#8 - Monarch butterflies must contend with single-celled

[Robert Carroll]

lina,

I think the chief problem with answer choice (C), and your explanation for it, is that we're still faced with a situation where a smaller percentage of those who migrate are affected. As you said, it's possible that 15% of those who migrate represents a larger number than 95% of those who don't migrate, if a lot more migrate than don't. The issue is, 85% of those who migrate aren't infected! So if 15% of the migrating population is larger than 95% of the non-migrating population, 85% of the migrating population is HUGE! So we're still faced with a situation where the odds are very good that a non-migrating butterfly is infected, and a migrating butterfly is not infected. Changing numbers can't change those percents, so the possible difference in population sizes is just not relevant.

Robert Carroll

[lsatstudent99966]

Hi there,

I answered this question correctly.

But I have one question each for (A) and (B).

(A): Doesn't this weaken the argument a bit? It does not provide an alternative explanation like (D) does, but it seems to undermine the author's causal claim a bit? If the butterflies are unable to determine which potential place for them to migrate is free of parasites, wouldn't it be less likely for them to avoid parasites by migrating (perhaps it's just as likely for them to migrate to a place with more parasites)?

(B): My only question is, I'm not sure what this means...does it refer to how far the butterflies migrate, or how long they migrate before they return?

Thank you very much!

[Adam Tyson]

Avoiding parasites isn't about their intentions, 99966. The stimulus isn't about what butterflies consciously choose to do. It's just about the cause and effect of it. The author thinks the reason the migrating ones don't have parasites is because migrating prevents the parasites from infecting them, or that it removes the infection. Nothing to do with what the butterflies think or know. That's why A is irrelevant.

As to answer B, it could mean duration, or distance, or both, and either way it doesn't matter. We don't care about which migrations are better or worse, we only care about whether migration is a cause, or if it could be an effect or just a coincidence.

[lsatstudent99966]

Avoiding parasites isn't about their intentions, 99966. The stimulus isn't about what butterflies consciously choose to do. It's just about the cause and effect of it. The author thinks the reason the migrating ones don't have parasites is because migrating prevents the parasites from infecting them, or that it removes the infection. Nothing to do with what the butterflies think or know. That's why A is irrelevant.

As to answer B, it could mean duration, or distance, or both, and either way it doesn't matter. We don't care about which migrations are better or worse, we only care about whether migration is a cause, or if it could be an effect or just a coincidence.

Big thanks, Adam!

Regarding (A), I understand that the argument has nothing to do with the intention of the butterfly. I just originally thought that if these butterflies can't choose to migrate to a place with fewer parasites, then the argument is less likely to be true.

But reading your explanation, I think I realized that (A) probably wouldn't weaken anything much. Am I right in understanding that the problem is this: the author is only claiming in general that migration causes fewer parasite infections; the author has not specified that "it is because the place they migrate to has fewer parasites that the migrating population is less infected"; as you point out, this is probably just one (of many) possible reasons why migration might cause fewer parasite infections. So attacking this specific scenario, which the author didn't even allude to, does very little to hurt the argument?

[Luke Haqq]

Hi lsatstudent99966!

I think your line of reasoning makes sense. As you note, "the author has not specified that 'it is because the place they migrate to has fewer parasites that the migrating population is less infected.'" To your question, rather than a matter of hurting the argument, the question here is what accurately describes a flaw in the argument. Since the author didn't allude at all to monarchs being able to detect which areas are free from parasites, (A) can't be describing a flaw in the stimulus.