CAT 2017 - Slot 1 - Verbal Ability and Reading Comprehension - Scientists have long recognised the incredible diversity within a species

Scientists have long recognised the incredible diversity within a species. But they thought it reflected evolutionary changes that unfolded imperceptibly, over millions of years. That divergence between populations within a species was enforced, according to Ernst Mayr, the great evolutionary biologist of the 1940s, when a population was separated from the rest of the species by a mountain range or a desert, preventing breeding across the divide over geologic scales of time. Without the separation, gene flow was relentless. But as the separation persisted, the isolated population grew apart and speciation occurred. In the mid-1960s, the biologist Paul Ehrlich - author of The Population Bomb (1968) - and his Stanford University colleague Peter Raven challenged Mayr's ideas about speciation. They had studied checkerspot butterflies living in the Jasper Ridge Biological Preserve in California, and it soon became clear that they were not examining a single population. Through years of capturing, marking and then recapturing the butterflies, they were able to prove that within the population, spread over just 50 acres of suitable checkerspot habitat, there were three groups that rarely interacted despite their very close proximity. Among other ideas, Ehrlich and Raven argued in a now classic paper from 1969 that gene flow was not as predictable and ubiquitous as Mayr and his cohort maintained, and thus evolutionary divergence between neighbouring groups in a population was probably common. They also asserted that isolation and gene flow were less important to evolutionary divergence than natural selection (when factors such as mate choice, weather, disease or predation cause better-adapted individuals to survive and pass on their successful genetic traits). For example, Ehrlich and Raven suggested that, without the force of natural selection, an isolated population would remain unchanged and that, in other scenarios, natural selection could be strong enough to overpower gene flow...

Q. 1: Which of the following best sums up Ehrlich and Raven’s argument in their classic 1969 paper?
A) Ernst Mayr was wrong in identifying physical separation as the cause of species diversity
B) Checkerspot butterflies in the 50-acre Jasper Ridge Preserve formed three groups that rarely interacted with each other
C) While a factor, isolation was not as important to speciation as natural selection
D) Gene flow is less common and more erratic than Mayr and his colleagues claimed.

Correct Answer:- C Explanation:-

(1) is tricky, as it does not come to the point – if Mayr was wrong, what was ‘right’? What is Ehrich and Raven’s case? Likewise (2) is evidence, where is the thesis? State your point of view on the topic directly and in one sentence! (4) gets close, refer to “gene flow  was not as predictable and ubiquitous as Mayr … maintained. ”. So? The answer is (3) – refer to the third paragraph again –

“isolation and gene flow were less important to evolutionary divergence than natural selection”. And the answer is (3).


Q. 2:All of the following statements are true according to the passage EXCEPT
A) Gene flow contributes to evolutionary divergence.
B) The Population Bomb questioned dominant ideas about species diversity
C) Evolutionary changes unfold imperceptibly over time.
D) Checkerspot butterflies are known to exhibit speciation while living in close proximity

Correct Answer:- B Explanation:-

That gene flow contributes to evolutionary divergence is acknowledged by Ehrlich and Raven in the third paragraph – refer to  “isolationand gene flow were less important to evolutionary divergence than natural selection”, which admits that isolation and  gene flow is important to evolutionary divergence to some extent. This point is also reiterated in the last sentence of the passage. Hence, (2) is correct. (3) is supported by information in the first paragraph “when a population was separated … over geologic    scales of time”. (4) is supported by information in the second paragraph – “there were three groups that rarely interacted despite  their very close proximity”.



Q. 3: The author discusses Mayr, Ehrlich and Raven to demonstrate that
A) evolution is a sensitive and controversial topic
B) Ehrlich and Raven’s ideas about evolutionary divergence are widely accepted by scientists.
C) the causes of speciation are debated by scientists
D) checkerspot butterflies offer the best example of Ehrlich and Raven’s ideas about speciation

Correct Answer:- C

Explanation:- Nowhere in the passage is it suggested that evolution is a sensitive or controversial topic, so (1) is ruled out. Whether Ehrlich and Raven’s thesis superceded Mayr’s is not determined in the passage, so (2) is also ruled out. The merits or otherwise, of checkerspot butterflies, cannot be determined from the passage, so (4) is also ruled out. The passage mentions Mayr, Ehrlich and Raven in the context of the theories of speciation, so (3) is the answer.

Checkout Other Questions of CAT 2017 Slot 1 Paper:

Verbal Ability :              |   Q.01- Q.06  |  Q.07- Q.12  |  Q.13- Q.18  |  Q.19- Q.21  |  Q.22- Q.24  |  Q.25- Q.29  |  Q.30 – Q.34  |

Logical Reasoning :    |   Q.01- Q.04  |  Q.05- Q.08  |  Q.09- Q.12  |  Q.13- Q.16  |  Q.17- Q.20  |  Q.21- Q.24  |  Q.25 – Q.28  |   Q.29 – Q.32  |

Quantitative Aptitude: |   Q.01- Q.05  |   Q.06- Q.10Q.11- Q.15  |  Q.16- Q.20  |  Q.21- Q.25  |   Q.26- Q.30  |  Q.31 – Q.34  |


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