Final answer:
The paleness of animals in northern areas compared to those farther south is an adaptation to lower UV radiation, aiding in Vitamin D absorption and is an example of a cline, which is a gradual change in a trait across a geographic distance.
Step-by-step explanation:
The principle regarding the paleness of animals in northern areas as compared to those farther south is related to the adaptations and changes occurring due to the distance from the equator. One key adaptation often seen is changes in skin pigmentation due to different levels of ultraviolet radiation exposure. In northern areas, where ultraviolet radiation is less intense, animals, including humans, have evolved paler skin to maximize the absorption of Vitamin D which is essential for several immune functions and maintaining strong bones. This pattern of gradual change in a trait, like skin pigmentation, across a geographic distance is known as a cline. Such adaptations in animal and plant species, which include Allen's rule and photoperiod sensitivity, are important for survival and successful reproduction in the varying conditions found at different latitudes.