解放军文职招聘考试Evolution and Wheels

 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.

进化与轮子从前，研究自然界没有轮子的进化论生物学家都同意不能用无此需要来解释 这种现象：轮子对于动物会像对于我们人类一样有好处。 

生物学家们推论，动物没有进化 出轮子是由下述困难所致：动物身上的活细胞通过血管与心脏相连，通过神经与大脑相连。

因为一个旋转的接头对轮子来说是至关重要的，由活的细胞构成的轮子在第一次转动时便会 扭伤其上的动脉和神经的连结，因而不现实。

不过，动物未能进化出轮子是受阻于无法解决接头问题的说法有一个缺陷。  这种理论 无法解释为何动物没有进化出由死组织构成的而无需动脉和神经的轮子。 

包括人在内的无 数动物都有一些没有血液供应和神经的体外构造，例如，我们的头发和指甲，或者鳞片、爪 子和其它一些动物的角。

为什么老鼠没有进化出类似于滑轮溜冰鞋的骨质的轮子呢?在某些 情况下，爪子可能比轮子更有用，但猫的爪子是可以伸缩的：  为什么不能有可以伸缩的轮

子呢?这样，我们便得出了一个被戏称为 RRR 的严肃的生物学悖论：大自然未能产生出有可 伸缩的滑轮溜冰鞋的老鼠。