argu150 求好心人尽情的拍~~鞠躬敬礼~

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ARGUMENT150 - 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."

Grounding on two studies about the decline of the species and numbers of amphibians in Yosemite National Park in California and his own deny about an explanation, the author draws a conclusion that the global pollution of water and air are clearly revealed by the decline in the numbers of amphibians worldwide. At the first glance, the reasoning seems to be appealing. However, after a close scrutiny of the evidence, I have to say that the argument is unconvincing for several fallacies in evidence.
Firstly, the study tells us that form 1915 to 1992, both numbers of species and the numbers of each species reduced in Yosemite National Park. For such a long time, the decline in the park does not mean that it is the pollution of the environment that leads to this and it is possible that all this happen naturally. Like the author mentioned, maybe there is new species which is dangerous to these amphibians coming to the Park and make the numbers of them reduce. Without ruling out this possibility, the conclusion of global pollution is not assured.
Even if the reduced number of amphibians is lead by the pollution of water and air in Yosemite National Park, there is no evidence it is the situation of the whole world. First, the decline in this national park does not mean that this is the trend of the whole world. It is highly possible that in other places, the numbers of the amphibians are increasing. Secondly, even if the number of amphibians worldwide is declined, it does not assure that the environment worldwide is polluted according to the decline worldwide. Consequently, without the information and explanation of the relationship among these facts, the conclusion could not be drawn simply as the speaker does.
Finally, the author’s deny of another explanation is logically unreasonable. At first, the author use the study of a park to prove the whole trends of the world is groundless. As a result, the reason of the opinion that this explanation cannot explain the worldwide decline is not warranted because the author still has not proved that worldwide decline. Then there is a possibility that it is the introduction of trout that result the decline in park and there is no worldwide decrease of the number of amphibians.
To sum up, the argument is logically unpersuasive as it stands. To better evaluate the argument, the author needs more information to make sure that if the decline in the park represents the trends of the whole world and the author should have a second thought when denying an explanation.