A

    When people first walked across the Bering Land Bridge thousands of years ago, dogs were by their sides, according to a study published in the journal Science.

    Robert Wayne of the University of California, Los Angeles, and Jennifer Leonard of the Smithsonian Institute, used DNA material—some of it unearthed by miners in Alaska—to conclude that today's domestic dog originated in Asia and accompanied the first humans to the New World about 10,000 to 15,000 years ago. Wayne suggests that man's best friend may have enabled the tough journey from Asia into North America. “Dogs may have been the reason people made it across the land bridge,” said Wayne. “They can pull things, carry things, defend you from fierce animals, and they're useful to eat.”

    Researchers have agreed that today's dog is the result of the domestication(驯化) of wolves thousands of years ago. Before this recent study, a common thought about the precise origin of North America's domestic dog was that Natives domesticated local wolves, the descendents(后代) of which now live with people in Alaska, Canada, and the Lower 48.

    Dog remains from a Fairbanks-area gold mine helped the scientists reach their conclusion. Leonard, an evolutionary biologist, collected DNA from 11 bones of ancient dogs that were locked in permafrost(永冻层) until Fairbanks miners uncovered them in the 1920s. The miners donated the preserved bones to the American Museum of Natural History in New York City, where they remained untouched for more than 70 years. After borrowing the bones from the museum, Leonard and her colleagues used radiocarbon techniques to find the age of the Alaska dogs. They found the dogs all lived between the years of 1450 and 1675 A.D., before Vitus Bering and Aleksey Chirikov who were the first known Europeans to view Alaska in 1741. The bones of dogs that wandered the Fairbanks area centuries ago should therefore be the remains of “pure native American dogs,” Leonard said. The DNA of the Fairbanks dogs would also expose whether they were the descendents of wolves from North America.

    Along with the Fairbanks samples, the researchers collected DNA from bones of 37 dog specimens(标本) from Mexico, Peru, and Bolivia that existed before the arrival of Columbus. In the case of both the Alaska dogs and the dogs from Latin America, the researchers found that they shared the most genetic material with gray wolves of Europe and Asia. This supports the idea of domestic dogs entering the New World with the first human explorers who wandered east over the land bridge.

    Leonard and Wayne's study suggests that dogs joined the first humans that made the adventure across the Bering Land Bridge to slowly populate the Americas. Wayne thinks the dogs that made the trip must have provided some excellent service to their human companions or they would not have been brought along. “Dogs must have been useful because they were expensive to keep,” Wayne said. “They didn't feed on mice; they fed on meat, which was a very guarded resource.”

    “We leave at dawn and head out overland by jeep towards Base One. We will get as far as we can before proceeding on foot,” Mark explained. The others sat and listened. Sarah, particularly, as a “casualty of events”, wouldn't have known what to say or suggest even if she'd been asked. But Harry had a lot to say.

    “We'll never make it,” he protested(抗议). “We'll still be crossing the desert when they catch up with us. They'll know where we're heading for and they seem to know every move we make or are going to make.”

    Mark said nothing, but spread his hands out as if to say “Well, what do we do then?” “We wouldn't be in this mess now,” Harry went on, almost ignoring Mark's gesture, “if we hadn't stopped to rescue Sarah.”( He glanced at her briefly.) “But since we did, we must get on—but not across the desert. There is the sand, and deep ravines (沟壑) which are almost invisible until you're right on them and then the heat. You have to be used to going out there, and none of us is. This is no ‘morning at leisure' on some pleasant holiday, you know! If we went north instead and made for the river,…"

    He broke off and looked around at the others, feeling somehow that his argument was pointless. No one said anything.

    “Good,” said Mark, look around with authority, and returned to checking their stores.

    A beautiful sunrise was about to burst over the horizon as the jeep headed out towards Base One.

    Food storing is common in members of the crow（乌鸦）family. A new study tested the birds outside this naturally occurring behaviour, which may have evolved（进化）specifically because it gives crows a survival advantage. Some crow species are known to naturally use tools to recover food. So the researchers tested whether the birds could store and recover a tool so they could get it at their food after a gap of 17 hours—something we wouldn't expect them to do naturally. But they were able to instantly select the tool out of a number of unnecessary items.

    In another experiment, the researchers taught crows to select a token （礼品券）from a number of items so that they could then exchange for food. Again, the birds then showed that they could plan for the future using this new behaviour. This is different from all of the previous studies in future planning, which have focused on naturally occurring behaviour. For example, we know that chimpanzees select, transport and save appropriate tools for future needs.

