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.

Correct Option (B)

The passage explicitly details how the domestication of cattle, a significant and permanent alteration in human food habits approximately 10,000 years ago, led to the evolution of lactose tolerance in certain populations. This adaptation, involving the continued production of the lactase enzyme beyond infancy, represents a genetic change directly influenced by a sustained dietary shift. Therefore, the most logical assumption is that a permanent change in the food habits of a community can induce a genetic change in its members.

Incorrect Options:

• Option (A) states that animal domestication occurred in some parts of the world about 10,000 years ago. While this is a factual statement presented in the passage as a premise, it is a historical detail rather than the primary logical assumption or evolutionary principle derived from the entire narrative. The passage uses this event to explain a subsequent biological adaptation.
• Option (C) suggests that only lactose-tolerant individuals can obtain simple sugars in their bodies. The passage specifically discusses the breakdown of lactose into simple sugars. It does not imply that simple sugars cannot be acquired from other food sources by any individual, regardless of their lactose tolerance status. This is an overgeneralization unsupported by the text.
• Option (D) claims that lactose-intolerant individuals cannot digest any dairy product. Lactose intolerance refers to the inability to digest lactose, a specific sugar found in milk. The passage does not provide information to conclude that all dairy products are indigestible, as some dairy products (e.g., certain cheeses, yogurt) contain significantly lower levels of lactose and may be digestible by some lactose-intolerant individuals. This is an unsupported generalization.