Skin color

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The skin color (also complexion ) is a physical characteristic that is primarily determined by the pigmentation of the skin and the structure of the blood vessels . In the case of a large number of living beings, especially those that are hairless and feathered, the skin color serves as camouflage or for signals , for example as a warning signal for poisonous animals or during courtship behavior .

Skin colors in the animal kingdom

Animals that have a skin include molluscs , amphibians , reptiles , birds and mammals , among others . In contrast, insects , for example, have no skin, but rather a chitin shell.

The variety of skin colors is greatest among molluscs, amphibians and reptiles. In birds, the skin is mostly covered by the plumage. However, some birds have conspicuous skin colors around the head and neck. This applies to turkeys and cassowaries , for example . In mammals, pigments from the range of white-yellow-red-brown-gray-black are predominantly found, while green, blue and violet pigments, for example, do not occur.

The skin color of an animal can be different in different places (so-called drawings ) or it can be almost uniform over the entire body. It can also change over time.

Changes in skin color

According to the speed, four types of color change can be distinguished:

  1. Some animals can change their skin color quickly and even unilaterally, such as chameleons or octopuses . The change takes place through the movement of pigment cells due to nervous stimuli and can serve both for camouflage and to express affections.
  2. Another change in color is caused by a change in the peripheral blood flow , this can be nervous or hormonally controlled, e.g. B. a red head or red-colored swellings of some monkeys ready to mate .
  3. Other possibilities are slow changes, for example through changes in pigmentation as a result of exposure to the sun. This can be metabolic performance as a reaction to environmental influences.
  4. Other animals have a fixed coloring that changes seasonally or with age.

Skin color in humans

Causes of the skin color

pigmentation

Different pigments have an effect on skin color. The amount of melanin that is present is particularly important in mammals . The proportion of melanin in the skin is genetically determined. However, within a certain range, melanin is also increasingly formed by exposure to sunlight ( ultraviolet radiation ). It occurs in two variants: on the one hand there is eumelanin , a brown to black pigment, and on the other hand phaeomelanin , a red to yellow pigment. The eumelanin thus determines the brightness of the skin. The proportion of pheomelanin then creates a reddish or yellowish undertone, especially for light skin. Red hair (rutilism) is often an indication that significantly more pheomelanin than eumelanin is formed. A hereditary deficiency in the formation of pigment or certain pigments is albinism .

Blood vessels

As the second color-influencing factor in light skin, the redness of the human skin is determined by the blood vessels that lie under the skin. These can narrow and widen in the short term, causing pale or blushing .

Body region

Father and son: The inner surface of a hand with little melanin is significantly lighter than the actual skin color.

The skin color is not the same everywhere on the body: the palms and soles of the feet are poor in melanin and therefore lighter and / or reddish than the rest of the skin. The lips are like the mucous membranes of red color, with strong pigmentation but often very dark. The skin of the fingertips , knuckles , ears and nose is also often a little reddish, as there are more blood vessels just below the surface. In the area of ​​the nipples and the genital organs , the skin is darker due to an increased melanin content.

gender

Gender also has an impact on skin color. On average, women have three to four percent lighter skin than men.

genetics

The genome of a person has a significant impact on skin color, which results in the different skin color distribution in different ethnic groups . For example, the Dinka in South Sudan have the darkest skin color of all ethnic groups, while the San , who also live in Africa, have a comparatively light (“beige”) skin color.

As a defect in one of the genes involved, albinism results in the presence of no or a very small amount of melanin, as a result of which the affected individuals obtain white or lighter skin and hair. In contrast, leucism leads to the absence of melanocytes, as a result of which the affected individuals have white or light-colored mottled skin and hair. Partial leucism known as piebaldism is known in humans .

The fair skin of Europeans and Asians is mainly caused by albinism of the OCA4 type . A large number of genes are involved in the inheritance of skin color, which can be seen from the fact that the inheritance of skin color does not clearly follow Mendel's laws . Most of the genes responsible for skin color have largely not yet been identified.

Importance of pigmentation

Dark skin has several advantages over light skin. Dark skin is a protection against the penetration of UV rays. In the case of insufficient pigmentation, the important vitamin B ( folic acid ) is destroyed by UV-A radiation, which can lead to malformations in the offspring if the mother was exposed to excessive UV rays during her pregnancy. The most common malformation in babies is spina bifida ("open back"). In addition, a folic acid deficiency has a negative effect on sperm production. This means that mostly only people with a low melanin content tend to have a deficiency in folic acid, which can be counteracted during pregnancy with additional folic acid supplements. Pigmentation also has the advantage that incident UV light from sunlight is already absorbed in the uppermost, dead skin cells and thus cannot penetrate deeper layers, where it can develop mutagenic and carcinogenic effects.

