Final answer:
The mutation in the SLC24A5 gene that contributed to lighter skin in most Europeans appeared about 8,500 years ago, with nearly all Europeans carrying the mutant allele. Dark skin is adaptive in equatorial regions due to its ability to protect against intense ultraviolet radiation. Skin pigmentation is a response to varying sunlight levels and facilitates vitamin D synthesis.
Step-by-step explanation:
The Mutation in the SLC24A5 Gene
The mutation in the SLC24A5 gene that led to lighter skin in most Europeans occurred roughly 8,500 years ago. This gene is associated with skin pigmentation, and its mutation has been linked to the evolution of lighter skin tones in European populations. Analysis suggests that homozygous carriers of the mutant allele are found in 99% of Europeans, indicating strong selection for this trait.
Adaptation to Equatorial Regions
In equatorial regions, dark skin evolved as an adaptive trait to protect against the harmful effects of ultraviolet (UV) radiation. High levels of melanin in dark skin provide a natural barrier to UV rays, reducing the risk of skin damage and other negative effects. UV radiation is intense near the equator, making dark skin an advantageous trait for populations in these areas because it protects against excessive synthesis of vitamin D, which could be detrimental, and shields skin cells from damage.
Evolutionary Advantages of Skin Pigmentation
Skin pigmentation varies across global populations as a response to differing levels of UV radiation exposure. In areas with less sunlight, such as northern Europe, lighter skin is favorable as it facilitates the synthesis of vitamin D. This nutrient is crucial for bone health and immune function. As humans migrated away from the equator, their skin pigmentation adapted over generations to allow for sufficient vitamin D absorption in regions with less intense sunlight.