Why did approximately 40% of the human population evolve to tolerate lactose into adulthood?

• A. Because populations with a history of dairy farming benefited from the ability to digest lactose, leading to increased survival and reproductive success.
• B. Because lactose tolerance developed as a random mutation with no selective advantage.
• C. Because lactose tolerance is a universal trait present in all mammals throughout their entire lifespan.
• D. Because lactose tolerance provides resistance to infectious diseases such as malaria.

Answer: (A)

Verified step by step guidance

1. Step 1: Begin by understanding the concept of lactose tolerance. Lactose tolerance refers to the ability of an individual to digest lactose, a sugar found in milk, into adulthood. This ability is determined by the presence of the enzyme lactase, which breaks down lactose into glucose and galactose.
2. Step 2: Recognize that in most mammals, lactase production decreases after weaning, leading to lactose intolerance in adulthood. However, in some human populations, lactase production persists due to genetic mutations.
3. Step 3: Analyze the evolutionary context. Populations with a history of dairy farming had access to milk as a consistent food source. Individuals who could digest lactose gained nutritional benefits, which increased their survival and reproductive success.
4. Step 4: Understand natural selection. The genetic mutation allowing lactase persistence provided a selective advantage in dairy-farming populations. Over generations, this trait became more common in these populations.
5. Step 5: Eliminate incorrect options. Lactose tolerance is not universal among mammals, does not provide resistance to diseases like malaria, and did not develop randomly without selective advantage. The correct explanation is tied to the benefits of digesting milk in dairy-farming populations.