LSAT 151 | Section 3 | Logical Reasoning: Q12

LR Question 12 Explanation

QUESTION TEXT: A recently discovered fossil, which is believed by some to come from …

QUESTION TYPE: Sufficient Assumption

CONCLUSION: The fossil doesn’t prove that birds evolved from dinosaurs.

REASONING: It would only prove that birds evolved from dinosaurs if the fossil was from one animal. But the fossil is made up of bones collected from different areas.

ANALYSIS: Let’s diagram the stimulus.

Sentence 1

• Evidence for birds evolving from dinosaurs -> single animal

• Contrapositive: Not single animal -> not evidence

Sentence 2

• Composite -> not evidence

So we have “not single animal -> not evidence” and “composite -> not evidence”.

We need a link between composite and not single animal. If we knew that a composite meant that it must be from different animals, we can conclude that it’s not evidence. That would complete the chain:

Composite -> not single animal -> not evidence

Otherwise, composite could just mean assembled from different parts of a site, not necessarily from multiple animals. In that case, we wouldn’t be able to conclude that because this fossil is a composite, it can’t provide evidence.

___________

1. What some paleontologists believe doesn’t allow us to conclude whether it’s actually from a single animal.
2. CORRECT. This allows us to complete the chain: If composite -> not single animal -> not evidence.
3. Other fossils are irrelevant to whether this fossil counts as evidence.
4. This introduces a new condition that’s not a part of the stimulus (well-preserved).
5. So there’s some shady business happening around the fossil which may cast doubt on its background. That doesn’t help us determine whether a composite is from multiple or only one animal.