UPSC Prelims 2019 CSAT Paper II · Q7 of 79 Comprehension medium

Passage

Passage - 6 A bat's wings may look like sheets of skin. But underneath, a bat has the same five fingers as an orangutan or a human, as well as a wrist connected to the same cluster of wrist bones connected to the same long bones of the arm. What can be more curious than that the hand of a man, formed for grasping, that of a mole for digging, the leg of the horse, the paddle of the porpoise, and the wing of the bat, should all be constructed on the same pattern ?

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

  1. (a) Different species having similar structure of hands is an example of biodiversity.
  2. (b) Limbs being used by different species for different kinds of work is an example of biodiversity.
  3. (c) Man and the aforementioned animals having similar structure of limbs is an example of coincidence in evolution.
  4. (d) Man and the aforementioned animals have a shared evolutionary history. ✓ UPSC's answer

Why the answer is (d)

• The passage highlights that the hand of a man, mole, horse, porpoise, and bat are all constructed on the same underlying pattern of bones (five fingers, wrist bones, arm bones). - This structural similarity despite different functions (grasping, digging, running, swimming, flying) is the definition of homologous structures. - Homologous structures are evidence of common ancestry, indicating that these species evolved from a common ancestor. - Therefore, the most logical scientific inference is that these species share an evolutionary history. - Option (d) correctly identifies this shared evolutionary history as the rational conclusion drawn from the anatomical evidence.

Why the other options are wrong

(a) Different species having similar structure of hands is an example of biodiversity.
While the existence of different species is part of biodiversity, the passage specifically focuses on the structural similarity (homology) which points to evolutionary relationships rather than just the variety of life.
(b) Limbs being used by different species for different kinds of work is an example of…
The passage emphasizes the identical underlying bone structure, not the different functions or uses of the limbs, which is the key evidence for common descent.
(c) Man and the aforementioned animals having similar structure of limbs is an example of…
The passage presents the structural similarity as a curious but systematic pattern, which in biology is interpreted as evidence of common ancestry, not a random coincidence.

Asked in the CSAT Paper II of the UPSC Civil Services Preliminary Examination 2019, held on 2 June 2019. Question and answer key: Union Public Service Commission. Explanation: UPSC Answer Check.

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