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I compared one genetic marker, skin reflectances, between Bolivians of European ancestry residing at high altitude in La Paz (3600 m; 41 boys and 65 girls) and at low altitude in Santa Cruz (400 m; 140 boys and 117 girls). Reflectances were measured at three wavelengths (425 nm, 545 nm, and 685 nm) on two different sites: the medial surface of the inner upper arm and the forehead. Principal components analysis was used to reduce age-, sex-, and surname-standardized reflectances to three independent components. The first principal component, which assesses the genetic component of melanin concentration, did not differ between samples, indicating that there are no significant differences between lowland and highland Bolivians of European ancestry with respect to the genetic component of skin reflectances. The second principal component, which assesses the influence of tanning on skin reflectance, also did not differ significantly between highlanders and lowlanders. Finally, the third principal component, which assesses the impact of vascularity on skin reflectance, was significantly lower in residents of La Paz than in residents of Santa Cruz, suggesting a greater vascularity-induced darkening of skin color in highlanders than lowlanders, possibly reflecting the higher hemoglobin concentrations that are typical of highland populations.