UPSC Prelims 2012 · CSAT

Question 4: Reading Comprehension

Passage beginning “Chemical pesticides lose their role in…” — Passage – 2 · as printed by UPSC

“The evolution of pesticide resistance is natural selection in action.” What does it actually imply ?

aIt is very natural for many organisms to have pesticide resistance.

bPesticide resistance among organisms is a universal phenomenon.

cSome individuals in any given population show resistance after the application of pesticides.

dNone of the statements (a), (b) and (c) given above is correct.

AnswerUPSC’s answer is (c).

Natural selection acts on variation already present in a population. When a pesticide is applied, susceptible individuals die, while the few that happen to carry resistant genes survive and breed, so resistant forms become common. That is why only some individuals in a population show resistance, which is what option (c) points to; the pesticide does not create resistance, it selects it. The printed passage never discusses resistance, so this question tests basic evolutionary biology.

Why each option is right or wrong

(a) Wrong. Resistance is not natural to organisms in general; it spreads only under the selection pressure of pesticide use.
(b) Wrong. It is not universal; only exposed populations, and only some individuals within them, show resistance.
(c) Right. Survivors of the spray are the resistant individuals, and they pass the trait on, which is selection at work.
(d) Wrong. Option (c) is correct, so this cannot be.

Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.

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Source: UPSC, Civil Services (Preliminary) Examination 2012, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.