NationMaster - Encyclopedia: Human skin color

Human skin colour can range from almost black to nearly colorless (appearing pinkish white due to the blood in the skin) in different people. Skin color is determined by the amount and type of melanin, the pigment in the skin. As a general pattern people with ancestors from tropical regions (hence greater sunlight exposure) have darker skin than people with ancestors from subtropical regions, this is far from a hard and fast rule however.^{[citation needed]} ^[1]^[2] Image File history File links Unbalanced_scales. ... Image File history File links Acap. ... Image File history File links Question_book-3. ... For other uses, see Blood (disambiguation). ... This article is about the organ. ... Homo sapiens (Latin: wise man) is the scientific name for the human species. ... Color is an important part of the visual arts. ... Broadly, melanin is any of the polyacetylene, polyaniline, and polypyrrole blacks and browns or their mixed copolymers. ... Natural Ultramarine pigment in powdered form. ... An ancestor is a parent or (recursively) the parent of an ancestor (i. ... The tropics are the geographic region of the Earth centered on the equator and limited in latitude by the two tropics: the Tropic of Cancer in the north and the Tropic of Capricorn in the southern hemisphere. ... Subtropical (or semitropical) areas are those adjacent to the tropics, usually roughly defined as the ranges 23. ...

Melanin and genes

Melanin comes in two types: pheomelanin (red) and eumelanin (dark brown to nearly black). Both amount and type are determined by four to six genes which operate under incomplete dominance. One copy of each of those genes is inherited from each parent. Each gene comes in several alleles, resulting in a great variety of different skin tones. Broadly, melanin is any of the polyacetylene, polyaniline, and polypyrrole blacks and browns or their mixed copolymers. ... Melanin is a polymer of either or both of two monomer molecules: indolequinone, and dihydroxyindole carboxylic acid. ... Melanin is a polymer of either or both of two monomer molecules: indolequinone, and dihydroxyindole carboxylic acid. ... For other uses, see Gene (disambiguation). ... It has been suggested that this article or section be merged with dominance relationship. ... An allele (pronounced , ) (from the Greek Î±Î»Î»Î·Î»Î¿Ï‚, meaning each other) is one member of a pair or series of different forms of a gene. ...

The evolution of the different skin tones is thought to have occurred as follows:^{[attribution needed]} the haired ancestors of humans, like modern great apes, had light skin under their hair. Once they encountered baldness, they evolved dark skin, needed to prevent low folate levels since they lived in sun-rich Africa. (The skin cancer connection is probably of secondary importance, since skin cancer usually kills only after the reproductive age and therefore does not exert much evolutionary pressure.) When humans migrated to less sun-intensive regions in the north, low vitamin D₃ levels became a problem and light skin color re-emerged. Image File history File linksMetadata No higher resolution available. ... Image File history File linksMetadata No higher resolution available. ... Albino redirects here. ... This article is about evolution in biology. ... Genera Subfamily Ponginae Pongo - Orangutans Gigantopithecus (extinct) Sivapithecus (extinct) Subfamily Homininae Gorilla - Gorillas Pan - Chimpanzees Homo - Humans Paranthropus (extinct) Australopithecus (extinct) Sahelanthropus (extinct) Ardipithecus (extinct) Kenyanthropus (extinct) Pierolapithecus (extinct) (tentative) The Hominids (Hominidae) are a biological family which includes humans, extinct species of humanlike creatures and the other great apes... Bald redirects here; for other uses see Bald (disambiguation). ... A world map showing the continent of Africa Africa is the worlds second-largest and second most-populous continent, after Asia. ...

The Inuit and Yupik are special cases: even though they live in an extremely sun-poor environment, they have retained their relatively dark skin. This can be explained by the fact that their traditional animal-based diet provides plenty of vitamin D. For other uses, see Inuit (disambiguation). ... This article is about Yupik peoples in general. ...

