案例研究:每天的演变

Case Study: Flu, from Pigs to You
::案例研究:从猪到你的流感

One night in April 2009, Eric woke up soaked in sweat. He had a fever of 102.4° F, chills, an intense headache, and body aches. He soon developed a sore throat and a bad cough. The next day, he felt so sick and exhausted that he could hardly get out of bed, and his fever and other symptoms lasted for days. Clearly, this was not just a mild cold virus — Eric most likely had influenza, commonly known as the flu.
::2009年4月的一天晚上,埃里克醒来时汗湿透,他发烧102.4摄氏度、寒冷、头痛和身体疼痛,很快发了喉咙痛和咳嗽,第二天,他感到非常生病和疲惫,几乎无法下床,发烧和其他症状持续了数天,显然,这不仅仅是一种温和的寒冷病毒,埃里克很可能有流感,通常称为流感。

While watching TV as he recovered in bed, Eric saw a news report about a new “swine flu” strain of the influenza virus that was spreading in people throughout North America, particularly in Mexico. It was called the swine flu because,  based on similarities in its genetic sequence with viruses that infect pigs,  scientists thought it most likely originated in pigs. People didn't need to have contact with pigs , however, to catch swine flu. This version seemed to spread directly between people, similar to the typical seasonal flu virus.
::Eric在睡觉时看电视时,他看到一篇关于流感病毒新“猪流感”的新闻报道,这种病毒正在北美各地,特别是在墨西哥蔓延。 猪流感被称为猪流感,因为基于其基因序列与感染猪的病毒的相似性,科学家认为它最可能起源于猪。 然而,人们不需要与猪接触来捕捉猪流感。这个版本似乎在人群之间直接传播,类似于典型的季节性流感病毒。

Eric’s symptoms were similar to those described in the news report on swine flu. Although he was beginning to recover, he saw that others were not so lucky. Many people with swine flu developed severe pneumonia, and some even died! Because this was a new strain of flu virus that was significantly different than the previous seasonal flu viruses, the existing flu vaccine was largely ineffective against swine flu. The only way to try to prevent infection by the swine flu was to limit exposure to the virus ( and people with the flu)  and to use  good hand washing practices. The news report showed people in Mexico wearing masks as they went about their daily lives, in hopes of preventing exposure.  
::Eric的症状与关于猪流感的新闻报道所描述的症状相似。 虽然他开始恢复,但他看到其他人并不那么幸运。 许多猪流感患者患上了严重的肺炎,有些人甚至死亡了。 由于这是一种新的流感病毒菌株,与以前的季节性流感病毒大不相同,现有的流感疫苗对猪流感基本上没有效果。 防止猪流感感染的唯一办法是限制病毒(和流感患者)的感染,并采用良好的洗手习惯。 新闻报道显示墨西哥人民在日常生活中戴面罩,希望防止感染。

By June 2009, Eric was back to normal, but many other people worldwide were not. Within just a few months, the swine flu had spread from North America to over 70 countries and territories throughout the world. The World Health Organization declared the spread of swine flu to be a pandemic, meaning that a significant portion of the world’s population was infected. In September 2009, over 99 percent of the influenza viruses circulating in the U.S. were  the swine flu strain, which is also known as the 2009 H1N1 virus. If you had the flu in the U.S. during this time period, chances are high that it was the swine flu.
::到了2009年6月,埃里克(Eric)恢复了正常,但全世界还有许多人没有恢复正常。仅在几个月之内,猪流感就从北美蔓延到全世界70多个国家和领土。世界卫生组织宣布猪流感蔓延为流行病,这意味着世界人口中有很大一部分是感染的。 2009年9月,99%以上在美国传播的流感病毒是猪流感菌株,也被称为2009 H1N1病毒。 如果在此期间,你在美国感染流感的可能性是猪流感。

How could a new viral strain like this emerge so suddenly? And how could it change from infecting pigs to infecting humans? This is an example of evolution in action. You may think of evolution as something that occurred in the distant past, for instance, the way  humans evolved from earlier primates — but evolution is occurring all the time. As you will learn in this chapter, evolution is the process by which characteristics of biological entities (such as living organisms or viruses) change over time. Evolution can occur very slowly or more quickly, but it is particularly rapid in viruses and bacteria. In the Case Study Conclusion for this chapter, you will learn specifically about how the 2009 H1N1 virus evolved from a virus that infects pigs to one that infects humans.
::这样一种新的病毒菌株怎么会突然出现呢?它是如何从感染猪变成感染人类的?这是一个行动进化的范例。你可以把进化看作是在遥远的过去发生的事物,例如人类从早期灵长类进化的方式,但进化一直在发生。正如你在本章中将学到的那样,进化是生物实体(如生物有机体或病毒)特性随时间变化的过程。进化可以非常缓慢或更快地发生,但病毒和细菌的进化特别快。在本章的案例研究结论中,你将具体了解2009年H1N1病毒是如何从感染猪的病毒演变到感染人类的病毒的。

