Q25 - Scientist: A small group of islands near

[mshinners]

Question Type:
Weaken

Stimulus Breakdown:
Some related lizards live near Australia and the Americas (and nowhere else). Since the islands formed after a supercontinent including America and Australia split, the lizards must have come from America to near Australia.

Answer Anticipation:
Why not the other way around? Or why not some other method of ending up on the island? When the conclusion of an argument picks one explanation when there are several plausible explanations, the correct answer will generally deal with the other potential explanations.

Correct answer:
(D)

Answer choice analysis:
(A) Out of scope. Other animals could be native to these islands with the iguanas still coming from the Americas.

(B) Premise booster-ish. The stimulus says they're related, not genetically identical. A few differences

(C) "Documented" makes this answer too qualified (since most of these instances may have happened before humans were documenting anything). Additionally, "uncommon" isn't the same as impossible or unheard of.

(D) Bingo. While these iguanas no longer live in Australia, closely related ones used to. We have a potential alternative explanation now: these iguanas came from Australia, not the Americas.

(E) These islands formed after the fracture. If anything, this is telling us something we already know: there are really old animals around.

Takeaway/Pattern:
When an argument's conclusion is just one of several potential explanations, the correct answer will probably deal with alternative explanations. However, it won't always do so directly.

#officialexplanation

[SabrinaC192]

Thank you for your explanation! I still can't seem to see how the argument's conclusion can be ruled out completely. Isn't is still possible for the iguanas to have arrived from the Americas? The fossils may be of the Iguanas that died AFTER the continental split in which the Iguanas floated to that island near Australia.

[LukeM22]

I still can't seem to see how the argument's conclusion can be ruled out completely. Isn't is still possible for the iguanas to have arrived from the Americas? The fossils may be of the Iguanas that died AFTER the continental split in which the Iguanas floated to that island near Australia.

Yes, but the argument would still be weakened. We're trying to reduce plausibility, not rule out possibility. You're approaching this as a Necessary Assumption rather than a Strengthen/Weaken.

[HunterB394]

I picked (E) originally because I thought it weakened the conclusion about floating debris. If the progenitors date back to when the super continent existed, they may not have needed to float on debris. The species could have just existed on a gradually separating land mass, thus weakening the argument.

In addition, I thought the floating debris conclusion sounded absurd, and as a result, I inferred that the writers were implying that that point was the most vulnerable part of the argument.

(D) seemed less attractive because if the progenitors floated on debris from America to the small islands, it's conceivable that they floated to Australia too? This would make the choice more neutral than weakening.

Where did my thinking take a wrong turn?

[RichardK852]

I picked (E) originally because I thought it weakened the conclusion about floating debris. If the progenitors date back to when the super continent existed, they may not have needed to float on debris. The species could have just existed on a gradually separating land mass, thus weakening the argument.

In addition, I thought the floating debris conclusion sounded absurd, and as a result, I inferred that the writers were implying that that point was the most vulnerable part of the argument.

(D) seemed less attractive because if the progenitors floated on debris from America to the small islands, it's conceivable that they floated to Australia too? This would make the choice more neutral than weakening.

Where did my thinking take a wrong turn?

If you read E, it seems that lineages of iguanas are not mentioned making (E) out of scope.

Hope that helped

[HughM388]

I picked (E) originally because I thought it weakened the conclusion about floating debris. If the progenitors date back to when the super continent existed, they may not have needed to float on debris. The species could have just existed on a gradually separating land mass, thus weakening the argument.

In addition, I thought the floating debris conclusion sounded absurd, and as a result, I inferred that the writers were implying that that point was the most vulnerable part of the argument.

(D) seemed less attractive because if the progenitors floated on debris from America to the small islands, it's conceivable that they floated to Australia too? This would make the choice more neutral than weakening.

Where did my thinking take a wrong turn?

If you read E, it seems that lineages of iguanas are not mentioned making (E) out of scope.

Hope that helped

Out of scope? My dear Richard (and mshinners), (E) explains that there are many species of plant and animal who have common ancestors who lived on Gondwana. This tells us that the progenitors of the two iguana species in question were very plausibly present on the Gondwana landmass before its breakup, neatly explaining the presence, today, of two closely related iguana species found in South America and on an island near Australia.

Consequently, we know that related species can exist in these two distantly located places without recourse to a floating-raft theory. The closely related iguana species in question shared a common ancestor who lived on Gondwana; when the supercontinent broke up, the population of iguanas were also split up, and thereafter the two populations evolved divergently into the distinct but related species now extant in far-flung locales, exactly as Hunter describes above. No progenitors needed to travel across the Pacific because there was already a common ancestor present to give rise to both species.

Meanwhile, (D) addresses iguanas specifically, and tells us that there are fossilized remains of a closely related iguana species located proximally to the small island, so it's probably the better answer, but only just barely. It's like a 51/49 split, and I don't think that's uncommon in the later part of the LR and RC sections.