#16 - Biologists agree that human beings evolved from a fish

[rpark8214]

Hi,
I have a question regarding answer choice (D). Assumptions are unstated premises, but this in case, the statement in question is explicitly stated in the stimulus. How can this be an assumption? Thanks!

[Emily Haney-Caron]

Hi rpark,

This is an excellent question. An assumption when we're diagramming a LR stimulus is, as you said, something unstated. In the broader meaning, though, an assumption is something a person believes without having or sharing definite evidence proving that fact. The proposition in question is stated in the stimulus, we don't have any evidence or proof for it, we just know that it's the starting place of both groups of scientists. I hope that helps!

[sneeze]

hi! I have a quick question regarding option C, which is what I picked before I blind reviewed this section.
After giving it some more thought, I realized that the statement in question was an assumption because the researchers don't explain what brings them all to the same justification.

I'm just not entirely sure on what makes C wrong :/

[Paul Marsh]

Hi sneeze! Great username. And nice job understanding why (D) is a good answer upon review.

As for (C), it presents a false dichotomy. At no point does the stimulus make the "contention that human beings must be descended from either lungfish or coelacanths" (italics added for emphasis). One scientist has a lungfish hypothesis, and another scientist has a coelacanths hypothesis, but nowhere in the stimulus do we have anything about anybody saying it has to be one or the other. A Method question must accurately describe what is happening in the stimulus, but (C) is talking about a contention that never occurred. If (C) said something along the lines of, "It is offered as evidence for a hypothesis that human beings are descended from lungfish, as well as a hypothesis that human beings are descended from coelacanths," it would be a much better answer.

Hope that helps!

[caroline222]

I have a follow up question about Emily's response. I eliminated answer choice D because it said assumption, but I found that none of the other answer choices matched what this portion of the stimulus described. I remember seeing on a forum discussion from a different question that "assumption" is not really a good answer choice for a Method-AP question because assumptions are unstated. Is the reason D works because, although the author isn't assuming this (they are stating it in the stimulus), Dr. Stevens and Dr. Grover are assuming this when they make their contentions???

Thank you in advance!

[Robert Carroll]

Caroline,

I dispute that assumptions MUST be unstated, although it's by far more common for assumptions to be unstated than made explicit. There is, in fact, an answer choice for at least one Method-AP question that describes something as an "explicit assumption." I think, though, that this possibility is beside the point for the reason you mention. The explicit mention of this piece of evidence is by the author of the stimulus, not Drs. Stevens-Hoyt and Grover. Their arguments wouldn't made sense unless the belief of biologists were taken to be an underlying assumption, but THEY don't explicitly state it.

Robert Carroll

[gabe_katz)=_]

Hi,

Would you mind explaining why the answer D instead of A?

My initial thought is that A is a little too strong of a conclusion for the argument presented, but I am not sure.

Thanks for your help,
Gabriel Katz

[Rachael Wilkenfeld]

Hi Gabe,

We aren't looking for a conclusion here. We are looking for a description of the particular part of the stimulus. In this case, our statement is used as support for the ultimate conclusion. There's a premise indicator ("since") before the statement, and we can see that it supports the ultimate conclusion on evolution of fish.

This is a method of reasoning question, which means we are looking for a description of what occurs in the stimulus. If any part of the answer choice does not describe what occurs in the stimulus, it's wrong and we can eliminate it.

For answer choice (A), we can eliminate it as soon as it says that humans didn't evolve from lungfish. The statement doesn't take a position on which species of fish humans evolved from. It just asserts that frog are related to the species of fish humans evolved from. Since answer choice (A) doesn't describe the stimulus, we can eliminate it.

Answer choice (D) does describe what we see in the stimulus. The statement in the question stem is something the author takes for granted. He provides the statement as a given. This is the correct description of the statement in the stimulus.

Hope that helps!

[zoezoe6021]

I am confused about the structure of the stimulus. Could you please help to explain?

Dr. Steyens-H cites the close match between the DNA of frogs and lungfish as evidence to prove that the human ancestor is lungfish.

However, Dr. Grover neither mentions frogs nor uses frogs as a piece of info to support his argument. I don't see how the sentence "frogs are definitely related to the species of fish from which human beings evolved" plays a role in Dr. Grover's argument, as AC D suggests.

[Dana D]

Hey Zoezoe,

The stimulus tells us "biologists agree that frogs are related" which we can read as 'all biologists' agree about this fact. Dr. Stevens-Hoyt uses this to draw similarities and conclude we evolved from lungfish, while Dr. Glover argues that the mitochondrial DNA seminaries between us and frogs is not a strong indicator because the DNA evolves too rapidly. The stimulus does not explicitly state this, but Dr. Glover, being a biologist, also agrees frogs are related to the same species of fish we evolved from, he just doesn't think looking at the mitochondrial DNA similarities between us and frogs is helpful in identifying what type of fish.

Hope that helps!