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5.7: The Biochemical and Evolutionary Foundations of Skin Color

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    At its core, human skin color is determined by melanin, a natural pigment produced by specialized cells called melanocytes located in the epidermis. The synthesis of melanin, or melanogenesis, begins with the amino acid tyrosine. The key enzyme tyrosinase converts tyrosine to dopaquinone, after which the pathway diverges to produce two main types of melanin: (1) eumelanin: brown-to-black pigment that is highly effective at absorbing and dissipating harmful UV radiation, providing photoprotection; and (2), pheomelanin: a red-to-yellow pigment that is less protective and may even generate free radicals upon UV exposure.

    The relative amount and combination of these pigments, along with the size, number, and distribution of the melanosome packages that carry them to skin cells, create the vast diversity of human skin tones. It is a critical adaptation: near the equator, where UV radiation is most intense, natural selection strongly favored populations with darker, eumelanin-rich skin to protect against DNA damage. At higher latitudes with lower UV levels, selection pressure favored lighter skin, which allows sufficient UVB penetration for the essential synthesis of vitamin D.

    Recent genomic research underscores that pigmentation genetics are far from simple, especially within highly diverse populations. A landmark study of KhoeSan populations in southern Africa revealed that near the equator, skin color is influenced by a vast, complex array of genes—a “stabilizing selection” that maintains variation. This finding challenges the older narrative that a handful of genes control pigmentation and highlights how underrepresented populations in genetics research have obscured a fuller understanding of human diversity.

    This page titled 5.7: The Biochemical and Evolutionary Foundations of Skin Color is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Salvador Jiménez Murguía.