PrepTest 133, Section 1, Question 19
Anthropologist: It was formerly believed that prehistoric Homo(35 more words not shown)
Which one of the following(8 more words not shown)
- AAt least some(19 more words not shown)
- BDNA testing of(13 more words not shown)
- CThe DNA of(23 more words not shown)
- DNeanderthals and prehistoric(13 more words not shown)
- EAny similarity in(11 more words not shown)
Reading the argument
One Neanderthal's remains are supposed to settle whether two populations ever interbred?
I want to know how representative that individual is. Even if this particular Neanderthal showed no sign of interbreeding, what about other Neanderthals or other groups of ancient humans? A broad conclusion about the populations needs more than assuming every individual has the same history.
What we’re looking for
The author compares that Neanderthal's DNA with the DNA of contemporary humans and concludes that our prehistoric ancestors didn't interbreed with Neanderthals. The question asks for an assumption required by that reasoning. My first thought is that the author needs this evidence to tell us about the wider history, rather than just the individuals examined. Let's see which missing connection the choices address.
Working the answers
- A
Living at the same time and in the same places would provide an opportunity for interbreeding. But the anthropologist is concluding that interbreeding didn't happen. That conclusion doesn't require the opportunity to have existed. The author could deny interbreeding whether the populations met or never encountered one another.
- B
The argument doesn't compare two methods of DNA testing. It relies on the test of the remains; it doesn't need to assume that this test is less reliable than testing living samples. Making the evidence less reliable would hardly supply the missing connection from today's DNA to prehistoric events.
- CCorrect
This identifies another problem in the comparison: today's humans aren't the prehistoric humans in the conclusion. What if our ancestors' DNA was much more similar to Neanderthal DNA, and the difference grew over the generations afterward? Then the present difference wouldn't show that the ancient populations never interbred.
C rules out that possibility by saying the ancestors' DNA wasn't significantly more similar than modern human DNA is. The author needs that connection to use the modern comparison as evidence about prehistoric humans. This doesn't fix every possible problem, including our concern about the single Neanderthal. An assumption can be required for the offered reasoning without making the whole argument conclusive.
- D
Complete geographic isolation would help explain a lack of interbreeding, but it isn't required. Two groups could live near each other without interbreeding, just as living on the same street doesn't mean every pair of neighbors has children together. The argument doesn't have to claim that physical separation was total.
- E
The evidence is a DNA difference, and the conclusion denies interbreeding. E instead says every similarity must come from interbreeding. The author doesn't need that sweeping claim about all similarities between species. Even accepting E wouldn't supply the missing comparison between modern humans and their prehistoric ancestors.
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