Final answer:
A mutation allowing adults to produce lactase helped early humans by providing an alternative source of nourishment, which included vital nutrients needed for survival.
Step-by-step explanation:
The mutation that allows some adults to continue to drink milk without discomfort relates to lactose tolerance, enabling them to produce the enzyme lactase. This mutation would have provided a significant evolutionary advantage by offering an alternative source of nourishment for early humans (D).
With the domestication of cattle and the ability to consume dairy, these humans had access to an additional food source rich in calcium, proteins, and vitamin D. This would have been particularly beneficial during times of scarcity or when other food resources were limited, contributing to survival and reproductive success.