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Until the 1970s it was assumed that, despite the very large number of

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New Project RC Butler 2019 - Practice 2 RC Passages Everyday
Passage # 32, Date : 16-FEB-2019
This post is a part of New Project RC Butler 2019. Click here for Details


Until the 1970s it was assumed that, despite the very large number of species that appeared during the Cambrian explosion, nearly all fit into the same rather small number of phyla that exist today. Each phylum—a group of organisms with the same basic pattern of organization, such as the radial symmetry of jellyfish and other coelenterates or the segmented structure of worms and other annelids—was seen as evolutionarily stable.

Innumerable individual species have arisen and died out, but development and extinction were assumed to take place within existing phyla; the elimination of entire phyla was thought to be extremely rare. A diverse group of marine fossils, known collectively as the Problematica, present difficulties for this interpretation. They show patterns of organization so bizarre that it is hard to fit any of them into present-day phyla. They include the banana-shaped Tullimonstrum and the spiked, spiny Hallucigenia, creatures whose very names reflect the classifier‘s discomfort.

The ―Ediacaran fauna,‖ which respired, absorbed nutrients, and eliminated wastes directly through their external surfaces, are also included among the Problematica. Theirs was an approach taken by only a few modern multicelled creatures (such as tapeworms) that are otherwise totally unlike them. Several theorists have argued that the Problematica are not just hard to classify—they are evidence that the conventional view of the Cambrian explosion is wrong. They contend that the Cambrian explosion represented the simultaneous appearance of a much larger number of animal phyla than exists today. Each was a separate ―experiment‖ in basic body design, and the Cambrian seas teemed with many different phyla, or basic body plans, each represented by only a few species.

Today, the number of phyla has fallen drastically, but each surviving phylum contains a much larger number of species. The Problematica, then, were not unsuccessful variants within present-day phyla; each represented a distinct phylum in its own right. Revisionists contend that the selection process eliminated not only particular unfavourable traits, but entire body plans and approaches to survival. The Ediacaran fauna, for example, represented a particular structural solution to the basic problems of gas and fluid exchange with the environment.

This approach to body engineering was discarded at the same time as the Ediacaran fauna themselves were wiped out; given the improbability of duplicating an entire body plan through chance mutation, it was unlikely that this particular approach would ever be tried again.

Revisionists and conventional theorists agree that modern marine species are products of natural selection. Up until 30 years ago, the pattern of early marine animal evolution seemed to be well established. Most present-day marine animal phyla had appeared during the ―Cambrian explosion,‖ an extraordinary burgeoning of multicellular life in the warm seas of the Cambrian period, between 570 and 500 million years ago.
1. The description by the author in the third paragraph of how the Ediacaran fauna carried out respiration, absorption, and excretion tends to support the view that the Ediacaran fauna:

A. were probably not members of any present-day phylum.
B. had physiological processes different from those of any other known organisms.
C. could not absorb or excrete fluids.
D. were members of the same phylum as Tullimonstrum.
E. were not much dissimilar from other existing fauna



2. The passage implies that conventional and revisionist theorists disagree about all of the following EXCEPT:

A. the accuracy of the conventional view of early marine evolution.
B. the probable number of marine animal phyla during the Cambrian period.
C. the likelihood of entire phyla becoming extinct.
D. the applicability of the theory of natural selection to the Cambrian period.
E. the number of species within individual phyla



3. According to the passage, the Problematica are difficult to classify because:

I. some had unusual shapes.
II. some of them functioned physiologically differently from modern organisms.
III. they became extinct at the end of the Cambrian period.

