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# How aquatic vertebrates evolved into land vertebrates has been difficu

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Re: How aquatic vertebrates evolved into land vertebrates has been difficu [#permalink]

Can you post the explanation for Q3?

thanks
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Re: How aquatic vertebrates evolved into land vertebrates has been difficu [#permalink]
Official Explanation

3. The author discusses the evolution of coelacanth DNA in the highlighted text primarily in order to

Difficulty Level: 750

Explanation

In this question and in general, the point of something in a decently written paragraph is the overall point of the paragraph in which it is contained. And GMAT passages tend to be decently written. The line mentioned comes in the last paragraph, which, as we have discussed, achieves two things: it settles the living-fossil question, and it settles the closest-relative question. This particular point probably contributes to one or the other. Indeed, the c-fish DNA was the key piece of evidence that the c-fish is not a living fossil. So the author discusses it in order to make that point. Let's look for that in the answer choices. Choice (A) matches our expectation, and none of the other choices do. Choice (B) describes something that also happens in the paragraph, but in the prior sentence.

Hope it helps

Mizar18

Can you post the explanation for Q3?

thanks
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Re: How aquatic vertebrates evolved into land vertebrates has been difficu [#permalink]
Quote:
6. The primary purpose of the third paragraph is to

A. draw a conclusion based on information presented in the previous paragraph
B. introduce a topic that is not discussed earlier in the passage
C. introduce evidence that contradicts a view presented earlier in the passage
D. answer questions raised in the previous two paragraphs
E. describe a different method of arriving at a conclusion reached in the previous paragraph.

The only question asked in previous two paras is :
To find out, How aquatic vertebrates evolved into land vertebrates ?
On this basis I eliminated option D.

I was able to eliminate all options using POE
Para 3 answers the questions raised in the third paragraph only.
Whether the coelacanth in particular is rightly called a living fossil and whether it is the closest living relative of the original tetrapods are two questions that have been illuminated more recently by genetic analysis

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Re: How aquatic vertebrates evolved into land vertebrates has been difficu [#permalink]
Harsh2111s
Quote:
6. The primary purpose of the third paragraph is to

A. draw a conclusion based on information presented in the previous paragraph
B. introduce a topic that is not discussed earlier in the passage
C. introduce evidence that contradicts a view presented earlier in the passage
D. answer questions raised in the previous two paragraphs
E. describe a different method of arriving at a conclusion reached in the previous paragraph.

The only question asked in previous two paras is :
To find out, How aquatic vertebrates evolved into land vertebrates ?
On this basis I eliminated option D.

I was able to eliminate all options using POE
Para 3 answers the questions raised in the third paragraph only.
Whether the coelacanth in particular is rightly called a living fossil and whether it is the closest living relative of the original tetrapods are two questions that have been illuminated more recently by genetic analysis

It tells us that lungfish is the closer relative of tetrapods so that is how aquatic vertebrates evolved into land vertebrates.
Also, paras 1 and 2 discuss both Coelacanths and lungfish but para 3 arrives at lungfish. So though the question is not given directly in paras 1 and 2, the confusion between the 2 is sorted in para 3.

So option (D) is correct.

As for (C), note that there is no contradiction in the paras. They start with generic ideas and arrive at lungfish specifically.
Para 1 introduces the species of interest.
Para 2 explains why they are species of interest.
Para 3 narrows down to one of of them as closer to tetrapods (land vertebrates).
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Re: How aquatic vertebrates evolved into land vertebrates has been difficu [#permalink]
Quote:
Coelacanths and lungfish are two of the only lobe-finned species that are not extinct, and since they have evolved minimally since the time of the appearance of tetrapods, they are sometimes referred to as "living fossils."

C: Coelacanths is "living fossil."

3rd paragraph proves : Coelacanths is not a living fossil.

Is not a contradictory view? Why? because they have not explicitly mentioned or used words to contradict "however " etc.?

For optionD:
the question is asked in 3rd paragraph but not in earlier paragraphs:
Quote:
Whether the coelacanth in particular is rightly called a living fossil and whether it is the closest living relative of the original tetrapods are two questions that have been illuminated more recently by genetic analysis.

Still some doubts prevailing on thought process. Kindly help.

