Q26 - The three-spine stickleback is a

[Laura Damone]

Question Type:
Weaken

Stimulus Breakdown:
Conclusion: Larger size is a better defense against lake stickleback's predators than having armor.

Evidence: Ocean stickleback have armor, but lake stickleback don't. Armor limits the speed of growth.

Answer Anticipation:
This argument implies a causal explanation of the difference between lake and ocean stickleback: the cause of lake sticklebacks' lack of armor is that size is a better defense than armor in the lake environment. Alternate causes would weaken this argument, so predict that a correct answer will present some other reason that the ocean-dwellers have armor but the lake-dwellers don't. That said, there are other ways to weaken causal arguments, too, like presenting counterexamples, so don't get too narrowly focused on alternatives and evaluate each answer on its own merits.

Correct answer:
B

Answer choice analysis:
(A) Boom. Right out of the gate, an alternate cause. Lacking armor makes the fish less vulnerable to fast-moving predators. But, where are these speedy predators? This would only weaken the argument if we knew that the speedsters are found in lakes more so than oceans. Without that fact, this doesn't impact our argument because it doesn't address the two different environments.

(B) Here we go! That's better. This alternate cause - size to survive the cold as opposed to size to defend against predators - is specific to lake stickleback. If this is true, it makes it less likely that the lack of armor is about defense, so it weakens the argument.

(C) What do insects vs. larger fish have to do with anything? Well, a lot, actually! If this were a Strengthen question, this would be a correct answer because it establishes that larger size would deter predation in a lake but not an ocean. But, this is a weaken question, so don't get stuck in this "opposites attract" trap!

(D) Establishing a similarity between the fish in different environments doesn't impact our argument. And anyway, we're worried about who eats them, not what they eat. Eliminate.

(E) This history lesson on sticklebacks doesn't give us any useful info about lake fish vs. ocean fish. Eliminate.

Takeaway/Pattern:
The easiest way to weaken a causal argument is to provide an alternate causal explanation, so that's always my go-to prediction when the argument is a standard correlation vs. causation argument. Beware alternate causes that don't actually offer an explanation of the facts presented (A), and "opposites attract" answers that strengthen rather than weaken.

#officialexplanation

[PretzelL30]

Hi Laura, can you explain more about this "opposites attract" concept? I picked C because I reasoned that, okay, so big size must defend against predators. I need to weaken. Here's an answer saying, actually, their predators are just insects. It sounds like made a few illicit assumption jumps. (I also completely missed the boat that it was a correlation/causation question).

I also can't figure out why it strengthens. Thank you for any help