Human skin color#Skin tone variability

{{See also|Melanin}}

Melanin is produced by cells called melanocytes in a process called melanogenesis. Melanin is made within small membrane–bound packages called melanosomes. As they become full of melanin, they move into the slender arms of melanocytes, from where they are transferred to the keratinocytes. Under normal conditions, melanosomes cover the upper part of the keratinocytes and protect them from genetic damage. One melanocyte supplies melanin to thirty-six keratinocytes according to signals from the keratinocytes. They also regulate melanin production and replication of melanocytes.{{cite book|last=Jablonski|first=Nina|title=Living Color|year=2012|publisher=University of California Press|location=Berkeley, Los Angeles, London|isbn=978-0-520-25153-3}} People have different skin colors mainly because their melanocytes produce different amount and kinds of melanin.

The genetic mechanism behind human skin color is mainly regulated by the enzyme tyrosinase, which creates the color of the skin, eyes, and hair shades.{{cite journal|last=Sturm|first=R. A.|title=A golden age of human pigmentation genetics|journal=Trends in Genetics|year=2006|volume=22|issue=9|pages=464–469|doi=10.1016/j.tig.2006.06.010|pmid=16857289}}{{cite journal|title=Human pigmentation genes: Identification, structure and consequences of polymorphic variation|journal=Gene|year=2001|volume=277 |issue=1–2|pages=49–62|pmid=11602344|doi=10.1016/s0378-1119(01)00694-1|last1=Sturm|first1=R. A. |last2=Teasdale |first2=R. D.|last3=Box|first3=N. F.}} Differences in skin color are also attributed to differences in size and distribution of melanosomes in the skin. Melanocytes produce two types of melanin. The most common form of biological melanin is eumelanin, a brown-black polymer of dihydroxyindole carboxylic acids, and their reduced forms. Most are derived from the amino acid tyrosine. Eumelanin is found in hair, areola, and skin, and the hair colors gray, black, blond, and brown. In humans, it is more abundant in people with dark skin. Pheomelanin, a pink to red hue is found in particularly large quantities in red hair,{{cite journal|title=Diversity of human hair pigmentation as studied by chemical analysis of eumelanin and pheomelanin|date=Dec 2011|journal=J Eur Acad Dermatol Venereol|issue=12|pages=1369–1380|volume=25 |doi=10.1111/j.1468-3083.2011.04278.x|pmid=22077870|last1=Ito|first1=S.|last2=Wakamatsu|first2=K.|s2cid=5121042}} the lips, nipples, glans of the penis, and vagina.{{cite web |title=pheomelanin |website=MetaCyc |url=http://www.metacyc.org/META/NEW-IMAGE?type=COMPOUND&object=CPD-12380 |access-date=2012-02-17 |url-status=live |archive-url=https://web.archive.org/web/20150121030624/http://www.metacyc.org/META/NEW-IMAGE?type=COMPOUND&object=CPD-12380 |archive-date=2015-01-21}}

Both the amount and type of melanin produced is controlled by a number of genes that operate under incomplete dominance.{{cite web|url=https://www.pbs.org/race/000_About/002_04-teachers-06.htm |title=The Genetics and Evolution of Skin Color: The Case of Desiree's Baby|date=2003|access-date=14 April 2015 |website=RACE—The Power of an Illusion|publisher=Public Broadcasting Service |last=Schneider |first=Patricia |url-status=live|archive-url= https://web.archive.org/web/20150506172623/http://www.pbs.org/race/000_About/002_04-teachers-06.htm |archive-date=6 May 2015}} One copy of each of the various genes is inherited from each parent. Each gene can come in several alleles, resulting in the great variety of human skin tones. Melanin controls the amount of ultraviolet (UV) radiation from the sun that penetrates the skin by absorption. While UV radiation can assist in the production of vitamin D, excessive exposure to UV can damage health.

{{Further|Melanocortin 1 receptor}}

Loss of body hair in Homo links to the thermoregulation through perspiration heat dissipation required for activity in hot open environments{{cite journal |last1=Ruxton |first1=Graeme D. |last2=Wilkinson |first2=David M. |date=2011-12-12 |title=Avoidance of overheating and selection for both hair loss and bipedality in hominins |journal=Proceedings of the National Academy of Sciences |volume=108 |issue=52 |pages=20965–20969 |doi=10.1073/pnas.1113915108 |pmid=22160694 |bibcode=2011PNAS..10820965R |issn=0027-8424|doi-access=free |pmc=3248486 }} and endurance running.{{cite journal |last1=Ruxton |first1=Graeme D. |last2=Wilkinson |first2=David M. |year=2011 |title=Thermoregulation and endurance running in extinct hominins: Wheeler's models revisited |journal=Journal of Human Evolution |volume=61 |issue=2 |pages=169–175 |doi=10.1016/j.jhevol.2011.02.012 |pmid=21489604 |bibcode=2011JHumE..61..169R |issn=0047-2484}} Humans as primates have a particular need for this thermoregulation since unlike other mammals they lack a carotid rete that allows precooling of blood to the brain, an organ extremely sensitive to changes in body temperature.{{cite journal |last1=Bruner |first1=Emiliano |last2=Mantini |first2=Simone |last3=Musso |first3=Fabio |last4=De La Cuétara |first4=José Manuel |last5=Ripani |first5=Maurizio |last6=Sherkat |first6=Shahram |date=2010-11-30 |title=The evolution of the meningeal vascular system in the human genus: From brain shape to thermoregulation |journal=American Journal of Human Biology |volume=23 |issue=1 |pages=35–43 |doi=10.1002/ajhb.21123 |pmid=21120884 |s2cid=24603018 |issn=1042-0533}} Given endurance running and its needs for thermoregulation arose with H. erectus,{{cite journal |last1=Bramble |first1=Dennis M. |last2=Lieberman |first2=Daniel E. |year=2004 |title=Endurance running and the evolution of Homo |journal=Nature |volume=432 |issue=7015 |pages=345–352 |doi=10.1038/nature03052 |pmid=15549097 |bibcode=2004Natur.432..345B |s2cid=2470602 |issn=0028-0836|url=http://doc.rero.ch/record/15289/files/PAL_E2588.pdf }} this links hairlessness with the origin of H. erectus about 2 million years ago.{{cite journal |last1=Branda |first1=Richard F. |last2=Eaton |first2=John W. |date=1978-08-18 |title=Skin Color and Nutrient Photolysis: An Evolutionary Hypothesis |journal=Science |volume=201 |issue=4356 |pages=625–626 |doi=10.1126/science.675247 |pmid=675247 |bibcode=1978Sci...201..625B |issn=0036-8075}}

As hominids gradually lost their fur between 1.2 and 4 million years ago, to allow for better cooling through sweating, their naked skin was exposed to sunlight. In the tropics, natural selection favoured dark-skinned human populations as high levels of skin pigmentation protected against the harmful effects of sunlight. Indigenous populations' skin reflectance (the amount of sunlight the skin reflects) and the actual UV radiation in a particular geographic area is highly inversely correlated, which supports this idea. Genetic evidence also supports this notion, demonstrating that around 1.2 million years ago there was a strong evolutionary pressure which acted on the development of dark skin pigmentation in early members of the genus Homo.{{cite journal |last=Nina |first=Jablonski |year=2004 |title=The evolution of human skin and skin color |journal=Annual Review of Anthropology |volume=33 |pages=585–623 |doi=10.1146/annurev.anthro.33.070203.143955 |s2cid=53481281}} Hairlessness exposes folate circulating subcutaneously and in the dermis to degradation from UV-radiation.{{cite journal |last=Rocha |first=Jorge |date=2019-07-30 |title=The Evolutionary History of Human Skin Pigmentation |journal=Journal of Molecular Evolution LLC |volume=88 |issue=1 |pages=77–87 |doi=10.1007/s00239-019-09902-7 |pmid=31363820 |s2cid=198998060 |issn=0022-2844}} The effect of sunlight on folic acid levels has been crucial in the development of dark skin and favored the emergence of skin pigmentation in order to protect from folate depletion due to the increased exposure to sunlight.{{cite book |last=Muehlenbein |first=Michael |title=Human Evolutionary Biology |publisher=Cambridge University Press |year=2010 |pages=192–213}}

