Bruce Rothschild of the University of Kansas knew all this when he began a study of ichthyosaur bones to find out how widespread the problem was in the past. What he particularly wanted to investigate was how ichthyosaurs adapted to the problem of decompression over the 150 million years. To this end, he and his colleagues traveled the world’s natural-history museums, looking at hundreds of ichthyosaurs from the Triassic period and from the later Jurassic and Cretaceous periods.
When he started, he assumed that signs of the bends would be rarer in younger fossils, reflecting their gradual evolution of measures to deal with decompression. Instead, he was astonished to discover the opposite. More than 15% of Jurassic and Cretaceous ichthyosaurs had suffered the bends before they died, but not a single Triassic specimen (标本) showed evidence of that sort of injury.
If ichthyosaurs did evolve an anti-decompression means, they clearly did so quickly—and, most strangely, they lost it afterwards. But that is not what Dr Rothschild thinks happened. He suspects it was evolution in other animals that caused the change.
Whales that suffer the bends often do so because they have surfaced to escape a predator (捕食动物) such as a large shark. One of the features of Jurassic oceans was an abundance of large sharks and crocodiles, both of which were fond of ichthyosaur lunches. Triassic oceans, by contrast, were mercifully shark- and crocodile-free. In the Triassic, then, ichthyosaurs were top of the food chain. In the Jurassic and Cretaceous, they were prey (猎物) as well as predator—and often had to make a speedy exit as a result.
61. Which of the following is a typical symptom of the bends?
A. A twisted body.
B. A gradual decrease in blood supply.
C. A sudden release of nitrogen in blood.
D. A drop in blood pressure.
62. The purpose of Rothschild’s study is to see ______.
A. how often ichthyosaurs caught the bends
B. how ichthyosaurs adapted to decompression
C. why ichthyosaurs bent their bodies
D. when ichthyosaurs broke their bones
63. Rothschild’s finding stated in Paragraph 4 ______.
A. confirmed his assumption B. speeded up his research process
C. disagreed with his assumption D. changed his research objectives
64. Rothschild might have concluded that ichthyosaurs ______.
A. failed to evolve an anti-decompression means
B. gradually developed measures against the bends
C. died out because of large sharks and crocodiles
D. evolved an anti-decompression means but soon lost it
D
Mark Twain has been called the inventor of the American novel. And he surely deserves additional praise: the man who popularized the clever literary attack on racism.
I say clever because anti-slavery fiction had been the important part of the literature in the years before the Civil War. H. B. Stowe’s Uncle Tom’s Cabin is only the most famous example. These early stories dealt directly with slavery. With minor exceptions, Twain planted his attacks on slavery and prejudice into tales that were on the surface about something else entirely. He drew his readers into the argument by drawing them into the story.
Again and again, in the postwar years, Twain seemed forced to deal with the challenge of race. Consider the most controversial, at least today, of Twain’s novels, Adventures of Huckleberry Finn. Only a few books have been kicked off the shelves as often as Huckleberry Finn, Twain’s most widely read tale. Once upon a time, people hated the book because it struck them as rude. Twain himself wrote that those who banned the book considered the novel “trash and suitable only for the slums (贫民窟).” More recently the book has been attacked because of the character Jim, the escaped slave, and many occurences of the word nigger. (The term Nigger Jim, for which the novel is often severely criticized, never appears in it.)
But the attacks were and are silly—and miss the point. The novel is strongly anti-slavery. Jim’s search through the slave states for the family from whom he has been forcibly parted is heroic. As J. Chadwick has pointed out, the character of Jim was a first in American fiction—a recognition that the slave had two personalities, “the voice of survival within a white slave culture and the voice of the individual: Jim, the father and the man.”
There is much more. Twain’s mystery novel Pudd’nhead Wilson stood as a challenge to the racial beliefs of even many of the liberals of his day. Written at a time when the accepted wisdom held Negroes to be inferior (低等的) to whites, especially in intelligence, Twain’s tale centered in part around two babies switched at birth. A slave gave birth to her master’s baby and, for fear that the child should be sold South, switched him for the master’s baby by his wife. The slave’s lightskinned child was taken to be white and grew up with both the attitudes and the education of the slave-holding class. The master’s wife’s baby was taken for black and grew up with the attitudes and intonations of the slave.
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