On the other hand, pigmentation has the disadvantage that as a result of the absorption of UV light in the uppermost, predominantly dead skin layer, less UV radiation penetrates into the deeper layers, which can be used by living cells to produce cholecalciferol (vitamin D). As a result, an adapted pigmentation should represent an optimization according to the actually available amount of UV. This is followed by the global distribution of skin color on a genetic basis, but also the use of UV blockers in sun protection and (in the opposite direction) sunbathing .

Furthermore, light skin makes it easier to find parasites, as many of the ectoparasites are arthropods and have dark sclerotin stored in the chitin of their cuticula for increased strength . Of course, this advantage only applies if (social) grooming takes place at all .

Methods for classifying human skin colors

Classification of skin colors according to the Von Luschan scale

At the beginning of the 20th century, the Von Luschan scale developed by the anthropologist Felix von Luschan (1854–1924) was one of the most common methods of classifying skin colors. The scale consists of 36 numbered ceramic discs whose color was compared with that of the skin to be classified. Since a person's skin can be clearly different in color in more and less light-exposed areas, it was necessary to compare an area of ​​skin that was “as little exposed to light” as possible with the ceramic discs. In practice, the technology turned out to be imprecise and different anthropologists came up with different measurement results. In 1911 , Luschan himself rejected skin color as a " racial " characteristic. The very differentiated scale has historical significance today.

A newer classification of skin types according to Fitzpatrick dates back to 1975. The further developed classification names the skin types from I to VI.

The skin color can be determined more reliably with a measuring device such as a colorimeter or spectrophotometer and categorized on the basis of the measured values. The skin tone is determined in one of the common color spaces Lab , XYZ or RGB .

Evolution of skin colors in humans

Worldwide distribution of skin colors in 1927 according to the Von Luschan scale
Cave painting from the Cova dels Cavalls , Barranco de la Valltorta , Tírig , Province of Castellón in Spain , approx. 13,000 years old

In the context of evolutionary theory , the question arises as to the causes of different skin colors within and between populations, especially in people between ethnic groups .

The Darwinism assumes that the relative frequency of particular occurrences increases with respect to a hereditary trait within a population then over other forms of the same feature when these characteristic values have a selective advantage, that is, that the carrier of the determining heredity have higher reproductive success.

The most common assumption was that the dark, African skin tone represented the original skin tone and that the lighter European and Asian skin tones emerged independently of each other later. However, genetic studies criticize this assumption. According to several studies, including one from the University of Pennsylvania in 2017, the proto-human's original skin color was white / beige to light brown. Very dark and sometimes almost black skin color is therefore an adaptation to strong sunlight and a genetic variation in the various groups of people.

In some cases, the skin color correlates with the geographical region in such a way that the higher the UV radiation, the stronger the pigmentation. In 2000, Nina Jablonski and George Chaplin put forward a theory that relied on the advantages and disadvantages of high and low melanin levels, respectively. Jablonski and Chaplin concluded that in the course of evolution, light and dark skin tones may not have emerged from dark skin tones, but rather light and dark skin tones as extreme stages of adaptation from a more ocher-colored initial tone similar to that of the San peoples in today's southern Africa.

Hypothesis of origin through natural selection

According to this hypothesis, selection advantages in the respective region are assumed to be the decisive cause for the development of regionally deviating skin colors. Adaptation to the light conditions and UV radiation in the respective region is the assumed mechanism.

Melanin protects skin from the sun's ultraviolet rays. The melanin prevents the mutagenic effects, especially UV-B radiation. In this respect, a high melanin content is an advantage in regions with strong solar radiation, but not necessarily to the same extent in regions with low solar radiation. However, this function essentially only applies to eumelanin and not to pheomelanin , which does not have any noteworthy UV-protective properties.

The second benefit of melanin is that folic acid circulating in the blood is protected from ultraviolet radiation. Without this protection, it would quickly degrade. Folic acid is important for the development of the young embryo and plays an important role in sperm production . People who tend to have a low melanin content, who get too much ultraviolet radiation and who do not take in more folic acid through their food, must therefore expect reduced fertility or an increased risk of developmental defects in the child.

