Anthropologist: It was formerly believed that prehistoric Homo sapiens

Question

Anthropologist: It was formerly believed that prehistoric Homo sapiens ancestors of contemporary humans interbred with Neanderthals, but DNA testing of a Neanderthal’s remains indicates that this is not the case. The DNA of contemporary humans is significantly different from that of the Neanderthal.

Which one of the following is an assumption required by the anthropologist’s argument?

(A) At least some Neanderthals lived at the same time and in the same places as prehistoric  Homo sapiens  ancestors of contemporary humans.
(B) DNA testing of remains is significantly less reliable than DNA testing of samples from living species.
(C) The DNA of prehistoric  Homo sapiens  ancestors of contemporary humans was not significantly more similar to that of Neanderthals than is the DNA of contemporary humans.
(D) Neanderthals and prehistoric  Homo sapiens  ancestors of contemporary humans were completely isolated from each other geographically.
(E) Any similarity in the DNA of two species must be the result of interbreeding.

Resource: LSAT

GMATNinja · Accepted Answer

The author uses the evidence that "the DNA of contemporary humans is significantly different from that of the Neanderthal" to conclude that prehistoric Homo sapiens ancestors of contemporary humans did NOT interbreed with Neanderthals. In other words, according to the author, if the PHS ancestors of contemporary humans HAD interbred with Neanderthals, the DNA of the Neanderthal would have been passed down to contemporary humans and there would not be significant differences between the DNA of contemporary humans and the DNA of the Neanderthal.

If we negate choice (C), that would mean that the differences between the DNA of contemporary humans and the DNA of their PHS ancestors are COMPARABLE to the differences between the DNA of contemporary humans and the DNA of the Neanderthal. This would tells us that we CANNOT rely on similarity of DNA to determine whether contemporary humans descended from a particular group (since we KNOW that contemporary humans descended from their PHS ancestors).

This would nullify the author's evidence, so choice (C) is the best answer.

I hope this helps!

akshayk · Answer

Old Belief - Prehistoric homesapinen ancestors of contemporary humans interbred with Neanderthals.
Contradiction - DNA testing of Neanderthal remains indicates this is NOT the case.
Result - DNA of contemporary humans is SIGNIFICANTLY different from that of N's.

Which one of the following is an assumption required by the anthropologist’s argument?
 
The argument is about the similarity or lack thereof of the DNA, so this is irrelevant. OUT!

This is a far-fetched assumption that LSAT has made for us, but the argument in no shape or form refers to this idea. OUT!

If pre-historic homosapien's interbred with neanderthals, then the author would have to assume that the contemporary human's DNA has not evolved at all to showcase similarity. And is further proven as the researcher test the DNA of contemporary humans with neanderthals. This is a good option. KEEP!

Contradicts the old belief i.e. the premise so this is OUT!

Let's say this is true, but we did not find any overlap in the DNA. Does that mean they did not interbreed especially when we have not compared the DNA of prehistoric homosapiens with neanderthals. Close, but C is better. This is OUT too!

C is the right answer.

arvind910619 · Answer

Hi mikemcgarry

I chose E but that is not the answer .
C is the answer .
I chose option E because it says similarity in DNA is caused by interbreeding than the DNAs are different and that is why the conclusion follows.
Regarding C I did not understood it in the first place but I'm more close reading it says that the DNA of ancestors is not more similar to the DNA of the Neanderthal than the DNA of the modern human beings .
Please help me in my reasoning and what is rationale for C to be the correct answer

subrataroy0210 · Answer

Anthropologist: It was formerly believed that prehistoric Homo sapiens ancestors of contemporary humans interbred with Neanderthals, but DNA testing of a Neanderthal’s remains indicates that this is not the case. The DNA of contemporary humans is significantly different from that of the Neanderthal.
 
Conclusion: Since DNA of contemporary humans is significantly different from that of the Neanderthal, the prehistoric Homo sapiens ancestors of contemporary humans did not interbreed with Neanderthals.

Falsification Situation: 
1) What if the remains only give partial information about the DNA of the Neanderthals?
2) It is not necessary that when A and B breed, the offspring C will have the DNA traces of both A and B in a significant amount.

Possible assumptions:
1) DNA does not destroy with time and thus the remains do not provide any partial information.
2) The offspring has DNA traces of both the parents in significant proportion.

Which one of the following is an assumption required by the anthropologist’s argument?

(A) At least some Neanderthals lived at the same time and in the same places as prehistoric Homo sapiens ancestors of contemporary humans.
 Negate: No Neanderthals lived at the same time and in the same places as prehistoric Homo sapiens ancestors of contemporary humans.
This rather supports the fact that prehistoric Homo sapiens and Neanderthals did not breed; they never got a chance.
 
(B) DNA testing of remains is significantly less reliable than DNA testing of samples from living species.
 Negate: DNA testing of remains is significantly reliable than DNA testing of samples from living species.
This means that the DNA testing of the remains is reliable and thus the conclusion is okay.

