Scientist: A small group of islands

Answer choices

1. A

   No Impact3% picked this

   A number of animal species that inhabit the islands are not found

   This would be attempting to attack the plausibility of the author's story by saying, "Not all the animals on these islands seem to have ancestors that lived in America!" But the author is only claiming these iguanas are like that, not that any other species on the islands is like that.

   3%
2. B

   Nothing New24% picked this

   Genetic analysis indicates that the iguana species on the islands are different in several respects from those

   This isn't telling us anything we didn't already know, in a sense. The passage identified the island iguanas as being "closely related" to the American ones. If you're closely related, rather than same species, then of course you have genetic differences.

   24%
3. C

   Weaker Impact11% picked this

   Documented cases of iguanas rafting long distances between land masses

   This somewhat calls into question the plausibility of the Author's Explanation. If it's uncommon for iguanas to raft long distances, then the author's hypothesis that these iguanas rafted from the Americas across the Pacific Ocean seems like a pretty exotic possibility. However, this answer isn't saying anything strong like, "An iguana couldn't possibly survive a rafting voyage from South America to Australian islands." It's just saying "documented cases are uncommon". If there are any documented cases, even if rare, that would strongly bolster the author's story by showing it is indeed possible for an iguana to raft that far. And given that we're talking about something that probably happened hundred of thousands of years ago, the lack of documentation seems less of a knock against this hypothesis. Because documented cases and uncommon leave lots of wiggle room (it's possible there are some rare documented cases / it's possible there are commonly undocumented cases of iguanas doing this), this answer doesn't have much punch to it. It definitely goes the right direction of lowering plausibility, but ever so faintly.

   11%
4. D

   Correct46% picked this

   Fossils of iguana species closely related to those that inhabit the islands have been

   Why this is right

   This suggests an Alternate Explanation (the #1 pattern for Weaken on Explain Curious Fact arguments). It suggests that back when the supercontinent was together, there were iguanas throughout the regions that would later be Australia and America. Then the supercontinent split apart, and so you had some iguanas left on the American continent and some left on the Australian continetn Then the islands form and somehow the iguanas get to the islands. The author is thinking they probably rafted over the entire Pacific Ocean on a three month voyage on a piece of floating debris, from America. This answer suggests that the iguanas probably just floated over from Australia. Since the islands are near Australia, that possibility it at least as plausible as the idea that they floated over from America. Since we've exposed an alternate possibility, we've weakened the author's certainty that, "these progenitors' must have rafted on floating debris from the Americas". We can counterargue, "They didn't have to raft on debris from the Americas. They could have rafted over from Australia."

   Skill tested: Weaken · how this choice captures the argument's function is the move to repeat next time.

   46%
5. E

   No Impact16% picked this

   The lineages of numerous plant and animal species found in Australia or in South America date back to a period prior

   This is just saying that other flora and fauna have an evolutionary past that goes back to the period before the supercontinent split up. That's a very generic fact about Earth's biological history that doesn't shed any light on this specific situation.

   16%