Thanks!
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How aquatic vertebrates evolved into land vertebrates has been difficu [#permalink]
Sajjad1994 i got most of the Qs wrong; Can you please share explanations for Qs 1,4,7?(got Q7 somehow right, but need clarification)

For Q4, passage's last line says deep sea environment may have helped "more slowly evolving" coelacanth to survive a long period. But how come we arrive at OA that harness of environment partly drives the rate of evolution of a species ? Or am i missing some other part of passage where the OA has been alluded to.

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Re: How aquatic vertebrates evolved into land vertebrates has been difficu [#permalink]
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dragonz91
Sajjad1994 i got most of the Qs wrong; Can you please share explanations for Qs 1,4,7?(got Q7 somehow right, but need clarification)

For Q4, passage's last line says deep sea environment may have helped "more slowly evolving" coelacanth to survive a long period. But how come we arrive at OA that harness of environment partly drives the rate of evolution of a species ? Or am i missing some other part of passage where the OA has been alluded to.

Official Explanation

1. The passage provides information in support of which of the following assertions?

Difficulty Level: 700

Explanation

In this question, as in every question that involves a statement "inferred from" or "supported by" a passage or prompt, we should first look for something that is required. If one of these statements is required by the passage, then it's certainly well supported. This slightly non-obvious relationship is not really a testmaker trick; rather, it is a byproduct of the testmaker's efforts to write questions in which one answer choice is objectively better than the others.

Digging in, we look for a statement that must be true or which is assumed by the passage. Choice (A) may be the most confusing, so we can come back to it.

Choice (B) involves physical similarities, choice (C) involves fossils and choice (D) involves physical similarities. What is the key point in this passage about fossils and physical similarities? It's that fossils are hard to obtain, so scientists used physical similarities in their studies. That's how the c-fish and the lungfish become fishes of interest. So the passage must believe (B); it's grounds for the line of reasoning.

(C) and (D) are somewhat opposite; if the author believed them, they would pose a threat to the passage, so the passage does not support them.

At this point, we could go fairly confidently with (B) or we could confirm objective flaws with choices (A) and (E).

Choice (A) is not supported by the passage. The passage admits a degree of uncertainty about who is the closest relative, but it ends up decisive that the lungfish, not the c-fish, is the closest relative of the land animals; this implies that a path has been identified as correct, contrary to (A). So (A) is out. (E), meanwhile, is a jumble of fragments from the passage. The c-fish and the lungfish became species of interest because of their morphology, their skeletons, not specifically because their DNA hadn't changed.

4. It can be inferred from the passage that which of the following is a true statement about the evolution of a species?

Difficulty Level: 700

Explanation

Since we are inferring, we will look for a statement that must be true. We aren't guaranteed such a statement will exist, but if it does, it will be objectively the best-inferable statement. We will also keep an eye out for answer choices that are important to the main ideas of the passage. Again, we aren't guaranteed such an answer choice, but they can be easier to evaluate. As it turns out, none of the answer choices are connected to the primary topic of the passage, which is the closest-relative question. They all seem to pertain to the portion of paragraph three in which it's established that c-fish are not living fossils.

Choice (E) is tempting. But we aren't given evidence that lungfish aren't living fossils; only c-fish are discussed directly in paragraph three. Otherwise, we have statements about species survival and the rate of change; these all seem to focus on the statement at line 34 that, since c-fish have evolved slowly, "the environment... [has] created favorable conditions."

Before turning back to the answer choices, we can ask ourselves, what must be true or what is assumed by this point? It's assuming a linkage between favorable conditions and the speed of evolution. Namely, harsher conditions induce faster evolution; favorable conditions allow slower evolution. Back to the answer choices. That's answer choice (D). Indeed, considering the contrary, if (D) isn't true, then the conclusion at line 34 is problematic, so (D) must be true by the argument.

7. In the passage, the author is primarily concerned with doing which of the following?

Difficulty Level: 650

Explanation

If we believe we are equipped to make a prediction to a question prior to looking at the answer choices, it's almost always worth taking a moment to articulate that prediction. There are two reasons. First, arming ourselves with a prediction will make it easier to run the gauntlet of temptation of the answer choices without getting drawn away by something that sounds plausible. Second, having a prediction makes the evaluation of answer choices swifter.

So, in this case: we want the author's primary purpose. We answer to ourselves: the author describes how the bodies of c-fish and lungfish shed light the shift from water to land that occurred in animals.

