Thanks for the great question!

The human body absorbs ultraviolet (UV) rays from the sun through the skin to create Vitamin D, which is crucial for preventing diseases. However, too much absorption of UV results in damage to the skin (sunburns and even skin cancer). Variations in human skin color evolved to optimize absorption of UV rays while preventing damage to the skin. Skin is made darker through the presence of a pigment called melanin, which acts as a natural sunscreen.

The first human ancestors evolved in Africa near the equator where sunlight is most direct and so they had darker skin to protect against overexposure. As humans migrated to more northern latitudes, where sunlight is less direct, lighter skin evolved to allow more absorption of sunlight. So why, as your question rightly points out, do the Inuit people of the Arctic Circle, where the sunlight is the least direct, retain skin darker than other ethnic groups that live in the north?

The Inuit people are masters of their harsh Arctic environment, creating technologies like canoes and harpoons to hunt marine animals for food. It turns out that the Inuit were very successful at hunting animals like fatty fish that were rich in Vitamin D. Thus, the Inuit were less reliant on sunlight to produce this vitamin as they could get it from their diet. For this reason, natural selection did not favor those individuals that happened to have lighter skin tones among the Inuit, and darker skin tones were able to persist among these populations.

Thanks again for the great question,