What is the selective pressure for lighter skin color in the northern hemisphere?

As humans migrated to the northern hemisphere, particularly in areas with lower sunlight, the need for efficient vitamin D synthesis became crucial. With less UV radiation available, lighter skin evolved as a selective advantage; it allows for better absorption of sunlight to produce vitamin D, which is essential for bone health and immune function. This adaptation helped populations survive and thrive in these regions. In addition to vitamin D synthesis, lighter skin also played a role in terms of social dynamics and reproductive advantages. In various cultures, lighter skin was sometimes associated with higher social status or beauty, influencing mate selection. As a result, the combination of environmental needs and social perceptions contributed to the prevalence of lighter skin in northern populations over generations.