LSAT Explanation PT 45, S1, Q2: Commentator: Many people argue that the

LSAT Question Stem

Which one of the following, if true, would most seriously weaken the commentator's argument? 

Logical Reasoning Question Type

This is a Weaken question. 

Correct Answer

The correct answer to this question is C. 

LSAT Question Complete Explanation

The question type for this problem is Weaken, which means we are looking for an answer choice that would undermine the commentator's conclusion or the relationship between the premises and the conclusion.

The commentator's argument can be broken down as follows:

Premise 1: A supernova 300,000 years ago greatly damaged the ozone layer without significant effect on our earliest ancestors.

Premise 2: The supernova's disruption was much greater than the estimated effect of chlorofluorocarbons today.

Conclusion: There is no reason to think that chlorofluorocarbons in the atmosphere harm humans in the same way as the supernova.

An "Evaluate" question for this argument would be: "Were our earliest ancestors as susceptible to the harmful effects of ultraviolet radiation as we are today?"

Now let's analyze the answer choices:

a) Extraterrestrial influences on the ozone layer tend to occur less often than terrestrial ones.

This choice does not weaken the argument because it discusses the frequency of events, not their impact. The commentator's argument is based on the comparison of the impact of two specific events, not their frequency.

b) Natural events, such as the eruption of volcanoes, continue to damage the ozone layer today.

This choice does not weaken the argument because it does not provide information about whether the estimation of the effect of chlorofluorocarbons took into account natural processes like volcanoes. If it did not, this choice might actually strengthen the conclusion by making the chlorofluorocarbons even less important.

c) Our earliest ancestors possessed genetic characteristics making them more resistant than we are to the harmful effects of ultraviolet radiation.

This is the correct answer choice. It weakens the commentator's argument by showing that our earliest ancestors were more resistant to the harmful effects of ultraviolet radiation than we are today. This means that even if the effect of chlorofluorocarbons is less than that of the supernova, it could still be harmful to humans today.

d) The ozone layer regenerates at a slow rate, barring counteractive processes.

This choice does not weaken the argument because it does not address the harm to humans. The commentator's argument is about the current harm to humans, not how harmful chlorofluorocarbons might become or might prove to be over the long run. This answer choice is off-topic and incorrect.

e) Scientists have discovered that genetic changes occurred in our ancestors during the period in which the supernova affected Earth.

This choice does not weaken the argument because it does not establish the nature of the genetic changes. We cannot assume that the changes were the result of increased ultraviolet radiation, that the changes had a harmful effect, or that the changes resulted in decreased genetic protection for today's humans. Because this answer offers no concrete information, this answer choice cannot weaken the argument.