LSAT Explanation PT 23, S2, Q8: The caterpillar of the monarch butterfly

LSAT Question Stem

Which one of the following, if it were discovered to be true, would most seriously undermine the argument? 

Logical Reasoning Question Type

This is a Weaken question. 

Correct Answer

The correct answer to this question is D. 

LSAT Question Complete Explanation

First, let's break down the argument in the passage. The argument's structure is as follows:

Premise 1: Monarch caterpillars feed on milkweed plants, making adult monarchs poisonous to many predators.

Premise 2: Viceroy butterflies look very similar to monarchs but do not feed on milkweed plants.

Conclusion: The viceroy is so seldom preyed on because of its visual resemblance to the monarch.

To make this more relatable, imagine two different types of candies: one is extremely spicy (monarchs), and the other looks almost identical but is not spicy (viceroys). If many people avoid the spicy candy, it might be assumed that they also avoid the non-spicy candy because it looks so similar to the spicy one.

An "Evaluate" question for this argument could be: "Are there any other reasons why predators might avoid the viceroy butterfly?"

Now, let's discuss the answer choices for the Weaken question, which asks us to find the choice that would most seriously undermine the argument.

a) Some predators do not have a toxic reaction to insects that feed on milkweed plants.

- This answer choice does not weaken the argument because it only addresses the predators that do not have a toxic reaction, leaving the argument about the visual resemblance intact.

b) Being toxic to predators will not protect individual butterflies unless most members of the species to which such butterflies belong are similarly toxic.

- This choice does not weaken the argument because it focuses on the protection of individual butterflies, not the reason why predators avoid the viceroy butterfly.

c) Some of the predators of the monarch butterfly also prey on viceroys.

- This choice does not weaken the argument because it only mentions that some predators prey on both butterflies, but it does not address the main reason why the viceroy is seldom preyed on.

d) The viceroy butterfly is toxic to most predators.

- This is the correct answer choice because it provides an alternative reason for why predators avoid the viceroy butterfly. If the viceroy is toxic as well, then predators might avoid it due to its toxicity, not just because it looks like the monarch butterfly.

e) Toxicity to predators is the principal means of protection for only a few butterfly species.

- This choice does not weaken the argument because it does not address the specific reason why predators avoid the viceroy butterfly. It only provides general information about butterfly species and their means of protection.