ANTH 1000 Lecture Notes - Lecture 5: Allele, Genotype, Weaning
31 Jan 2017
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Hemoglobin also pigments the skin, oxygenated blood is red due to iron in hb. Note the clinical variation (gradual change) rather than discrete grouping. Melanin protects against skin cancer, sunburn, and uv radiation. Darker skinned people have lower rates of skin cancer because the higher concentration of melanin blocks more of the uv. Melanin protects against skin cancer, so high melanin at equator may reflect selection for this. Skin cancer usually effects people after they are past reproductive age, so is not a big selective disadvantage. But severe sunburn can lead to infection and reduced fitness, so maybe dark skin is protection against this (not cancer) Many nutrients break down when exposed to uv light. Perhaps dark skin is an adaptation to prevent this. For example, the vitamin folate is decomposed by uv. Uv radiation needed to synthesize vitamin d, which is needed by humans for proper bone growth.