Health related effects

Dark skin protects against ultraviolet light; this light causes mutations in skin cells, which in turn cause skin cancers. Light-skinned persons have about a tenfold greater risk of dying from skin cancer under equal sunlight exposure, with redheads having the greatest risk.^{[citation needed]} Furthermore, dark skin prevents radiation of UV-A rays from destroying the essential folic acid, derived from B vitamins. Folic acid (or folate) is needed for the synthesis of DNA in dividing cells and folate deficiency in pregnant women are associated with birth defects.^{[citation needed]} For other uses, see Ultraviolet (disambiguation). ... For linguistic mutation, see Apophony. ... Skin cancer is a malignant growth on the skin which can have many causes. ... Prism splitting light High Resolution Solar Spectrum Sunlight in the broad sense is the total spectrum of the electromagnetic radiation given off by the Sun. ... Woman with red hair Man with red hair Red hair (also referred to as auburn, ginger, ranga or titian) varies from a deep orange-red through burnt orange to bright copper. ... For other uses, see Radiation (disambiguation). ... Spectrum of a fluorescent black light source. ... Folic acid and folate (the anion form) are forms of the water-soluble Vitamin B9. ... The B vitamins are eight water-soluble vitamins that play important roles in cell metabolism. ... The structure of part of a DNA double helix Deoxyribonucleic acid, or DNA, is a nucleic acid molecule that contains the genetic instructions used in the development and functioning of all known living organisms. ...

While dark skin better preserves vitamin B, it can lead to vitamin D deficiency in dark skin people which can lead to being at a higher risk of certain kinds of deadly cancers such as colon, lung and prostate, dark skin people are at higher risk for the bone disease rickets,also dark skin people are at higher risk of cardiovascular disease,diabetes and multiple sclerosis^[3].To address this issue, some countries have programs to ensure fortification of milk with vitamin D. The advantage of light skin is that it allows more sun absorption, leading to increased production of vitamin D₃, necessary for calcium absorption and bone growth. The lighter skin of women may result from the higher calcium needs of women during pregnancy and lactation. Rickets is a softening of the bones in children potentially leading to fractures and deformity. ... Cardiovascular disease refers to the class of diseases that involve the heart or blood vessels (arteries and veins). ... This article is about the disease that features high blood sugar. ... For the fortification of food, see Food fortification. ... Vitamin D is a fat soluble vitamin that contributes to the maintenance of normal levels of calcium and phosphorus in the bloodstream. ... For other uses, see Calcium (disambiguation). ... This article is about human pregnancy in biological females. ... Kittens nursing Lactation describes the secretion of milk from the mammary glands, the process of providing that milk to the young, and the period of time that a mother lactates to feed her young. ...

Albinism is a condition characterized by the absence of melanin, resulting in very light skin and hair; it is caused by a particular recessive gene. Albino redirects here. ...

Cultural effects

Skin tone has sometimes been used in an (often controversial; see racism) attempt to define human races. On a cultural level, color terminology for race has evolved, based upon genetic variations in human skin tone and changing customs or traditions of what arbitrary criteria and the amount of categories to use. Manifestations Slavery Racial profiling Lynching Hate speech Hate crime Genocide (examples) Ethnocide Ethnic cleansing Pogrom Race war Religious persecution Blood libel Paternalism Police brutality Movements Policies Discriminatory Race / Religion / Sex segregation Apartheid Redlining Internment Ethnocracy Anti-discriminatory Emancipation Civil rights Desegregation Integration Equal opportunity Counter-discriminatory Affirmative action Racial quota... For other uses, see Race. ... In some societies, color terminology are or were used in racial classifications. ... For other uses, see Tradition (disambiguation). ...

Research on skin tone variability

The tone of human skin can vary from a dark brown to nearly a colorless pigmentation, which appears pale pink due to the blood in the skin. Europeans have lighter skin, hair, and eyes than any other group on Earth. In attempting to discover the mechanisms that have generated such a wide variation in human skin tone, Jablonski & Chaplin (2000) discovered that there is a high correlation between the tone of human skin of indigenous peoples and the average annual ultraviolet (UV) radiation available for skin exposure where the indigenous peoples live. Accordingly, Jablonski and Chaplin plotted the skin tone (W) of indigenous peoples who have stayed in the same geographical area for the last 500 years versus the annual UV available for skin exposure (AUV) for over 200 indigenous persons and found that skin tone lightness W is related to the annual UV available for skin exposure AUV according to^[4] For other uses, see Ultraviolet (disambiguation). ...

