Q20 - Amphibian populations are declining

[vragosta3]

I am obviously missing something crucial here. I can eliminate answer choices B, C, D and E based on the fact that they each give further strength to the argument (that the primary cause of the decreasing amphibian population is the depleting ozone layer, and not some other cause).

However, I do not see how the correct answer choice (i.e., A) weakens or is irrelevant to the argument. If anything, I see A as strengthening the argument as follows: If UV-B is the only type of radiation that can damage genes, and the ozone layer is depleting (which in turn lets in more UV-B radiation) then the argument that the primary cause of the declining amphibian population is the depleting ozone layer is reasonable. I obviously have something very confused.

[ManhattanPrepLSAT1]

So I think what you're saying is that because answer choice (A) says that UV-B is dangerous (that it can damage genes) and because it is blocked by the ozone, that the conclusion is strengthened.

But we know both of those things from the stimulus. We know that UV-B is blocked by the ozone and that it can damage genes. The only other implication of answer choice (A) is that there are no other types of radiation blocked by the ozone that can damage genes. But that certainly doesn't help the argument that the depleted ozone is responsible.

So what I'm saying is that answer choice (A) doesn't add anything new, and so cannot be said to strengthen the argument.

Does that clear this one up?

[sebrof27]

I still find this question a little confusing. Yes, we already know that UV-B is dangerous, but answer choice (A) states that this is the ONLY type of radiation that can cause damage. In my mind, this limited the number of alternative potentially harmful effects. I do see, though, that this doesn't really have an affect on the depletion of the ozone idea. However, I don't understand how choice (D) does have this effect. One explanation I read was that (D) eliminates an alternate explanation, thus making the argument stronger, but I saw it as outside of scope. Just because the habitat are not the same thing, and that habitat size has not changed does not imply population density has. I also linked that explanation back to (A), which in my mind also eliminated some potential explanations.

Maybe I'm just being stubborn and things will make more sense after some sleep, but I'd really appreciate any advice in where I'm screwing things up.

Thanks for your help!

[ManhattanPrepLSAT1]

Good question, thanks for asking!

However, I don't understand how choice (D) does have this effect. One explanation I read was that (D) eliminates an alternate explanation, thus making the argument stronger, but I saw it as outside of scope.

When the argument presents an explanation for why something has happened, an alternative explanation may seem out of scope, but if it is possible alternative explanation, it would weaken the argument. A common way the LSAT strengthens an explanation is by ruling out a competing explanation. Check out the following example to see this in action:

PT46, S3, Q22 - Over the last 10 years

So while answer choice (D) doesn't support the idea that the ozone is being depleted, it does support the idea that the declining amphibian population is due to the depletion of the ozone layer.

I still find this question a little confusing. Yes, we already know that UV-B is dangerous, but answer choice (A) states that this is the ONLY type of radiation that can cause damage. In my mind, this limited the number of alternative potentially harmful effects. I do see, though, that this doesn't really have an affect on the depletion of the ozone idea.

Remember that we're not trying support the idea that ozone is being depleted. We're trying to support that it's the depletion of the ozone that is causing the amphibian population to decline. Answer choice (A) does not strengthen the argument. Suppose there were other forms of radiation that are blocked by the ozone - which is a possibility given the argument. But so what? The argument focuses on UV-B because amphibian populations are particularly vulnerable to UV-B. Essentially, the whole issue of UV-B is a mechanism that supports the depletion of the ozone theory for why amphibian populations are declining.

Hope that helps!

[wj097]

Answer choice like (D) puts me into an interesting situation, that I often find myself. I can perceive (D) in 2 different ways:
1) Subject matter i.e., size of natural habitat being a potential alternate cause, in which case its not a problem seeing this as a strengthener.
2) More interestingly, if we consider (D) as just merely describing an end state of what happens after all, then we can't deduce anything about the cause; the habitat size can be whatever regardless of the decreased population (we know nothing about the density).

In such case, (D) can either strengthen as in 1) or be irrelevant as in 2)..now should we still rule out (D) since it has a possibility of being a strengthener or keep (D) as we cannot determine what role it can play... plz help.

[griffin.811]

The issue with (A) is that it strengthens the idea that UV-B radiation is responsible for the decrease in population.

This doesn't directly strengthen the argument though, which is that the decline in ozone is responsible for the decrease in amphibious animal population.

[rickytucker]

Aside from restating what we already know, would another reason to eliminate (A) be that the stimulus doesn't establish a causal link between "damaged genes" and "amphibian death"?

In other words, even if the depletion of the ozone causes damaged genes in amphibians (by way of UV-B), (A) doesn't strengthen the conclusion that depletion of ozone causes declining amphibian populations.

That was my line of reasoning but I can't decide whether I chose (A) for the wrong reason.

[SecondWind180]

I understand why (A) is correct, but I can't logically wrap my head around how the test authors can support that (D) unquestionably strengthens the argument.

From (D), we can conclude two things:

1) Amph's habitat did not become smaller
2) Amph's habitat stayed the same OR got larger

There is no indication that habitat size has any effect on population numbers.

