PATHOLOGY

Detailed explanation-1: -Nature has selected for people with darker skin in tropical latitudes, where ultraviolet radiation from the sun is the most intense. Melanin acts as a protective biological shield against ultraviolet radiation. Melanin in the skin helps prevent sunburn and skin damage that could cause DNA changes and skin cancer.

Detailed explanation-2: -This graph indicates that darker-skinned individuals (individuals with more eumelanin in their skin that reflects less visible light) tend to live around the equator, where UV intensity is highest.

Detailed explanation-3: -As explained in Question 9, in high-UV environments, darker skin offers protection from the damaging effects of UV radiation, especially on DNA and the valuable nutrient folate. Thus, people with dark skin in these high-UV environments would have had an advantage in survival and reproduction.

Detailed explanation-4: -At higher latitudes, the sun is lower in the sky, so UV rays must travel a greater distance through ozone-rich portions of the atmosphere and, in turn, expose those latitudes to less UV radiation. UV intensity increases with altitude because there is less atmosphere to absorb the damaging rays.