where the skin tone lightness W is measured as the percentage of light reflected from the upper inner arm at which location on humans there should be minimal tanning of human skin due to personal exposure to the sun; a lighter skinned human would reflect more light and would have a higher W number. Judging from the above linear fit to the empirical data, the theoretical lightness maximum of human skin would reflect only 70 per cent of incident light for a hypothetical indigenous human-like population that lived where there was zero annual UV available for skin exposure (AUV = 0 in the above formula). Jablonski and Chaplin evaluated average annual UV available for skin exposure AUV from satellite measurements that took into consideration the measured daily variation in the thickness of the ozone layer that blocked UV hitting the Earth, measured daily variation in opacity of cloud cover, and daily change in angle at which the sunlight containing UV radiation strikes the Earth and passes through different thicknesses of Earth's atmosphere at different latitudes for each of the different human indigenous peoples' home areas from 1979 to 1992.

Jablonski and Chaplin proposed an explanation for the observed variation of untanned human skin with annual UV exposure. By Jablonski and Chaplin's explanation, there are two competing forces affecting human skin tone: For other uses, see Natural selection (disambiguation). ...

Jablonski and Chaplin note that when human indigenous peoples have migrated, they have carried with them a sufficient gene pool so that within a thousand years, the skin of their descendants living today has turned dark or turned light to adapt to fit the formula given above—with the notable exception of dark-skinned peoples moving north, such as to populate the seacoast of Greenland, to live where they have a year-round supply of food rich in vitamin D, such as fish, so that there was no necessity for their skin to lighten to let enough UV under their skin to synthesize the vitamin D that humans need for healthy bones. Vitamin D is a fat soluble vitamin that contributes to the maintenance of normal levels of calcium and phosphorus in the bloodstream. ... This article is about the skeletal organs. ... Front view of a skeleton of an adult human Back view of a skeleton of an adult human The human skeleton consists of both fused and individual bones supported and supplemented by ligaments, tendons, muscles and cartilage. ...

In considering the tone of human skin in the long span of human evolution, Jablonski and Chaplin note that there is no empirical evidence to suggest that the human ancestors six million years ago had a skin tone different from the skin tone of today's chimpanzees—namely light-skinned under black hair. But as humans evolved to lose their body hair a parallel evolution permitted human populations to turn their base skin tone dark or light over a period of less than a thousand years to adjust to the competing demands of 1) increasing eumelanin to protect from UV that was too intense and 2) reducing eumelanin so that enough UV would penetrate to synthesize enough vitamin D. By this explanation, in the time that humans lived only in Africa, humans had dark skin to the extent that they lived for extended periods of time where the sunlight is intense. As some humans migrated north, over time they developed light skin, though they retained within the gene pool the capability to develop dark skin when they migrated to areas with intense sunlight again, such as across the Bering Strait and south to the Equator.^(Chaplin) For the history of humans on Earth, see History of the world. ... Type species Simia troglodytes Blumenbach, 1775 distribution of Species Pan troglodytes Pan paniscus Chimpanzee, often shortened to chimp, is the common name for the two extant species of apes in the genus Pan. ... Hair is also a musical: see Hair (musical) and Hair (movie) Hair is the filamentous outgrowth of the epidermis found in mammals. ... In paleoanthropology, the single-origin hypothesis (or Out-of-Africa model) is one of two accounts of the origin of anatomically modern humans, Homo sapiens. ... Net migration rates for 2006: positive (blue), negative (orange) and stable (green). ... Satellite photo of the Bering Strait Photo across the Bering Strait Nautical chart of the Bering Strait The Bering Strait (Russian: ) is a sea strait between Cape Dezhnev, Russia, the easternmost point (169Â°43 W) of the Asian continent and Cape Prince of Wales, Alaska, the westernmost point (168Â°05...

