argument150 sally 组作业..必回拍

foreveraUID: 202035

150.The following is a letter to the editor of an environmental magazine.

"The decline in the numbers of amphibians worldwide clearly indicates the global pollution of water and air. Two studies of amphibians in Yosemite National Park in California confirm my conclusion. In 1915 there were seven species of amphibians in the park, and there were abundant numbers of each species. However, in 1992 there were only four species of amphibians observed in the park, and the numbers of each species were drastically reduced. The decline in Yosemite has been blamed on the introduction of trout into the park's waters, which began in 1920 (trout are known to eat amphibian eggs). But the introduction of trout cannot be the real reason for the Yosemite decline because it does not explain the worldwide decline."


Obviously, the argument is ostensively well presented, but not logically reasoned. In the argument the author presents two studies of amphibians in Yosemite National Park and the exclusion of the effect of trout to claim that the decreasing amount of amphibians in Yosemite is the result of water and air pollution. The logic of the author indeed seems credible at the first glance.

However, in the first place, the two studies of amphibians in Yosemite are not convincing to support the conclusion that pollution leads to the decline of amphibians. I have enough reason to doubt that the information in the studies can not represent the real situation of amphibians in Yosemite. For example, by the time in 1992 when the study is made, Yosemite might have been experiencing a regular drop of the amount of amphibians, which may be the result of seasonal change of climate or periodical physical activities of amphibians. Or in 1915 there might be an abnormal increase of amphibians in Yosemite, which misled the investigators of the studies to trust that the number of amphibians in Yosemite is sufficient. Therefore, without mentioning that the conditions and methods of the study are absolutely the same, the data of the studies would not make any sense.

What is more, by simply presenting that the introduction of trout can not the reason for worldwide decline, the author improperly equal the worldwide conditions as those of Yosemite. Quite possibly, the environment in Yosemite is too comfortable for trout to live, and further redundant amount of trout restrains the number of survival amphibian eggs. Meanwhile, as a National Park, it is entirely reasonable that the environment in Yosemite is at least no worse than that of the rest of the world, thus, water and air pollution should not be the most significant reason for the decline. Under this circumstance, improper exclusion of the possibility that it is the introduction of trout that result in the decline of amphibians seriously undermines the credibility of the argument.

Finally, failing to put other possible but reasonable factors into account, the author too hastily asserts there is casualty between pollution and decline of amphibians. Consider, for instance, the decline of amphibians in Yosemite is largely due to the phenomena that most of the amphibians alter their living location to an absolutely new one to continuing their race. Or perhaps because of the changed climate of water quality, the environment of Yosemite is no longer fit for the survival of many species of amphibians. Again, it is even acceptable that some certain species fall in annihilation as now they can not acclimate themselves to the absolutely new environment. Consequently, the argument is far from persuasive as the author omits many paramount factors which might influence the decrease of amphibians.

To sum up, on the basis of the points above, the argument would not definitely lead to the conclusion as the author puts. To better improve the argument, the author needs to make some remedy to overcome these defects.

[ 本帖最后由 staralways 于 2006-2-21 23:36 编辑 ]