The melanin content of the skin has it also has a direct impact on the production of vitamin D . The more melanin there is in the skin, the less vitamin D can be produced. People who tend to have a high melanin content and who live in high latitudes can suffer from vitamin D deficiency and can choose their diet accordingly if deficiency symptoms occur. People with a tendency to have a low melanin content are less prone to corresponding deficiency symptoms and could therefore have had a selection advantage or no selection disadvantage in the temperate to polar climatic zones.

The speed with which the different mutations spread in the respective human populations also indicate that in regions with low solar radiation a positive selection took place in favor of light skin, while in regions with high solar radiation dark skin color became dominant. However, another purely genetic factor must also have an impact, because some peoples in Africa, such as the Khoisan , have a relatively light skin color. The light skin color of Europeans and Asians is independent of one another and can be traced back to genes of albinism .

Hypothesis of origin through sexual selection

The American anthropologist and physiologist Jared Diamond sees - on the basis of similar assumptions by Charles Darwin - the mechanisms of sexual selection as a probable reason for the development of different skin colors. According to this, the preferences that were shaped in early childhood indicated that when choosing a partner, people tend to orientate themselves more towards the external appearance of previous caregivers in the family and their environment. Over generations, this could have led to the development of populations with a similar appearance and also explain the strange effect why in climatically very similar regions with a comparable way of life of the populations, similar or identical skin colors did not necessarily develop over a long period of time.

Meaning in racism

Racism assumes that people can be divided according to race . “ Racial theories ”, which have long made a “claim to scientificity” since Kant and the Enlightenment , pick out “individual features (such as skin color) from a multitude of mostly visually visible physical characteristics” in order to use them as a basis as a “naturally given” and “relevant criterion” such as skin color and their nature . In addition, certain social, cultural and religious characteristics and behavioral patterns are assigned to the individual as "racial characteristics". As Albert Memmi showed, the differences created in this way are generalized, absolutized and evaluated in a process of hegemonic practice. On the basis of a constructed standard setting of the “own”, the “other” is identified and homogenized . The "others" are usually assigned negative characteristics.

In racism, skin color is usually represented as "one color", although skin color always moves in a spectrum of colors. The classification of people according to the not always clearly distinguishable characteristic of skin color, especially the rough classification according to “white” or “black”, is based on the criteria of biologism and an ideological “essentialization” that follows it.

For example, Carl von Liné , the founder of biological systematics , classified people in four “varieties” in the 10th edition of his work Systema Naturae (1758). He assigned a geological origin, skin color, temperament and posture to each “variety” . For example, the white Europaeus was described as sanguine and muscular and the black Afer as phlegmatic and limp.

The concept of race, as a definable group of people, has been rated as "completely obsolete" and scientifically unsustainable since the end of the 20th century.

Significance in business and technology

Cosmetics such as make-up and sunscreen are important products for regulating skin color . Mineral ocher was already used by humans to color the skin at least 60,000 years ago.

Skin lightening

As a means of skin lightening , the method practiced is to consistently expose the skin to as little sunlight as possible . This is done, for example, through appropriate clothing, hats, parasols, towels, face masks or gloves. There are also a large number of cosmetic products for skin lightening, some of which are very harmful, such as the poisonous white lead , which has been known since ancient times . Modern products also contain mercury . Therefore the distribution in the EU and many African countries, z. B. in Rwanda , prohibited.

In Japan, the artificial compound rucinol was developed as an active ingredient for skin lightening . The synthetic active ingredient is up to 100 times more effective than hydroquinone , as it inhibits two enzymes necessary for melanin synthesis. This inhibits the general synthesis of melanin and then the production of dark melanin. As a result, the melanin content in the skin drops.

Skin tanning

Probably the most common means of tanning the skin is to expose it to more sunlight. Sunscreens and similar products are used to reduce the damage that they cause to the skin. Alternatively, artificial light ( solariums ) is used for sunbathing . There are also cosmetic products such as self-tanners .