In 2017, a study showed that both dark and light pigmentation alleles arose before the origin of modern humans,{{Cite journal |last1=Crawford |first1=Nicholas G. |last2=Kelly |first2=Derek E. |last3=Hansen |first3=Matthew E. B. |last4=Beltrame |first4=Marcia H. |last5=Fan |first5=Shaohua |last6=Bowman |first6=Shanna L. |last7=Jewett |first7=Ethan |last8=Ranciaro |first8=Alessia |last9=Thompson |first9=Simon |last10=Lo |first10=Yancy |last11=Pfeifer |first11=Susanne P. |last12=Jensen |first12=Jeffrey D. |last13=Campbell |first13=Michael C. |last14=Beggs |first14=William |last15=Hormozdiari |first15=Farhad |date=2017-11-17 |title=Loci associated with skin pigmentation identified in African populations |journal=Science |language=en |volume=358 |issue=6365 |doi=10.1126/science.aan8433 |issn=0036-8075 |pmc=5759959 |pmid=29025994}} with the older version of the variants in many cases being associated with lighter skin.{{Cite web |date=2017-10-12 |title=Penn-led Study Identifies Genes Responsible for Diversity of Human Skin Colors |url=https://penntoday.upenn.edu/news/penn-led-study-identifies-genes-responsible-diversity-human-skin-colors |access-date=2024-04-16 |website=Penn Today |language=en}} The earliest hominid ancestors of humans most likely had pale non-pigmented skin covered with dark black hair, like the chimpanzee and other great apes.{{Cite news |last=Wade |first=Nicholas |date=2003-08-19 |title=Why Humans and Their Fur Parted Ways |url=https://www.nytimes.com/2003/08/19/science/why-humans-and-their-fur-parted-ways.html |access-date=2024-01-13 |work=The New York Times |language=en-US |issn=0362-4331}}{{Cite journal |last=Greaves |first=Mel |date=2014-04-22 |title=Was skin cancer a selective force for black pigmentation in early hominin evolution? |journal=Proceedings of the Royal Society B: Biological Sciences |volume=281 |issue=1781 |pages=20132955 |doi=10.1098/rspb.2013.2955 |issn=0962-8452 |pmc=3953838 |pmid=24573849}}

With the evolution of hairless skin, abundant sweat glands, and skin rich in melanin, early humans could walk, run, and forage for food for long periods of time under the hot sun without brain damage due to overheating, giving them an evolutionary advantage over other species. Research on the MC1R alleles using assumptions about past population size and an absence of population bottlenecks suggests the allele for dark skin present in modern Africans arose at least by 1.2 million years ago.{{Harvnb|Rogers|Iltis|Wooding|2004b|p=107}}.

This was the genotype inherited by anatomically modern humans, but retained only by part of the extant populations, thus forming an aspect of human genetic variation. About 100,000–70,000 years ago, some anatomically modern humans (Homo sapiens) began to migrate away from the tropics to the north where they were exposed to less intense sunlight. This was possibly in part due to the need for greater use of clothing to protect against the colder climate. Under these conditions there was less photodestruction of folate and so the evolutionary pressure working against the survival of lighter-skinned gene variants was reduced. In addition, lighter skin is able to generate more vitamin D (cholecalciferol) than darker skin, so it would have represented a health benefit in reduced sunlight if there were limited sources of vitamin D. Hence the leading hypothesis for the evolution of human skin color proposes that:

1. From the origin of hairlessness and exposure to UV-radiation to less than 100,000 years ago, archaic humans, including archaic Homo sapiens, were dark-skinned.
2. As some Homo sapiens populations began to migrate, the evolutionary constraint keeping skin dark decreased proportionally to the distance north a population migrated, resulting in a range of skin tones within northern populations, although the bulk of humans remained dark-skinned.
3. At some point, some northern populations experienced positive selection for lighter skin due to the increased production of vitamin D from sunlight and the genes for darker skin disappeared from these populations.
4. Subsequent migrations into different UV environments and admixture between populations have resulted in the varied range of skin pigmentations we see today.

The genetic mutations leading to light skin, though partially different among East Asians and Western Europeans, suggest the two groups experienced a similar selective pressure after settlement in northern latitudes.{{cite journal |last1=Juzeniene |first1=Asta |last2=Setlow |first2=Richard |last3=Porojnicu |first3=Alina |last4=Steindal |first4=Arnfinn Hykkerud |last5=Moan |first5=Johan |title=Development of different human skin colors: A review highlighting photobiological and photobiophysical aspects |journal=Journal of Photochemistry and Photobiology B: Biology |volume=96 |pages=93–100 |year=2009 |doi=10.1016/j.jphotobiol.2009.04.009 |pmid=19481954 |issue=2|bibcode=2009JPPB...96...93J }}

The theory is partially supported by a study into the SLC24A5 gene which found that the allele associated with light skin in Europe "determined […] that 18,000 years had passed since the light-skin allele was fixed in Europeans" but may have originated as recently as 12,000–6,000 years ago "given the imprecision of method" , which is in line with the earliest evidence of farming.{{cite book |first=Luc-Normand |last=Tellier |year=2009 |url=https://books.google.com/books?id=cXuCjDbxC1YC&pg=PA26 |title=Urban world history: an economic and geographical perspective |page=26 |isbn=978-2-7605-1588-8}} Paleolithic Cro-Magnon groups, as well as Early Holocene Western and central European hunter-gatherers (Western Hunter Gatherers) have been suggested to have been dark skinned based on DNA analysis,{{Cite journal |last1=Posth |first1=Cosimo |last2=Yu |first2=He |last3=Ghalichi |first3=Ayshin |last4=Rougier |first4=Hélène |last5=Crevecoeur |first5=Isabelle |last6=Huang |first6=Yilei |last7=Ringbauer |first7=Harald |last8=Rohrlach |first8=Adam B. |last9=Nägele |first9=Kathrin |last10=Villalba-Mouco |first10=Vanessa |last11=Radzeviciute |first11=Rita |last12=Ferraz |first12=Tiago |last13=Stoessel |first13=Alexander |last14=Tukhbatova |first14=Rezeda |last15=Drucker |first15=Dorothée G. |date=2023-03-02 |title=Palaeogenomics of Upper Palaeolithic to Neolithic European hunter-gatherers |journal=Nature |language=en |volume=615 |issue=7950 |pages=117–126 |doi=10.1038/s41586-023-05726-0 |issn=0028-0836 |pmc=9977688 |pmid=36859578|bibcode=2023Natur.615..117P }} with a number of the most prominent light-skin tone gene variants found in modern Europeans being introduced by Anatolian Neolithic Farmers that migrated into Europe beginning around 9,000 years ago,{{Cite journal |last1=Ju |first1=Dan |last2=Mathieson |first2=Iain |date=2021-01-05 |title=The evolution of skin pigmentation-associated variation in West Eurasia |journal=Proceedings of the National Academy of Sciences |language=en |volume=118 |issue=1 |doi=10.1073/pnas.2009227118 |doi-access=free |issn=0027-8424 |pmc=7817156 |pmid=33443182|bibcode=2021PNAS..11809227J }} with selection pressure for lighter skin intensifying from the Neolithic period onwards.{{Cite journal |last1=Lazaridis |first1=Iosif |last2=Alpaslan-Roodenberg |first2=Songül |last3=Acar |first3=Ayşe |last4=Açıkkol |first4=Ayşen |last5=Agelarakis |first5=Anagnostis |last6=Aghikyan |first6=Levon |last7=Akyüz |first7=Uğur |last8=Andreeva |first8=Desislava |last9=Andrijašević |first9=Gojko |last10=Antonović |first10=Dragana |last11=Armit |first11=Ian |last12=Atmaca |first12=Alper |last13=Avetisyan |first13=Pavel |last14=Aytek |first14=Ahmet İhsan |last15=Bacvarov |first15=Krum |date=2022-08-26 |title=A genetic probe into the ancient and medieval history of Southern Europe and West Asia |journal=Science |language=en |volume=377 |issue=6609 |pages=940–951 |doi=10.1126/science.abq0755 |issn=0036-8075 |pmc=10019558 |pmid=36007020|bibcode=2022Sci...377..940L }}

