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

[nicizle]

I'm having trouble making sense of this question. Out of all the questions I've done, this is probably a contender for the worst.

I would've noted the causal relationship in the conclusion as follows: if armor limits speed of stickleback's growth --> size is a better defense. Or, in other words, if no armor --> then size is better defense. I'm confused on why the explanation noted the causal relationship differently.

To weaken the conclusion, wouldn't we need to search for an answer choice that details an alternate explanation for why size is the better defense? How does B provide any kind of weakener to that point? I don't understand how lake stickleback having a larger size that enables them to survive colder winter provides an alternative explanation for why size is the better defense.

[Jeff Wren]

Hi nicizle,

This question was definitely a tricky one!

First, if you haven't already done so, I'd recommend reading Dave's explanation found here:

viewtopic.php?f=1331&t=31625

Second, it's important to separate the final sentence of the stimulus into two parts, the first half is actually a premise and the second half is the conclusion. This is a common sentence construction used on the LSAT (Since A, therefore B), so you'll want to be familiar with it.

Here, the fact that armor limits the speed of the stickleback's growth (combined with the fact that the lake stickleback do not have armor) indicates that a larger size is a better defense than armor against the lake stickleback's predators according to the conclusion.

This conclusion is providing the reason (or cause) for why the lake sticklebacks do not have armor.

Often the hardest part of solving questions with causal reasoning is correctly identifying it when it appears because the arguments don't always use the words "cause" or "effect." Usually, something happens, such as an odd phenomenon (the effect), and then someone gives a reason for how/why that thing happened (the cause).

Here, the odd phenomenon (effect) is that lake stickleback don't have armor, which would seem to be a helpful thing to have in general. By explaining that armor inhibits growth and then concluding that larger size must be a better defense for these fish than armor, the argument provides a cause for this effect.

With the correct cause/effect identified, this question becomes considerably easier, especially if you're able to recognize that Answer B is providing an alternate cause for the effect, which is one of the best ways to weaken a causal argument.

[benndur]

Didn't have any questions about this one, but wanted to share my thoughts with others who might be struggling with answer C).

Dave said that,

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.

I think this answer misses something pretty important, especially given how often C is incorrectly selected as the correct answer; while C) doesn't weaken the argument, it actually strengthens it and thus can be ruled out.

The argument is that, "a larger size is a better defense against the lake stickleback's predators than having armor. "

Based on the stimulus, we have zero knowledge about the types of predators that either the ocean stickleback or lake stickleback have to deal with.
We only know that "lake stickleback have virtually no armor " and that "ocean stickleback are covered with armor to protect them from their predators."

C) says, "Unlike ocean stickleback, the lake stickleback are more often preyed upon by predatory insects than by larger fish."

If this is true, the two different morphs/species of stickleback have two very different primary predators, likely resulting in distinctly different evolutionary pressures since fish and insects generally have very different methods of predation.

Given a basic understanding of evolution, which tells us that organisms with characteristics that make them more likely to survive in their environment are more likely to pass on on their genes, (and thus their characteristics to subsequent generations) C) directly supports/strengthens the argument that "a larger size is a better defense against the lake stickleback's predators than having armor" since this statement suggests that they have different kinds of predators which is exactly what C) says.

If they had the same types of predators, then having a larger size would weaken the argument that size is a better defense than armor, since a similar defense would likely be advantageous against against a similar predator.

[Luke Haqq]

Hi benndur!

Even if you are right that answer choice (C) strengthens the argument in the stimulus, that's not necessary for an explanation of why it's incorrect. It's true that an answer choice that strengthened the argument should be eliminated on a weaken question. However, to be incorrect, it's sufficient that the answer choice simply not weaken it. In addition, it may be worth noting that no outside knowledge about evolution is necessary to arrive the correct answer choice on the LSAT, though sometimes an LSAT passage or stimulus will provide that information.

[benndur]

Hi benndur!

Even if you are right that answer choice (C) strengthens the argument in the stimulus, that's not necessary for an explanation of why it's incorrect. It's true that an answer choice that strengthened the argument should be eliminated on a weaken question. However, to be incorrect, it's sufficient that the answer choice simply not weaken it. In addition, it may be worth noting that no outside knowledge about evolution is necessary to arrive the correct answer choice on the LSAT, though sometimes an LSAT passage or stimulus will provide that information.

Hi Luke!

Do you mean to say that it's unclear or untrue that C) strengthens the argument? It definitely doesn't need to weaken the argument to be incorrect, I'm just pointing out that because it does, it is most surely is not correct.

Your comment about no outside knowledge about evolution being necessary is definitely true well. In this case, you don't actually need even the basic understanding of evolution; simply knowing that two different animals have two different kinds of predators on a basic level is enough to give reason for them having different defences from a purely logical standpoint - I just added it for more context.

[Jeff Wren]

Hi benndur,

I agree with you that if we knew that the ocean and lake stickleback had the same predators, this would weaken the argument. (Although to be clear, it still may be possible that ocean and lake stickleback had developed different defenses even against the same predators because the different environments (lake vs. ocean) may make a particular defense better in that particular environment. For example, perhaps the larger stickleback also swim faster and that is more important in the lake environment for some reason.)

However, knowing that the ocean and lake stickleback have different predators does not necessarily strengthen the argument without actually knowing how the different defenses (size versus armor) compare against the different predators. For example, in Answer C, it is possible that armor would actually better protect the lake stickleback against predatory insects than having a large size, in which case this answer would weaken the argument. The problem, though, is that we don't know how armor compares to larger size in protecting against predatory insects. You definitely do not want to assume that difference physical characteristics are adaptations to the stickleback's predators.

First, in addition to different predators, there are presumably other differences in the environments of lakes and oceans. Even if the physical changes were passed because they increase survivability, they need not specifically be related to predators. For example, as Answer B points out, increasing the ability to survive cold winters would also explain the changes.

Second, the difference physical characteristics may not be beneficial at all. Perhaps the lake stickleback had some genetic mutation that is actually harmful and they are on their way to extinction? We really can't assume anything beyond what we're given in the argument and the answers.