Q12 - A recently discovered fossil, which is believed

[Laura Damone]

Question Type:
Sufficient Assumption

Stimulus Breakdown:
Conclusion: The fossil doesn’t provide evidence that birds evolved from dinosaurs. Premises: The fossil could provide evidence that birds evolved from dinosaurs only if the entire fossil came from a single animal. The fossil is a composite of bones collected from various parts of the discovery site.

Answer Anticipation:
In order to prove this conclusion, we need to use the contrapositive of the first premise. In other words, we need to establish that this fossil did not come from a single animal. But all we know is that it's a composite of bones from various parts of the discovery site. So, we should predict an answer that bridges that gap, saying something to the effect of "if it's a composite from various parts of a site, it didn't come from a single animal."

Correct answer:
B

Answer choice analysis:
(A) Doesn’t address the gap. Even if this is true, the argument still has that gaping hole.

(B) A bridge! A perfect match for our prediction. If this is true, it guarantees that the fossil in question isn't from a single animal and therefore can't provide evidence that birds evolved from dinos.

(C) Like A, this one doesn't address the gap or make the argument airtight.

(D) Well-preserved specimen? What's that got to do with anything? This answer could only help us reach our conclusion if we could establish that the fossil in question is not a well-preserved specimen. Then, by contrapositive logic, we could conclude that it isn't from a single animal. But since we don't know how well-preserved our specimen is, this answer doesn't help us prove anything.

(E) Theft? Profits? The accuracy of the fossil record? What's going on here?! This is way outside the scope of this argument, and there's no way it can prove our conclusion.

Takeaway/Pattern:
Most Sufficient Assumption questions have a new concept in the conclusion, but not this one. This argument follows a less common pattern: it applies a principle badly. To make the argument valid, we need to fix this, and establish that the principle does indeed apply to the particular case in question. In cases like these, be on the lookout for term shifts in the stimulus (composite vs. not from a single animal). They tend to account for the gap in reasoning. Predict a Bridge Assumption that will get you from point A to point B and rule out any answers that won't make the argument airtight.

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