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Human skin color From Wikipedia, the free encyclopedia Extended Coloured family from South Africa showing some spectrum of human skin coloration Human skin color ranges in variety from the darkest brown to the lightest pinkish-white hues. Human skin pigmentation is the result of natural selection. Skin pigmentation in human beings evolved primarily to regulate the amount of ultraviolet radiation penetrating the skin, controlling its biochemical effects.[1] The actual skin color of different humans is affected by many substances, although the single most important substance is the pigment melanin. Melanin is produced within the skin in cells called melanocytes and it is the main determinant of the skin color of darker-skinned humans. The skin color of people with light skin is determined mainly by the bluish-white connective tissue under the dermis and by the hemoglobin circulating in the veins of the dermis. Oxygenated hemoglobin has a reddish hue, which produces a pinkish tint to lightly pigmented skin. Deoxygenated hemoglobin has a purplish color, which produces a bluish tint to lightly pigmented skin. The red color underlying the skin becomes more visible, especially in the face, when, as consequence of physical exercise or the stimulation of the nervous system (anger, fear), arterioles dilate.[2] Carotene, the least common skin pigment, results in a yellowing of the skin. It results primarily from the overconsumption of carotene containing foods, like carrots. There is a direct correlation between the geographic distribution of UV radiation (UVR) and the distribution of indigenous skin pigmentation around the world. Areas that receive higher amounts of UVR, generally located closer to the equator, tend to have darkerskinned populations. Areas that are far from the tropics and closer to the poles have lower intensity of UVR, which is reflected in lighterskinned populations.[3] Researchers suggest that human populations over the past 50,000 years have changed from dark-skinned to light-skinned and vice versa as they migrated to different UV zones,[4] and that such major changes in pigmentation may have happened in as little as 100 generations (~2,500 years) through selective sweeps.[4][5][6] Natural skin color can also darken as a result of tanning due to exposure to sunlight. The leading theory is that skin color adapts to intense sunlight irradiation to provide partial protection against the ultraviolet fraction that produces damage and thus mutations in the DNA of the skin cells.[7] In addition, it has been observed that adult human females on average are significantly lighter in skin pigmentation than males. Females need more calcium during pregnancy and lactation. The body synthesizes vitamin D from sunlight, which helps it absorb calcium. Females evolved to have lighter skin so their bodies absorb more calcium.[8] Questions: 1. What are the factors that determine skin color? 2. What is the function of melanocytes? 3. What is the function of melanin from an evolutionary perspective? Muehlenbein, Michael (2010). Human Evolutionary Biology. Cambridge University Press. pp. 192–213. Jablonski, N.G. (2006). Skin: a Natural History. Berkeley: University of California Press. Webb, A.R. (2006). "Who, what, where, and when: influences on cutaneous vitamin D synthesis". Progress in Biophysics and Molecular Biology 92 (1): 17–25. doi:10.1016/j.pbiomolbio.2006.02.004. PMID 16766240. Jablonski, Nina G. (Spring 2011). "Why Human Skin Comes in Colors" (PDF). AnthroNotes 32 (1). Retrieved 2013-07-20. "The Human Family Tree Facts". National Geographic. Retrieved 2013-07-20. Jablonski, Nina (2012). Living Color. Berkeley, Los Angeles, London: University of California Press. ISBN 978-0-520-25153-3. Jablonski, N. G.; Chaplin, G. (2010). "Colloquium Paper: Human skin pigmentation as an adaptation to UV radiation". Proceedings of the National Academy of Sciences 107: 8962–8. Bibcode:2010PNAS..107.8962J. doi:10.1073/pnas.0914628107. PMC 3024016. PMID 20445093. Jablonski, Nina; Chaplin, George (2000). "The evolution of human skin coloration" (PDF). Journal of Human Evolution 39 (1): 57–106. doi:10.1006/jhev.2000.0403. PMID 10896812.