#26 - The three-spine stickleback is a small fish that lives

[Dave Killoran]

Complete Question Explanation

Weaken, CE. The correct answer choice is (B).

This question was notorious, with many students complaining about the difficulty of the problem after the November LSAT.

The stimulus begins with a set of relatively straightforward facts:

• The stickleback is small, and lives in oceans and lakes
  Ocean fish have armor, but lake fish don't

Neither of those pieces of information are all that difficult to understand, so most students were in good shape through the first half of the stimulus.

The trouble comes in the last sentence, which starts with another premise and ends with the conclusion. The premise states that armor limits the speed of the growth of the fish, and that consequently indicates that that for the lake fish, size is a better defense than armor.

This conclusion is confusing, and the last sentence forced most students to stop and hash out what it was being said. If you ever read a stimulus and something isn't clear, stop and make sure you understand what was said!

In this case, a causal argument is being made. Why don't the lake fish have armor? According to the author it is because size is a better defense:

• Cause Effect
  
  Size is No armor
  better defense

This is a confusing relationship because it contains a negative ("no armor"), but the point is that the author is claiming that because having armor causes slower growth, it must be that faster growth is preferable for these fish, and thus the faster growth/size preference (a sort of resilience to predators) is the cause here.

Now, with this confusing causal conclusion in hand, we can move the answer choices.


Answer choice (A): This answer was often selected by students incorrectly on the basis that speed was the explanation for the no armor (and not size). But, we have no information about the predators of the lake stickleback, and whether any of those possess enough speed where this would be an advantage. There is also the possibility that the larger size of the lake stickleback helps the swim faster, thus eliminating this as a possible alternate cause. Size and speed do not have to be mutually exclusive.

This answer can also appear attractive because the stimulus mentions speed, but that is in relation to speed of growth, not speed of swimming. Just the use of the term "speed" in the answer can be enough to attract some test takers.

Answer choice (B): This is the correct answer choice. This answer presents an alternate cause for the lack of armor, namely that size is a factor in surviving the winter for the lake stickleback. Thus, weather (or specifically, winter survivability) is the cause of not having armor, as opposed to size being a better defense against predators causing the lack of armor (or, it's not that size is a better defense, but rather that it's a better way to survive winter). This is a confusing yet distinct difference, which made (B) a difficult answer for many students to spot.

To simplify, the author thought predatory defense (size) was the cause of the lake stickleback not having armor, but (B) suggests that instead it was weather (winter survivability) that caused the lack of armor.

Answer choice (C): This does not provide us with any information to weaken the argument, since we only know how the stickleback responds, not what is actually preying upon the stickleback or how it acts.

Answer choice (D): While this shows a similarity between the two species, it doesn't help us undermine the given cause for the difference between ocean and lake stickleback.

Answer choice (E): The timeline here is no help in weakening the argument since the conclusion is based on what has happened, not exactly when it happened.

[cargostud]

I really disliked this question. The fact that a lake stickleback is larger in size so it can survive cold winters does not reflect information that the average person would be expected to know as common knowledge. I have no idea if having a larger size is better for surviving cold winters. No one told the dinosaurs that.

[Jeremy Press]

Hi cargostud,

I get the dislike, as this is a tough one!

Remember, though, that with Weaken questions the question stem allows you to assume the truth of the answer choices. Notice the phrase "if true" in the question stem. So, you don't have to know independently (or even wonder whether it could be the case) that larger size contributes to survival of cold winters. You're allowed to assume it's true. The only question then becomes whether that fact (assuming its truth) weakens the argument. For the reasons Dave stated in his detailed post, it does!

I hope this helps!

Jeremy

[cargostud]

Thanks Jeremy. I forgot the answer stem allows you to assume the truth of the answer choices for weaken questions. Sometimes the correct answer is an inconvenient and ridiculous truth.

[intent228]

I can get this question correct but it drives me crazy that I am still struggling to eliminate C as a contender.

P - species of fish lives in oceans and lakes
P - ocean fish have armor for protection
P - lake fish don't have armor
P - armor stunts growth
C - size is better defense for lake than having armor

Answer choice B gives us an alternative reason for the size, thus weakens the argument.

Answer choice C - "Unlike ocean stickleback, the lake stickleback are more often preyed upon by predatory insects than by larger fish." In this answer, the lake fish are still being preyed upon in spite of their size advantage. Which, to me, sounds like it weakens the claim made.

[KelseyWoods]

Hi intent228!

I think the issue you may be having is in differentiating between the concept of having defenses against predators and being preyed upon. Even though the fish possess defenses to help protect them from predators, that doesn't mean they won't still have predators trying to prey upon them. Their defenses just give them an advantage, but don't make them 100% invulnerable to being preyed upon. Maybe it's because they're more likely to be preyed upon by predatory insects that makes their large size a better advantage for them--it may make it harder for insects to eat them if they are bigger than the insects.

Hope this helps!

Best,
Kelsey

[Legallyconfused]

Hi there!

I am still really confused about answer choice C. The conclusion that we are trying to weaken is that for the lake stickleback, being larger in size is a better defense against its predators than armor. Answer C says that lake stickleback are more often eaten by insects than by larger fish. Maybe that is why they don't have armor or are larger? I know answer choice B is clearly correct because it weakens the original conclusion by providing an alternative explanation for the difference between the ocean and lake stickleback. I just feel like answer choice C almost gives another reason for the difference as well. But obviously B is waaaay better at giving that clear alternative.

Thanks!

[Adam Tyson]

This is a subtle difference, Legallyconfused, but the conclusion in this argument is actually not that the for lake fish being larger is a better defense. The conclusion is that the lack of armor INDICATES that being larger is a better defense. Answer choice C fails because it doesn't give us any information about the lack of armor! Answer B is all about giving us another reason for the lack of armor, suggesting that it actually may not indicate anything about defenses against predators.

Also regarding answer C, the argument is about larger size being a better defense against predators, but it never says anything about the kind of predators. Perhaps being larger is a better defense against insect predators than is armor? Might answer C actually strengthen the argument, by telling us that lake stickleback fish have different kinds of predators than ocean sticklebacks, and that they therefore need different defense mechanisms?

[ashpine17]

Are there two causal relationships in the last sentence?

if armor limits the speed of the stickleback's growth, then doesn't that imply that lack of armor causes a stickleback to grow faster, if not bigger, than their ocean counterparts? And the second causal relationship is the main conclusion: that larger size results in better defenses for the lake stickleback against their particular predators?

[ashpine17]

I take back the imply bit because it states as a fact that armor limits the speed of the stickleback's growth but is the rest of what I wrote legit?