Let's look for that in the answer choices. (A) is quite close. (B) is out, because we don't hear all that much about the evolutionary history, especially about the lungfish. (C) happens in the passage, but it's not the main point; the term "living fossil" comes up only in the context of explaining the main point, which is described by (A).

(D) is out because it describes a degree of opinion that never comes in the passage. (E) describes a fact which is false, because lungfish can't survive on land; they are still fish.

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Re: How aquatic vertebrates evolved into land vertebrates has been difficu [#permalink]
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dragonz91
Sajjad1994 i got most of the Qs wrong; Can you please share explanations for Qs 1,4,7?(got Q7 somehow right, but need clarification)

For Q4, passage's last line says deep sea environment may have helped "more slowly evolving" coelacanth to survive a long period. But how come we arrive at OA that harness of environment partly drives the rate of evolution of a species ? Or am i missing some other part of passage where the OA has been alluded to.

Look at the structure of the passage:

Para 1:
How did aquatic vertebrates evolve into land vertebrates? Hard to say because it happened quickly and didn't leave many fossils. Morphological considerations provided clues before DNA sequencing became available. Morphological considerations pointed at coelacanth and the lungfish.

Para 2:
Why coelacanths and lungfish?
They are lobe-finned species so have bony skeleton necessary for living on land.
Coelacanths and lungfish are two of the only lobe-finned species that are not extinct, They have changed minimally and are called "living fossils" (They give info about old days like fossils do but they are alive)

Para 3:
Now genetic analysis have provided answers - Lungfish is the closer relative of tetrapods. Coelacanth DNA has shown evolution over time--although at a rate much slower than that of most animals. Possibly, the fish's morphology and its environment deep in the Indian Ocean have created favorable conditions allowing a more slowly evolving species to have survived for the last 400 million years.

Now look at the questions:

1. The passage provides information in support of which of the following assertions?

A. Although a set of possible evolutionary paths leading to a specific result can be identified, no one of them can be conclusively identified as correct.
B. Physical similarities between species give some justification to believe those species may have an evolutionary link.
C. Studies of living fossils enable conclusions about evolutionary history that could not be drawn based on other types of evidence.
D. Species with close physical similarities may nevertheless have widely different evolutionary histories.
E. How quickly an organism's DNA changes over time indicates the role that organism has played in the evolution of related species.

Para 1 tells us that morphological considerations point at lungfish and coelacanth. This means physical similarities do point to evolutionary link. So (B)
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How aquatic vertebrates evolved into land vertebrates has been difficu [#permalink]
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dragonz91
Sajjad1994 i got most of the Qs wrong; Can you please share explanations for Qs 1,4,7?(got Q7 somehow right, but need clarification)

For Q4, passage's last line says deep sea environment may have helped "more slowly evolving" coelacanth to survive a long period. But how come we arrive at OA that harness of environment partly drives the rate of evolution of a species ? Or am i missing some other part of passage where the OA has been alluded to.

Look at the structure of the passage:

Para 1:
How did aquatic vertebrates evolve into land vertebrates? Hard to say because it happened quickly and didn't leave many fossils. Morphological considerations provided clues before DNA sequencing became available. Morphological considerations pointed at coelacanth and the lungfish.

Para 2:
Why coelacanths and lungfish?
They are lobe-finned species so have bony skeleton necessary for living on land.
Coelacanths and lungfish are two of the only lobe-finned species that are not extinct, They have changed minimally and are called "living fossils" (They give info about old days like fossils do but they are alive)

Para 3:
Now genetic analysis have provided answers - Lungfish is the closer relative of tetrapods. Coelacanth DNA has shown evolution over time--although at a rate much slower than that of most animals. Possibly, the fish's morphology and its environment deep in the Indian Ocean have created favorable conditions allowing a more slowly evolving species to have survived for the last 400 million years.

Now look at the questions:

4. It can be inferred from the passage that which of the following is a true statement about the evolution of a species?

A. If a species evolves more slowly than competing species, it will have to seek out a new environment in which to live in order to survive.
B. The longer a species survives without going extinct, the more likely it is to maintain identical or nearly identical DNA over time.
C. A species' rate of evolution can be inferred from the degree of change over time of its morphology.
D. A species' rate of evolution is driven partly by the degree of harshness of the conditions in which it lives.
E. If true living fossils exist, they are not lobe-finned fish.