Maybe I'm wrong, but IMO this isn't an air tight answer because it leaves open the possibility that the habitat got larger which we don't know the effect of. (Maybe the Amph's spread out with more habitat (lower population density) and thus mated less decreasing the birth rate.)

Had the answer limited itself to saying that the Amph's habitat had not change/stayed the same size (i.e. it had no effect on the population because it was a constant) then it would be clear that this answer strengthens the author's conclusion by removing an alternative cause.

[maryadkins]

(D) doesn't have to be airtight to strengthen. If the habitat didn't get smaller, you're right that that means it stayed the same or got larger. This doesn't have to tell us that there's then nothing but the ozone that could have negatively affected amphibians; it's just eliminated ONE possible reason for their declining numbers, which is having a smaller habitat. Eliminating one alternative is still strengthening.

Hope this helps!

[WaltGrace1983]

"(A) Of the various types of radiation blocked by atmospheric ozone, UV-B is the only type that can damage genes."

...but so what? Let's say this is true. It doesn't address the correlation/causation issue. We have two things that are correlated (Amphibian populations are declining in numbers / UV-B has been continuously depleting over the last 50 years) and the argument posits a causal connection (UV-B causes declining populations).

If (A) is the only type of radiation that does damage to genes, this still doesn't make the idea that it is the ozone that is causing the depleting populations. Maybe it is X, Y, or Z. Is that a good way to think about it?

Now from a theoretical standpoint, how do the rest of the answers operate?

(B) Comparing same "cause" / same "effect" to ~same "cause" / ~same "effect"?

(C) More correlation (which strengthens/weakens apparently)?

(D) Rule out alternative cause.

(E) More correlation?

I just want to be able to understand this question from a theoretical perspective so I can use this knowledge to help with other questions.

[maryadkins]

Looks good!

[redskateboard]

I don't see why A) doesn't strengthen here.

The conclusion is that there is a causal link between declining populations and ozone depletion.

The support is that ozone blocks one type of radiation (UV-B) that damages genes.

A) says:
1. Ozone blocks more than one kind of radiation... let's call them UV-A, UV-B, and UV-C.
2. UV-A and UV-C do not damage genes.

Doesn't this strengthen the argument? It rules out alternative explanations that the argument is vulnerable to (for example, "No, it's UV-A that is actually causing the decline populations, the amount of UV-B present without the ozone layer is not hurting the amphibians at all.")

[roflcoptersoisoi]

Ok, I get why D) is wrong. However could we not also say that for D) to strengthen we would need to operate on conjecture i.e, smaller habitat= declining population? or is that me just being dumb.

[maryadkins]

Not dumb! For (D) to strengthen, we have to infer that a smaller habitat COULD be the cause of the declining population, yep. It's a possible cause that's being eliminated. We don't have to assume that it DEFINITELY would lead to a smaller population, though. It just is a possible explanation we can knock off the table.

[brettboresow]

I don't see why A) doesn't strengthen here.

The conclusion is that there is a causal link between declining populations and ozone depletion.

The support is that ozone blocks one type of radiation (UV-B) that damages genes.

A) says:
1. Ozone blocks more than one kind of radiation... let's call them UV-A, UV-B, and UV-C.
2. UV-A and UV-C do not damage genes.

Doesn't this strengthen the argument? It rules out alternative explanations that the argument is vulnerable to (for example, "No, it's UV-A that is actually causing the decline populations, the amount of UV-B present without the ozone layer is not hurting the amphibians at all.")

I thought A strengthened for the longest time. I went through and looked at all the posts and couldn't see why A did not strengthen. Finally, after going through the argument for the 10th time I think it dawned on me.

We know that UV-B damages genes. We know that ozone blocks UV-B. We know that a depleted ozone would allow more UV-B radiation in. So it's true that the UV-B would damage genes. However, it's not clear that the fact it damages genes actually causes the amphibian population to decrease.

Think of it like tanning. When we tan the UV light causes damage to our genes however we can't infer that damage to our skin actually causes the human population to decrease.

If the argument talked about the genes inhibiting the ability for the eggs to hatch, or amphibians becoming infertile then I think A would be a strengthen, but it doesn't so it does not have any effect on the argument.

[AnnaT620]

I picked E here - is that incorrect because it strengthens the correlation? I thought it was mostly a re-statement of the premises and therefore didn't really strengthen the argument. How do I make sure I pick up on this going forward? Many thanks

[Misti Duvall]

I picked E here - is that incorrect because it strengthens the correlation? I thought it was mostly a re-statement of the premises and therefore didn't really strengthen the argument. How do I make sure I pick up on this going forward? Many thanks

Yep! (E) is a little different from the premise that mentions 50 years, because that premise is talking about the ozone layer being continuously depleted for the past 50 years. If amphibian populations (which is what E talks about) have done the same, that helps strengthen the causal relationship.

If you see something in an answer that looks like a restatement of a premise, double check to make sure the concepts in both are the same.

[EmaD316]

Can anyone go into more detail about why B is wrong?