Biologists agree that human beings evolved from a fish, but they

Question

Biologists agree that human beings evolved from a fish, but they disagree about which species of fish. Since biologists agree that frogs are definitely related to the species of fish from which human beings evolved, on the basis of a close match between the mitochondrial DNA of lungfish and that of frogs Dr. Stevens-Hoyt claims that this ancestor must be lungfish. Dr. Grover, on the other hand, contends that mitochondrial DNA evolves too rapidly to be a reliable indicator of relationships between species over long periods of time, and citing the close chemical match between the hemoglobin of coelacanths (a saltwater fish) and that of tadpoles, claims that human beings must be descended from coelacanths.

Which one of the following most accurately describes the role played in the dispute above by the proposition that frogs are definitely related to the species of fish from which human beings evolved?

(A) Since it implies that human beings are not descended from lungfish, it is cited as evidence against the claim that humans are descended from lungfish.

(B) Since it implies that human beings are not descended from coelacanths, it is offered as evidence against the claim that human beings are descended from coelacanths.

(C) It is offered as evidence for the contention that human beings must be descended from either lungfish or coelacanths.

(D) It is an assumption that both parties to the dispute use as a starting point for their arguments about human evolution.

(E) It implies that either a match of mitochondrial DNA or a match of hemoglobin between lungfish and coelacanths would show that human beings evolved from one of these two species.

AshutoshB · Answer

In the above premise, the boldfaced statement is something on the basis of which the two scientists presented their claims, so it is something which is agreed by both scientist

(A) Since it implies that human beings are not descended from lungfish, it is cited as evidence against the claim that humans are descended from lungfish.   Wrong as stated above

(B) Since it implies that human beings are not descended from coelacanths, it is offered as evidence against the claim that human beings are descended from coelacanths.  WRONG it is not the evidence

(C) It is offered as evidence for the contention that human beings must be descended from either lungfish or coelacanths.  WRONG it is not the evidence

(D) It is an assumption that both parties to the disputed use as a starting point for their arguments about human evolution.   Correct as per our thinking

(E) It implies that either a match of mitochondrial DNA or a match of hemoglobin between lungfish and coelacanths would show that human beings evolved from one of these two species.

Skywalker18 · Answer

Biologists agree that human beings evolved from a fish, but they disagree about which species of fish. Since biologists agree that frogs are definitely related to the species of fish from which human beings evolved, on the basis of a close match between the mitochondrial DNA of lungfish and that of frogs Dr. Stevens-Hoyt claims that this ancestor must be lungfish. Dr. Grover, on the other hand, contends that mitochondrial DNA evolves too rapidly to be a reliable indicator of relationships between species over long periods of time, and citing the close chemical match between the hemoglobin of coelacanths (a saltwater fish) and that of tadpoles, claims that human beings must be descended from coelacanths.

Boil it down-Scientists all agree that humans came from fish
Biologists all agree that frogs are related to the kind of fish humans came from

Dr. Stevens-Hoyt- a close match between the mitochondrial DNA of lungfish--> ancestor must be lungfish

Dr. Grover- mitochondrial DNA unreliable
 close chemical match between the hemoglobin of coelacanths (a saltwater fish) and that of tadpoles ---> ancestor must be coelacanths

Which one of the following most accurately describes the role played in the dispute above by the proposition that frogs are definitely related to the species of fish from which human beings evolved?

(A) Since it implies that human beings are not descended from lungfish, it is cited as evidence against the claim that humans are descended from lungfish. - It is not used as evidence and it is also not used as evidence AGAINST anything. No one is even arguing AGAINST anything; both doctors are simply arguing for their hypothesis.
(B) Since it implies that human beings are not descended from coelacanths, it is offered as evidence against the claim that human beings are descended from coelacanths. - Correct
(C) It is offered as evidence for the contention that human beings must be descended from either lungfish or coelacanths. - Incorrect - The doctors definitely only argue for lungfish or coelacanth.But this doesn't mean that the statement is used to say that "Because frogs are definitely related to the fish from which human beings evolved, so humans only evolved from either X or Y." 
(D) It is an assumption that both parties to the dispute use as a starting point for their arguments about human evolution. - Correct
(E) It implies that either a match of mitochondrial DNA or a match of hemoglobin between lungfish and coelacanths would show that human beings evolved from one of these two species. - Irrelevant

