Melanin: Difference between revisions
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===Melanin and human adaptation=== |
===Melanin and human adaptation=== |
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Melanocytes insert granules of melanin called ''melanosomes'' into the other skin cells of the human epidermis. The melanosomes in each recipient cell accumulate atop the cellular nucleus, where they protect the nuclear [[DNA]] from mutations caused by the sun's ionizing radiation. People whose ancestors lived for long periods in the regions of the globe near the [[Equator]] generally have more active melanocytes, and therefore larger quantities of melanin in their skins. This makes their skins dark brown or black and protects them against high levels of exposure to the sun. In areas of the globe closer to the poles, people have far less need for protection from ionizing radiation, so their skin is usually lighter in colour. This allows sunlight to stimulate [[vitamin D]] production by the liver. |
Melanocytes insert granules of melanin called ''melanosomes'' into the other skin cells of the human epidermis. The melanosomes in each recipient cell accumulate atop the cellular nucleus, where they protect the nuclear [[DNA]] from mutations caused by the sun's ionizing radiation. People whose ancestors lived for long periods in the regions of the globe near the [[Equator]] generally have more active melanocytes, and therefore larger quantities of melanin in their skins. This makes their skins dark brown or black and protects them against high levels of exposure to the sun. In areas of the globe closer to the poles, people have far less need for protection from ionizing radiation, so their skin is usually lighter in colour. This allows sunlight to stimulate [[vitamin D]] production by the liver. Having lighter skin while living near the Equator or having darker skin while living far from the Equator causes the problems discussed below. |
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The most recent scientific evidence indicates that all humanity originated in [[Africa]]. As a result, all original people had relatively large numbers of active melanocytes and, accordingly, darker skin. As some of these original tribes of people migrated and settled in areas of [[Asia]] and [[Europe]], their melanin production gradually decreased to allow [[acclimation]] to climates where radiation from the sun was less intense. It is estimated that this color [[evolution]] in an immigrated populace takes approximately 10,000 years to complete. |
The most recent scientific evidence indicates that all humanity originated in [[Africa]]. As a result, all original people had relatively large numbers of active melanocytes and, accordingly, darker skin. As some of these original tribes of people migrated and settled in areas of [[Asia]] and [[Europe]], their melanin production gradually decreased to allow [[acclimation]] to climates where radiation from the sun was less intense. It is estimated that this color [[evolution]] in an immigrated populace takes approximately 10,000 years to complete. |
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As with peoples that migrated northward, those with |
As with peoples that migrated northward, those with light skin that migrated southward had to acclimate to the much stronger solar radiation. Those people, who produced more skin-protecting melanin, were less likely to suffer from [[skin cancer]], as well as other health problems related to exposure to strong [[solar radiation]], including the photodegradation of certain vitamins such as [[riboflavin]]s, [[carotinoid]]s, [[tocopherol]], and [[folate]]. |
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Most people's skin darkens when exposed to UV light, giving them more protection when it is needed. The closer one lives to the Equator, where the sun's radiation is strongest, the greater the advantage of having high melanin levels in the skin. |
Most people's skin darkens when exposed to UV light, giving them more protection when it is needed. The closer one lives to the Equator, where the sun's radiation is strongest, the greater the advantage of having high melanin levels in the skin. Dark skin affords far greater protection than fair skin against sunburn and the development of [[melanoma]], a potentially extremely deadly form of skin cancer. |
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In people of color, however, high melanin levels also can be a disadvantage. Dark skin is a complicating factor in the laser removal of [[port-wine stain]]s. Effective in treating [[Caucasian]] skin, lasers have less success in removing port-wine stains in [[Asians]] and [[blacks]]. Higher concentrations of melanin in darker-skinned individuals simply absorb the laser radiation, preventing light absorption by the targeted tissue. Melanin similarly can complicate laser treatment of other dermatological conditions in people of color. Also, people with darker skin have a greater tendency toward [[vitamin D]] deficiency when living far from the Equator. |