Chapter Overview: Biological Evolution
::第一章 概述:生物演变

In this chapter, you will learn about the theory of evolution, evidence for evolution, how evolution works, and the evolution of living organisms on Earth. Specifically, you will learn about:
::在本章中,你们将学习进化理论,进化的证据,进化如何运作,以及地球上生物体的进化。具体来说,你们将了解:

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• Darwin’s theory of evolution by natural selection and how he developed this theory
  ::达尔文的自然选择进化理论以及他如何发展这一理论
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• Evidence for the theory of evolution from fossils, DNA, and observations of living organisms
  ::化石、DNA和生物生物体观测进化理论的证据
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• Microevolution, which is evolution that occurs over a relatively short period of time within a population
  ::微进,这是在人口内部相对较短的一段时期内发生的演变过程。
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• How allele frequencies in a population change due to the forces of evolution, which include mutation, gene flow, genetic drift, and natural selection
  ::包括突变、基因流动、基因漂移和自然选择在内的演变力量导致人口变化的频率如何变化
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• Macroevolution, which is evolution that occurs at or above the species level. This includes the generation of new species and coevolution between species.
  ::宏观进化,即在物种水平上或以上发生的演化,包括新物种的产生和物种之间的演化。
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• Influences on the timing of macroevolution
  ::对宏观革命时间的影响
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• The tools used by scientists to study evolution, including the fossil record, methods of establishing the age of fossils, and molecular clocks based on DNA or amino acid sequences
  ::科学家用来研究演变的工具,包括化石记录、确定化石时代的方法和以DNA或氨基酸序列为基础的分子钟
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• How the history of Earth can be broken into units of geologic time, which helps in the study of evolution
  ::如何将地球历史分解成地质时间的单位,帮助研究进化
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• The formation of the earth, the possible origins of life on Earth, the earliest cells, and the evolution of eukaryotes
  ::地球的形成,地球上生命的可能起源,最早的细胞,以及eukaryotes的进化
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• The evolution of sexual reproduction and multicellular organisms, including invertebrates, vertebrates, plants, dinosaurs, and mammals during the late Precambrian and Mesozoic Eras; and the roles of climate and geologic changes in mass extinctions and evolution
  ::性生殖和多细胞生物,包括无脊椎动物、脊椎动物、植物、恐龙和哺乳动物在已故Precambrian和Mesozoic Eras期间的演变;气候和地质变化在大规模灭绝和演变中的作用
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• Our current geologic time period (the Cenozoic Era) and the climate, geologic, and evolutionary changes during this era, including the diversification and dominance of mammals and the evolution of our species , Homo sapiens
  ::我们目前的地质时期(生态时代)和这个时代的气候、地质和进化变化,包括哺乳动物的多样化和主导地位,以及我们人类的进化,人类的基因人

As you read this chapter and learn more about evolution, think about the following questions about the swine flu virus:
::想想猪流感病毒的以下问题:

1. Viruses can replicate quickly. Why does this contribute to their rapid rate of evolution?  
::1. 病毒可以迅速复制,为什么这会促使其迅速演变?

2. Mutation plays an important role in the evolution of viruses. How does mutation relate to evolution?
::2. 变异在病毒进化中起着重要作用,变异与进化有何关系?

3. One of the reasons that  the 2009 H1N1 swine flu virus evolved is that different types of influenza viruses can exchange genetic material with each other if they infect the same host. This process is called reassortment. Why might this lead to a new strain of influenza virus with different characteristics? How is this similar to the genetic variation produced by sexual reproduction?
::3. 2009年H1N1猪流感病毒演变的原因之一是,不同种类的流感病毒如果感染同一宿主,可以相互交换遗传物质,这一过程被称为再保险,为什么这会导致具有不同特性的新流感病毒菌株?这与性生殖产生的基因变异有何相似之处?

4. It is thought that contact between North American and Eurasian pigs (possibly through international trade) may have contributed to the evolution of the swine flu virus. What are some other cases in which the movement of organisms or contact between organisms has contributed to evolutionary changes?
::4. 据认为,北美猪与欧亚猪之间的接触(可能通过国际贸易)可能有助于猪流感病毒的演变,而生物体的移动或生物体之间的接触又促成进化变化的其他情况又有哪些?