Answer D

Loser94 · Answer

S1 on the basis of a close match between the mitochondrial DNA of lungfish and that of frogs Dr. Stevens-Hoyt claims that this ancestor must be lungfish.
S2 r. Grover, on the other hand,citing the close chemical match between the hemoglobin of coelacanths (a saltwater fish) and that of tadpoles, claims that human beings must be descended from coelacanths

Which one of the following most accurately describes the role played in the dispute above by the proposition that frogs are definitely related to the species of fish from which human beings evolved?
or role played in dispute in form of examples 
(A) Since it implies that human beings are not descended from lungfish, it is cited as evidence against the claim that humans are descended from lungfish.
No, irrelevant 
(B) Since it implies that human beings are not descended from coelacanths, it is offered as evidence against the claim that human beings are descended from coelacanths.
Same as A irrelevant 
(C) It is offered as evidence for the contention that human beings must be descended from either lungfish or coelacanths.
This is not evidence as , they used word claim 
(D) It is an assumption that both parties to the dispute use as a starting point for their arguments about human evolution. 
Correct answer
(E) It implies that either a match of mitochondrial DNA or a match of hemoglobin between lungfish and coelacanths would show that human beings evolved from one of these two species.
No , implication only claim

BY POE ,
D is correct

MacT750 · Answer

why c is incorrect and frogs are related is a accepted fact among biologist no? so how can we take it as assumption

guddo · Answer

Two scientists agree frogs are related to the fish species humans evolved from.

Dr. Stevens-Hoyt uses lungfish-frog DNA similarity to argue for lungfish as the ancestor.
Dr. Grover says DNA changes too fast to be reliable and uses coelacanth-tadpole hemoglobin similarity to argue for coelacanth.

A: Incorrect.
The proposition does  not  imply humans are  not  descended from lungfish. In fact, Stevens-Hoyt uses it to argue humans  are  from lungfish.

B: Incorrect.
The proposition does  not  imply humans are  not  descended from coelacanths. Grover uses it to argue humans  are  from coelacanths.

C: Incorrect.
The proposition does  not  say humans must come from one of these two fish. It only says frogs are related to the fish ancestor of humans. That fish could be another species entirely, the two doctors merely present their own candidates.

D:  Correct. 
Both scientists  begin  their arguments by accepting that frogs are related to the fish ancestor of humans. Each then uses different evidence (DNA or hemoglobin) to identify  which  fish that is. So it’s their shared starting point.

E: Incorrect.
The proposition itself doesn’t imply that a match of DNA or hemoglobin  between lungfish and coelacanths  would show anything; each doctor compares one fish to frogs/tadpoles, not the two fish to each other.

guddo · Answer

Why C is incorrect:

The fact states: "Frogs are related to the fish ancestor of humans."

It does  not  say: "The only possible fish ancestors are lungfish or coelacanths."

C incorrectly claims the fact is evidence humans must come from  one of those two . The ancestor could be a different fish related to frogs. The two doctors are each championing one candidate, but the given fact doesn't limit it to just those two.

Why it's still an assumption in the argument (supporting D):

"Assumption" here means a  premise both debaters accept without proving in this dispute .

Even though biologists agree it's true, in  this specific debate  both doctors start from it as their common ground to argue which fish it is. Stevens-Hoyt and Grover don't question the frog connection; they use it as their foundation to advocate for their own candidate.

gullyboy09 · Answer

I wasn't aware what's tadpole is and took me a lot of time to be sure of D. Had to assume it's frog only.

miag · Answer

Hi,
A tadpole is simply the larval (early life) stage of a frog. So when the passage mentions "the hemoglobin of coelacanths and that of tadpoles," it’s still talking about frogs - just at a different stage of development.
In these cases, I would advise building a vocabulary dictionary of whatever words you across both in CR and RC that you didn't understand or didn't know the meaning of and then keep revising it.

Hope this helps!

gullyboy09

I wasn't aware what's tadpole is and took me a lot of time to be sure of D. Had to assume it's frog only.

Biologists agree that human beings evolved from a fish, but they

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Biologists agree that human beings evolved from a fish, but they

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