LSAT 152 | Section 1 | Logical Reasoning: Q8

LR Question 8 Explanation

QUESTION TEXT: Monarch butterflies must contend with single-celled parasites …

QUESTION TYPE: Flawed Reasoning

CONCLUSION: Migration allows monarch butterflies to avoid parasites.

REASONING: Parasite infections damage butterflies’ ability to fly. Migrating butterflies have way less parasite infections than non-migrating butterflies.

ANALYSIS: The first sentence is the key clue. If you’re infected by the parasites, it’s more difficult to fly.

That gives us an alternative explanation for why migrating populations have lower infection rates: infected butterflies may be less able to migrate in the first place.

In other words, it’s not that non-migrating butterflies have infections because they didn’t migrate. It’s because they’re infected, they can’t fly, so they’re not migrating.

So the argument confuses correlation with causation. It assumes that migration helps butterflies avoid parasites, but the data can also point to the opposite causation: infections prevent migration.

___________

1. Sure, but this disadvantage applies to all monarch butterflies. It doesn’t help explain the difference in infections between different butterflies.
2. The argument compares migration to no migration. We don’t care about types of migration.
3. We’re dealing with percentages, not absolute numbers. So the relative size of each population doesn’t affect the argument.
4. CORRECT. This is the flaw I described. Maybe migration doesn’t prevent parasites, but infected butterflies can’t migrate. That means mostly uninfected butterflies are left in the migrating populations.
5. This might give another reason to explain the decision to migrate or not. But it doesn’t help explain the difference in infections.