Editing Brown (section)

== Brown in science and nature ==

=== Optics ===
Brown is a dark orange color. It can be thought of as dark [[orange (color)|orange]], but it can also be made in other ways. In the [[RGB color model]], which uses red, green and blue light in various combinations to make all the colors on computer and television screens, it is made by mixing red and green light.

In terms of the [[visible spectrum]], "brown" refers to long wavelength hues, [[yellow]], [[orange (colour)|orange]], or [[red]], in combination with low [[luminance]] or [[Saturation (color theory)|saturation]].<ref>"Some Experiments on Color", ''Nature'' '''111''', 1871, in {{cite book | title = Scientific Papers | author = [[John William Strutt]] (Lord Rayleigh) | year = 1899 | publisher = University Press | url = https://books.google.com/books?id=KWMSAAAAIAAJ&q=date:0-1923+light+red+green+yellow-or-orange&pg=PA84 }}</ref>
Since ''brown'' may cover a wide range of the visible spectrum, composite adjectives are used such as red brown, yellowish brown, dark brown or light brown.

As a color of low intensity, brown is a [[tertiary color]]: a mix of the three subtractive [[primary color]]s is brown if the [[cyan]] content is low. Brown exists as a color perception only in the presence of a brighter color contrast.<ref>"Color Vision", in {{cite book | title = The Feynman Lectures on Physics | author = [[Richard Feynman]] | year = 1964 | publisher = Addison Wesley Longman | url = https://feynmanlectures.caltech.edu/I_35.html}}</ref> Yellow, orange, red, or rose objects are still perceived as such if the general illumination level is low, despite reflecting the same amount of red or orange light as a brown object would in normal lighting conditions.
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File:Optical grey squares orange brown.svg|The colored disks appear to be brown and orange, but are actually an identical shade; their perceived color depends on the shade of grey they are surrounded by<ref>G. M. Johnson and M. D. Fairchild, "Visual psychophysics and color appearance", (chapter) in ''CRC Digital Color Imaging Handbook'', 115–171 (2003).</ref>
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=== Brown pigments, dyes and inks ===
* Raw [[umber]] and burnt umber are two of the oldest pigments used by humans. Umber is a brown clay, containing a large amount of [[iron oxide]] and between five and twenty percent [[manganese oxide]], which give the color. Its shade varies from a greenish brown to a dark brown. It takes its name from the Italian region of [[Umbria]], where it was formerly mined. The principal source today is the island of [[Cyprus]]. Burnt umber is the same pigment which has been roasted (calcined), which turns the pigment darker and more reddish.<ref name="Fabien Petillion p. 30">Isabellle Roelofs and Fabien Petillion, ''La Couleur explquée aux artistes'', p. 30.</ref>
* Raw [[sienna]] and burnt sienna are also clay pigments rich in iron oxide, which were mined during the [[Renaissance]] around the city of Siena in Tuscany. Sienna contains less than five percent manganese. The natural sienna earth is a dark yellow [[ochre]] color; when roasted it becomes a rich reddish brown called burnt sienna.<ref name="Fabien Petillion p. 30" />
* '''[[Mummy brown]]''' was a pigment used in oil paints made from ground Egyptian mummies.<ref>{{cite web|last1=Eveleth |first1=Rose |author-link=Rose Eveleth |title=Ground Up Mummies Were Once an Ingredient in Paint |url=http://www.smithsonianmag.com/smart-news/ground-mummies-were-once-ingredient-paint-180950350/?no-ist |website=Smithsonian |access-date=29 February 2016}}</ref>
* '''[[Caput mortuum (pigment)|Caput mortuum]]''' is a haematite iron oxide pigment, used in painting. The name is also used in reference to mummy brown.
* '''Van Dyck brown''', known in Europe as Cologne earth or Cassel earth, is another natural earth pigment, that was made up largely of decayed vegetal matter. It made a rich dark brown, and was widely used during the Renaissance to the 19th century It takes its name from the painter [[Anthony van Dyck]], but it was used by many other artists before him. It was highly unstable and unreliable, so its use was abandoned by the 20th century, though the name continues to be used for modern synthetic pigments. The color of Van Dyck brown can be recreated by mixing ivory black with mauve or with Venetian red, or mixing cadmium red with cobalt blue.<ref>Isabellle Roelofs and Fabien Petillion, ''La Couleur explquée aux artistes'', p. 148.</ref>
* '''Mars brown'''. The names of the earth colors are still used, but very few modern pigments with these names actually contain natural earths; most of their ingredients today are synthetic.<ref name="Fabien Petillion p. 30" /> Mars brown is typical of these new colors, made with synthetic iron oxide pigments. The new colors have a superior coloring power and opacity, but not the delicate hue as their namesakes.<ref name="Fabien Petillion p. 30" />
* [[Walnuts]] have been used to make a brown dye since antiquity. The Roman writer [[Ovid]], in the first century BC described how the [[Gauls]] used the juice of the hull or husk inside the shell of the walnut to make a brown dye for wool, or a reddish dye for their hair.<ref>Anne Varichon, ''Couleurs- pigments et teintures dans les mains des peuples'', pp. 264–265</ref>
* The [[chestnut]] tree has also been used since ancient times as a source brown dye. The bark of the tree, the leaves and the husk of the nuts have all been used to make dye. The leaves were used to make a beige or yellowish-brown dye, and in the Ottoman Empire the yellow-brown from chestnut leaves was combined with indigo blue to make shades of green.<ref>Anne Varichon, ''Couleurs- pigments et teintures dans les mains des peuples'', pp. 262–263</ref>
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File:IronOxidePigmentUSGOV.jpg|[[Iron oxide]] is the most common ingredient in brown pigments
LimoniteUSGOV.jpg|[[Limonite]] is a form of yellowish iron ore. A clay of limonite rich in iron oxide is the source of raw sienna and burnt sienna.
File:Terra ombra naturale umber.jpg|Natural or raw [[umber]] pigment is clay rich in [[iron oxide]] and [[manganese]]
File:Pigment sienna burnt iconofile.jpg|Burnt [[sienna]] pigment, from the region around [[Siena]] in [[Tuscany]]
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=== Brown eyes ===
{{main|Eye color#Brown}}

