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.”
小题1: The underlined word “remains” is closed in meaning to ______.
| A．leftover food | B．animal waste |
| C．dead bodies | D．living environment |
小题2:According to the study described in Paragraph 4, we can learn that ______.
| A．ancient dogs entered North America between 1450 and 1675 AD |
| B．the 11 bones of ancient dogs are not from native American dogs |
| C．the bones discovered by the gold miners were from North American wolves |
| D．the bones studied were not from dogs brought into North America by Europeans |
小题3:What can we know from the passage?
| A．Native Americans domesticated local wolves into dogs. |
| B．Scientists discovered some ancient dog remains in 1920s. |
| C．Latin America’s dogs are different from North America’s in genes. |
| D．Ancient dogs entered North America across the Bering Land Bridge. |
小题4:The first humans into the New World brought dogs along with them because ______.
| A．dogs fed on mice | B．dogs were easy to keep |
| C．dogs helped protect their resources | D．dogs could provide excellent service |
小题5:What does the passage mainly talk about ______.
| A．the origin of the North American dogs |
| B．the DNA
本试题 “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 jour...” 主要考查您对 科教类阅读 等考点的理解。关于这些考点您可以点击下面的选项卡查看详细档案。
科教类阅读的概念：
科教类阅读主要考查考生对书面语篇的整体领悟能力和接受及处理具体信息的能力。试题的取材，密切联系当前我国和世界经济、科技等方面的变化，有关数据的来源真实可信。 科教类文章阅读技巧：
一、材料特点：
这类文章的总体特点是：科技词汇多，句子结构复杂，理论性强，逻辑严谨。具体说来它有以下几个特点：
1、文章中词汇的意义比较单一、稳定、简明，不带感情色彩，具有单一性和准确性的特点。这类文章通常不会出现文学英语中采用的排比、比喻、夸张等修辞手法，一词多义的现象也不多见。
2、句子结构较复杂，语法分析较困难。为了描述一个客观事物，严密地表达自己的思想，作者经常会使用集多种语法现象于一体的长句。
3、常使用被动语态，尤其是一些惯用被动句式。
二、命题特点：
科普类阅读的主要命题形式有事实细节题、词义猜测题、推理判断题以及主旨概括题等，其中推理判断题居多。
三、应对策略：
1、要想做好科普英语阅读理解题，同学们就要注意平时多读科普知识类文章，学习科普知识，积累常见的科普词汇，从根本上提高科普英语的阅读能力。
2、要熟悉科普类文章的结构特点。科普类文章一般由标题(Head line)，导语(Introduction)，背景(Back ground)，主体(Main body)和结尾(End)五部分构成。标题是文章中心思想高度而又精辟的概括，但根据历年的高考情况来看，这类阅读理解材料一般不给标题，而要同学们选择标题。导语一般位于整篇文章的首段。背景交待一个事实的起因。主体则对导语概括的事实进行详细叙述，这一部分命题往往最多，因此，阅读时，同学们要把这部分作为重点。结尾往往也是中心思想的概括，并与导语相呼应，命题者常在此要设计一道推理判断题。
3、在进行推理判断时，同学们一定要以阅读材料所提供的科学事实为依据，同时所得出的结论还应符合基本的科普常识。 科普类阅读应试策略：
【命题趋势】
阅读理解题主要考查考生对书面语篇的整体领悟能力和接受及处理具体信息的能力。试题的取材，密切联系当前我国和世界经济、科技等方面的变化，有关数据的来源真实可信。因此科普知识类文章是每年的必考题。分析历年的科普类文章我们不难发现以下特点：
1、文章逻辑性强，条理清楚，语法结构简单，用语通俗。
2、文章内容注重科技领域的新发现。内容新颖，从而使文章显得陌生，内容抽象复杂。
3、命题方面注意对具体细节的准确理解和以之为依据的推理判断。
4、以人们的日常行为或饮食健康入手，探讨利弊，诠释过程，阐述概念。
【应试对策】
许多考生在考试时感到困惑的是：为什么一些没有超越中学语法和词汇范围的篇章，读起来却不能正确理解，或者要花费很多时间才能读懂呢？这种现象的产生与阅读方法有很大的关系。例如，有的考生在考试时一见到文章就立刻开始读，结果读了半天，还不知道短文讲的是什么，试题要求了些什么，结果浪费了大量的时间，而阅读效果并不好。那么，怎样读效果才好呢？任何一种阅读方法或技巧的使用，都是由篇章特点和试题本身的要求决定的，应根据不同的体裁和试题要求采取不同的策略。
1、浏览。浏览的主要目的就是确定文章的体裁。如果文章属于人物传记、记叙文、故事、科普小品和有关社会文化、文史知识的文章，一般来说，应该先看看文章的试题考查内容，对题目类型做到心中有数，针对不同问题，在通读时有粗有细地去阅读，这样不仅能把握篇章的基本结构和逻辑线索，也能做好有关具体事实信息考查的试题。
2、挖掘寓意，掌握中心思想，推出结论。任何文章，作者在行文时都有一定的写作目的和主要话题。在通读篇章时应该吃透作者的写作意图，抓住文章的主题句，充分发挥自己的想象力和概括力，作出对中心思想的归纳和结论的推断。
3、把握篇章结构，利用上下文进行推测。高考中的阅读理解篇章往往是一个较完整的短文，其结构、思想，前后上下连贯统一。考试时应充分利用这一特点推测一些生词、短语在句中的含义，切莫盲目孤立猜测。
4、综观全篇，前后呼应。这是阅读理解的最后一步，在做完阅读理解题后，要立足于文章整体，再迅速读一遍短文，短文中的问题和答案的设置前后都是相关联的，有着一定的连续性，体现着文章的基本脉络。
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