2017 考博英语 阅读题源经济学人文章每日精析（五十一）

考博英语阅读大部分博士研究生招生院校都使用《经济学人》杂志文章作为题源，考博信息网|http://www.kaoboinfo.com教育考博频道为考博生们将其中的文章进行深度分析，希望能提高大家的考博英语阅读水平，读懂长难句。

导读

从生物的形成到进化的历程中，我几乎都能找到相对应的化石来证明，但是在3亿6千万至3亿4千万年前我们却很难找到这一时期的化石来证明节肢动物和脊椎动物的进化历程，这一时期就被称为柔默空缺。有学者指出是因为石化问题，地层不适合形成化石，也有学者指出是考古挖掘人员没有找对地方。

New fossils illuminate the route that led ultimately to human beings

最新发掘的化石照亮了人类进化之路

A 25m-year dark age known as Romer’s gap is dark no longer

柔默空缺这段2500万年的黑暗时代终于揭开神秘面纱

Dec 10th 2016

2016年12月10日

ONE of the most important steps on the journey to Homo sapiens was that made by the first fish to crawl onto dry land. It was both a metaphorical and a literal step, but knowing exactly when it happened is tricky. It depends, for one thing, on the definition of “dry land”. Scrambling over the mud from one pool to another, assisted by fins that had evolved to walk along the seabed in the way modern coelacanths do, was probably going on by 385m years ago.

鱼类首次爬上陆地无疑是生物向“智人”进化阶段中的众多重要步骤中的一步。这是既有字面又有隐喻意义的一步，但是要想弄清楚具体发生时间却很难。这取决于“陆地”一次的定义。可能在大约3亿8千5百万年前，鱼类就可以借助鱼鳍从一个泥潭爬到另一个泥潭了。就像现代腔棘鱼那样，它们的鱼鳍已经进化到可以在海床上行走了。

By 375m years ago, the descendants of these first-footers had evolved four limbs clearly recognisable as legs. They were no longer fish, but “tetrapods”. Their legs, though, could have as many as eight digits each, and do not look capable of supporting an animal properly when it was out of the water. Some might thus argue that even by this stage, the step onto dry land had not been truly made.

大约3亿7千5百万年前，第一批鱼类“登陆者”的后代进化出了四肢(可以清晰的看出来是腿)。它们已经不再属于鱼类，而是“四足动物”。尽管它们每个腿的脚趾最多可以达到八个，但是看起来并不能够支撑它们在陆地行走。因此有人认为甚至直到这一时期，鱼类还没有真正地从海洋爬上陆地。

All of these events occurred during a period called the Devonian when, though the oceans teamed with organisms no less varied than today’s, life on the continents was just getting going. Vascular plants (those bigger than mosses and liverworts) had evolved only recently. Insects were evolving fast, too. But there were no large land animals. Occupying the new habitat thus looked like an evolutionary open goal for the tetrapods. But then, 359m years ago, in a mass extinction as big as that which did for the dinosaurs, the Devonian came crashing to an end. (读者试译) For 25m years after this the tetrapods more or less disappear from the fossil record. When they re-emerge, in what is called the Lower Carboniferous period, they do, indeed, live up to their potential. They are now proper terrestrial animals, possessing five-digit limbs powerful enough to support them without the assistance of water’s buoyancy. But how they got there has been a mystery.

这一切都发生在泥盆纪时期，虽然当时的海洋生物多种多样，种类一点也不比现在少，但陆地上的生命才刚刚开始。在这一时期，维管植物(比苔藓和苔类要大)才刚刚出现。昆虫类生物也在快速进化。但尚未有大型陆地生物。2千5百万年后，四足动物差不多已从化石记录里消失了。当它们再次出现时，已经到了始石炭纪时期。它们确实充分发挥了自身的潜力。现在它们已经是标准的陆生生物了，四肢都有五趾，无需借助海水的浮力即可支撑身体。但是四足动物如何进化成今天的样子仍是个迷。

Buoyancy: n. 浮力

注：石炭纪：石炭纪(Carboniferous)约处于地质年代两亿八千六百万至三亿六千万年前，它可以区分为两个时期:始石炭纪(又叫密西西比纪，三亿两千至三亿六千万年前)、和后石炭纪(又叫宾夕法尼亚纪，两亿八千六百至三亿两千万年前)。 石炭纪(Carboniferous period)是古生代的第5个纪，开始于距今约3.55亿年至2.95亿年，延续了6500万年。石炭纪时陆地面积不断增加，陆生生物空前发展。当时气候温暖、湿润，沼泽遍布。大陆上出现了大规模的森林，给煤的形成创造了有利条件。