Research by Nina Jablonski suggests that an estimated time of about 10,000 to 20,000 years is enough for human populations to achieve optimal skin pigmentation in a particular geographic area but that development of ideal skin coloration may happen faster if the evolutionary pressure is stronger, even in as little as 100 generations. The length of time is also affected by cultural practices such as food intake, clothing, body coverings, and shelter usage which can alter the ways in which the environment affects populations.

File:Evolutionary model of human pigmentation in three continental populations.png

Population and admixture studies suggest a three-way model for the evolution of human skin color, with dark skin evolving in early Homo sapiens in Africa and light skin evolving only recently after modern humans had expanded out of Africa. For the most part, the evolution of light skin has followed different genetic paths in Western and Eastern Eurasian populations; however, some mutations associated with lighter skin have estimated origin dates after humans spread out of Africa but before the divergence of the two lineages.

According to Crawford et al. (2017), most of the genetic variants associated with light and dark pigmentation in African populations appear to have originated more than 300,000 years ago.{{cite web |url=https://www.sciencedaily.com/releases/2017/10/171012143324.htm |date=2017 |title=Genes responsible for diversity of human skin colors identified |website=ScienceDaily}} African, South Asian and Australo-Melanesian populations also carry derived alleles for dark skin pigmentation that are not found in Europeans or East Asians.{{cite journal |journal=Science |volume=358 |issue=6365 |date=2017 |title=Loci associated with skin pigmentation identified in African populations |last1=Crawford |first1=Nicholas |pages=eaan8433 |doi=10.1126/science.aan8433|pmid=29025994 |pmc=5759959 }} Huang et al. 2021 found the existence of "selective pressure on light pigmentation in the ancestral population of Europeans and East Asians", prior to their divergence from each other. Skin pigmentation was also found to be affected by directional selection towards darker skin among Africans, as well as lighter skin among Eurasians.{{cite journal |journal=Biology Open |volume=10 |issue=2 |date=2021 |title=Dissecting dynamics and differences of selective pressures in the evolution of human pigmentation |last1=Huang |first1=Xin |doi=10.1242/bio.056523|pmid=33495209 |pmc=7888712 }} Crawford et al. (2017) similarly found evidence for selection towards light pigmentation prior to the divergence of West Eurasians and East Asians.

Elias et. al. in 2010 showed a superior barrier function in darkly pigmented skin. Most protective functions of the skin, including the permeability barrier and the antimicrobial barrier, reside in the stratum corneum and the researchers surmise that the stratum corneum has undergone the most genetic change since the loss of human body hair. Natural selection would have favored mutations that protect this essential barrier; one such protective adaptation is the pigmentation of interfollicular epidermis, because it improves barrier function as compared to non-pigmented skin.

The authors argue that lack of significant differences between modern light-skinned and dark-skinned populations in vitamin D deficiency, early death from UV-induced cancers and birth defects — as well as instances of light and dark populations living side-by-side in areas with similar UV — suggest the standard model is insufficient to explain the strong selection drive for pigmented skin.{{cite journal |last1=Elias |first1=PM |last2=Menon |first2=G |last3=Wetzel |first3=BK |last4=Williams |first4=J |journal=American Journal of Human Biology |pmid=20209486 |year=2010 |volume=22 |issue=4 |pages=526–537 |title=Barrier Requirements as the Evolutionary "Driver" of Epidermal Pigmentation in Humans |doi=10.1002/ajhb.21043 |pmc=3071612}} Jablonski rejects this theory on the grounds that the human tanning response is driven by UV-B exposure, not xeric stress, and that the positive selection for vitamin D production is "well-established".

{{See also|Human genetic variation|Race and genetics}}

To some extent, skin color is determined independently of eye and hair color, as can be seen from variation in skin coloration in human populations.{{cite journal |journal=Human Molecular Genetics |year=2006 |volume=15 |issue=2 |pages=176–181 |doi=10.1093/hmg/ddl217 |title=The genetic architecture of normal variation in human pigmentation: an evolutionary perspective and model |last1=McEvoy |first1=B. |pmid=16987881 |doi-access=free }}{{cite journal|journal=Human Molecular Genetics |year=2009 |volume=18 |issue=R1 |pages=9–17 |doi=10.1093/hmg/ddp003 |title=Molecular genetics of human pigmentation diversity|last1=Sturm |first1=R. A. |pmid=19297406|doi-access=free }}{{cite journal |url=http://mbe.oxfordjournals.org/content/early/2012/08/25/molbev.mss207.short|title=The timing of pigmentation lightening in Europeans |journal=Molecular Biology and Evolution |year=2012 |doi=10.1093/molbev/mss207 |pmid=22923467 |pmc=3525146 |volume=30 |issue=1 |pages=24–35 |last2=Santos |first2=A. M. |last3=McEvoy |first3=B. |last4=Alves |first4=I. |last5=Martinho |first5=C. |last6=Cameron |first6=E. |last7=Shriver |first7=M. D. |last8=Parra |first8=E. J. |last9=Rocha |first9=J. |last1=Belezal |first1=Sandra |url-status=live |archive-url=https://web.archive.org/web/20120829050356/http://mbe.oxfordjournals.org/content/early/2012/08/25/molbev.mss207.short|archive-date=2012-08-29 }}

For skin color, heritability is very high, even though it can be modified by exposure to sunlight.{{cite journal |last1=Norton |first1=H. L. |last2=Kittles |first2=R. A. |last3=Parra |first3=E. |last4=McKeigue |first4=P. |last5=Mao |first5=X. |last6=Cheng |first6=K. |last7=Canfield |first7=V. A. |last8=Bradley |first8=D. G. |last9=McEvoy |first9=B. |last10=Shriver |first10=M. D. |title=Genetic Evidence for the Convergent Evolution of Light Skin in Europeans and East Asians |journal=Molecular Biology and Evolution |volume=24 |issue=3 |pages=710–22 |year=2006 |pmid=17182896 |doi=10.1093/molbev/msl203 |doi-access=free }}

