Reading Comprehension – Passage
The passage below is accompanied by a set of three questions. Choose the best answer to each question.
Scientists have long recognized 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…
Q1) 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.
Q2) 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
Q3) 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
Q1: Option (C)
Q2: Option (B)
Q3: Option (C)
Acc to Ernst Mayr in paragraph 1 of CAT 2017 – Reading Comprehension – Passage, there is no gene flow when species are separated from other species. In paragraph 2, Ehrlich and Raven found out that in 50 acres of area there were 3 species of butterflies that never interacted with each other. This led them put forth the argument in 1969 paper that, while a factor, Isolation was not as important to speciation as natural selection.
Option (C) is the correct answer.
In paragraph 3 CAT 2017 – Reading Comprehension – Passage, it is said that “isolation and gene flow were less important to evolutionary divergence. So, gene flow does contribute to evolutionary divergence.
In the first line of paragraph 1, we can see that “evolutionary changes unfold imperceptibly, over millions of years”.
In the second paragraph CAT 2017 – Reading Comprehension – Passage, we can see that even though three species of Checkerspot butterflies were living within 50 acres, they did not interact with each other which led to speciation.
Option (B) is the correct answer.
The scientists are in debate with each other over the fact the fact that speciation occurs when species are isolated from each other. Mayr concluded in the first paragraph CAT 2017 – Reading Comprehension – Passage that when populations are isolated, speciation occurs. But Ehrlich and Raven observe that even though Checkerspot butterflies lived in close proximity, they did not interact with each other. This leads to a debate between the scientists.
Option (C) is the correct answer.
CAT 2017 Questions from Reading Comprehension
Reading Comprehension – Set 1: Despite their fierce reputation. Vikings may not have always been the plunderers and pillagers popular culture imagines them to be.
Reading Comprehension – Set 2: Typewriters are the epitome of a technology that has been comprehensively rendered obsolete by the digital age.
Reading Comprehension – Set 3: The end of the age of the internal combustion engine is in sight. There are small signs everywhere: the shift to hybrid vehicles is already under way among manufacturers.
Reading Comprehension – Set 4: During the frigid season…it’s often necessary to nestle under a blanket to try to stay warm.
Reading Comprehension – Set 5: Creativity is at once our most precious resource and our most inexhaustible one.
Reading Comprehension – Set 6: Do sports mega events like the summer Olympic Games benefit the host city economically?
Reading Comprehension – Set 7: This year alone, more than 8,600 stores could close, according to industry estimates, many of them the brand -name anchor outlets that real estate developers once stumbled over themselves to court.
Reading Comprehension – Set 8: I used a smartphone GPS to find my way through the cobblestoned maze of Geneva’s Old Town, in search of a handmade machine that changed the world more than any other invention.
Reading Comprehension – Set 9: Understanding where you are in the world is a basic survival skill, which is why we, like most species come hard-wired with specialized brain areas to create congnitive maps of our surroundings.
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