With few exceptions, all mammals have brown or darkly-pigmented irises.<ref>{{cite journal | url=https://pubmed.ncbi.nlm.nih.gov/19278018/ | pmid=19278018 | year=2009 | last1=Bradley | first1=B. J. | last2=Pedersen | first2=A. | last3=Mundy | first3=N. I. | title=Blue eyes in lemurs and humans: Same phenotype, different genetic mechanism | journal=American Journal of Physical Anthropology | volume=139 | issue=2 | pages=269–273 | doi=10.1002/ajpa.21010 }}</ref> In humans, brown eyes result from a relatively high concentration of [[melanin]] in the [[stroma of iris|stroma]] of the iris, which causes light of both shorter and longer wavelengths to be absorbed<ref>Fox, Denis Llewellyn (1979). Biochromy: Natural Coloration of Living Things. University of California Press. p. 9. {{ISBN|0-520-03699-9}}.</ref><ref>{{cite journal |author=Eiberg H, Mohr J |title=Assignment of genes coding for brown eye colour (BEY2) and brown hair colour (HCL3) on chromosome 15q |journal=Eur. J. Hum. Genet. |volume=4 |issue=4 |pages=237–41 |year=1996 |pmid=8875191 |doi=10.1159/000472205|s2cid=26700451 }}</ref> and in many parts of the world, it is nearly the only iris color present.<ref>{{OMIM|227220|SKIN/HAIR/EYE PIGMENTATION, VARIATION IN, 1; SHEP1}}</ref> Dark pigment of brown eyes is most common in [[East Asia]], [[Central Asia]], [[Southeast Asia]], [[South Asia]], [[West Asia]], [[Oceania]], [[Africa]], [[Americas]], etc. as well as parts of [[Eastern Europe]] and [[Southern Europe]].<ref name="Sulem">{{cite journal |title=Genetic determinants of hair, eye and skin pigmentation in Europeans |journal=Nat. Genet. |volume=39 |issue=12 |pages=1443–52 |year=2007 |pmid=17952075 |doi=10.1038/ng.2007.13 |last1=Sulem |first1=Patrick |last2=Gudbjartsson |first2=Daniel F |last3=Stacey |first3=Simon N |last4=Helgason |first4=Agnar |last5=Rafnar |first5=Thorunn |last6=Magnusson |first6=Kristinn P |last7=Manolescu |first7=Andrei |last8=Karason |first8=Ari |last9=Palsson |first9=Arnar |last10=Thorleifsson |first10=Gudmar |last11=Jakobsdottir |first11=Margret |last12=Steinberg |first12=Stacy |last13=Pálsson |first13=Snæbjörn |last14=Jonasson |first14=Fridbert |last15=Sigurgeirsson |first15=Bardur |last16=Thorisdottir |first16=Kristin |last17=Ragnarsson |first17=Rafn |last18=Benediktsdottir |first18=Kristrun R |last19=Aben |first19=Katja K |last20=Kiemeney |first20=Lambertus A |last21=Olafsson |first21=Jon H |last22=Gulcher |first22=Jeffrey |last23=Kong |first23=Augie |last24=Thorsteinsdottir |first24=Unnur |last25=Stefansson |first25=Kari |s2cid=19313549 |display-authors=8 }}</ref> The majority of people in the world overall have dark brown eyes. Brown irises range from highly pigmented, dark brown (almost black) eyes, to very light, almost amber or hazel irises composed partially of [[lipochrome]]. of Light or medium-pigmented brown eyes are common in [[Europe]], [[Afghanistan]], [[Pakistan]] and [[North India|Northern India]], as well as some parts of the [[Middle East]], and can also be found in populations in [[East Asia]] and [[Southeast Asia]], but are proportionally rare. (See [[eye color]]).
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File:Epicanthic KR03.jpg|A dark brown iris is most common in [[East Asia]], [[Southeast Asia]], and [[South Asia]]
File:Picture of brown eyes.jpg|Medium brown iris
File:Human eye with limbal ring, anterior view.jpg|Light brown irises can also be found in [[East Asia]] and [[Southeast Asia]], but are relatively rare
File:Hazel eyes S7307583.jpg|A light brown iris is most common in [[North Africa]], [[Eastern Europe]], the [[Americas]] and [[West Asia]] 
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=== Brown hair ===
{{main|Brown hair}}

