genes and are therefore irreversible, others may be the result of genes being switched off. If these silent genes are somehow switched back on, they argued, long-lost traits could reappear.

從那時(shí)起，發(fā)現(xiàn)了如此之多的其他例子，以至于堅(jiān)持進(jìn)化不可逆這一理論不再有什么意義。這就提出了一個(gè)難題：那些幾百萬(wàn)年前消失的特征怎么會(huì)再次突然出現(xiàn)？1994年，美國(guó)印第安納大學(xué)Rudolf Raff和他的同事決定利用基因?qū)W量化進(jìn)化倒退的可能性。他們考慮到，雖然一些進(jìn)化變化涉及到基因的缺失，并因此是不可逆的。但其他的則可能是基因被關(guān)閉的結(jié)果。他們認(rèn)為，如果這些沉默的基因以某種方式再次被打開(kāi)，消失了很長(zhǎng)時(shí)間的特征就會(huì)再次出現(xiàn)。

第6段

Raff’s team went on to calculate the likelihood of it happening. Silent genes accumulate random mutations, they reasoned, eventually rendering them useless. So how long can a gene survive in a species if it is no longer used? The team calculated that there is a good chance of silent genes surviving for up to 6 million years in at least a few individuals in a population, and that some might survive as long as 10 million years. In other words, throwbacks are possible, but only to the relatively recent evolutionary past.

Raff的團(tuán)隊(duì)繼續(xù)計(jì)算這一現(xiàn)象發(fā)生的可能性。他們認(rèn)為沉默的基因會(huì)積累隨機(jī)突變，并最終使得它們變得毫無(wú)用處。所以，如果一個(gè)基因不再被使用，那么它在一個(gè)物種中可以存在多長(zhǎng)時(shí)間呢？該團(tuán)隊(duì)計(jì)算，有很大概率，沉默的基因在種群中的一些個(gè)體里可以存在600萬(wàn)年，一些甚至可能延續(xù)1000萬(wàn)年那么久。換句話(huà)說(shuō)，退化完全可能，但僅僅是退回相對(duì)較近的進(jìn)化階段。

第7段

As a possible example, the team pointed to the mole salamanders of Mexico and California. Like most amphibians these begin life in a juvenile ‘tadpole’ state, then metamorphose into the adult form—except for one species, the axolotl, which famously lives its entire life as a juvenile. The simplest explanation for this is that the axolotl lineage alone lost the ability to metamorphose, while others retained it. From a detailed analysis of the salamanders’ family tree, however, it is clear that the other lineages evolved from an ancestor that itself had lost the ability to metamorphose. In other words, metamorphosis in mole salamanders is an atavism. The salamander example fits with Raff’s 10-million-year time frame.

該團(tuán)隊(duì)列舉了墨西哥和加利福尼亞的鈍口螈為證。與大多數(shù)兩棲動(dòng)物類(lèi)似，它們以一種年幼的“蝌蚪”形態(tài)開(kāi)始自己的一生，然后轉(zhuǎn)變?yōu)槌赡晷螒B(tài)。只有一個(gè)品種例外：蠑螈。它因一生都保持著年幼狀態(tài)而聞名。這一現(xiàn)象最簡(jiǎn)單的解釋是，蠑螈這一單獨(dú)分支失去了變形的能力，而其他分支則保留了這一能力。然而，通過(guò)對(duì)蠑螈家族譜系的細(xì)致分析發(fā)現(xiàn)，其他分支顯然是從某一個(gè)已經(jīng)失去變形能力的祖先進(jìn)化而來(lái)的。話(huà)句話(huà)說(shuō)，鈍口螈的變形能力是一種返祖現(xiàn)象。鈍口螈的例子符合Raff一千萬(wàn)年的時(shí)間框架。

第8段

More recently, however, examples have been reported that break the time limit, suggesting that silent genes may not be the whole story. In a paper published last year, biologist Gunter Wagner of Yale University reported some work on the evolutionary history of a group of South American lizards called Bachia. Many of these have minuscule limbs; some look more like snakes than lizards and a few have completely lost the toes on their hind limbs. Other species, however, sport up to four toes on their hind legs. The simplest explanation is that the toed lineages never lost their toes, but Wagner begs to differ. According to his analysis of the Bachia family tree, the toed species re-evolved toes from toeless ancestors and, what is more, digit loss and gain has occurred on more than one occasion over tens of millions of years.

然而，更近一些被報(bào)道的例子打破了時(shí)間限制，表明沉默的基因可能還不是故事的全部。在去年發(fā)表的一篇論文中，耶魯大學(xué)生物學(xué)家Gunter Wagner公布了一些自己對(duì)一種名為Bachia的南美洲蜥蜴的進(jìn)化歷史所做的研究。它們?cè)S多都有微型四肢。一些看起來(lái)更像是蛇而不是蜥蜴。一些已經(jīng)完全失去了后肢的指頭。然而，其他物種的后肢上則出現(xiàn)了最多四個(gè)指頭。最簡(jiǎn)單的解釋是，有指頭的分支從未喪失過(guò)這一特征。但Wagner持不同意見(jiàn)。根據(jù)他對(duì)Bachia家族譜系的研究，有指頭的物種從沒(méi)有指頭的祖先那里再次進(jìn)化出了指頭。此外，這種腳趾的消失和再現(xiàn)在過(guò)去上千萬(wàn)年里曾不只出現(xiàn)過(guò)一次。

第9段

So what’s going on? One possibility is that these traits are lost and then simply reappear, in much the same way that similar structures can independently arise in unrelated species, such as the dorsal fins of sharks and killer whales. Another more intriguing possibility is that the genetic information needed to make toes somehow survived for tens or perhaps hundreds of millions of years in the lizards and was reactivated. These atavistic traits provided an advantage and spread through the population, effectively reversing evolution.

那么，到底是怎么回事呢？一種可能是，這些特征先是消失，然后只是簡(jiǎn)單的再次出現(xiàn)而已。就跟一些相似的結(jié)構(gòu)可能獨(dú)立出現(xiàn)在不相關(guān)的物種身上一樣，比如鯊魚(yú)和虎鯨的背鰭。另外一種更為有趣的可能是，需要用來(lái)制造指頭的基因信息在蜥蜴中存在了數(shù)千萬(wàn)甚至上億年，然后被再次激活了。這些返祖體征提供了一項(xiàng)優(yōu)勢(shì)，并在族群中傳播開(kāi)來(lái)，有效地逆轉(zhuǎn)了進(jìn)化進(jìn)程。

第10段

But if silent genes degrade within 6 to 10 million years, how can long-lost traits be reactivated over longer timescales? The answer may lie in the womb. Early embryos of many species develop ancestral features. Snake embryos, for example, sprout hind limb buds. Later in development, these features disappear thanks to developmental programs that say ‘lose the leg’. If for any reason this does not happen, the ancestral feature may not disappear, leading to an atavism.

但如果沉默的基因在600萬(wàn)到1000萬(wàn)年的時(shí)間里退化，那么已經(jīng)消失了很久的特征又是如何在更長(zhǎng)的時(shí)間跨度里重現(xiàn)的呢？答案可能存在于子宮內(nèi)部。許多物種的早期胚胎都發(fā)展出祖先的特征。例如，蛇的胚胎會(huì)長(zhǎng)出后腿突起物。在隨后的發(fā)育過(guò)程中，這些特征會(huì)由于發(fā)育程序的命令（丟掉這些腿）而消失。如果因?yàn)槟撤N原因，這一機(jī)制沒(méi)有起作用，那么祖先的特征就不會(huì)消失，導(dǎo)致返祖現(xiàn)象。

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