A recent systematic study found 169 genes involved in human skin coloration. Most of the genes were involved in melanosome biogenesis, endosomal transport, and gene regulation. Notably, the function of these genes was verified in tissue culture experiments using CRISPR-Cas9 knockouts, showing that these genes are indeed involved in melanin production.{{Cite journal |last1=Bajpai |first1=Vivek K. |last2=Swigut |first2=Tomek |last3=Mohammed |first3=Jaaved |last4=Naqvi |first4=Sahin |last5=Arreola |first5=Martin |last6=Tycko |first6=Josh |last7=Kim |first7=Tayne C. |last8=Pritchard |first8=Jonathan K. |last9=Bassik |first9=Michael C. |last10=Wysocka |first10=Joanna |date=2023-08-11 |title=A genome-wide genetic screen uncovers determinants of human pigmentation |journal=Science |language=en |volume=381 |issue=6658 |pages=eade6289 |doi=10.1126/science.ade6289 |pmid=37561850 |s2cid=260776374 |issn=0036-8075|pmc=10901463 }}

{{Main|Dark skin}}

All modern humans share a common ancestor who lived around 200,000 years ago in Africa.{{cite journal |title=Correcting for purifying selection: an improved human mitochondrial molecular clock |journal=Am. J. Hum. Genet. |volume=84 |issue=6 |pages=740–59 |date=June 2009 |pmid=19500773 |pmc=2694979 |doi=10.1016/j.ajhg.2009.05.001 |last1=Soares |first1=P |last2=Ermini |first2=L |last3=Thomson |first3=N |last4=Mormina |first4=M |last5=Rito |first5=T |last6=Röhl |first6=A |last7=Salas |first7=A |last8=Oppenheimer |first8=S |last9=MacAulay |first9=V |last10=Richards |first10=M. B.}} Comparisons between known skin pigmentation genes in chimpanzees and modern Africans show that dark skin evolved along with the loss of body hair about 1.2 million years ago and that this common ancestor had dark skin.{{cite journal |title=Genetic Variation at the MC1R Locus and the Time since Loss of Human Body Hair |journal=Current Anthropology |volume=45 |issue=6 |pages=105–108 |year=2004b |doi=10.1086/381006 |jstor=381006|last1=Rogers |first1=Alan R. |last2=Iltis |first2=David |last3=Wooding |first3=Stephen|s2cid=224795768 }} Investigations into dark-skinned populations in South Asia and Melanesia indicate that skin pigmentation in these populations is due to the preservation of this ancestral state and not due to new variations on a previously lightened population.{{cite journal |last1=Harding |first1=R |last2=Healy |first2=E |last3=Ray |first3=A |last4=Ellis |first4=N |last5=Flanagan |first5=N |last6=Todd |first6=C |last7=Dixon |first7=C |last8=Sajantila |first8=A |last9=Jackson |first9=I |last10=Birch-Machin |first10=Mark A. |last11=Rees |first11=Jonathan L. |title=Evidence for Variable Selective Pressures at MC1R |journal=The American Journal of Human Genetics |volume=66 |pages=1351–61 |year=2000 |doi=10.1086/302863 |pmid=10733465 |issue=4 |pmc=1288200}}

File:MC1R (rs885479).png

The melanocortin 1 receptor (MC1R) gene is primarily responsible for determining whether pheomelanin and eumelanin are produced in the human body. Research shows at least 10 differences in MC1R between African and chimpanzee samples and that the gene has probably undergone a strong positive selection (a selective sweep) in early Hominins around 1.2 million years ago.{{cite journal|title=Genetic variation at the MC1R locus and the time since loss of human body hair|journal=Current Anthropology|year=2004a|volume=45|issue=1|pages=105–124|doi=10.1086/381006|last1=Rogers|first1=Alan R.|last2=Iltis|first2=David|last3=Wooding|first3=Stephen|s2cid=224795768 }} This is consistent with positive selection for the high-eumelanin phenotype seen in Africa and other environments with high UV exposure.

{{Main|Light skin}}

File:Archaeogenetic analysis of human skin pigmentation in Europe (with Asia geographic extension).png based on genetics]]

For the most part, the evolution of light skin has followed different genetic paths in European and East Asian populations.

File:KITLG (rs1881227).png

The KIT ligand (KITLG) gene is involved in the permanent survival, proliferation and migration of melanocytes.{{cite journal |last1=Wehrle-Haller |first1=Bernhard |title=The Role of Kit-Ligand in Melanocyte Development and Epidermal Homeostasis |journal=Pigment Cell Research |volume=16 |issue=3 |pages=287–96 |year=2003 |pmid=12753403 |doi=10.1034/j.1600-0749.2003.00055.x}} A mutation in this gene, A326G (rs642742[https://www.ncbi.nlm.nih.gov/projects/SNP/snp_ref.cgi?rs=642742 Reference SNP(refSNP) Cluster Report: rs642742 **clinically associated**] {{webarchive|url= https://web.archive.org/web/20180328071821/https://www.ncbi.nlm.nih.gov/projects/SNP/snp_ref.cgi?rs=642742 |date=2018-03-28 }}. Ncbi.nlm.nih.gov (2008-12-30). Retrieved 2011-02-27.), has been positively associated with variations of skin color in African-Americans of mixed West African and European descent and is estimated to account for 15–20% of the melanin difference between African and European populations.{{cite journal |last1=Miller |first1=Craig T. |last2=Beleza |first2=Sandra |last3=Pollen |first3=Alex A. |last4=Schluter |first4=Dolph |last5=Kittles |first5=Rick A. |last6=Shriver |first6=Mark D. |last7=Kingsley |first7=David M. |title=cis-Regulatory Changes in Kit Ligand Expression and Parallel Evolution of Pigmentation in Sticklebacks and Humans |journal=Cell |volume=131 |issue=6 |pages=1179–89 |year=2007 |pmid=18083106 |pmc=2900316 |doi=10.1016/j.cell.2007.10.055}}{{cite journal |title=Signals of recent positive selection in a worldwide sample of human populations |journal=Genome Research |year=2009 |volume=19 |pages=826–837 |doi=10.1101/gr.087577.108 |issue=5 |pmid=19307593 |pmc=2675971 |last1=Pickrell |first1=J. K. |last2=Coop |first2=G |last3=Novembre |first3=J |last4=Kudaravalli |first4=S |last5=Li |first5=J. Z. |last6=Absher |first6=D |last7=Srinivasan |first7=B. S. |last8=Barsh |first8=G. S. |last9=Myers |first9=R. M. |last10=Feldman |first10=M. W. |last11=Pritchard |first11=J. K. }} and occurs in over 80% of European and Asian samples, compared with less than 10% in African samples.

