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Industrial Melanism: The Case of the Peppered Moth

自然选择的概念是，在一个物种中，具有有利生存特征的有机体最有可能生存下来，并产生具有相同特征的后代。

The idea of natural selection is that organisms in a species that have characteristics favoring survival are most likely to survive and produce offspring with the same characteristics.

因为在同一物种中，具有特定特征的生物比没有这些特征的其他生物更容易生存，所以该物种的后代很可能会包括更多具有这些特征的生物。

Because the survival of organisms with particular characteristics is favored over the survival of other organisms in the same species that lack these characteristics, future generations of the species are likely to include more organisms with the favorable characteristics.

自然选择的一个最彻底的分析例子是在过去的100年里，在欧洲工业地区的某些种群中发生的颜色变化。

One of the most thoroughly analyzed examples of natural selection in operation is the change in color that has occurred in certain populations of the peppered moth, Biston betularia, in industrial regions of Europe during the past 100 years.

最初，蛾子的颜色都是灰白色；深色（黑色）个体是罕见的，只占种群数量的不到2%。

Originally moths were uniformly pale gray or whitish in color; dark-colored (melanic) individuals were rare and made up less than 2 percent of the population.

经过几十年的时间，深色的形体在某些种群中所占的比例越来越大，并最终在某些地区成为斑点蛾种群的主导——尤其是那些极端工业化的地区，如德国的鲁尔山谷和英国的中部地区。

Over a period of decades, dark-colored forms became an increasingly large fraction of some populations and eventually came to dominate peppered moth populations in certain areas—especially those of extreme industrialization such as the Ruhr Valley of Germany and the Midlands of England.

工业用煤向环境中排放了大量的黑色煤烟，但深色斑点蛾的增加并不是由于工业污染引起的基因突变。

Coal from industry released large amounts of black soot into the environment, but the increase of the dark-colored forms was not due to genetic mutations caused by industrial pollution.

例如，以被煤烟覆盖的树叶为食的毛虫不会长成深色的成虫。

For example, caterpillars that feed on soot-covered leaves did not give rise to dark-colored adults.

相反，污染促进了深色斑点蛾在被煤烟覆盖的树上的生存。

Rather, pollution promoted the survival of dark forms on soot-covered trees.

在非工业地区，深色蛾通常通过逆向选择迅速消失；鸟类很容易就发现了它们。

Melanics were normally quickly eliminated in nonindustrial areas by adverse selection; birds spotted them easily.

在污染地区深色突变体的频率增加，这种现象被称为工业化黑变。

This phenomenon, an increase in the frequency of dark-colored mutants in polluted areas, is known as industrial melanism.

这个故事在北美的对应是另一种飞蛾，它是Biston cognataria的swettaria种类，在20世纪初首次发现于芝加哥和纽约市等工业化地区。

The North American equivalent of this story is another moth, the swettaria form of Biston cognataria, first noticed in industrialized areas such as Chicago and New York City in the early 1900s.

到1961年，它占了密歇根州部分地区种群的90%以上。

By 1961 it constituted over 90 percent of the population in parts of Michigan.

20世纪50年代，牛津大学的H·B·D·凯特维尔（H· B· D·Kettlewell）提出了“自然选择导致了深色和浅色斑点蛾比例的变化”的观点。

The idea that natural selection was responsible for the changing ratio of dark- to light-colored peppered moths was developed in the 1950s by H.B.D. Kettlewell of Oxford University.

如果自然选择能够解释，那么深色和浅色蛾子的存活率应该是不同的。

If natural selection was the explanation, then there should be different survival rates for dark- and light-colored moths.

为了确定这是否是真的，凯特维尔在农业和工业地区释放了数千只明暗相间的蛾子——每只蛾子上都有一个油漆斑点标记。

To determine whether this was true, Kettlewell released thousands of light and dark moths (each marked with a paint spot) into rural and industrialized areas.