Brown is the second most common color of human hair, after black. It is caused by higher levels of the natural dark pigment [[eumelanin]], and lower levels of the pale pigment [[pheomelanin]]. Brown eumelanin is more common among Europeans, while black eumelanin is more often found in the hair on non-Europeans. A small amount of black eumelanin, in the absence of other pigments, results in grey hair. A small amount of brown eumelanin in the absence of other pigments results in blond hair.

<gallery mode="packed" heights="200px">
File:Brunette red lipstick.jpg|Brunette comes from ''brune'', the French term for a woman with brown hair
File:Nadeeka Perera.jpg|Brown hair with highlights. [[Nadeeka Perera]], a fashion model
File:Susan Sarandon 3 by David Shankbone.jpg|[[Auburn hair]] is a reddish brown. This is actress [[Susan Sarandon]]
File:Yvonne Catterfeld.jpg|Chestnut color hair also has a reddish tint, but is less red and more brown than auburn hair. This is German singer [[Yvonne Catterfeld]]
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=== Brown skin ===
A majority of people in the world have skin that is a shade of brown, from a very light honey brown or a golden brown, to a copper or bronze color, to a coffee color or a dark chocolate brown. Skin color and race are not the same; many people classified as "white" or "black" actually have skin that is a shade of brown. Brown skin is caused by [[melanin]], a natural pigment which is produced within the skin in cells called [[melanocyte]]s. Skin pigmentation in humans evolved to primarily regulate the amount of [[ultraviolet radiation]] penetrating the skin, controlling its biochemical effects.<ref name=jabl1>{{cite book|last=Muehlenbein|first=Michael|title=Human Evolutionary Biology|year=2010|publisher=Cambridge University Press|pages=192–213}}</ref>

Natural skin color can darken as a result of [[Sun tanning|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 radiation|ultraviolet]] fraction that produces damage and thus mutations in the [[DNA]] of the skin cells.<ref name=pmid20445093>{{cite journal |last1=Jablonski |first1=N. G. |last2=Chaplin |first2=G. |title=Colloquium Paper: Human skin pigmentation as an adaptation to UV radiation |journal=Proceedings of the National Academy of Sciences |volume=107 |pages=8962–8 |year=2010 |issue=Suppl 2 |doi=10.1073/pnas.0914628107 |pmid=20445093 |pmc=3024016 |bibcode=2010PNAS..107.8962J|doi-access=free }}</ref> There is a correlation between the geographic distribution of ultraviolet radiation (UVR) and the distribution of indigenous skin pigmentation around the world. Darker-skinned populations are found in the regions with the most ultraviolet, closer to the equator, while lighter skinned populations live closer to the poles, with less UVR, though immigration has changed these patterns.<ref name=webb06>{{cite journal|last=Webb|first=A.R.|title=Who, what, where, and when: influences on cutaneous vitamin D synthesis|journal=Progress in Biophysics and Molecular Biology|volume=92|issue=1|pages=17–25|pmid=16766240|year=2006|doi=10.1016/j.pbiomolbio.2006.02.004|doi-access=}}</ref>

