Q21 - Even the earliest known species

[caro9]

I had difficulty with the wording in the answer choice. Can you please explain the argument and the answer. Thanks.

[ManhattanPrepLSAT1]

The trick on this one is to focus on the conclusion. That's never bad advice if you're not certain of the correct answer. It's easy to get distracted from our task, which is to evaluate whether the conclusion follows from the evidence.

The evidence establishes that the land animals had adaptations that the amphibious and aquatic animals did not. The conclusion is that the land animals "evolved very rapidly" once they emerged onto land.

Hold up, we could only say the land animals evolved very rapidly if we knew that the fossils dated from fairly soon right after the land animals emerged. Otherwise, if the fossils dated from a much later period, then the land animals may have remained the same for a very long time, before evolving to show the adaptations in these fossils. Answer choice (A) brings the date of the fossils to relatively soon after the emergence of land animals.

Let's run through the incorrect answers.

(B) is irrelevant, because these fossils still show the adaptations, so even if others didn't, we could still stay that land animals had evolved special adaptations.
(C) is irrelevant. Plants don't matter.
(D) is tempting in that it makes you wonder whether that's important. But even if some animals living in aquatic environments did descend from land animals, that would have only occurred after the emergence of land animals.
(E) is not necessary to the argument. Amphibious animals are even mentioned in the argument.

Hope that helps! Let me know if you have any more questions.

[austindyoung]

So, this question through me off because of the wording in this stimulus.

It states that, "neither aquatic nor amphibious animals exhibit these adaptations..."

Exhibit. Not exhibited

Maybe I was being too picky, but the wording in this sentence is in the present tense. Also, it says "aquatic and amphibious animals." Not "fossils," which lead me to think it was in the present time as well (for the 2nd sentence).

But, looking at it as Matt did, that they are speaking about past animals (which is what the question is intending) the gap is obvious. Otherwise... not so much.

Anybody else do this?

[pewals13]

Does this argument improperly assume that land animals evolved from amphibious ones? Doesn't the idea that life evolved from a Primordial Soup on land need to be ruled out?

[ohthatpatrick]

You're correct, it DOES also make that assumption.

Of course, that doesn't make (A) incorrect. Arguments usually contain many assumptions, so just because you think of one valid one doesn't mean it's going to show up in the answers. We have to stay flexible and judge the answers by whether they're necessary to the author's argument.

As the previous poster indicated, another valid objection to the argument could have been, "Just because current day aquatic/amphibious animals don't PRESENTLY exhibit land adaptations doesn't mean that the aquatic and amphibious animals 400 millions years ago didn't exhibit land adaptations".

i.e. perhaps those water-based ancestors evolved land adaptations BEFORE they left the water, but present day members of those water-based species no longer exhibit the traits.

So another correct answer could have been
(A) Aquatic and amphibious animals who do not presently exhibit highly evolved land adaptations did not at one point exhibit them in their ancestral past

Good thinking with your objection!

[WaltGrace1983]

Land animal fossils show evolved adaption to life on land
+
Aquatic/amphibious don't exhibit these
-->
Early species of land animals evolved rapidly

I might be wrong here, but I don't even know if the aquatic/amphibious premise really matters for answering this question. This seems to be your standard "the information (the fossils) shows a fairly complete relative timeframe" assumption.

From the premise that fossils are 400 million years old, the author assumes that land animals weren't that much older. However, what if land animals have been around for 800 million years? This would hardly be a "very rapid" evolution.

So when I did this question, I honed in on the "very rapidly" premise. We need something temporal to sure that up!

(A) does this. If these known fossils didn't include a few that were from pretty recently after the origin of land animals, how would we make that conclusion?

Exhibit. Not exhibited
...
Maybe I was being too picky, but the wording in this sentence is in the present tense.
...
Anybody else do this?

I DID do this and I was wondering the same thing. The author is also assuming some relevance of the amphibious and aquatic animals (perhaps of present-day).

Does this argument improperly assume that land animals evolved from amphibious ones? Doesn't the idea that life evolved from a Primordial Soup on land need to be ruled out?

I think that it is just the conclusion that assumes this, not necessarily the argument but we are just splitting hairs now.

(A) Aquatic and amphibious animals who do not presently exhibit highly evolved land adaptations did not at one point exhibit them in their ancestral past

But how would this affect the idea of land animals evolving? We are only concerned with JUST land animals right? That is why I don't think this whole aquatic/amphibious premise doesn't really matter.

What do you think?

[ohthatpatrick]

Yup, I think the aquatic / amphibious part ends up being a bit of a red herring. (is a red herring aquatic or amphibious?)

If you're an inveterate LSAT taker, you'll recognize the familiar game of "author assumes KNOWN fossils are good enough to conclude what he's trying to conclude".

But the other ideas raised, particularly the one about current-day amphib / aquatics certainly COULD have been ammunition for a different type of correct answer.