Para 3 tells us - "the fish's morphology and its environment deep in the Indian Ocean have created favorable conditions allowing a more slowly evolving species to have survived for the last 400 million years."
The conditions have impact on evolution. Since Coelacanth's environment had favourable conditions, it evolved slowly but still survived.

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Re: How aquatic vertebrates evolved into land vertebrates has been difficu [#permalink]
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dragonz91
Sajjad1994 i got most of the Qs wrong; Can you please share explanations for Qs 1,4,7?(got Q7 somehow right, but need clarification)

For Q4, passage's last line says deep sea environment may have helped "more slowly evolving" coelacanth to survive a long period. But how come we arrive at OA that harness of environment partly drives the rate of evolution of a species ? Or am i missing some other part of passage where the OA has been alluded to.

Look at the structure of the passage:

Para 1:
How did aquatic vertebrates evolve into land vertebrates? Hard to say because it happened quickly and didn't leave many fossils. Morphological considerations provided clues before DNA sequencing became available. Morphological considerations pointed at coelacanth and the lungfish.

Para 2:
Why coelacanths and lungfish?
They are lobe-finned species so have bony skeleton necessary for living on land.
Coelacanths and lungfish are two of the only lobe-finned species that are not extinct, They have changed minimally and are called "living fossils" (They give info about old days like fossils do but they are alive)

Para 3:
Now genetic analysis have provided answers - Lungfish is the closer relative of tetrapods. Coelacanth DNA has shown evolution over time--although at a rate much slower than that of most animals. Possibly, the fish's morphology and its environment deep in the Indian Ocean have created favorable conditions allowing a more slowly evolving species to have survived for the last 400 million years.

Now look at the questions:

7. In the passage, the author is primarily concerned with doing which of the following?

A. Explaining characteristics of lobe-finned fish that establish their role in the evolution of tetrapods
B. Comparing the evolutionary history of the coelacanth with that lungfish
C. Refuting the validity of terming the lobe-finned fish in question "living fossils"
D. Pointing out features of the coelacanth and lungfish that make them superior to ray-finned species
E. Explaining how the lungfish possesses the necessary characteristics to survive on land

The passage deals with the role of lobe-finned fish in evolution of tetrapods. Hence (A) is the best.

B. Comparing the evolutionary history of the coelacanth with that lungfish

There is no focus on the comparison of the two.

C. Refuting the validity of terming the lobe-finned fish in question "living fossils"

Though the passage does suggest that Coelacanth may not be loving fossils since their DNA has evolved albeit slowly. But in any case, that is not the main intent of the passage.

D. Pointing out features of the coelacanth and lungfish that make them superior to ray-finned species

No discussion on "superiority".

E. Explaining how the lungfish possesses the necessary characteristics to survive on land

Explaining lungfish's characteristics is not the aim.

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How aquatic vertebrates evolved into land vertebrates has been difficu [#permalink]
Great passage and the only issue I have is with the wording of the correct answer for question 6, along with the official explanation.

There are no questions about the coleancath (sp?) raised in the prior two paragraphs. The purpose of the third paragraph is to answer questions regarding whether the fish is validly considered a living fossil. However, such a question (or anything similar to it) is not raised in the prior two paragraphs.

In the first paragraph we are introduced to some of the difficulties of evolutionary biology before the advent of DNA sequencing. We are also introduced to the 2 fish that are discussed more in depth in the next 2 paragraphs.

In the second paragraph, there is no indication given that there is a difference between the coelencanth and lobefish. The paragraph is used to discuss some of the characteristics of this particular type of fish and why the 2 fish within this type are considered “living fossils.” Any question regarding the use of the colencanth as a living fossil or as a tool to understand evolutionary biology is not discussed.

It isn’t until we reach the 3rd paragraph that the deficiencies of calling the coelencath a valid “living fossil” are actually discussed.

Inferring that the author raised questions in the prior 2 paragraphs is.....difficult.

Other than that little discrepancy in answer choice D, this is a great passage with great questions.

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Re: How aquatic vertebrates evolved into land vertebrates has been difficu [#permalink]
for Ques 6, no where it is asked which among the 2 is living fossil which the third Para answers. So answer is wrong as per me.
Re: How aquatic vertebrates evolved into land vertebrates has been difficu [#permalink]
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