Origins of light skin in humans

According to (Norton et al., 2006), white skin observed in Europeans, South Asians and East Asians is due to independent genetic mutations in at least three loci. They concluded that light pigmentation in Europeans is at least partially due to sexual selection. The European peoples are the various nations and ethnic groups of Europe. ... Composite satellite image of the Indian subcontinent Map of South Asia. ... East Asia is a subregion of Asia. ... In biology, mutations are permanent, sometimes transmissible (if the change is to a germ cell) changes to the genetic material (usually DNA or RNA) of a cell. ... Short and long arms Chromosome. ... Illustration from The Descent of Man and Selection in Relation to Sex by Charles Darwin showing the Tufted Coquette Lophornis ornatus, female on left, ornamented male on right. ...

Several genes have been invoked to explain variations of skin tones in humans, including SLC45A2,^[5] ASIP, MATP, TYR, and OCA2.^[6] A recently discovered gene, SLC24A5 has been shown to account for a substantial fraction of the difference in the average of 30 or so melanin units between Europeans and Africans. SLC24A5 (solute carrier family 24, member 5) is a gene that is thought to be one of many genes that control skin pigmentation in humans, and therefore implicated in defining race. ...

Wide variations in human skin tones have been correlated with mutations in another gene; the MC1R gene ^[7]. The "MC1R" label for the gene stands for melanocortin 1 receptor, where For other uses, see Gene (disambiguation). ... The Melanocortin-1 receptor (Mc1r) is one of the key proteins in hair colour production. ...

Accordingly, the MC1R gene specifies the amino acid sequence in the receptor protein that relays through the cell membrane the hormone signal from the pituitary gland to produce the melanin that makes human skin very dark. Many variations in the amino acid sequence of this receptor protein result in lighter or darker skin. Melanocyte-stimulating hormone (MSH) is a peptide hormone produced by cells in the intermediate lobe of the pituitary gland. ... | Latin = hypophysis, glandula pituitaria | GraySubject = 275 | GrayPage = 1275 | Image = Gray1180. ... Broadly, melanin is any of the polyacetylene, polyaniline, and polypyrrole blacks and browns or their mixed copolymers. ... In biochemistry, a receptor is a protein on the cell membrane or within the cytoplasm that binds to a specific factor (a ligand), such as a neurotransmitter, hormone, or other substance, and initiates the cellular response to the ligand. ... Look up cell membrane in Wiktionary, the free dictionary. ...

The human MC1R gene consists of a string of 954 nucleotides, where each nucleotide is one of the four bases Adenine (A), Guanine (G), Thymine (T), or Cytosine (C). But 261 of the nucleotides in the MC1R gene can change with no effect on the amino acid sequence in the receptor protein produced from the gene. For example, the nucleotide triplets GGT, GGC, GGA, and GGG are all synonymous and all produce the amino acid Glycine^[8], so a mutation in the third position in the triplet GGT is a "silent mutation" and has no effect on the amino acid produced from the triplet. (Harding et al., 2000, pg.1355) analyzed the amino acid sequences in the receptor proteins from 106 individuals from Africa and 524 individuals from outside Africa to find why the tone of all the Africans' skin was dark. Harding found that there were zero differences among the Africans for the amino acid sequences in their receptor proteins, so the skin of each individual from Africa was dark. In contrast, among the non-African individuals, there were 18 different amino acid sites in which the receptor proteins differed, and each amino acid that differed from the African receptor protein resulted in skin lighter than the skin of the African individuals. Nonetheless, the variations in the 261 silent sites in the MC1R were similar between the Africans and non-Africans, so the basic mutation rates among the Africans and non-Africans were the same. Why were there zero differences and no divergences in the amino acid sequences of the receptor protein among the Africans while there were 18 differences among the populations in Ireland, England, and Sweden? A nucleotide is a chemical compound that consists of 3 portions: a heterocyclic base, a sugar, and one or more phosphate groups. ... For the programming language Adenine, see Adenine (programming language). ... Guanine is one of the five main nucleobases found in the nucleic acids DNA and RNA; the others being adenine, cytosine, thymine, and uracil. ... For the similarly-spelled vitamin compound, see Thiamine Thymine, also known as 5-methyluracil, is a pyrimidine nucleobase. ... Cytosine is one of the 5 main nucleobases used in storing and transporting genetic information within a cell in the nucleic acids DNA and RNA. It is a pyrimidine derivative, with a heterocyclic aromatic ring and two substituents attached (an amine group at position 4 and a keto group at... Synonyms (in ancient Greek syn συν = plus and onoma όνομα = name) are different words with similar or identical meanings. ... Silent mutations or synonymous mutations are DNA mutations that, although they alter a particular codon, they do not alter the final amino acid, and hence do not affect the final protein. ...

