PrepTest 115, Section 2, Question 16
Biologists agree that human beings evolved from a(107 more words not shown)
Which one of the following(28 more words not shown)
- ASince it implies(22 more words not shown)
- BSince it implies(23 more words not shown)
- CIt is offered(16 more words not shown)
- DIt is an(18 more words not shown)
- EIt implies that(27 more words not shown)
Reading the argument
How good is the DNA evidence? A match sounds promising, but we'd need to know whether mitochondrial DNA stays similar enough over time to help identify a distant ancestor. That's the objection Dr. Grover raises: this DNA changes too quickly to do the job reliably.
Dr. Stevens-Hoyt favors lungfish based on the DNA match with frogs. Dr. Grover favors coelacanths based on a hemoglobin match with tadpoles. We don't have to decide which scientist has the better test. We need to keep track of what they agree on and where they go their separate ways.
Why are both scientists comparing a fish with a frog or tadpole? They share a starting belief: frogs are related to the fish species from which humans evolved. That makes a resemblance to frogs relevant to the search. The scientists then use different kinds of resemblance to identify different fish.
What we’re looking for
The question asks what role that shared belief plays. I'd describe it as a starting point both scientists accept. Their disagreement concerns which fish to choose, not whether the frog connection is relevant.
Working the answers
- A
The shared belief doesn't rule out lungfish. In fact, Dr. Stevens-Hoyt uses the frog connection to support the lungfish claim. Saying the ancestor was related to frogs leaves open which species of fish it was.
- B
This makes the same mistake with the other candidate. Dr. Grover relies on a resemblance to tadpoles to support the coelacanth claim. The shared starting point does not say that coelacanths are excluded.
- C
Two proposed answers aren't necessarily the only possible answers. Perhaps another scientist would argue for a third species. The passage describes the lungfish and coelacanth positions without claiming that human ancestry must come down to those two choices.
- DCorrect
Both scientists begin with the frog connection and use it in their arguments about human ancestry. One then looks at mitochondrial DNA; the other looks at hemoglobin. Their different conclusions do not erase the assumption they share.
- E
Watch what is being compared. The scientists compare fish with frogs or tadpoles, not lungfish with coelacanths. And the shared belief doesn't establish that either kind of chemical match would settle human ancestry. Dr. Grover specifically disputes the reliability of mitochondrial DNA for that purpose. E turns a common starting point into a much stronger claim about what would prove the answer.
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