    These studies have shown that animals can plan for the future—but they left an important question open for debate. Are animals only able to plan to use abilities that have evolved to give them a specific advantage, or can they flexibly and intelligently apply planning behaviour across various actions? Most critics would say the former, as the animals were tested in naturally occurring behaviours.

    But the new research provides the first evidence that animal species can plan for the future using behaviour that doesn't typically occur in nature. This supports the view that at least some recognitive abilities in animals don't evolve just in response to specific problems. Instead, it suggests that animals can apply these behaviours flexibly across problems in a similar way to humans. We need to investigate how flexible behaviour evolved. Then we might be able to see how crows' ability to plan for the future fits in with their broader cognitive powers.

    The year is 2094. It has been announced that a comet (彗星) is heading towards the Earth. Most of it will miss our planet, but two pieces will probably hit the southern half of the Earth.

    On 17 July, a piece four kilometers wide enters the Earth's atmosphere with a massive explosion. About half of the piece is destroyed, but the remaining part hits the South Atlantic at 200 times the speed of sound. The sea boils and a huge hole is made in the sea bed.  Huge waves are created and spread outwards from the hole. The wall of water, a kilometer high, rushes towards southern Africa at 800 kilometers an hour. Cities on the African coast are totally destroyed and millions of people are drowned.

    Before the waves reach South America, the second piece of the comet lands in Argentina. Earthquakes and volcanoes are set off in the Andes Mountains. The shock waves move north into California and all around the Pacific Ocean. The cities of Los Angeles, San Francisco and Tokyo are completely destroyed by earthquakes. Millions of people in the southern half of the earth are already dead, but the north won't escape for long. Because of the explosions, the sun is hidden by clouds of dust, temperatures around the world fall to almost zero. Crops are ruined. The sun won't be seen again for many years. Wars break out as countries fight for food. A year later, no more than 10 million people remain alive.

    Could it really happen? In fact, it has already happened more than once in the history of the Earth. The dinosaurs were on the Earth for over 160 million years. Then 65 million years ago they suddenly disappeared. Many scientists believe that the Earth was hit by a piece of object in space. The dinosaurs couldn't live through the cold climate that followed and they died out. Will we meet the same end?

    According to a British study presented to an international conference on smoking, within a few short years, more girls in Europe will be smokers than boys, for reasons experts still fail to understand.

    Anti-smoking activists (积极分子) at the second "Tobacco or Health" conference on the Canary Islands pointed out that while adults were giving up smoking in ever growing numbers, more and more young people were taking up the habit, especially girls.

    One 15-year-old in four is a regular smoker, according to a study made in 27 countries in Europe, the United States, Canada and Israel by Edinburgh University together with the World Health Organization.

    In Western Europe, girls were more likely than boys to smoke. In Germany and England, one third of the girls were smokers compared to one in four boys. In Eastern Europe, the girls "still fall behind" those in the Western Europe but were "catching up" quickly, said the study.

    The study dealt with the behaviour of 15-year-olds in seven European countries over a four-year period.

    The percentages of young women smoking went from 17 percent to 36 percent in Austria, from 17 percent to 28 percent in Norway, and from 21 percent to 28 percent in Hungary.

    Of the seven countries and regions studied (Austria, Finland, Hungary, Norway, Sweden, Switzerland and Wales), more girls than boys smoked in 1998, with the exception of Hungary.

    The Lantern Festival falls on the 15th of the first month of the lunar calendar. This day is always the first full moon in the new year. Ancient people also called it Shangyuan Festival. Celebrations and traditions on this day began from the Han Dynasty and became popular in the Tang Dynasty.

    Watching the red lanterns is one of the main traditions. Lanterns of different shapes and sizes are usually put on trees, or along river banks on show. It is said that sky lanterns were first used by Zhuge Kongming to ask for help when he was in trouble. Today, when the lanterns slowly rise into the air, people make wishes. Another tradition is guessing lantern riddles. The riddles are usually short, wise, and sometimes humorous. The answer to a riddle can be a Chinese character, a famous person's name, or a place name.

    The most important thing is to eat sweet dumplings with different tastes. In northern China, they are called yuanxiao while in southern part they're named tangyuan. Because making sweet dumplings is like a game or an activity, they are usually done happily by a group of friends or family members.

    In old times, the Lantern Festival was also a good time for young people to find love. Watching lanterns gave young people a chance to meet each other. And there were many romantic stories about this festival. A line from Xin Qiji, a poet during the Song Dynasty, shows this, "Hundreds and thousands of times I searched for her in the crowd. Suddenly I turned, and there she stood in the dim light. "

    In a word, the Lantern Festival has brought us Chinese so much fun and joy over the years. We hope the young people can carry on these traditions and take pride in Chinese culture.