Studies have found two alleles in the vicinity of ASIP Agouti signalling peptide are associated with skin color variation in humans. One, rs2424984,[https://www.ncbi.nlm.nih.gov/projects/SNP/snp_ref.cgi?rs=2424984 Reference SNP(refSNP) Cluster Report: rs2424984] {{webarchive|url= https://web.archive.org/web/20160501175840/http://www.ncbi.nlm.nih.gov/projects/SNP/snp_ref.cgi?rs=2424984 |date=2016-05-01 }}. Ncbi.nlm.nih.gov (2008-12-30). Retrieved 2011-02-27. has been identified as an indicator of skin reflectance in a forensics analysis of human phenotypes across Caucasian, African-American, South Asian, East Asian, Hispanic and Native American populations{{cite journal |last1=Valenzuela |pages=315–22 |first1=Robert K. |issue=2 |last2=Henderson |first2=Miquia S. |last3=Walsh |first3=Monica H. |last4=Garrison |first4=Nanibaa' A. |last5=Kelch |first5=Jessica T. |last6=Cohen-Barak |first6=Orit |last7=Erickson |first7=Drew T. |last8=John Meaney |first8=F. |last9=Bruce Walsh |first9=J. |last10=Cheng |first10=Keith C. |last11=Ito |first11=Shosuke |last12=Wakamatsu |first12=Kazumasa |last13=Frudakis |first13=Tony |last14=Thomas |first14=Matthew |last15=Brilliant |first15=Murray H. |volume=55 |title=Predicting Phenotype from Genotype: Normal Pigmentation |year=2010 |pmid=20158590 |doi=10.1111/j.1556-4029.2009.01317.x |journal=Journal of Forensic Sciences |url=http://www.pennstatehershey.org/c/document_library/get_file?uuid=7b0b4263-ec43-40b2-9b76-f129ad14d4e9&groupId=101483 |pmc=3626268 |url-status=live |archive-url=https://web.archive.org/web/20130613160844/http://www.pennstatehershey.org/c/document_library/get_file?uuid=7b0b4263-ec43-40b2-9b76-f129ad14d4e9&groupId=101483 |archive-date=2013-06-13 }} and is about three times more common in non-African populations than in Africa.[http://hapmap.ncbi.nlm.nih.gov/cgi-perl/snp_details_phase3?name=rs2424984&source=hapmap3r3_B36&tmpl=snp_details_phase3 HapMap: SNP report for rs2424984]. Hapmap.ncbi.nlm.nih.gov (2009-10-19). Retrieved 2011-02-27. The other allele, 8188G (rs6058017{{cite web |url=https://www.ncbi.nlm.nih.gov/projects/SNP/snp_ref.cgi?rs=6058017 |title=Reference SNP (refSNP) Cluster Report: rs6058017 ** With Pathogenic allele ** |publisher=Ncbi.nlm.nih.gov |date=2006-01-28 |access-date=2015-02-03 |url-status=live |archive-url=https://web.archive.org/web/20150203174915/http://www.ncbi.nlm.nih.gov/projects/SNP/snp_ref.cgi?rs=6058017 |archive-date=2015-02-03 }}) is significantly associated with skin color variation in African-Americans and the ancestral version occurs in only 12% of European and 28% of East Asian samples compared with 80% of West African samples.{{cite journal |title=The 8818G allele of the agouti signaling protein (ASIP) gene is ancestral and is associated with darker skin color in African Americans |journal=Human Genetics |year=2005 |volume=116 |issue=5 |pages=402–6 |doi=10.1007/s00439-004-1251-2|pmid=15726415 |last1=Bonilla |first1=C |last2=Boxill |first2=L. A. |last3=Donald |first3=S. A. |last4=Williams |first4=T |last5=Sylvester |first5=N |last6=Parra |first6=E. J. |last7=Dios |first7=S |last8=Norton |first8=H. L. |last9=Shriver |first9=M. D. |last10=Kittles |first10=R. A.|s2cid=12910408 }}

A number of genes have been positively associated with the skin pigmentation difference between European and non-European populations. Mutations in SLC24A5 and SLC45A2 are believed to account for the bulk of this variation and show very strong signs of selection. A variation in TYR has also been identified as a contributor.

Research indicates the selection for the light-skin alleles of these genes in Europeans is comparatively recent, having occurred later than 20,000 years ago and perhaps as recently as 12,000 to 6,000 years ago. In the 1970s, Luca Cavalli-Sforza suggested that the selective sweep that rendered light skin ubiquitous in Europe might be correlated with the advent of farming and thus have taken place only around 6,000 years ago;{{cite journal |last1=Gibbons |first1=A. |doi=10.1126/science.316.5823.364a |title=European Skin Turned Pale Only Recently, Gene Suggests |year=2007 |pages=364a |volume=316 |journal=Science |issue=5823|pmid=17446367|s2cid=43290419 |url=http://galsatia.files.wordpress.com/2007/04/blanche_paleur.pdf |archive-url= https://web.archive.org/web/20101103171424/http://galsatia.files.wordpress.com//2007//04//blanche_paleur.pdf |archive-date=2010-11-03 |url-status=dead |access-date=2011-01-26}} "a suggestion made 30 years ago by Stanford University geneticist L. Luca Cavalli-Sforza … that the early immigrants to Europe … survived on ready-made sources of vitamin D in their diet. But when farming spread in the past 6,000 years, he argued, Europeans had fewer sources of vitamin D in their food and needed to absorb more sunlight to produce the vitamin in their skin." This scenario found support in a 2014 analysis of Mesolithic (7,000 years old) hunter-gatherer DNA from La Braña, Spain, which showed a version of these genes not corresponding with light skin color.{{cite journal |title= Derived immune and ancestral pigmentation alleles in a 7,000-year-old Mesolithic European|journal=Nature|volume=507|issue=7491|pages=225–228 |doi=10.1038/nature12960|pmid=24463515|quote=The La Braña individual carries ancestral alleles in several skin pigmentation genes, suggesting that the light skin of modern Europeans was not yet ubiquitous in Mesolithic time|year=2014|last1=Olalde|first1=Iñigo|last2=Allentoft|first2=Morten E.|last3=Sánchez-Quinto |first3=Federico|last4=Santpere|first4=Gabriel|last5=Chiang|first5=Charleston W. K.|last6=Degiorgio |first6=Michael|last7=Prado-Martinez|first7=Javier|last8=Rodríguez|first8=Juan Antonio|last9=Rasmussen |first9=Simon|last10=Quilez |first10=Javier|last11=Ramírez|first11=Oscar|last12=Marigorta|first12=Urko M. |last13=Fernández-Callejo|first13=Marcos|last14=Prada|first14=María Encina|last15=Encinas|first15=Julio Manuel Vidal|last16=Nielsen|first16=Rasmus |last17=Netea|first17=Mihai G.|last18=Novembre|first18=John |last19=Sturm|first19=Richard A.|last20=Sabeti|first20=Pardis|author20-link=Pardis Sabeti|last21=Marquès-Bonet|first21=Tomàs |last22=Navarro|first22=Arcadi|last23=Willerslev|first23=Eske |last24=Lalueza-Fox|first24=Carles |pmc=4269527|bibcode=2014Natur.507..225O}}

In 2015, researchers analysed for light skin genes in the DNA of 94 ancient skeletons ranging from 8,000 to 3,000 years old from Europe and Russia. They found c. 8,000-year-old hunter-gatherers in Spain, Luxembourg, and Hungary were dark skinned while similarly aged hunter gatherers in Sweden were light skinned (having predominately derived alleles of SLC24A5, SLC45A2 and also HERC2/OCA2). Neolithic farmers entering Europe at around the same time were intermediate, being nearly fixed for the derived SLC24A5 variant but only having the derived SLC45A2 allele in low frequencies. The SLC24A5 variant spread very rapidly throughout central and southern Europe from about 8,000 years ago, whereas the light skin variant of SLC45A2 spread throughout Europe after 5,800 years ago.{{cite journal |last=Gibbons |first=Ann |date=2 April 2015 |url=https://www.science.org/content/article/how-europeans-evolved-white-skin |title=How Europeans evolved white skin |doi=10.1126/science.aab2435 |archive-url=https://web.archive.org/web/20150414000323/http://news.sciencemag.org/archaeology/2015/04/how-europeans-evolved-white-skin |archive-date=2015-04-14 |journal=Science |access-date=13 April 2015 |url-status=live}}{{cite bioRxiv |biorxiv=10.1101/016477|title=Eight thousand years of natural selection in Europe|year=2015 |last1=Mathieson |first1=I. |last2=Lazaridis |first2=I. |last3=Rohland |first3=N. |last4=Mallick |first4=S. |last5=Llamas |first5=B. |last6=Pickrell |first6=J. |last7=Meller |first7=H. |last8=Rojo Guerra |first8=M. A. |last9=Krause |first9=J. |last10=Anthony |first10=D. |last11=Brown |first11=D. |last12=Lalueza Fox |first12=C. |last13=Cooper |first13=A. |last14=Alt |first14=K. W. |last15=Haak |first15=W. |last16=Patterson |first16=N. |last17=Reich |first17=D.}}