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[[Freckles]] and [[mole (skin marking)|mole]]s are formed where there is a greater concentration of melanin in the skin. |
[[Freckles]] and [[mole (skin marking)|mole]]s are formed where there is a greater concentration of melanin in the skin. |
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==Role in social and race bias== |
==Role in social and race bias== |
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The concentration of melanin and its resultant tone of [[skin color]] have long been a criterion in determining an individual's [[race]], with corresponding social and political impacts. Such characterstics as the amount of hair and skin pigmentation often are prejudicial in the assessment of a person or group's innate intelligence, character and general merit. See [[white supremacy]], [[black supremacy]], and [[racism]] for details. |
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When skin pigmentation as a characteristic of [[race]] becomes significant in some way, this phenomenon is known as [[racialism]]. Many people and societies overlay racialism with [[racism|racist]] perceptions and systems which arbitrarily assign to groups of people a status of inherent superiority or inferiority, privilege or disadvantage based on skin color or racial classification. [[Apartheid]]-era [[South Africa]] is an example of a [[white supremacy|white supremacist]] society based on a system of stratification of power and privilege by skin color, as well as racial admixture. Similar examples can be found in [[India]]'s [[caste]] system; [[Brazil]]'s highly socially color-stratified society; and, in the U.S., [[racial segregation|segregation]] and [[institutional racism]] on the part of white-controlled institutions, and internal "color consciousness" on the part many ethnic minorities. Because of the pervasive influence of white supremacist values worldwide, prejudice against people with more highly pigmented skin is the most pervasive form of color bias. Many other societies remain informally divided on the basis of skin color and, often, related ethnicity. See also [[white supremacy]], [[Nazism]], [[colonialism]]. |
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Conversely, [[black supremacy]]— usually expressed within a bilateral, [[Blacks|black]]-[[Caucasians|white]] context— is the belief that blacks as a group are superior to people of other races. Sometimes, '''Melanin Theory''' underlies this notion (see [[Black supremacy]]). |
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Illogical presumptions about people with regard to hair color are far less common than skin color bias, have far fewer real-word implications, and are more often applied to women than to men. Common stereotypes are dumb [[Blonde|blondes]], hot-tempered [[Red hair|redheads]] and vixen [[Brunette|brunettes]]. |
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==See also== |
==See also== |
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Revision as of 01:40, 10 March 2005
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Melanin is a polymer of either or both of two monomer molecules: indolequinone, and dihydroxyindole carboxylic acid. Melanin exists in the plant, animal and protista kingdoms, where, among other functions, it serves as a pigment. The presence of melanin in the archaea and bacteria kingdoms is an issue of ongoing scholarly disagreement.
Melanin in humans
In humans melanin is found in skin, hair, the coat of the retina, the medulla and zona reticularis of the adrenal gland, the inner ear, and the substantia nigra of the brain. Melanin is produced by melanocytes, which in the skin are found in the stratum basale of the epidermis. Although human beings generally possess a similar concentration of melanocytes in their skin, the melanocytes in some individuals and races more frequently express the melanin-producing genes, thereby conferring a greater concentration of skin melanin. Some individual animals and humans have no or very little melanin in their bodies, which is a condition known as albinism.
Because melanin is an aggregate of smaller component molecules, there are a number of different types of melanin with differing proportions and bonding patterns of these component molecules. Eumelanin is found in skin and hair, and is the most abundant melanin in humans as well as the form most likely to be deficient in albinism.
Eumelanin polymers have long been thought to comprise numerous cross-linked dihydroxyindole polymers; recent research into the electrical properties of eumelanin, however, has indicated that it may consist of more basic oligomers adhering to one another by some other mechanism. Thus, the precise nature of eumelanin's molecular structure is once again the object of study.
