您IP所在的地区,暂不支持官方真题素材

建议使用其他功能进行阅读练习

返回
小站备考
托福
托福阅读
Official36阅读真题

托福official36阅读第3篇Industrial Melanism: The Case of the Peppered Moth题目解析

展开
Industrial Melanism: The Case of the Peppered Moth
Tip:单击查看句义;划选/双击查生词
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 Kettleweir'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.

1.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.

你的答案:
正确答案:D
题目解析:
 后才能查看题目解析,还没有账号? 马上注册
本题所说高亮部分定位在这里: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. 这句话的大意是黑色的蛾子在所有蛾子中所占比例逐渐加大,进而在某些地区成为了优势物种,特别是在有大型工业的地区。选项D是这句话的同义转述,选择;选项A是说这种黑色蛾子在英国和德国工业地区数量增长最快,原文里并没有提,错误;选项B是说黑色蛾子来到了两个工业地区,并快速繁殖,占领优势地位,因果关系错误;选项C是说黑色蛾子把浅色蛾子赶走了,原文里也没有说。选择D。

学习页面

Medi

terr

anean

加强 + 政府 + 名词后缀

加强的政府——管理

原文例句

加入生词

本文生词 0

色块区域是你收藏过的生词;

查询次数越多,颜色越深哦~

显示文中生词

登录后才能收藏生词哦,现在登录注册>

本文重点词 45

文中加粗单词为本文重点词;

根据词频与核心词范围精心挑选,托福考试必掌握词汇。

显示文中重点词
学习本文词汇

文中划选/双击的生词、加粗重点词已收纳至词盒

可随时点击词盒查看哦~

只有在词句精学模式下才能开启词盒功能哦~

我知道了

词盒
收藏
笔记
我的笔记
5000
保存
反馈