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UPSC CSE CSAT 2019 · Question 66 · Reading comprehension

On the basis of the above passage, the following assumptions have been made:

Passage—4

A research team examined a long-term owl roost. Owls prey on small mammals and the excreted remains of those meals that accumulated over the time, provide us an insight into the composition and structure of small mammals over the past millennia. The research suggested that when the Earth went through a period of rapid warming about 13,000 years ago, the small mammal community was stable and resilient. But, from the last quarter of the nineteenth century, human-made changes to the environment had caused an enormous drop in biomass and energy flow. This dramatic decline in energy flow means modern ecosystems are not adapting as easily as they did in the past.

CSAT 2019 · Q66

Reading comprehension Medium

On the basis of the above passage, the following assumptions have been made:

  1. 1.Global warming is a frequently occurring natural phenomenon.
  2. 2.The impending global warming will not adversely affect small mammals.
  3. 3.Humans are responsible for the loss of the Earth’s natural resilience.

Which of the above assumptions is/are valid?

Answer & explanation

Answer: (b) 3 only

Small mammals stayed stable through natural warming 13,000 years ago, but human-made changes since the late nineteenth century cut biomass and energy flow, so ecosystems no longer adapt as easily. That places the loss of resilience on humans. The passage mentions one past warming, not frequent ones, and implies modern ecosystems are more vulnerable.

  • ✗ 1. A single period of warming 13,000 years ago does not show that warming is 'frequently occurring'.
  • ✗ 2. Modern ecosystems 'are not adapting as easily as they did in the past' — the passage points to greater risk, not safety.
  • ✓ 3. 'Human-made changes' caused the drop in biomass and energy flow that weakened ecosystems' ability to adapt.

Remember · One example cannot establish 'frequent'; when a passage contrasts past resilience with present weakness, the cause is what changed in between.

Question and answer: UPSC's official GS Paper II (2019, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). ·

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