(C) The DNA of prehistoric Homo sapiens ancestors of contemporary humans was not significantly more similar to that of Neanderthals than is the DNA of contemporary humans.
 Negate: The DNA of PHS ancestors of contemporary humans was significantly more similar to that of Neanderthals than is the DNA of contemporary humans.
This information tells us that the PHS is not the ancestors of contemporary human as the DNA will not match. This information destroys the conclusion from within because it makes us believe that the DNA-testing is faulty. This option is a possible conclusion. 
 
(D) Neanderthals and prehistoric Homo sapiens ancestors of contemporary humans were completely isolated from each other geographically.
 Negate: Neanderthals and prehistoric Homo sapiens ancestors of contemporary humans were not completely isolated from each other geographically.
This does not affect the conclusion.

(E) Any similarity in the DNA of two species must be the result of interbreeding.
 Negate: No similarity in the DNA of two species must be the result of interbreeding.
As per the argument, the DNA of contemporary humans and the DNA of the remains of Neanderthals are significantly different but we cannot say that there is no similarity between them. Thus, this information does not affect the conclusion.

Kritisood · Answer

I was down to C and E because of POE, but didnt really understand C, hence chose E. After reading C 5 plus times, i still cant understand how it proves that contemporary humans DNA hasnt evolved at all to showcase similarity. Please help.

CrackverbalGMAT · Answer

One good reason to eliminate option E is the fact that E is a blanket statement of sorts ("any two species") and is extreme. Look at the keywords "any similarity" and "must be".

Now, let's look at Option C: 
(C) The DNA of prehistoric Homo sapiens ancestors of contemporary humans was not significantly more similar to that of Neanderthals than is the DNA of contemporary humans.

One of the reasons why C is overlooked is the convoluted language. Once you disentangle the reasoning, it will be easy to see why it is the right answer.

Let’s try paraphrasing option C – 
The DNA of the PH ancestors was more similar to the DNA of contemporary humans than it was similar to the Neanderthals. This means that the contemporary human’s DNA was not evolved at all—only then would it be significantly more similar to that of the Homo sapiens (ancestors). Does that help?

ngochuyen1904 · Answer

Premise:    
The DNA of contemporary humans is significantly different from that of the Neanderthal

Conclusion:    
Prehistoric Homo sapiens ancestors of contemporary humans interbred with Neanderthals

Pre-think:    
In order to analyze this argument, we have to assume another thing is that If Homo sapiens are ancestors of contemporary humans, then the DNA of contemporary humans has at least some similarity with DNA of Homo sapiens

So, what if DNA of contemporary humans has more similarity with that of Neanderthal than with that of Homo sapiens?
Now, our conclusion collapses. Since how come contemporary humans whose DNA has more similarity with DNA of Neanderthal but contemporary humans are descendants of Homo sapiens, not of Neanderthal? It’s illogical

That’s exactly what  option C  is saying

yc168 · Answer

OE for reference:

Overview:  
The only premise of the anthropologist's argument is that the DNA of contemporary humans is significantly different from that of Neanderthals. The argument concludes that prehistoric  Homo sapiens  did not interbreed with Neanderthals. You are asked to identify an assumption required by this argument.

The Correct Answer:

C  The only support offered in the argument for the conclusion that prehistoric  Homo sapiens  did not interbreed with Neanderthals is that the DNA of contemporary humans is significantly different from that of Neanderthals. But this premise supports the conclusion only by giving us reason to think that the DNA of prehistoric  Homo sapiens  is significantly different than that of Neanderthals. If (C) were not true—if the DNA of prehistoric  Homo sapiens  is a lot closer to that of Neanderthals than the DNA of contemporary humans is—then the fact that the DNA of contemporary humans is significantly different from that of Neanderthals doesn't mean much. So the argument needs to assume that (C) is true in order for the premise to support the conclusion.

The Incorrect Answer Choices:

A  If the anthropologist were arguing that prehistoric  Homo sapiens  did interbreed with Neanderthals, then the argument would need to assume that they lived in roughly the same place at the same time. But this assumption has no place in the argument the anthropologist actually gives, which argues that prehistoric  Homo sapiens  did not interbreed with Neanderthals. The argument that the anthropologist gives is based entirely on the results of DNA testing and never touches on the issue of whether it was possible for Neanderthals and prehistoric  Homo sapiens  to interbreed.

B  In order for the argument's premise about similarity of DNA to support the conclusion, DNA testing of Neanderthal remains has to be reasonably reliable. So (B), which says that testing of remains is significantly less reliable than testing of samples from living species, calls the argument into question. Thus, (B) is not required by the argument.

