Final answer:
Lighter skin in humans developed as an adaptation to different levels of ultraviolet radiation. This process may have taken as few as 100 generations to appear.
Step-by-step explanation:
The development of lighter skin in humans occurred as an adaptation to different levels of ultraviolet radiation. As humans migrated to regions with less sunlight, their skin pigmentation became lighter to allow for greater absorption of Vitamin D. This process may have taken as few as 100 generations to appear in humans.
For example, humans who left Africa and settled in Europe about 40,000 years ago most likely had dark skin with high levels of melanin to protect against ultraviolet radiation. However, about 8,500 years ago, early hunter-gatherers in Spain, Luxembourg, and Hungary also had darker skin. Skin pigmentation is an adaptation to ultraviolet radiation, with different skin tones offering different advantages depending on the distance from the equator.
Over thousands of years, human phenotypes evolved to thrive in various climates and environments, with skin pigmentation being a noticeable adaptation. The traditional theory, known as directional selection, explains that dark skin is an evolutionary adaptation that helps protect people in sunnier regions. However, dark skin may be disadvantageous in areas with less sunlight, like northern Europe, where lighter skin allows for sufficient Vitamin D absorption.