Some authors have expressed caution regarding the skin pigmentation predictions. According to Ju et al. (2021), in a study addressing 40,000 years of modern human history, stated:

"Relatively dark skin pigmentation in Early Upper Paleolithic Europe would be consistent with those populations being relatively poorly adapted to high-latitude conditions as a result of having recently migrated from lower latitudes. On the other hand, although we have shown that these populations carried few of the light pigmentation alleles that are segregating in present-day Europe, they may have carried different alleles that we cannot now detect."{{cite journal |journal=PNAS |volume=118 |issue=1 |date=2021 |title=The evolution of skin pigmentation-associated variation in West Eurasia |last1=Ju |first1=Dan |last2=Mathieson |first2=Ian|pages=e2009227118 |doi=10.1073/pnas.2009227118|pmid=33443182 |pmc=7817156 |bibcode=2021PNAS..11809227J |quote="Relatively dark skin pigmentation in Early Upper Paleolithic Europe would be consistent with those populations being relatively poorly adapted to high-latitude conditions as a result of having recently migrated from lower latitudes. On the other hand, although we have shown that these populations carried few of the light pigmentation alleles that are segregating in present-day Europe, they may have carried different alleles that we cannot now detect." |doi-access=free }}

Solute carrier family 24 member 5 (SLC24A5) regulates calcium in melanocytes and is important in the process of melanogenesis.{{cite journal |last1=Ginger |first1=R. S. |last2=Askew |first2=S. E. |last3=Ogborne |first3=R. M. |last4=Wilson |first4=S. |last5=Ferdinando |first5=D. |last6=Dadd |first6=T. |last7=Smith |first7=A. M. |last8=Kazi |first8=S. |last9=Szerencsei |first9=R. T. |last10=Winkfein |first10=R. J. |last11=Schnetkamp |first11=P. P. M. |last12=Green |first12=M. R. |title=SLC24A5 Encodes a trans-Golgi Network Protein with Potassium-dependent Sodium-Calcium Exchange Activity That Regulates Human Epidermal Melanogenesis |journal=Journal of Biological Chemistry |volume=283 |issue=9 |pages=5486–95 |year=2007 |pmid=18166528 |doi=10.1074/jbc.M707521200|doi-access=free }} The SLC24A5 gene's derived Ala111Thr allele (rs1426654{{Cite web |title=rs1426654 RefSNP Report |author= |work=ncbi.nlm.nih.gov |date= |access-date=15 February 2021 |url= https://www.ncbi.nlm.nih.gov/snp/rs1426654 |quote=}}) has been shown to be a major factor in light skin pigmentation and is common in Western Eurasia. Recent studies have found that the variant represents as much as 25–40% of the average skin tone difference between Europeans and West Africans.{{cite journal |last1=Lamason |first1=R. L. |last2=Mohideen |first2=MA |last3=Mest |first3=JR |last4=Wong |first4=AC |last5=Norton |first5=HL |last6=Aros |first6=MC |last7=Jurynec |first7=MJ |last8=Mao |first8=X |last9=Humphreville |first9=VR |last10=Humbert |first10=J. E. |last11=Sinha |first11=S |last12=Moore |first12=J. L. |last13=Jagadeeswaran |first13=P |last14=Zhao |first14=W |last15=Ning |first15=G |last16=Makalowska |first16=I |last17=McKeigue |first17=P. M. |last18=O'Donnell |first18=D |last19=Kittles |first19=R |last20=Parra |first20=E. J. |last21=Mangini |first21=N. J. |last22=Grunwald |first22=D. J. |last23=Shriver |first23=M. D. |last24=Canfield |first24=V. A. |last25=Cheng |first25=K. C. |title=SLC24A5, a Putative Cation Exchanger, Affects Pigmentation in Zebrafish and Humans |journal=Science |volume=310 |issue=5755 |pages=1782–6 |year=2005 |pmid=16357253 |doi=10.1126/science.1116238 |bibcode=2005Sci...310.1782L |s2cid=2245002}} This derived allele is a reliable predictor of phenotype across a range of populations.{{cite journal |last1=López |first1=Saioa |title=The Interplay between Natural Selection and Susceptibility to Melanoma on Allele 374F of SLC45A2 Gene in a South European Population |journal=PLOS ONE |volume=9 |issue=8 |pages=e104367 |date=5 August 2014 |doi=10.1371/journal.pone.0104367 |pmid=25093503 |pmc=4122405 |bibcode=2014PLoSO...9j4367L |doi-access=free }} It has been the subject of recent selection in Western Eurasia, and is fixed in European populations.{{cite journal |last1=Soejima |first1=Mikiko |last2=Koda |first2=Yoshiro |title=Population differences of two coding SNPs in pigmentation-related genes SLC24A5 and SLC45A2 |journal=International Journal of Legal Medicine |volume=121 |issue=1 |pages=36–9 |year=2006 |pmid=16847698 |doi=10.1007/s00414-006-0112-z|s2cid=11192076 }}{{cite journal |title=Skin Color Variation in Orang Asli Tribes of Peninsular Malaysia |journal=PLOS ONE |volume=7 |issue=8 |pages=e42752 |doi=10.1371/journal.pone.0042752 |year=2012 |pmid=22912732 |pmc=3418284 |bibcode=2012PLoSO...742752A |last1=Ang |first1=K. C. |last2=Ngu |first2=M. S. |last3=Reid |first3=K. P. |last4=Teh |first4=M. S. |last5=Aida |first5=Z. S. |last6=Koh |first6=D. X. |last7=Berg |first7=A |last8=Oppenheimer |first8=S |last9=Salleh |first9=H |last10=Clyde |first10=M. M. |last11=Md-Zain |first11=B. M. |last12=Canfield |first12=V. A. |last13=Cheng |first13=K. C. |doi-access=free }}

Solute carrier family 45 member 2 (SLC45A2 or MATP) aids in the transport and processing of tyrosine, a precursor to melanin. It has also been shown to be one of the significant components of the skin color of modern Europeans through its Phe374Leu (rs16891982{{Cite web |title=rs16891982 RefSNP Report - dbSNP - NCBI |url=https://www.ncbi.nlm.nih.gov/snp/rs16891982 |access-date=2022-10-02 |website=www.ncbi.nlm.nih.gov}}) allele that has been directly correlated with skin color variation across a range of populations.{{cite journal |last1=Adhikari |first1=Kaustubh |title=A GWAS in Latin Americans highlights the convergent evolution of lighter skin pigmentation in Eurasia |journal=Nature Communications |volume=10 |issue=1 |pages=358 |date=21 January 2019 |doi=10.1038/s41467-018-08147-0 |pmid=30664655 |pmc=6341102 |bibcode=2019NatCo..10..358A }}{{cite journal |last1=Deng |first1=Lian |title=Adaptation of human skin color in various populations |journal=Hereditas |volume=155 |pages=1 |date=15 June 2017 |doi=10.1186/s41065-017-0036-2 |pmid=28701907 |pmc=5502412 |doi-access=free }} This variation is ubiquitous in European populations but extremely rare elsewhere and shows strong signs of selection.{{cite journal |title=Evidence for Recent Positive Selection at the Human AIM1 Locus in a European Population |journal=Molecular Biology and Evolution |date=January 2006 |volume=23 |issue=1 |pages=179–188 |doi=10.1093/molbev/msj018 |pmid=16162863 |last1=Soejima |first1=M |last2=Tachida |first2=H |last3=Ishida |first3=T |last4=Sano |first4=A |last5=Koda |first5=Y }}