D  If Neanderthals and prehistoric  Homo sapiens  were completely isolated, that would imply that the argument's conclusion is true. But the anthropologist's argument presents a completely different case for the conclusion. The case made by that argument has nothing to do with Neanderthals and prehistoric  Homo sapiens  being isolated from each other. So even if (D) is not true, the anthropologist's argument is not adversely affected.

E  The argument uses evidence about differences in DNA to argue that there was no interbreeding between two species. So the argument is clearly assuming that if the DNA of two species share certain significant similarities, it is evidence of interbreeding. But that doesn't mean that the argument is assuming that any similarity in the DNA of two species must be the result of interbreeding. That assumption is far broader than what the anthropologist's argument assumes.

kushallagg · Answer

KarishmaB  could you please help with this question?

My thought process:
 Conclusion:  Prehistoric Homo sapiens ancestors of contemporary humans did not interbred with Neanderthals
 Reasoning / Premise:  DNA of contemporary humans is significantly different from that of the Neanderthal
 (C) The DNA of prehistoric Homo sapiens ancestors of contemporary humans was not significantly more similar to that of Neanderthals than is the DNA of contemporary humans:  On negation, this means that ancestors' DNA was similar to Neanderthals but different from contemporary humans.   But   How does this break the conclusion?

egmat · Answer

Hi kushallagg,

You've done the hard part: you negated (C) correctly. The negation says the  ancestors'  DNA  was  significantly more similar to Neanderthal DNA (even though  contemporary  humans' DNA is not). The piece to add is  why that similarity points to interbreeding.

Start with the gap GMATNinja flagged. Look at what the anthropologist actually measured versus what they concluded:

-  Evidence:  the DNA of  contemporary humans  differs a lot from Neanderthal DNA.
-  Conclusion:  the  prehistoric ancestors  did not interbreed with Neanderthals.

Those are two different populations. The anthropologist is quietly using contemporary DNA as a stand-in for the ancestors' DNA. That only works if the ancestors' DNA looked like ours - i.e., if (C) is true.

Now run the negated world.  Suppose the ancestors' DNA  was  very close to Neanderthal DNA. In this argument, DNA similarity is treated as the fingerprint of interbreeding (that's the whole logic of the premise). So ancestors having Neanderthal-like DNA is exactly what interbreeding would produce - the similarity simply got  diluted  over generations until today's humans no longer show it. In that case, contemporary humans' DNA being different from Neanderthals' proves nothing about whether the  ancestors  interbred. The premise no longer supports the conclusion, so the argument falls apart.

That collapse is the test for a required assumption: negate it, and the argument breaks. (C) passes.

Answer: C

guddo · Answer

Anthropologist: It was formerly believed that prehistoric  Homo sapiens  ancestors of contemporary humans interbred with Neanderthals, but DNA testing of a Neanderthal’s remains indicates that this is not the case. The DNA of contemporary humans is significantly different from that of the Neanderthal.
 
 Which one of the following is an assumption required by the anthropologist’s argument?

The anthropologist concludes that prehistoric  Homo sapiens  did not interbreed with Neanderthals because contemporary human DNA is significantly different from Neanderthal DNA.  The argument therefore assumes that contemporary human DNA is sufficiently representative of the DNA of prehistoric human ancestors for this comparison to be meaningful.

(A) At least some Neanderthals lived at the same time and in the same places as prehistoric  Homo sapiens  ancestors of contemporary humans.

Incorrect. This would matter if the argument were trying to show that interbreeding occurred. The argument instead concludes that it did not occur, so geographic and temporal overlap is not required.

(B) DNA testing of remains is significantly less reliable than DNA testing of samples from living species.

Incorrect. This would weaken confidence in the DNA evidence. The argument would instead need the testing to be reasonably reliable.

(C) The DNA of prehistoric  Homo sapiens  ancestors of contemporary humans was not significantly more similar to that of Neanderthals than is the DNA of contemporary humans.

Correct.   If this were false, prehistoric human DNA could have been much more similar to Neanderthal DNA than contemporary human DNA is. In that case,  the present-day DNA difference would tell us little about whether prehistoric humans interbred with Neanderthals . The conclusion might still be true, but the stated evidence would no longer support it. Therefore, the argument requires this assumption.

(D) Neanderthals and prehistoric  Homo sapiens  ancestors of contemporary humans were completely isolated from each other geographically.

Incorrect. If true, this would independently support the conclusion. But the anthropologist’s actual argument is based on DNA evidence and does not require geographic isolation.

(E) Any similarity in the DNA of two species must be the result of interbreeding.

Incorrect. Too strong. The argument may require significant DNA similarity to provide evidence of interbreeding, but it does not require  every similarity  between two species to result from interbreeding.

Answer: (C)

Anthropologist: It was formerly believed that prehistoric Homo sapiens

Prep Toolkit

Top 5 GMAT Debrief Videos

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards

GMAT Critical Reasoning (CR) Questions

Anthropologist: It was formerly believed that prehistoric Homo sapiens

Prep Toolkit

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards