#9 - Paleontologists have discovered fossils of centipedes

[Rachael Wilkenfeld]

Hi emily,

Answer choice (D) is a great example of a no-effect/limited effect sort of answer choice. Since this is a strengthen except question, four answer choices will strengthen, and one will not strengthen. It could weaken the argument in the ways that you described. But it also could just have no impact at all on the stimulus. Something with no impact isn't strengthening. It isn't always weakening. It could be doing nothing at all. And that's what we see happening here.

Some words in your explanation should be able to help you identify this in the future. You noted "why does it matter that ....". Those words are a hint that your brain is telling you that this answer choice doesn't have a impact on the argument. It doesn't matter. That's your right answer in a strengthen except.

Hope that helps!

[cd1010]

I got this correctly, but just want to ask about some uncertainties I had in answering this question.

for B: "All of the centipedes that...were land dwellers". My first gut reaction was -- "well, do we know how the fossils of the centipedes being discussed in the stimulus relate to all the other previously discovered ones? What if the ones we're talking about are function differently?". I think I was primed to think this way because the first stimulus talked about how old these fossils were. But then I did a second look at B and then said to myself: "I guess if other centipedes were land dwellers, and we're talking about centipede fossils then you have some grounds for claiming that these 415-M-year-old centipedes are also land dwellers." But when I thought this way, I was uncertain if I was trying to be generous to the AC and making it work (Which I know we're not supposed to). I ask this because of other LR questions where it's a logical fallacy to assume that just because something has happened in the past means that it can be evidence for future things (i.e. evidence that centipedes previously discovered were land animals becomes evidence that the centipedes which are 414 M years old are also land dwelling)

for D: "Fossils of the earliest...water-dwelling animals.". If I understood the explanations above, they say that D says that these fossils of land-dwelling animals are not found in rocks with fossils of water-dwelling animals. I'm still confused how it weakens? I thought this AC had no effect since it deals with the earliest land-dwelling animals, and the stimulus says that the centipede fossils found were 20 M years older, and we haven't been given any information about how the centipede fossils relate to the earliest land-dwelling animals.

[Dana D]

Hey CD,

It's important to note that this question is not asking us to weaken; it is asking which answer choice does not strengthen, which means the correct answer can be irrelevant or just not strengthen the conclusion that these centipedes were land-dwellers.

Looking at the answer choices with that in mind, answer choice (B) says that all previous centipedes discovered - all variations of this species - have been land dwellers. With no new information added, there's not a reason to think that these older centipedes were also land dwellers. Think about if this applied to another animal - what if all variations of dogs have always been land dwellers and tomorrow we found a super old fossil of a dog. Would we have any reason to think that dog lived in water? Based on the fossil alone, of course not.

Answer choice (D), meanwhile, raises questions about why these land dwelling centipedes were captured in a fossile with water dwelling animals. Some of the other answer choices attempt to provide explainations for why this could occur, but answer choice (D) further highlights just how strange it is for these two to be in the same fossile by telling us that no other fossile of land dwellers has ever been in a fossile with a water dweller - so if these centipedes were really land dwellers why the heck were they trapped in a fossile with the water dwellers?? We don't know, but it's a little suspicious. It certainly doesn't strengthen the paleontologists' position that the centipedes have to be land dwellers, therefore it is the correct answer.