The TYR gene encodes the enzyme tyrosinase, which is involved in the production of melanin from tyrosine. It has an allele, Ser192Tyr (rs1042602[https://www.ncbi.nlm.nih.gov/projects/SNP/snp_ref.cgi?rs=1042602 Reference SNP(refSNP) Cluster Report: rs1042602 **clinically associated**] {{webarchive|url= https://web.archive.org/web/20160416220943/http://www.ncbi.nlm.nih.gov/projects/SNP/snp_ref.cgi?rs=1042602 |date=2016-04-16 }}. Ncbi.nlm.nih.gov (2008-12-30). Retrieved 2011-02-27.), found solely in 40–50% of Europeans and linked to light-colored skin in studies of South Asian{{cite journal |last1=Stokowski |first1=R |last2=Pant |first2=P |last3=Dadd |first3=T |last4=Fereday |first4=A |last5=Hinds |first5=D |last6=Jarman |first6=C |last7=Filsell |first7=W |last8=Ginger |first8=R |last9=Green |first9=M |last10=Van Der Ouderaa |first10=Frans J. |last11=Cox |first11=David R. |title=A Genomewide Association Study of Skin Pigmentation in a South Asian Population |journal=The American Journal of Human Genetics |volume=81 |pages=1119–32 |year=2007 |doi=10.1086/522235 |pmid=17999355 |issue=6 |pmc=2276347 }} and African-American{{cite journal|url=http://dl.dropbox.com/u/38568440/admixture/shriver01.pdf |title=Skin pigmentation, biogeographical ancestry and admixture mapping |journal=Human Genetics |year=2003 |volume=112 |issue=4 |pages=387–399 |doi=10.1007/s00439-002-0896-y |pmid=12579416 |last1=Shriver|first1=MD |last2=Parra|first2=EJ |last3=Dios|first3=S |last4=Bonilla |first4=C |last5=Norton|first5=H |last6=Jovel|first6=C |last7=Pfaff |first7=C |last8=Jones|first8=C |last9=Massac|first9=A |last10=Cameron|first10=N |last11=Baron|first11=A |last12=Jackson|first12=T |last13=Argyropoulos|first13=G |last14=Jin|first14=L |last15=Hoggart|first15=CJ |last16=McKeigue|first16=PM |last17=Kittles|first17=RA |s2cid=7877572 |url-status=dead |archive-url= https://web.archive.org/web/20120415112141/http://dl.dropbox.com/u/38568440/admixture/shriver01.pdf |archive-date=2012-04-15}} populations.

A number of genes known to affect skin color have alleles that show signs of positive selection in East Asian populations. Of these, only OCA2 has been directly related to skin color measurements, while DCT, MC1R and ATRN are marked as candidate genes for future study.

File:OCA2 (rs12913832).png

Oculocutaneous albinism II (OCA2) assists in the regulation of pH in melanocytes. The OCA2 gene's derived His615Arg (rs1800414{{Cite web |title=rs1800414 RefSNP Report |author= |work=ncbi.nlm.nih.gov |date= |access-date=15 February 2021 |url= https://www.ncbi.nlm.nih.gov/snp/rs1800414 |quote=}}) allele has been shown to account for about 8% of the skin tone difference between African and East Asian populations in studies of an East Asian population living in Toronto and a Chinese Han population. This variant is essentially restricted to East Asia, with highest frequencies in Eastern East Asia (49–63%), midrange frequencies in Southeast Asia, and the lowest frequencies in Western China and some Eastern European populations.{{cite journal |last1=Edwards |first1=Melissa |last2=Bigham |first2=Abigail |last3=Tan |first3=Jinze |last4=Li |first4=Shilin |last5=Gozdzik |first5=Agnes |last6=Ross |first6=Kendra |last7=Jin |first7=Li |last8=Parra |first8=Esteban J. |editor1-last=McVean |editor1-first=Gil |title=Association of the OCA2 Polymorphism His615Arg with Melanin Content in East Asian Populations: Further Evidence of Convergent Evolution of Skin Pigmentation |journal=PLOS Genetics |volume=6 |issue=3 |pages=e1000867 |year=2010 |pmid=20221248 |pmc=2832666 |doi=10.1371/journal.pgen.1000867 |doi-access=free }}{{cite journal|title=A global view of the OCA2-HERC2 region and pigmentation |year=2012 |url=http://medicine.yale.edu/labs/kidd/www/511.pdf |last1=Donnelly |doi=10.1007/s00439-011-1110-x |journal=Human Genetics |volume=131 |issue=5 |pages=683–696 |first1=Michael P. |pmid=22065085 |pmc=3325407 |last2=Paschou |first2=Peristera |last3=Grigorenko |first3=Elena |last4=Gurwitz |first4=David |last5=Barta |first5=Csaba |last6=Lu |first6=Ru-Band |last7=Zhukova |first7=Olga V. |last8=Kim |first8=Jong-Jin |last9=Siniscalco |first9=Marcello |last10=New |first10=Maria |last11=Li |first11=Hui |last12=Kajuna |first12=Sylvester L. B. |last13=Manolopoulos |first13=Vangelis G. |last14=Speed |first14=William C. |last15=Pakstis |first15=Andrew J. |last16=Kidd |first16=Judith R. |last17=Kidd |first17=Kenneth K. |archive-url=https://web.archive.org/web/20131103050619/http://medicine.yale.edu/labs/kidd/www/511.pdf |archive-date=2013-11-03 |url-status=dead}}

A number of studies have found genes linked to human skin pigmentation that have alleles with statistically significant frequencies in Chinese and East Asian populations. While not linked to measurements of skin tone variation directly, dopachrome tautomerase (DCT or TYRP2 rs2031526{{Cite web |title=rs2031526 RefSNP Report |author= |work=ncbi.nlm.nih.gov |date= |access-date=15 February 2021 |url= https://www.ncbi.nlm.nih.gov/snp/rs2031526 |quote=}}{{cite journal |title=Identifying genes underlying skin pigmentation differences among human populations|year=2006 |journal=Human Genetics|volume=120|issue=5|pages=613–621|doi=10.1007/s00439-006-0256-4 |pmid=16977434 |last1=Myles|first1=S |last2=Somel|first2=M |last3=Tang|first3=K |last4=Kelso|first4=J |last5=Stoneking|first5=M |s2cid=32371450}}), melanocortin 1 receptor (MC1R) Arg163Gln (rs885479[https://www.ncbi.nlm.nih.gov/projects/SNP/snp_ref.cgi?rs=885479 Reference SNP(refSNP) Cluster Report: rs885479] {{webarchive|url= https://web.archive.org/web/20160919022256/http://www.ncbi.nlm.nih.gov/projects/SNP/snp_ref.cgi?rs=885479 |date=2016-09-19 }}. Ncbi.nlm.nih.gov (2008-12-30). Retrieved 2011-02-27.{{cite journal |last1=Shi |first1=Peng |last2=Lu |first2=Xue Mei |last3=Luo |first3=Huai Rong |last4=Xiang-Yu |first4=Jin-Gong |last5=Zhang |first5=Ya Ping |title=Melanocortin-1 receptor gene variants in four Chinese ethnic populations |journal=Cell Research |volume=11 |issue=1 |pages=81–4 |year=2001 |pmid=11305330 |doi=10.1038/sj.cr.7290070|doi-access=free }}) and attractin (ATRN) have been indicated as potential contributors to the evolution of light skin in East Asian populations.

