At the bottom layer of the epidermis are melanocytes, cells that produce a brown pigment: melanin. This pigment accumulates in the keratinocytes and darkens the skin. The process of melanogenesis is responsible for long-term pigmentation that's designed to protect the epidermis from UV-B radiation damage and ensure the functionality of other organs and tissues. Researchers have found melanin also plays a role in the immune system and the ongoing health of vital systems in the body.
Skin color variations are adaptation mechanisms, according to natural history research. As humans moved around hot environments looking for food, the body had to make certain changes to cool itself. This need for thermoregulation led to an increase in the number of sweat glands and a decrease in body hair, which in turn left the skin more exposed to the intense sun, especially in locations near the equator. Darker pigmentation was a natural sunscreen. Those who lived in colder climates developed lighter skin because they had to deal with lower UV radiation and needed skin that allowed sunlight to help the body to produce vitamin D naturally.
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