A. I only
B. II only
C. I and II only
D. I and III only
E. I, II and III




Aristotle RC-99 The Definitive RC Guide, Passage #91

Originally posted by sahilchaudhary on 08 Jan 2014, 12:48.
Last edited by SajjadAhmad on 12 Sep 2019, 07:48, edited 4 times in total.
Updated - Complete topic (531).
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Re: Until the 1970s it was assumed that, despite the very large number of  [#permalink]

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New post 19 Feb 2019, 12:39
1
Official Explanation


Topic and Scope - Traditional and revisionist theories on phyla in early marine evolution

Mapping the Passage

1st and 2nd Para discuss a traditional theory of phyla evolution.
2nd and 3rd present fossil evidence, the Problematica, that challenges the traditional view of phyla.
3rd presents theorists who argue that the Problematica disprove the traditional view.
4th and 5th present the new view‘s main tenet: natural selection involved not only experiments with individual traits within a phyla, but also with whole phyla.
6th reviews the traditional theory of phyla evolution.


1. The description by the author in the third paragraph of how the Ediacaran fauna carried out respiration, absorption, and excretion tends to support the view that the Ediacaran fauna:

(A): Before reading the text closely, predict based on your map. What does para 3rd present? Evidence that challenges the traditional view that everything can be classified according to presently-existing phyla. (A) rewards the strong map instantly.

(B): Opposite. The author says that the Edicarian physiological processes took an approach ―taken by only a few modern multicelled creatures,‖ which means that these processes were not unique.

(C): Opposite. The author states explicitly in lines 21 and 22 that they could absorb and excrete.

(D): Distortion. Though the Tullimonstrum phylum is part of Problematica too, the author doesn‘t suggest that it and the Edicarian fauna are part of the same phylum.

(E): Opposite, as explained in A.

Answer: A


2. The passage implies that conventional and revisionist theorists disagree about all of the following EXCEPT:

Evaluate the wording carefully. The two sides disagree on all the answer choices except the correct one, which means that they agree on the correct choice. Predict a point of agreement between the two sides. Para 6th opening line gives a big hint: The two sides agree that ―modern marine species are products of natural selection.‖ (D) jumps out quickly when the prediction is made beforehand.

(A): Opposite. The basis of the revisionist view is that the conventional view of static phyla is wrong.

(B): Opposite. Traditionalists think that there were only a few phyla with lots of species; revisionists believe that there were many phyla, as discussed in ¶3.

(C): Opposite. Since revisionists believe that many ancient species fit into existing phyla and revisionists believe that they belonged to now-extinct phyla, the two sides would disagree on whether phyla are likely to become extinct.

(D): The correct answer

(E): Opposite, as described in B

Answer: D


3. According to the passage, the Problematica are difficult to classify because:

Where are the Problematica discussed? Evaluate the Roman Numerals with an eye to Para 2 and 3. Start with RN I, which appears in three choices: The author says in lines 17-18 that their patterns of organization were bizarre, and that this makes it hard to fit them into modern phyla. RN I therefore fits, eliminate (B). Evaluate RN II: The Edicarian fauna are an example of different physiological functioning, so this statement is valid also. At this point, only (C) is a viable answer choice, and there‘s no need to evaluate RN III. A quick look at RN III shows a statement with no support in the passage: the author doesn‘t discuss when the Problematica went extinct, only that they did.

(A): Opposite. As described above.
(B): Opposite. As above.
(C): The correct answer
(D): Opposite. As above.
(E): Opposite. As above.

Answer: C


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Re: Until the 1970s it was assumed that, despite the very large number of  [#permalink]

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New post 09 Jan 2014, 00:43
Please post the questions for the above passage.
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Re: Until the 1970s it was assumed that, despite the very large number of  [#permalink]

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New post 09 Jan 2014, 00:50
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cbo wrote:
Please post the questions for the above passage.


Hi cbo,

The questions are already posted along side the question. I would suggest you to access this site using a computer as there might be problem accessing it from mobile device.
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Re: Until the 1970s it was assumed that, despite the very large number of  [#permalink]

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New post 09 Jan 2014, 02:53
Get them all right but took me too long to solve this one..

Was stupid at the beginning, wanted to train and did a lot of analysis but finally did a lot of addition work that ended to be useless!

This text is hard but still clear in its meaning (hopefully)!

thank for sharing!
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Re: Until the 1970s it was assumed that, despite the very large number of   [#permalink] 09 Jan 2014, 02:53
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