PrepTest 156

As expected, this strengthens the argument by establishing a correlation between a growing population and overcrowding. This would be an example of "same cause, same effect": historically, as the cause grows ("the size of the world population"), the effect grows too ("frequency and severity of overcrowding increases"). This strengthens the argument by providing evidence that a higher population will generally result in more overcrowding. If more overcrowding increases aggressive behavior, (A) supports the author's conclusion that a higher population will result in more aggressive behavior. We're looking for the answer choice that doesn't strengthen the argument, so let's eliminate (A).

This strengthens the cause-and-effect relationship the author asserts in the conclusion. The author thinks that a growing population will cause more aggressive behavior. This would be an example of "same cause, same effect": this century, as the cause grows ("the world population also increased"), the effect grows too ("frequency and severity of war and crime"). This provides more evidence that a higher population will generally result in more aggressive behavior, strengthening the author's argument. Since we're looking for the answer choice that doesn't strengthen the argument, we can cross off (B).

This doesn't strengthen the argument. Experienced test-takers will immediately notice the weak, wishy-washy language ("some forms"). Answer choices that strengthen (or weaken!) arguments tend to make bolder, more certain claims than this one.

Moreover, this answer choice discusses what happens outside of overcrowded areas. To strengthen this argument, the answer choice would need to show that people are generally less aggressive in these situations. That would be an example of "no cause, no effect" (since overcrowding is the cause and aggressive behavior is the effect). However, this answer choice says that people can be aggressive in these uncrowded areas! So, even ignoring the wishy-washy language, this still doesn't strengthen the argument. Therefore, we can select this and give the remaining answer choices a quick glance.

This strengthens the cause-and-effect relationship the author asserts in the premise/conclusion. The author thinks that overcrowding causes more aggressive behavior. The author bases this on just a few examples — people's behavior in rush-hour traffic and at crowded sporting events. Those two specific examples aren't enough to make a broad claim about human behavior in general. This answer choice establishes that rush-hour traffic is an example of overcrowding, showing that the author's premise is relevant and tends to prove the statement made in the premise/conclusion. Since we're looking for the answer choice that doesn't strengthen the argument, we can eliminate (D).

This strengthens the cause-and-effect relationship the author asserts in the conclusion. The author thinks that a growing population will cause more aggressive behavior. This answer choice is, therefore, an example of "same cause, same effect": historically, as the cause grows ("population density in [a] region"), the effect grows too ("increasingly aggressive, competitive behavior"). This provides more evidence that a higher population will generally result in more aggressive behavior, strengthening the author's argument. Although this answer choice is about mammals generally, human beings are mammals, making this answer choice relevant to the author's conclusion. Since we're looking for the answer choice that doesn't strengthen the argument, we can cross off (E).