Pheomelanin is found in human skin and hair, though it is considerably less abundant in humans than eumelanin. Pheomelanin imparts a reddish hue, and is found in particularly large quantities in red hair.
Neuromelanin is a byproduct of dopamine metabolism, and is found in the substantia nigra of the human brain.
Melanin and human adaptation
Melanocytes insert granules of melanin called melanosomes into the other skin cells of the human epidermis. The melanosomes in each recipient cell accumulate atop the cellular nucleus, where they protect the nuclear DNA from mutations caused by the sun's ionizing radiation. People whose ancestors lived for long periods in the regions of the globe near the Equator generally have more active melanocytes, and therefore larger quantities of melanin in their skins. This makes their skins dark brown or black and protects them against high levels of exposure to the sun. In areas of the globe closer to the poles, people have far less need for protection from ionizing radiation, so their skin is usually lighter in colour. This allows sunlight to stimulate vitamin D production by the liver. Having lighter skin while living near the Equator or having darker skin while living far from the Equator causes the problems discussed below.
The most recent scientific evidence indicates that all humanity originated in Africa. As a result, all original people had relatively large numbers of active melanocytes and, accordingly, darker skin. As some of these original tribes of people migrated and settled in areas of Asia and Europe, their melanin production gradually decreased to allow acclimation to climates where radiation from the sun was less intense. It is estimated that this color evolution in an immigrated populace takes approximately 10,000 years to complete.
As with peoples that migrated northward, those with light skin that migrated southward had to acclimate to the much stronger solar radiation. Those people, who produced more skin-protecting melanin, were less likely to suffer from skin cancer, as well as other health problems related to exposure to strong solar radiation, including the photodegradation of certain vitamins such as riboflavins, carotinoids, tocopherol, and folate.
Most people's skin darkens when exposed to UV light, giving them more protection when it is needed. The closer one lives to the Equator, where the sun's radiation is strongest, the greater the advantage of having high melanin levels in the skin. Dark skin affords far greater protection than fair skin against sunburn and the development of melanoma, a potentially extremely deadly form of skin cancer.
In people of color, however, high melanin levels also can be a disadvantage. Dark skin is a complicating factor in the laser removal of port-wine stains. Effective in treating Caucasian skin, lasers have less success in removing port-wine stains in Asians and blacks. Higher concentrations of melanin in darker-skinned individuals simply absorb the laser radiation, preventing light absorption by the targeted tissue. Melanin similarly can complicate laser treatment of other dermatological conditions in people of color. Also, people with darker skin have a greater tendency toward vitamin D deficiency when living far from the Equator.
Freckles and moles are formed where there is a greater concentration of melanin in the skin.
Albinism is a condition in which an animal (such as a human or a mouse) is incapable of producing melanin, and hence appears white with pink eyes.
Physical properties and technological applications
Melanin is a biopolymer and a neuropeptide. In the early 1970's, researchers found melanin to be an organic semiconductor. Studies revealed that melanin acted as an electrical threshold switch, emitting a flash of light— electroluminescence— when it switched. This knowledge was considered "lost" for a time, but in 2000, the Nobel Prize in Chemistry was awarded to three scientists for their work in the "discovery" and development of conductive polymers. The polymers utilized in the research included melanins.
An organic semiconductor, melanin influences neural activity and mediates the conduction of light, heat and kinetic energy. As such, it is the subject of intense interest in biotech research and development, most notably in plastic electronics and nanotechnology. Already used in the manufacture of transistors, melanin in both its organic and synthesized forms may one day routinely supplant conventional, inorganic materials like gallium arsenide and silicon in microchips and other high-tech devices.
Role in social and race bias
The concentration of melanin and its resultant tone of skin color have long been a criterion in determining an individual's race, with corresponding social and political impacts. Such characterstics as the amount of hair and skin pigmentation often are prejudicial in the assessment of a person or group's innate intelligence, character and general merit. See white supremacy, black supremacy, and racism for details.