UPSC Prelims 2016 CSAT Paper II · Q65 of 79 Comprehension medium

Passage

Passage-2 All humans digest mother's milk as infants, but until cattle began being domesticated 10,000 years ago, children once weaned no longer needed to digest milk. As a result, they stopped making the enzyme lactase, which breaks down the sugar lactose into simple sugars. After humans began herding cattle, it became tremendously advantageous to digest milk, and lactose tolerance evolved independently among cattle herders in Europe, the middle East and Africa. Groups not dependant on cattle, such as the Chinese and Thai, remain lactose intolerant.

Which among the following is the most logical assumption that can be made from the above passage ?

  1. (a) About 10,000 years ago, the domestication of animals took place in some parts of the world
  2. (b) A permanent change in the food habits of a community can bring about a genetic change in its members ✓ UPSC's answer
  3. (c) Lactose tolerant people only are capable of getting simple sugars in their bodies
  4. (d) People who are not lactose tolerant cannot digest any dairy product

Why the answer is (b)

• The passage states that after cattle domestication, the ability to digest milk (lactose tolerance) evolved independently in specific populations, indicating a biological adaptation.

• This evolution occurred because digesting milk became advantageous, linking a change in food habits (consuming milk) to a genetic change (production of lactase).

• The text explicitly contrasts cattle-herding groups, who developed tolerance, with non-herding groups like the Chinese and Thai, who remained intolerant.

• Therefore, the most logical assumption is that a permanent shift in diet can drive genetic changes in a community over time.

Why the other options are wrong

(a) About 10,000 years ago, the domestication of animals took place in some parts of the world
The passage specifically mentions the domestication of cattle, not animals in general, and focuses on the biological consequence rather than the event of domestication itself.
(c) Lactose tolerant people only are capable of getting simple sugars in their bodies
The passage states that lactase breaks down lactose into simple sugars, but it does not claim that lactose-tolerant people are the *only* ones capable of obtaining simple sugars from other food sources.
(d) People who are not lactose tolerant cannot digest any dairy product
The passage defines lactose intolerance as the inability to digest the sugar lactose, not as an inability to digest all dairy products, which may contain other digestible components.

Asked in the CSAT Paper II of the UPSC Civil Services Preliminary Examination 2016, held on 7 August 2016. Question and answer key: Union Public Service Commission. Explanation: UPSC Answer Check.

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