Final answer:
Lighter skin color in humans in northern, temperate climates in prehistoric times was an adaptation to compensate for less ultraviolet radiation and reduce the risk of Vitamin D deficiency.
Step-by-step explanation:
In prehistoric times, lighter skin color in humans was found most commonly in northern, temperate climates due to the distance from the equator and the need for greater exposure to ultraviolet radiation. As humans migrated to the Northern Hemisphere, they were exposed to less ultraviolet radiation, resulting in less absorption of Vitamin D. To compensate for this, skin pigmentation became lighter. This adaptation allowed for the formation of Vitamin D below the skin in areas where sunlight is relatively weak.