(Harding et al., 2000, pp.1359-1360) concluded that the intense sun in Africa created an evolutionary constraint that reduced severely the survival of progeny with any difference in the 693 sites of the MC1R gene that resulted in even one small change in the amino acid sequence of the receptor protein—because any variation from the African receptor protein produced significantly lighter skin that gave less protection from the intense African sun. In contrast, in Sweden, for example, the sun was so weak that no mutation in the receptor protein reduced the survival probability of progeny. Indeed, for the individuals from Ireland, England, and Sweden, the mutation variations among the 693 gene sites that caused changes in amino acid sequence was the same as the mutation variations in the 261 gene sites at which silent mutations still produced the same amino acid sequence. Thus, Harding concluded that the intense sun in Africa selectively killed off the progeny of individuals who had a mutation in the MC1R gene that made the skin lighter. However, the mutation rate toward lighter skin in the progeny of those African individuals who had moved North to areas with weaker sun was comparable to the mutation rate of the folks whose ancient ancestors grew up in Sweden. Hence, Harding concluded that the lightness of human skin was a direct result of random mutations in the MC1R gene that were non-lethal at the latitudes of Sweden. Even the mutations that produce red hair with little ability to tan were non-lethal in the northern latitudes.

(Rogers, Iltis & Wooding 2004) examined Harding's data on the variation of MC1R nucleotide sequences for people of different ancestry to determine the most probable progression of the skin tone of human ancestors over the last five million years. Comparing the MC1R nucleotide sequences for chimpanzees and humans in various regions of the Earth, Rogers concluded that the common ancestors of all humans had light skin tone under dark hair—similar to the skin tone and hair color pattern of today's chimpanzees. That is 5 million years ago, the human ancestors' dark hair protected their light skin from the intense African sun so that there was no evolutionary constraint that killed off the progeny of those who had mutations in the MC1R nucleotide sequences that made their skin light. (Sweet 2002) argues that based on cave paintings, Europeans may have been dark as recently as 13,000 years ago. The painters depicted themselves as having darker complexions than the animals they hunted.

However, over 1.2 million years ago, judging from the numbers and spread of variations among human and chimpanzee MC1R nucleotide sequences, the human ancestors in Africa began to lose their hair and they came under increasing evolutionary pressures that killed off the progeny of individuals that retained the inherited lightness of their skin. Folate breakdown in sun-exposed skin is inhibited by the presence of melanin and is essential for human fetal development. It is likely that folate conservation played an important role in the selection of dark skin in the ancient African ancestors of modern humans. By 1.2 million years ago, all people having descendants today had exactly the receptor protein of today's Africans; their skin was dark, and the intense sun killed off the progeny with any lighter skin that resulted from mutational variation in the receptor protein (Rogers, Iltis & Wooding 2004, p. 107).

However, the progeny of those humans who migrated North away from the intense African sun had another evolutionary constraint: vitamin D availability. Human requirements for vitamin D (cholecalciferol) are in part met through photoconversion of a precursor to vitamin D3. As humans migrated north from the equator, they were exposed to less intense sunlight, in part because of the need for greater use of clothing to protect against the colder climate. Thus, under these conditions, evolutionary pressures would tend to select for lighter-skinned humans as there was less photodestruction of folate and a greater need for photogeneration of cholecalciferol. Tracking back the statistical patterns in variations in DNA among all known people sampled who are alive on the Earth today, it appears that

Contents

Melanin and genes

Health related effects

Cultural effects

Research on skin tone variability

Origins of light skin in humans

See also

Footnotes

References

Further reading

External links