PrepTest 124, Section 2, Question 22
Paleontologists recently discovered teeth from several woolly mammoths(64 more words not shown)
Which one of the following,(10 more words not shown)
- ANeither tooth size(16 more words not shown)
- BThe tooth wear(30 more words not shown)
- CUnusually small mammoth(19 more words not shown)
- DTooth size among(14 more words not shown)
- EWoolly mammoths of(21 more words not shown)
Reading the argument
Small teeth could belong to a small mammoth. But do they have to?
On first reading, I'd also wonder how the teeth reached the island. Could people have carried them there? And are the teeth we found a good sample? Notice, though, that the conclusion expressly assumes the teeth represent their respective populations. We should work within that condition rather than keep attacking the sampling issue it sets aside.
The remaining question is what the teeth tell us about the animals' bodies. Perhaps the island mammoths had full-sized bodies but smaller teeth because they ate different food. That's a hypothetical alternative, not an established explanation. It shows the missing link between the size of one body part and the size of the animal.
What we’re looking for
We need an assumption that makes the conclusion follow. My prediction is a reliable size connection: adult mammoth tooth size must track overall body size. If the relationship is fixed, the smaller average teeth would establish smaller average mammoths, given the representative samples the conclusion specifies.
Working the answers
- A
Variation in size doesn't tell us how tooth size and body size relate. Adult animals can vary without smaller teeth reliably indicating smaller bodies. A leaves open the possibility of large-bodied mammoths with small teeth, so it cannot establish the proposed comparison.
- B
This removes tooth wear as an explanation for substantially smaller teeth. But even if no teeth wore down at all, we would still need to connect their size with body size. Ruling out one explanation for the teeth doesn't prove that the animals themselves were smaller.
- C
We are explicitly told the island teeth are adult teeth. Finding that unusually small teeth elsewhere came from juveniles doesn't supply the missing relationship between adult tooth size and adult body size. It doesn't establish the size of these island adults.
- DCorrect
A fixed proportional relationship lets us use adult tooth size as a measure of overall mammoth size. With that rule, a mammoth's smaller teeth indicate a proportionately smaller body. Apply the same relationship across the representative samples, and the smaller average teeth on the island establish the smaller average body size.
This closes the gap the argument left open. We no longer have the possibility of the same-sized adult mammoths simply having disproportionately small teeth.
- E
Having the same number and kinds of teeth doesn't tell us how large the body is. Two mammoths could have the same assortment of teeth but different relationships between tooth size and body size. We need a size connection, not merely a matching dental inventory.
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