UPSC Prelims 2019 · CSAT

Question 7: Reading Comprehension

Passage beginning “A bat's wings may look like sheets…” — Passage - 6 · as printed by UPSC

Which one of the following is the most logical, scientific and rational inference that can be made from the above passage ?

aDifferent species having similar structure of hands is an example of biodiversity.

bLimbs being used by different species for different kinds of work is an example of biodiversity.

cMan and the aforementioned animals having similar structure of limbs is an example of coincidence in evolution.

dMan and the aforementioned animals have a shared evolutionary history.

AnswerUPSC’s answer is (d).

The passage points out that a human hand, a bat's wing, a mole's digging limb, a horse's leg and a porpoise's paddle share one bone plan despite their different uses. Such similarity of underlying structure, called homology, is explained by descent from a common ancestor, so these animals share an evolutionary history. Coincidence would not produce the same bone-by-bone pattern across so many different-looking limbs.

Why each option is right or wrong

(a) Wrong: biodiversity means variety of life; shared structure is evidence of common descent, not of variety.
(b) Wrong: different uses show adaptation, but the puzzle in the passage is the common pattern beneath them.
(c) Wrong: an identical bone plan across species is not coincidence; it reflects shared ancestry.
(d) Right: homologous structures indicate a common evolutionary origin.

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

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Source: UPSC, Civil Services (Preliminary) Examination 2019, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.