LR Question 25 Explanation
QUESTION TEXT: Scientist: A small group of islands near Australia…
QUESTION TYPE: Weaken
CONCLUSION: The ancestors of the iguana species must have rafted on debris across the pacific ocean, from the Americas to Australia.
REASONING: There are some iguanas on small Australian islands. Close relatives of this species live in the Americas, but nowhere else. The islands formed after Australia and North America split apart.
ANALYSIS: I had trouble prephrasing this question. The information seems clear enough, but it’s not obvious how to weaken it. You should just keep an open mind, and look for an answer that shows another possibility.
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- We would expect this. The argument wasn’t saying that all the species on the island rafted across the pacific!
- This is tempting, but…the iguanas are different species. Of course there are going to be some differences. This would only matter if the differences were so large that it no longer seemed the iguanas had common ancestors.
- How would you document an iguana rafting across long distances….follow it in a boat, and write it down? For a lot of things like this in science, researchers will make educated guesses. It can be near impossible to decisively prove what happened millions of years ago.
Further, something can be rare but still possible. I don’t imagine it’s every day that species cross an ocean, but it doesn’t have to happen frequently – it just has to happen once. And this answer doesn’t show it’s impossible or implausible for iguanas to raft. - CORRECT. This doesn’t conclusively disprove the argument, but it does muddy the waters. It raises some other possibilities. The existence of these other possibilities is enough to weaken the argument’s story.
1. The iguanas came from Australia originally (and maybe even rafted to America)
2. The iguanas did come from America, but they rafted to Australia first. And then they rafted to the island. They later went extinct in Australia but survived in the islands. - I don’t see how this relates. If lineages are from before the fragmentation of Gondwana, then that means those species could walk from one continent to the other. But, this isn’t relevant to iguanas: they come from after the separation. And it’s natural for us to presume that some old species did exist before Gondwana split, so it’s not clear this adds anything new.
Recap: The question begins with “Scientist: A small group of islands near”. It is a Weaken question. To practice more Weaken questions, have a look at the LSAT Questions by Type page.
More Resources for Weaken Questions
- Intro Course lesson: This intro course lesson covers Weaken questions.
- Mastery Seminar lesson: This LR Mastery seminar lesson covers weaken questions.
Your explanation for E says that iguanas date from after the separation of Gondwana, but they don’t. The islands they are found on were formed after that separation, but not the iguana species itself. That means that iguanas existing on Gondwana could have continued existing on the landmasses that became Australia and S. America. The small group of islands near Australia were almost certainly part of Australia at some point, or at least Gondwana, making E much more reasonable. The upside to D is that iguanas are specifically mentioned and it specifically mentions Australia, making it the better choice. But E isn’t nearly as unrelated as you make it seem.
Oh, I was imprecise. I meant they arrived after the separation. So what use would it be to know the age of the lineages of various species? The answer implies these species could have walked over. But that isn’t possible for iguanas, who arrived on the island after the separation and after it became an island.
I don’t know where I’m misinterpreting the stim, but I don’t see anywhere where its concretely stated that the iguanas arrived after the separation. Except being possibly suggested by the conclusion of an obviously flawed argument that the iguanas must have drifted over. The stim states that they just inhabit two different areas and that those two areas came from a super continent long ago. To suggest as to the “when” they came to inhabit the areas feels like an assumption.
You’re right that the stimulus doesn’t explicitly say when the iguanas arrived, but that’s actually part of why the argument is flawed (and why D weakens it). The scientist infers timing based on the premise that the islands formed long after the fragmentation of Gondwana. Since the islands didn’t exist when Gondwana split, the scientists concludes the iguanas couldn’t have originated from Australia or South America via continental drift. That’s why they reason that the iguanas must have rafted across the Pacific after the islands formed.
Answer D weakens this by introducing an alternative origin: fossils in Australia suggests the iguanas (or their ancestors) might have already existed there independently, meaning they didn’t have to raft from the Americas at all.
So when Graeme says they arrived after separation, I believe he’s operating from the inference that the scientist made (since we’re asked to weaken the scientist’s argument after all). But you’re right that that’s not a solid fact, which is the entire basis of how we can weaken it.
Hope that helps! Let me know if you have further questions.
I completely agree that D is correct, and I think a clearer explanation is that the stimulus rules out the islands from ever being connected to the Americas, but it says South America and Australia were connected on the ancient supercontinent, so no rafting would be required.
I found this question hilarious, especially after picking C about how uncommon reports of iguanas commandeering flotsam rafts are, LOL. Should’ve known that answer should have been “non-existent” instead of “uncommon” – if worded that way do you think it would have been the correct answer?
Still not quite. Iguanas could have rafted even if no one reported it.
Note: This is an old comment but I wanted to clarify the point.