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Why Do We Have Different Skin Colours?

BiologyGenetics

Quick Answer

Skin colour variation is primarily determined by the amount and type of melanin pigment, which evolved as an adaptation to different levels of ultraviolet radiation at various latitudes.

The Full Story

Human skin colour is mainly controlled by melanin produced by melanocyte cells. Two forms exist: eumelanin (brown-black) and pheomelanin (red-yellow). Populations near the equator evolved darker skin with more eumelanin to protect against intense UV radiation, which can destroy folate (essential for DNA repair and fetal development) and cause skin cancer. Populations at higher latitudes evolved lighter skin to allow more UV penetration for vitamin D synthesis, which is critical for bone health and immune function. This gradient — darker skin near the equator, lighter toward the poles — is one of the strongest examples of natural selection in humans. Genetic studies have identified over 170 genes influencing skin pigmentation, with key variants in genes like MC1R, SLC24A5, and TYR.

Key Facts

1.All humans have roughly the same number of melanocytes (about 1,000-2,000 per square millimetre); skin colour differences come from the amount, type, and distribution of melanin they produce.
2.The SLC24A5 gene variant associated with lighter skin in Europeans arose only about 6,000-10,000 years ago, making light skin a relatively recent adaptation.
3.UV radiation levels at the equator can be up to 6 times higher than at 45 degrees latitude, driving the strongest selection pressure on skin pigmentation.

YouTube Angle

Suggested video title for this topic:

"The Science of Skin Colour — Evolution, UV, and Melanin"