Human skin color

"Skin pigmentation" redirects here. For animal skin pigmentation, see Biological pigment.

Extended Coloured (Afrikaans: Kleurlinge or Bruinmense) family from South Africa showing some spectrum of human skin coloration

Human skin color ranges from the darkest brown to the lightest hues. Differences in skin color among individuals is caused by variation in pigmentation, which is the result of genetics (inherited from one's biological parents), exposure to the sun, disorders, or some combination thereof. Differences across populations evolved through natural selection or sexual selection, because of social norms and differences in environment, as well as regulations of the biochemical effects of ultraviolet radiation penetrating the skin.[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-skin 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. The red color underlying the skin becomes more visible, especially in the face, when, as consequence of physical exercise or sexual arousal, or the stimulation of the nervous system (anger, embarrassment), arterioles dilate.[2] Color is not entirely uniform across an individual's skin; for example, the skin of the palm and the sole is lighter than most other skin, and this is especially noticeable in darker-skinned people.[3]

There is a direct correlation between the geographic distribution of ultraviolet 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 darker-skinned populations. Areas that are far from the tropics and closer to the poles have lower intensity of UVR, which is reflected in lighter-skinned populations.[4] By the time modern Homo sapiens evolved, all humans were dark-skinned.[5][6] Some 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,[7] and that such major changes in pigmentation may have happened in as little as 100 generations (≈2,500 years) through selective sweeps.[7][8][9] 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.[6][10]

In some populations, women are significantly lighter-skinned than men. However, in other populations, notably those of European descent, men are significantly lighter-skinned than women.[11] European women may have darker skin than European men due to the female sex hormone estrogen, which darkens light skin.[12] Women from darker-skinned populations may have evolved to lighter skin than men so their bodies could absorb more vitamin D during pregnancy, which improves calcium absorption.[13]

The social significance of differences in skin color has varied across cultures and over time, as demonstrated with regard to social status and discrimination.

  1. ^ Muehlenbein, Michael (2010). Human Evolutionary Biology. Cambridge University Press. pp. 192–213.
  2. ^ Jablonski, N.G. (2006). Skin: A Natural History. Berkeley: University of California Press.
  3. ^ Milburn, Peter B.; Sian, Corazon S.; Silvers, David N. (1982). "The color of the skin of the palms and soles as a possible clue to the pathogenesis of acral-lentiginous melanoma". American Journal of Dermatopathology. 4 (5): 429–33. doi:10.1097/00000372-198210000-00009. PMID 7149195.
  4. ^ 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.
  5. ^ Muehlenbein, Michael (2010). Human Evolutionary Biology. Cambridge University Press. pp. 192–213.
  6. ^ a b Jablonski, Nina; Chaplin, George (May 2017). "The colours of humanity: the evolution of pigmentation in the human lineage". Philosophical Transactions of the Royal Society B. 372 (1724): 20160349. doi:10.1098/rstb.2016.0349. PMC 5444068. PMID 28533464.
  7. ^ a b Jablonski, Nina G. (Spring 2011). "Why Human Skin Comes in Colors" (PDF). AnthroNotes. 32 (1). Archived (PDF) from the original on 2014-02-25. Retrieved 2013-07-20.
  8. ^ "The Human Family Tree Facts". National Geographic. Archived from the original on 2013-08-05. Retrieved 2013-07-20.
  9. ^ Cite error: The named reference LivCol was invoked but never defined (see the help page).
  10. ^ 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 (Suppl 2): 8962–8. Bibcode:2010PNAS..107.8962J. doi:10.1073/pnas.0914628107. PMC 3024016. PMID 20445093.
  11. ^ Cite error: The named reference Frost 2007 pp. 779–780 was invoked but never defined (see the help page).
  12. ^ Cite error: The named reference scie_Rese was invoked but never defined (see the help page).
  13. ^ 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. Archived from the original (PDF) on January 5, 2015.