Because the native salmon in Lake Clearwater had nearly disappeared,

Question

Because the native salmon in Lake Clearwater had nearly disappeared, sockeye salmon were introduced in 1940. After being introduced, this genetically uniform group of sockeyes split into two distinct populations that do not interbreed, one inhabiting deep areas of the lake and the other inhabiting shallow areas. Since the two populations now different genetically, some researchers hypothesize that each has adapted genetically to its distinct habitat.

Which of the following, if true, most strongly supports the researchers' hypothesis?

(A) Neither of the two populations of sockeyes has interbred with the native salmon

(B) When the native salmon in Lake Clearwater were numerous, they comprised two distinct populations that did not interbreed

(C) Most types of salmon that inhabit lakes spend part of the time in shallow water and part in deeper water

(D) One of the populations of sockeyes is virtually identical genetically to the sockeyes originally introduced in 1940

(E) The total number of sockeye salmon in the lake is not as large as the number of native salmon had been many years ago

Saasingh · Answer

A for me.

If one of the newer generation of salmon interbred with the ancient ones, that would be one reason for being "genetically different" from the other group.

So we need to assume A to ensure that "being genetically different" is not because of the above reason, and thus strengthens the facts that genetic difference could be because of habitat.

vpoddar · Answer

Basically, if both the populations of the sockeye salmon interbred with the native ones, there would be some genetic similarity and we need to avoid that, right?

HarshaBujji · Answer

Conclusion :  Distinct Habitat ---> 2 Genetically diff. species (Casual Passage)

Pre-Thinking : 
 Assumption :  As it is a casual passage, All the generic assumptions to a casual passage such as Cause happed before effect, Cause is the only reason for effect ,etc can be applied.

Here, Distinct Habitat should be the  only reason  for the origination of these genetic species.

Which of the following, if true,  most strongly supports the researchers' hypothesis?

(A) Neither of the two populations of sockeyes has interbred with the native salmon 
  In line with our pre-thinking, If this is negated it will shatter the conclusion.

Negation: At least one of the sockeyes interbred with the native salmon.
So this is the reason for the origination of these genetic species, not the habitat. Hence this is an assumption.

(B) When the native salmon in Lake Clearwater were numerous, they comprised two distinct populations that did not interbreed  Irrelvant

(C) Most types of salmon that inhabit lakes spend part of the time in shallow water and part in deeper water  Weakens the conclusion

(D) One of the populations of sockeyes is virtually identical genetically to the sockeyes originally introduced in 1940  OFS

(E) The total number of sockeye salmon in the lake is not as large as the number of native salmon had been many years ago  OFS,Irrelvant

sssanskaar · Answer

First things first. Whenever I start solving a CR that is posted by the legendary nightblade354 , I take a step back and start praying to GMAT gods first. Many trickiest CR questions and explanations posted by you sir have challenged me to the core and have helped me in honing my reasoning ability to my sharpest level. A big thank you!

Coming to the question, I'll admit - initially I was skeptical of option A. I parked it in the backseat but didn't eliminate it altogether. Obviously, as many others have posted, you can reject B,C,D and E because they don't support the conclusion that the two sockeye species are completely different genetically and then it hit me! We HAVE to eliminate any other possibility! And now option A made complete sense. Negating alternate reasoning is the route that the author has taken. Sometimes, a beautifully worded correct option may not strike you at once but in the second read after eliminating the obvious incorrect choices, if you know what you are looking for, you will certainly find the answer!

Pranjal3107 · Answer

This was my line of reasoning too. Can someone please explain if the thinking is correct ?

kartickdey · Answer

Bunuel   bb  
That the two populations are genetically different has been already mentioned as the premise in the argument. This is not the hypothesis of the researchers. Their hypothesis is all about adaptation to habitat because of genetic modification.I really can not understand how option A can weaken the reasercher's hypothesis. Please explain

AbhishekP220108 · Answer

kartickdey . I guess you have read the question incorrectly, the question is about supporting the hypothesis that adaptation of habitat happened because of genetics, not because of any other reasons.

eaat · Answer

I chose B incorrectly, can someone explain why it's A and not B?

A - no they have adapted genetically 
Maybe I am misunderstanding what "adapted genetically" means

B - yes this gives support for the previously native salmons?
C - no this wouldn’t make then adapted genetically to its distinct habitat 
D - no, we are told that they split into 2 distinct populations 
E - has nothing to do this

miag · Answer

Hi,

A) is the classic ruling out a possible theory/alternative option choice type strengthener. By saying that the 2 sockeyes population didn't interbreed with salmon, its ruling out an alternative possible option that could have led to the genetic difference. => more likely to have arisen due to adaptation to deep vs. shallow habitats
B) is irrelevant, it only tells us that native salmon once split into two non-interbreeding groups. It gives no evidence that the sockeye salmon's genetic differences are caused by adaptation to deep vs. shallow habitats.

Hope this helps!

egmat · Answer

Great question! You've correctly identified the hypothesis,  now let me show you how (A) supports it .

The Key Insight: 
You're looking for a direct connection between (A) and habitat adaptation. But  strengthen questions often work indirectly by eliminating alternative explanations .

Here's the logic:

Observed Fact:  The two populations are now genetically different.

Possible Causes: 
• Cause 1: They adapted to their respective habitats (the hypothesis)
• Cause 2: They interbred with native salmon (an alternative explanation)

What (A) Does:

(A) tells us:  "Neither population interbred with native salmon."

This  eliminates Cause 2 . If interbreeding didn't cause the genetic differences, then  habitat adaptation becomes more likely  as the explanation.

The Trap:  Thinking strengtheners must directly mention the hypothesis. They don't! Ruling out competing explanations = strengthening.

Simple Analogy:

Your friend gained  20  pounds. You hypothesize: "It's the pizza."

What strengthens this?
→ "He didn't start any medication that causes weight gain."

This doesn't prove pizza did it, but it eliminates one alternative, making your hypothesis stronger by comparison.

Takeaway: 
 In CR, "strengthen by elimination" is a common pattern . When you see an answer choice ruling out an alternative cause, that's often the correct strengthener!

Answer: (A)

Hope this helps! 🎯

Because the native salmon in Lake Clearwater had nearly disappeared,

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Because the native salmon in Lake Clearwater had nearly disappeared,

Prep Toolkit

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

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Perfect 805 Score Debrief by Julia

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