在多塞特的非工业地区，他捕回了14.6%的浅色形态，但只捕回了4.7%的深色形态。

In the nonindustrial area of Dorset, he recaptured 14.6 percent of the pale forms but only 4.7 percent of the dark forms.

在伯明翰的工业区，情况发生了逆转：13%的浅色形态和27.5%的深色形态被重新捕获。

In the industrial area of Birmingham, the situation was reversed: 13 percent of pale forms but 27.5 percent of dark forms were recaptured.

很明显，某些环境因素导致了黑蛾存活率的提高。

Clearly some environmental factor was responsible for the greater survival rates of dark moths.

凯特维尔假设，正常的浅色形态在苔藓覆盖的树上很难看到，而深色形态则很明显。

Kettlewell hypothesized that the normal pale forms are difficult to see when resting on lichen-covered trees, whereas dark forms are conspicuous.

在工业化地区，地衣被污染破坏，树皮变黑，深色蛾是鸟类很难发现的。

In industrialized areas, lichens are destroyed by pollution, tree barks become darker, and dark moths are the ones birds have difficulty detecting.

作为一个测试，凯特维尔设置了隐藏的观察位置，观察鸟儿贪婪地捕食放在不同颜色树干上的蛾子。

As a test, Kettlewell set up hidden observation positions and watched birds voraciously eat moths placed on tree trunks of a contrasting color.

这个测试似乎证明了自然选择的作用产生了一个微小但高度重要的进化，其中鸟类成为选择的力。

The action of natural selection in producing a small but highly significant step of evolution was seemingly demonstrated, with birds as the selecting force.

并不是每个研究人员都相信鸟类的自然选择是观察到的深色斑蛾和浅色斑蛾频次的唯一解释。

Not every researcher has been convinced that natural selection by birds is the only explanation of the observed frequencies of dark and light peppered moths.

然而，最近的数据为凯特维尔关于自然选择的观点提供了额外的支持。

More recent data, however, provide additional support for Kettlewell’s ideas about natural selection.

淡色的斑纹飞蛾正在强势回归。

The light-colored form of the peppered moth is making a strong comeback.

在英国，1965年通过了《清洁空气法》。

In Britain, a Clean Air Act was passed in 1965.

自1959年以来，西里尔·克拉克爵士（Sir Cyril Clarke）一直在他位于利物浦的家中捕捉飞蛾。

Sir Cyril Clarke has been trapping moths at his home in Liverpool, Merseyside, since 1959.

在1975年以前，90%的蛾子是黑色的，但从那以后，黑色的蛾子数量急剧下降，到1989年，只有29.6%的蛾子是黑色的。

Before about 1975, 90 percent of the moths were dark, but since then there has been a steep decline in melanic forms, and in 1989 only 29.6 percent of the moths caught were melanic.

二氧化硫污染的平均浓度从1970年的每立方米约300微克下降到1975年的每立方米不到50微克，此后一直保持相当稳定的状态。

The mean concentration of sulphur dioxide pollution fell from about 300 micrograms per cubic meter in 1970 to less than 50 micrograms per cubic meter in 1975 and has remained fairly constant since then.

如果浅色蛾子的传播速度和上个世纪黑色蛾子的传播速度一样，那么很快黑色蛾子将再次成为利物浦地区的偶尔出现的居民。

If the spread of the light-colored form of the moth continues at the same speed as the melanic form spread in the last century, soon the melanic form will again be only an occasional resident of the Liverpool area.

Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.

The phrase “give rise to” in the passage is closest in meaning to

Paragraph 3 answers all of the following questions about Kettlewell’s experiment EXCEPT:

The word “conspicuous” in the passage is closest in meaning to

Paragraph 4 suggests which of the following about the survival of peppered moths?

The word “convinced” in the passage is closest in meaning to

What is the purpose of paragraph 5 in the passage?

In paragraph 5 the change in the frequency of melanic forms is attributed to which of the following?

Look at the four squares  that indicate where the following sentence could be added to the passage. These contrasting numbers of pale and dark forms recaptured must reflect different survival rates.  Where would the sentence best fit? Click on a square  to add the sentence to the passage.

Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.

Industrial Melanism: The Case of the Peppered Moth The idea of natural selection is that organisms in a species that have characteristics favoring survival are most likely to survive and produce offspring with the same characteristics. Because the survival of organisms with particular characteristics is favored over the survival of other organisms in the same species that lack these characteristics, future generations of the species are likely to include more organisms with the favorable characteristics. One of the most thoroughly analyzed examples of natural selection in operation is the change in color that has occurred in certain populations of the peppered moth, Biston betularia, in industrial regions of Europe during the past 100 years. Originally moths were uniformly pale gray or whitish in color; dark-colored (melanic) individuals were rare and made up less than 2 percent of the population. Over a period of decades, dark-colored forms became an increasingly large fraction of some populations and eventually came to dominate peppered moth populations in certain areas—especially those of extreme industrialization such as the Ruhr Valley of Germany and the Midlands of England. Coal from industry released large amounts of black soot into the environment, but the increase of the dark-colored forms was not due to genetic mutations caused by industrial pollution. For example, caterpillars that feed on soot-covered leaves did not give rise to dark-colored adults. Rather, pollution promoted the survival of dark forms on soot-covered trees. Melanics were normally quickly eliminated in nonindustrial areas by adverse selection; birds spotted them easily. This phenomenon, an increase in the frequency of dark-colored mutants in polluted areas, is known as industrial melanism. The North American equivalent of this story is another moth, the swettaria form of Biston cognataria, first noticed in industrialized areas such as Chicago and New York City in the early 1900s. By 1961 it constituted over 90 percent of the population in parts of Michigan. The idea that natural selection was responsible for the changing ratio of dark- to light-colored peppered moths was developed in the 1950s by H. B. D. Kettlewell of Oxford University. If natural selection was the explanation, then there should be different survival rates for dark- and light-colored moths.  To determine whether this was true, Kettlewell released thousands of light and dark moths (each marked with a paint spot) into rural and industrialized areas.  In the nonindustrial area of Dorset, he recaptured 14.6 percent of the pale forms but only 4.7 percent of the dark forms.  In the industrial area of Birmingham, the situation was reversed: 13 percent of pale forms but 27.5 percent of dark forms were recaptured.  Clearly some environmental factor was responsible for the greater survival rates of dark moths. Birds were predators of peppered moths. Kettlewell hypothesized that the normal pale forms are difficult to see when resting on lichen-covered trees, whereas dark forms are conspicuous. In industrialized areas, lichens are destroyed by pollution, tree barks become darker, and dark moths are the ones birds have difficulty detecting. As a test, Kettlewell set up hidden observation positions and watched birds voraciously eat moths placed on tree trunks of a contrasting color. The action of natural selection in producing a small but highly significant step of evolution was seemingly demonstrated, with birds as the selecting force. Not every researcher has been convinced that natural selection by birds is the only explanation of the observed frequencies of dark and light peppered moths. More recent data, however, provide additional support for Kettlewell’s ideas about natural selection. The light-colored form of the peppered moth is making a strong comeback. In Britain, a Clean Air Act was passed in 1965. Sir Cyril Clarke has been trapping moths at his home in Liverpool, Merseyside, since 1959. Before about 1975, 90 percent of the moths were dark, but since then there has been a steep decline in melanic forms, and in 1989 only 29.6 percent of the moths caught were melanic. The mean concentration of sulphur dioxide pollution fell from about 300 micrograms per cubic meter in 1970 to less than 50 micrograms per cubic meter in 1975 and has remained fairly constant since then. If the spread of the light-colored form of the moth continues at the same speed as the melanic form spread in the last century, soon the melanic form will again be only an occasional resident of the Liverpool area.