Final answer:
The evolution of lighter skin pigmentation in regions farther from the equator was driven by the need for efficient Vitamin D synthesis in environments with lower UV radiation.
Step-by-step explanation:
The hypothesis that explains why lighter skin variations evolved farther from the Equator is related to Vitamin D synthesis and UV radiation exposure. As humans migrated out of Africa and into areas with less intense sunlight, such as Northern Europe, their skin pigmentation lightened to compensate for reduced ultraviolet (UV) radiation. This adaptation allowed for more efficient production of Vitamin D in conditions where sunlight is less direct and intense. Dark skin, rich in melanin, is protective against UV radiation in tropical regions near the equator but can inhibit Vitamin D synthesis in regions with less sunlight. The evolution of lighter skin pigmentation in populations living farther from the equator was a result of natural selection, favoring individuals with a greater ability to produce Vitamin D in low-UV environments.