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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.