If a diver surfaces too quickly, he may suffer the bends. Nitrogen (氮) dissolved (溶解) in his blood is suddenly liberated by the reduction of pressure. The consequence, if the bubbles (气泡) accumulate in a joint, is sharp pain and a bent body—thus the name. If the bubbles form in his lungs or his brain, the consequence can be death.

    Other air-breathing animals also suffer this decompression (减压) sickness if they surface too fast: whales, for example. And so, long ago, did ichthyosaurs. That these ancient sea animals got the bends can be seen from their bones. If bubbles of nitrogen form inside the bone they can cut off its blood supply. This kills the cells in the bone, and consequently weakens it, sometimes to the point of collapse. Fossil (化石) bones that have caved in on themselves are thus a sign that the animal once had the bends.

    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.

    A killer whale(虎鲸) that can copy words such as “hello” and “bye-bye” is thought to be the first of its kind to copy human speech.

    The female killer whale learned to “speak” some human words by copying a trainer at a park in France. The animal's ability includes speaking the name “Amy” and “one, two, three”.

    Whales and dolphins are among the few animals except humans that can learn to produce a sound just by hearing it. “It is not often seen,” said Dr Josep Call, a co-researcher on the study. “Humans are good at it…Interestingly, the animals that can do best are marine mammals(海洋哺乳动物).” The researchers start to find out whether killer whales could learn new words by copying others. They studied a female named Wikie at Marineland Aquarium in Antibes, France. She was taught to speak human words.

    Dr Jose Abramson, a co-researcher on the study, said basic “conversations” with Wikie may one day be possible. He said,” It has been done before with a famous grey parrot and dolphins using American sign language(手势语).” However, he said they have to be careful about introducing human ideas on animals, as there is more to learn by trying to understand the natural way each kind communicates in its own environment. Wikie made sounds in water, which may be quite different.

    Dr Alex Thornton, senior speaker at the University of Exeter, said they still don't fully understand why some animals learn to copy. Some animals copy sounds to attract possible partners, while others copy sounds to become a member of a group. “Some whales, for example, learn their calls from one another to mark them out as members of their social group,” said Dr Thornton, who doesn't join in the research.

    Researchers are often interested in how culture changes over time. All cultures go through periods of change and some cultures change faster than others. For example, in the past 10 years, Chinese culture has changed rapidly as western products have become popular. Other countries, such as France, have created rules to prevent their culture from changing too quickly.

    Even though cultures change at different paces, the causes of cultural change are quite similar around the world. One of these is technology and medicine. In the United States the invention and development of birth control pills and other measures helped parents to limit the size of their families. As a result, families grew smaller and parents could give more attention to fewer children.  On the other hand, new technology has also created emotional distance among families.

    Cultures also change when they come into contact with other cultures. Immigration, for example, often results in cultural change for both immigrants and the host culture. Immigrants often bring with them different ideas, food, music, language, and manners when they move to a new culture. In Canada, for example, the government has a policy of multiculturalism where immigrants are encouraged to share their background cultures with Canadians while adopting and accepting Canadian culture.

    Cultural change can occur due to larger events. For example, economic depression, war, and disaster can endanger societies, which must adapt to these challenges and events. Because of these changes in society, ideas and ways of life also affect the entire culture. For example, during World War II, many American men were sent far off to fight. Consequently, women were suddenly needed to work in the factories. As a result of this change, it is no longer culturally acceptable to believe that they should not have the right to work.

    I always feel sorry for world leaders busy dealing with fights between nations. When my three children were young, most days it was hard to keep my house from becoming a battlefield.

    It got worse as they grew older. Three years ago, Zack, then 16, couldn't make it through a day without making his sisters, Alex 11 and Taryn 9, angry.

    My husband and I tried to be understanding the boy at such an age. We reasoned, punished, and left heartfelt notes on his bed about how he was hurting our family. His answer was" I say it because it's true."

    I even tried telling the girls to fight back. Bad idea. Now I had three children at war. Whatever I said to them, they paid no attention. When there was no way out, I told everything to my sister, Mary, in an e-mail. She replied, "Don't e-mail me. E-mail him."

    Our son was online every day, mailing and talking with his friends. Maybe he would actually hear me this way. I didn't say anything different, but e-mail just took the tension away. There'd be no shouting or door banging. Zack wouldn't feel under attack.

    Zack didn't reply for days. When he finally did, his entire message was four small words. I smiled when I read them: "You're right. I'm sorry."

    The children still fought, of course, but Zack changed. Best of all, I now have a better way to talk with not one but three of them. I like it that they don't tune me out as much as they used to. They like not having to listen to me shouting to them. Or as Alex says, "You're so much nicer online."

    All I know is that the house is quiet. But we're talking.

    Peter Damon produces about 30 paintings a year and sells them for between US$250 and US$1,500. That's not enough to make ends meet, but it has made him whole again. He lost both arms in an accident.

    "Having this skill that even normal people find difficult was something that really helped me and made me feel like I fit in more in the world," Damon said.

    He was a worker in a car factory. One day when he was working, there was a gas explosion (爆炸), killing one worker and injuring him.

    "I lost my right arm above the elbow, about three inches above the elbow, and my left about six inches below," he explained.

    "How am I going to make a living and take care of my family? I had always worked with my hands," he said.

    Then with a simple little drawing, a new future opened up for him.

    "I thought it was wonderful in a way," Damon said. "Something was telling me to focus on this and everything will be alright." Damon doesn't have a perfect prosthetic arm (假肢)—just a hook (钩子), which he finds works best.

He and his wife Jen run True Grit Art Gallery in Middleboro, Massachusetts, where he shows the works of local artists. With his disability check from the government, he can afford to be an artist. He is a man doing what he wants with his life, and doesn't look at his situation as a hard time.

    "I don't see it that way," Damon said. "Suffering an injury like this has a way of making you focus on what's important in life."

    He believes his best work is still ahead of him. But with his pictures of simple American scenes, Damon has already produced his best work.

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