Q15

[pistachio2014]

Hi, I narrowed it down to choices A and C and ultimately selected A. Could you please explain why A is wrong?

[bbirdwell]

This one is rather tricky, and there are a couple of different ways to think about it.

I think the most succinct explanation is that high speciation is equivalent to high diversity. We know this. And the first two sentences state directly that the Amazon and the deep sea mud-dwellers have high a diversity of species. Therefore we really need not assume (A) -- it's actually given.

Another way to think about it is more subtle. Here's a short version.

His argument looks like this:
Premise: deep sea has diversity
conclusion ("he argues"): this diversity is due to an absence of fluctuations in climate and physical conditions.

Do you see an assumption? It's tough because it's staring us right in the face. What must we assume in order to draw that conclusion?
That there actually is an absence of climate fluctuation in the deep sea.

Go back and read the sentence that states this (line 6). You'll notice that his conclusion does not include "deep sea." Therefore, we must assume it.

I know, I know. But it's true.

Later, he "argues" that the Amazon is analogous. He goes into detail and spells out what that means, which is distracting. Stop there, though. If we're assuming that the deep sea has an absence of climate fluctuation, and we're concluding that the Amazon is analogous, then we must also be assuming that this is true of the Amazon.

Tricky question. Hope that helps. If you're taking the test on the 9th, I'd work with more recent tests if i were you. The questions have gotten a bit sharper over time, and these days we don't see many at all that are quite as nebulous as this one.

[wgutx08]

Mmmmm, I see this Q completely differently ---

First, high speciation is NOT equivalent to high diversity. Paragraph 1 stated very clearly (especially L10-14) that

diversity = speciation - extinction;

and the observed high diversity is not a result of high speciation but low extinction rate, which is actually the central point of the Sanders theory (L5-L14).

So A is wrong, because nobody says there is an "unusually" high rate of speciation, but rather, an unusually low rate of extinction.

Am I missing something here?

[tommywallach]

Hey Wgut,

You're absolutely right. The problem with (A) is that neither ecosystem is said to have particularly high speciation.

This is good news, because now (C) is clearly the best answer we have. (The previous explanation makes (A) and (C) very difficult to choose between, because both seem like statements directly made in the passage, as opposed to assumptions.)

Good catch!

-t