literature

Web links

Wiktionary: skin color  - explanations of meanings, word origins, synonyms, translations
Wiktionary: Complexion  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. ↑ Spectrum of Science, June 2003.
  2. ^ Nicholas G. Crawford et al .: Loci associated with skin pigmentation identified in African populations. In: Science . Advance online publication of October 12, 2017, doi: 10.1126 / science.aan8433
  3. ↑ New gene variants reveal the evolution of human skin color. On: sciencemag.org from October 12, 2017
  4. ↑ The skin under UV bombardment. (PDF; 516 kB) Friedrich Verlag, accessed on August 5, 2012 .
  5. ↑ typical! Clichés about Jews and others. Book accompanying the exhibition of the Jewish Museum Berlin and the Jewish Museum Vienna , Berlin 2008, p. 80.
  6. ^ Genetic Evidence for the Convergent Evolution of Light Skin in Europeans and East Asians. (PDF; 2.4 MB) (No longer available online.) Oxford Journals, archived from the original on June 16, 2007 ; Retrieved December 20, 2006 (English). Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / mbe.oxfordjournals.org
  7. ↑ Nicholas G. Crawford, Derek E. Kelly, Matthew EB Hansen, Marcia H. Beltrame, Shaohua Fan: Loci associated with skin pigmentation identified in African populations . In: Science . October 12, 2017, ISSN  0036-8075 , p. eaan8433 , doi : 10.1126 / science.aan8433 , PMID 29025994 ( sciencemag.org [accessed July 9, 2018]).
  8. ^ A b The Paleo-Etiology of Human Skin Tone. Retrieved December 5, 2002 .
  9. ↑ Nicholas G. Crawford, Derek E. Kelly, Matthew EB Hansen, Marcia H. Beltrame, Shaohua Fan: Loci associated with skin pigmentation identified in African populations . In: Science . October 12, 2017, ISSN  0036-8075 , p. eaan8433 , doi : 10.1126 / science.aan8433 , PMID 29025994 ( sciencemag.org [accessed July 9, 2018]).
  10. ↑ eurekalert.org of February 20, 2011: "Skin color: Handy tool for teaching evolution."
  11. ↑ Nicholas G. Crawford, Derek E. Kelly, Matthew EB Hansen, Marcia H. Beltrame, Shaohua Fan: Loci associated with skin pigmentation identified in African populations . In: Science . October 12, 2017, ISSN  0036-8075 , p. eaan8433 , doi : 10.1126 / science.aan8433 , PMID 29025994 ( sciencemag.org [accessed July 9, 2018]).
  12. ↑ a b O. Lao, JM de Gruijter, K. van Duijn, A. Navarro, M. Kayser: Signatures of positive selection in genes associated with human skin pigmentation as revealed from analyzes of single nucleotide polymorphisms. In: Ann Hum Genet. 71 (Pt 3), 2007 May, pp. 354-369. Epub 2007 Jan 18. PMID 17233754
  13. ↑ a b c H. L. Norton, RA Kittles, E. Parra, P. McKeigue, X. Mao, K. Cheng, VA Canfield, DG Bradley, B. McEvoy, MD Shriver: Genetic evidence for the convergent evolution of light skin in Europeans and East Asians. In: Mol Biol Evol. 24 (3), 2007 Mar, pp. 710-722. Epub 2006 Dec 20.
  14. ↑ Jared Diamond: Sexual Selection and the Origin of the Human Race. In: The Third Chimpanzee. Evolution and future of man . 3. Edition. Frankfurt 2007, pp. 142–157.
  15. ^ Arnold Farr : How whiteness becomes visible. Enlightenment racism and the structure of a racialized consciousness In: Eggers / Kilomba / Piesche / Arndt (eds.): Myths, masks and subjects. Critical whiteness research in Germany. Munster 2005.
  16. ^ A b Susan Arndt, Antje Hornscheidt (ed.): Africa and the German language. A critical reference work. P. 10ff.
  17. ^ Albert Memmi: Racism. Frankfurt am Main 1987.
  18. ^ Bauer / Petrow: Colored / Colored. In: S. Arndt, A. Hornscheid: Africa and the German language. Unrast-Verlag, Münster 2004, ISBN 3-89771-424-8 .
  19. ^ David R. Roediger: Towards the Abolition of Whiteness. New York 1994. In: S. Arndt, A. Hornscheid: Africa and the German language. Unrast-Verlag, Münster 2004, ISBN 3-89771-424-8 .
  20. ^ Carl von Liné: Systema Naturae . 10th edition. 1758, ( gdz.sub.uni-goettingen.de ), p. 20-22 .
  21. ^ The Schlaining Declaration: Against Racism, Violence and Discrimination. (PDF) Section II: "On the obsolete concept of 'race'". June 1995, accessed February 26, 2020 .
  22. ↑ AAPA statement on biological aspects of race . In: American Journal of Physical Anthropology, Volume 101 . 1996, p. 569 f .
  23. ↑ GEO 07/2019, p. 27: "The toxic business with the skin"