Human Skin Color: Melanin Biology, Genetic Architecture, and Environmental Modulation

Skin color is a polygenic trait determined by the amount, type, and distribution of melanin produced by epidermal melanocytes.

Melanin Types

• Eumelanin (black‑brown) – photoprotective; predominant in darker skin.
• Pheomelanin (red‑yellow) – less protective; higher in fair skin/red hair.

Genetic Control

Major loci: MC1R (melanocortin‑1 receptor), TYR, OCA2, SLC24A5, TYRP1, KITLG, among >150 identified variants. Polygenic scores explain ~35% of variance.

Environmental Modulation

• UV Radiation – Stimulates melanogenesis (tanning); chronic exposure → photoaging, cancer risk.
• Nutrition – Folate, vitamin D pathways interact with pigmentation genetics.

Evolutionary Perspective

Latitudinal cline: dark skin near equator (folate protection), lighter skin at high latitudes (vitamin D synthesis). Modern migration/mobility creates mismatch scenarios.

Skin color is a beautiful example of recent human adaptation—social meanings are cultural, not biological.