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).
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 Whether Ehrlich and Raven’s thesis superceded Mayr’s is not determined in the passage, so (2) is also ruled out.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.