公共英語五級閲讀文章

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Evolution and Wheels

In the past, evolutionary biologists contemplating the absence of wheels in nature agreed that the explanation was not undesirability: wheels would be good for animals, just as they are for us. Animals were prevented from evolving wheels, the biologists reasoned, by the following dilemma: living cells in an animal's body are connected to the heart by blood vessels, and to the brain by nerves. Because a rotating joint is essential to a wheel, a wheel made of living cells would twist its artery vein and nerve connections at the first revolution, making living impracticable. However, there is a flaw in the argument that the evolution of wheeled animals was thwarted by the insoluble joint problem. The theory fails to explain why animals have not evolved wheels of dead tissue with no need for arteries and nerves. Countless animals, including us, bear external structures without blood supply or nerves - for example, our hair and fingernails, or the scales, claws, and ho rns of other animals. Why have rats not evolved bony wheels, similar to roller skates?Paws might be more useful than wheels in some situations, but cats' claws are retractable: why not retractable wheels?We thus arrive at the serious biological paradox flippantly termed the RRR dilemma: nature's failure to produce rats with retractable roller skates.

進化與輪子

從前，研究自然界沒有輪子的進化論生物學家都同意不能用無此需要來解釋這種現象：輪子對於動物會像對於我們人類一樣有好處。生物學家們推論，動物沒有進化出輪子是由下述困難所致：動物身上的活細胞通過血管與心臟相連，通過神經與大腦相連。因為一個旋轉的接頭對輪子來説是至關重要的，由活的細胞構成的輪子在第一次轉動時便會扭傷其上的動脈和神經的連結，因而不現實。

不過，動物未能進化出輪子是受阻於無法解決接頭問題的説法有一個缺陷。這種理論無法解釋為何動物沒有進化出由死組織構成的而無需動脈和神經的輪子。包括人在內的'無數動物都有一些沒有血液供應和神經的體外構造，例如，我們的頭髮和指甲，或者鱗片、爪子和其它一些動物的角。為什麼老鼠沒有進化出類似於滑輪溜冰鞋的骨質的輪子呢?在某些情況下，爪子可能比輪子更有用，但貓的爪子是可以伸縮的：為什麼不能有可以伸縮的輪 子呢?這樣，我們便得出了一個被戲稱為 RRR 的嚴肅的生物學悖論：大自然未能產生出有可伸縮的滑輪溜冰鞋的老鼠。

　Population Growth

The growth of population during the past few centuries is no proof that population will continue to grow straight upward toward infinity and doom. On the contrary, demographic history offers evidence that population growth has not been at all constant. According to paleoecologist Edward Deevey, the past million years show three momentous changes. The first, a rapid increase in population around one m illion B. C., followed the innovations of tool making and tool using. But when the new power from the use of tools has been exploited, the rate of world population growth fell and became almost stable. The next rapid jump in population started perhaps 10,000 years ago, when mankind began to keep herds, plow and plant the earth. Once again when initial productivity gains had been absorbed, the rate of population growth abated. These two episodes suggest that the third great change, the present rapid growth, which began in the West between 250 and 350 years ago, may also slow down when, or if, technology begins to yield fewer innovations. Of course, the current knowledge revolution may continue without foreseeable end. Either way - contrary to popular belief in constant geometric growth - population can be expected in the long run to adjust to productivity. And when one takes this view, population growth is seen to represent economic progress and human triumph rather than social failure.

　人口增長

以往幾個世紀人口的增長並不能證明人口會無限地直線向上增長直到毀滅的地步。相反地，人口統計史料證明人口的增長完全不是穩定的。古生態學家愛德華·狄維認為，在過去100 萬年間出現過3 次重大的變動。第一次在公元前 100 萬年左右，隨着在工具的製作和使用上的革新而出現人口迅速增長。但當工具的使用所產生的新動力被充分利用以後，世界人口增長率下降並且趨於穩定。第二次人口劇增大約始於人類開始蓄畜、墾耕的10，000 年前。一旦最初的生產力增長被吸收殆盡，人口的增長再次衰落。以上兩段説明，若技術革新的成果開始減少，從250 到350 年前就在西方開始出現的並且目前還在 繼續的人口迅速增長可能也會放慢。當然，當前的知識革命也許會持續下去而無法預見其 末來。無論如何，與那種認為人口以幾何級數持續增長的觀點相反，從長遠的觀點來説，人口可望受到生產力的調節。接受了這一觀點，人口的增長就可以被看成是經濟進步和人類勝利的標誌，而不是社會衰敗的標誌。