While ''white ''and'' black'' are commonly used to describe racial groups, ''[[Brown (racial classification)|brown]]'' is rarely used, because it crosses all racial lines.
In [[Brazil]], the Portuguese word ''[[pardo]]'', which can mean different shades of brown, is used to refer to multiracial people. The Brazilian Institute of Geography and Statistics (IBGE) asks people to identify themselves as ''branco'' (white), ''pardo'' (brown), ''negro'' (black), or ''amarelo'' (yellow). In 2008 43.8 percent of the population identified themselves as pardo.<ref>IBGE. 2008 PNAD. [http://www.sidra.ibge.gov.br/bda/tabela/protabl.asp?c=262&i=P&nome=on&notarodape=on&tab=262&unit=0&pov=1&opc1=1&poc2=1&OpcTipoNivt=1&opn1=2&nivt=0&orc86=3&poc1=1&orp=6&qtu3=27&opv=1&poc86=2&sec1=0&opc2=1&pop=1&opn2=0&orv=2&orc2=5&qtu2=5&sev=1000093&opc86=1&sec2=0&opp=1&opn3=0&sec86=0&sec86=2776&sec86=2777&sec86=2779&sec86=2778&sec86=2780&sec86=2781&ascendente=on&sep=43344&orn=1&qtu7=9&orc1=4&qtu1=1&cabec=on&pon=1&OpcCara=44&proc=1&opn7=0&decm=99 População residente por cor ou raça, situação e sexo].</ref> (See [[human skin color]]).
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File:Elderly Gambian woman face portrait.jpg|An elderly woman from Gambia
File:Flickr - DavidDennisPhotos.com - Man at Ruins in Cairo.jpg|A man from Egypt
File:Gisele Bundchen2 cropped.jpg|A woman from Brazil
File:Sera Monastery13.jpg|A man from Tibet
File:Peruvian woman in hat smiling.jpg|A young woman from Peru
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=== Soil ===
The thin top layer of the Earth's crust on land is largely made up of [[soil]] colored different shades of brown.<ref name="Birkeland">Birkeland, Peter W. ''Soils and Geomorphology''. 3rd edition. New York: Oxford University Press, 1999.</ref> Good soil is composed of about forty-five percent minerals, twenty-five percent water, twenty-five percent air, and five percent organic material, living and dead. Half the color of soil comes from minerals it contains; soils containing iron turn yellowish or reddish as the iron oxidizes. Manganese, nitrogen and sulfur turn brownish or blackish as they decay naturally.

Rich and fertile soils tend to be darker in color; the deeper brown color of fertile soil comes from the decomposing of the organic matter. Dead leaves and roots become black or brown as they decay. Poorer soils are usually paler brown in color, and contain less water or organic matter.
* [[Mollisols]] are the soil type found under grassland in the [[Great Plains]] of America, the [[Pampas]] in Argentina and the Russian Steppes. The soil is 60–80 centimeters deep and is rich in nutrients and organic matter.
* [[Loess]] is a type of pale yellow or buff soil, which originated as wind-blown silt. It is very fertile, but is easily eroded by wind or water.
* [[Peat]] is an accumulation of partially decayed vegetation, whose decomposition is slowed by water. Despite its dark brown color, it is infertile, but is useful as a fuel.
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File:Soil profile.png|A typical soil profile; dark-brown [[topsoil]]s, rich with organic matter, above reddish-brown lower layers
File:Mollisol.jpg|A profile of layers of [[Mollisols]], the soil type found in the [[Great Plains]] of the U.S., the [[Pampas]] in Argentina, and the Russian Steppes
File:Loess landscape china.jpg|A landscape of [[loess]] soil in [[Datong]], [[Shanxi]], China. Loess originated as windblown silt. It is very fertile but erodes easily
File:Peat-Stack in Ness, Outer Hebrides, Scotland.jpg|A stack of [[peat]] cut from the Earth in the Outer [[Hebrides]], [[Scotland]]. Peat is partially decayed vegetative matter
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=== Mammals and birds ===
A large number of mammals and predatory birds have a brown coloration. This sometimes changes seasonally, and sometimes remains the same year-round. This color is likely related to [[camouflage]], since the backdrop of some environments, such as the forest floor, is often brown, and especially in the spring and summertime when animals like the [[snowshoe hare]] get brown fur. Most mammals are [[Dichromacy|dichromats]] and so do not easily distinguish brown fur from [[green]] grass.
* The [[brown rat]] or ''Norwegian rat'' (''Rattus norvegicus'') is one of the best known and most common [[rat]]s.
* The [[brown bear]] (''Ursus arctos'') is a large [[bear]] distributed across much of northern [[Eurasia]] and [[North America]].
* The [[Stoat|ermine]] (''Mustela erminea'') has a brown back in summer, or year-round in the southern reaches of its range.
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File:Brown bear.jpg|The [[brown bear]] is found across Eurasia and North America
File:Tawny owl at night (42511916510).jpg|The [[tawny owl]]. The color [[tawny (color)|tawny]] takes its name from the old French word ''tané'', which means to tan leather. The same word is the root of suntan and the color tan
File:Lepus americanus 5459 cropped.jpg|The fur of the [[snowshoe hare]] is brown in the summer and turns white in winter, as a form of all-season natural [[camouflage]]
File:Camelcalf-feeding.jpg|[[Camel (color)|Camel]] is an effective color for camouflage in the [[Sahara desert]], and is also a popular color for blankets and winter overcoats
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=== Biology ===
* The solid waste excreted by human beings and many other animals is characteristically brown in color due to the presence of [[bilirubin]], a byproduct of destruction of [[red blood cells]].