Final answer:
The mutation in the SLC24A5 gene that produced lighter skin in Europeans occurred around 8,500 years ago. Dark skin is adaptive in equatorial regions because it protects against UV radiation and prevents excess vitamin D synthesis.
Step-by-step explanation:
The mutation in the SLC24A5 gene that led to lighter skin pigmentation in most Europeans is believed to have occurred approximately 8,500 years ago. This gene plays a role in the synthesis of melanosomes, which affect skin pigmentation. The homozygous mutant gene, associated with lighter skin, is found in 99% of individuals with European origins. Skin pigmentation varies with distance from the equator and is a result of adaptation to levels of ultraviolet radiation. In equatorial regions, darker skin provides protection against the harmful effects of UV radiation and prevents the synthesis of excessive vitamin D, which could be detrimental. Conversely, lighter skin is advantageous in areas with less sunlight, such as northern Europe, because it allows for adequate vitamin D synthesis, which is vital for bone health and immune function.