gre范文：GRE作文范文大全（138）
In this argument the speaker claims that increased ultraviolet radiation due to thinning of the
Earth's ozone layer is responsible for the significant decline in the number of salamanders who
lay their eggs in mountain lakes, and that this thinning will cause population declines in other
species. To justify these claims the speaker points out that salamander eggs lack a protective
shell and thus their tissues are highly susceptible to radiation damage, then reasons that the
increased radiation must damage these eggs and prevent them from hatching. The argument
is problematic in several critical respects, which render it unconvincing.
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To begin with, the argument assumes that the salamander population is in fact declining, yet
this assumption is not bom out by the mere fact that the number of salamanders laying eggs in
mountain lakes is declining. It is entirely possible that in other locations the salamander
population is increasing. For that matter, perhaps the number of eggs a salamander lays in a
mountain lake is increasing on average. Either scenario, if true, would seriously call into
question any prediction about population changes for salamanders or for other species.
Even if the total salamander population is declining, an inverse correlation between
ultraviolet radiation and salamander population does not suffice in itself to prove that the
former causes the latter. The speaker must account for the possibility that the number of eggs
salamanders lay is declining in all areas--regardless of the amount of radiation reaching the
surface. The speaker must also eliminate all other reasonable explanations for the decline. For
example, if the population of species that prey on salamanders or eat their eggs is increasing,
this would explain the population decline and therefore undermine the speaker's entire
argument.
Even assuming that the total salamander population is declining as a result of increasing
radiation, the speaker cannot reasonably infer that other species are equally vulnerable to a
population decline as a result. Perhaps the absence of a shell, combined with its
mountain-lake location, renders a salamander egg more vulnerable to ultraviolet radiation than
any other type of egg. If so, this fact would cast considerable doubt on the speaker's prediction
for other species. 感谢您阅读《GRE作文范文大全（138） 》一文，出国留学网(liuxue86.com)编辑部希望本文能帮助到您。
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