Tanning response in humans is controlled by a variety of genes. MC1R variants Arg151Sys (rs1805007[https://www.ncbi.nlm.nih.gov/projects/SNP/snp_ref.cgi?rs=1805007 Reference SNP(refSNP) Cluster Report: rs1805007] {{webarchive|url= https://web.archive.org/web/20161108195136/https://www.ncbi.nlm.nih.gov/projects/SNP/snp_ref.cgi?rs=1805007 |date=2016-11-08 }}. Ncbi.nlm.nih.gov (2008-12-30).), Arg160Trp (rs1805008[https://www.ncbi.nlm.nih.gov/projects/SNP/snp_ref.cgi?rs=1805008 Reference SNP(refSNP) Cluster Report: rs1805008] {{webarchive|url= https://web.archive.org/web/20161108140647/https://www.ncbi.nlm.nih.gov/projects/SNP/snp_ref.cgi?rs=1805008 |date=2016-11-08 }}. Ncbi.nlm.nih.gov (2008-12-30).), Asp294Sys (rs1805009[https://www.ncbi.nlm.nih.gov/projects/SNP/snp_ref.cgi?rs=1805009 Reference SNP(refSNP) Cluster Report: rs1805009] {{webarchive|url= https://web.archive.org/web/20161108135958/https://www.ncbi.nlm.nih.gov/projects/SNP/snp_ref.cgi?rs=1805009 |date=2016-11-08 }}. Ncbi.nlm.nih.gov (2008-12-30).), Val60Leu (rs1805005[https://www.ncbi.nlm.nih.gov/projects/SNP/snp_ref.cgi?rs=1805005 Reference SNP(refSNP) Cluster Report: rs1805005] {{webarchive|url= https://web.archive.org/web/20180328064754/https://www.ncbi.nlm.nih.gov/projects/SNP/snp_ref.cgi?rs=1805005 |date=2018-03-28 }}. Ncbi.nlm.nih.gov (2008-12-30).) and Val92Met (rs2228479[https://www.ncbi.nlm.nih.gov/projects/SNP/snp_ref.cgi?rs=2228479 Reference SNP(refSNP) Cluster Report: rs2228479] {{webarchive|url= https://web.archive.org/web/20180328111055/https://www.ncbi.nlm.nih.gov/projects/SNP/snp_ref.cgi?rs=2228479 |date=2018-03-28 }}. Ncbi.nlm.nih.gov (2008-12-30).) have been associated with reduced tanning response in European and/or East Asian populations. These alleles show no signs of positive selection and only occur in relatively small numbers, reaching a peak in Europe with around 28% of the population having at least one allele of one of the variations.{{cite journal |title=Variants of the melanocyte-stimulating hormone receptor gene are associated with red hair and fair skin in humans|journal=Nature Genetics |year=1995 |volume=11 |issue=3 |pages=328–30 |doi=10.1038/ng1195-328|pmid=7581459 |last1=Valverde|first1=P|last2=Healy|first2=E|last3=Jackson|first3=I|last4=Rees|first4=J. L.|last5=Thody|first5=A. J.|s2cid=7980311 }} A study of self-reported tanning ability and skin type in American non-Hispanic Caucasians found that SLC24A5 Phe374Leu is significantly associated with reduced tanning ability and also associated TYR Arg402Gln (rs1126809{{cite web |url=https://www.ncbi.nlm.nih.gov/SNP/snp_ref.cgi?rs=1126809 |title=Reference SNP (refSNP) Cluster Report: rs1126809 ** With Pathogenic allele ** |publisher=Ncbi.nlm.nih.gov |date=2006-01-28 |access-date=2015-02-03 |archive-url=https://web.archive.org/web/20150722102440/http://www.ncbi.nlm.nih.gov/SNP/snp_ref.cgi?rs=1126809 |archive-date=2015-07-22 |url-status=live}}), OCA2 Arg305Trp (rs1800401{{cite web |url=https://www.ncbi.nlm.nih.gov/projects/SNP/snp_ref.cgi?rs=1800401 |title=Reference SNP (refSNP) Cluster Report: rs1800401 ** With Pathogenic allele ** |publisher=Ncbi.nlm.nih.gov |date=2006-01-28 |access-date=2015-02-03 |url-status=live |archive-url=https://web.archive.org/web/20150203171523/http://www.ncbi.nlm.nih.gov/projects/SNP/snp_ref.cgi?rs=1800401 |archive-date=2015-02-03 }}) and a 2-SNP haplotype in ASIP (rs4911414[https://www.ncbi.nlm.nih.gov/projects/SNP/snp_ref.cgi?rs=4911414 Reference SNP(refSNP) Cluster Report: rs4911414 **clinically associated**] {{webarchive|url= https://web.archive.org/web/20180328061736/https://www.ncbi.nlm.nih.gov/projects/SNP/snp_ref.cgi?rs=4911414 |date=2018-03-28 }}. Ncbi.nlm.nih.gov (2008-12-30). Retrieved 2011-02-27. and rs1015362[https://www.ncbi.nlm.nih.gov/projects/SNP/snp_ref.cgi?rs=1015362 Reference SNP(refSNP) Cluster Report: rs1015362 **clinically associated**] {{webarchive|url= https://web.archive.org/web/20180328105513/https://www.ncbi.nlm.nih.gov/projects/SNP/snp_ref.cgi?rs=1015362 |date=2018-03-28 }}. Ncbi.nlm.nih.gov (2008-12-30). Retrieved 2011-02-27.) to skin type variation within a "fair/medium/olive" context.{{cite journal |last1=Nan |first1=Hongmei |last2=Kraft |first2=Peter |last3=Hunter |first3=David J. |last4=Han |first4=Jiali |title=Genetic variants in pigmentation genes, pigmentary phenotypes, and risk of skin cancer in Caucasians |journal=International Journal of Cancer |volume=125 |pages=909–17 |year=2009 |doi=10.1002/ijc.24327 |pmid=19384953 |issue=4 |pmc=2700213}}

{{Main|Albinism in humans}}

Oculocutaneous albinism (OCA) is a lack of pigment in the eyes, skin and sometimes hair that occurs in a very small fraction of the population. The four known types of OCA are caused by mutations in the TYR, OCA2, TYRP1, and SLC45A2 genes.[https://www.ncbi.nlm.nih.gov/omim/203100 Albinism, Oculocutaneous, Type IA; OCA1A] {{webarchive|url= https://web.archive.org/web/20100803161806/http://www.ncbi.nlm.nih.gov/omim/203100 |date=2010-08-03 }}, Johns Hopkins University

In hominids, the parts of the body not covered with hair, like the face and the back of the hands, start out pale in infants and turn darker as the skin is exposed to more sun. All human babies are born pale, regardless of what their adult color will be. In humans, melanin production does not peak until after puberty.

The skin of children becomes darker as they go through puberty and experience the effects of sex hormones.{{Cite web |title=Everything You Wanted to Know About Puberty (for Teens) - Nemours KidsHealth |url=https://kidshealth.org/en/teens/puberty.html |access-date=2022-05-24 |website=kidshealth.org}} This darkening is especially noticeable in the skin of the nipples, the areola of the nipples, the labia majora in females, and the scrotum in males. In some people, the armpits become slightly darker during puberty. The interaction of genetic, hormonal, and environmental factors on skin coloration with age is still not adequately understood, but it is known that men are at their darkest baseline skin color around the age of 30, without considering the effects of tanning.

Human skin color fades with age. Humans over the age of thirty experience a decrease in melanin-producing cells by about 10% to 20% per decade as melanocyte stem cells gradually die.{{Cite journal|title=Aging of the Hair Follicle Pigmentation System|journal = International Journal of Trichology|volume = 1|issue = 2|pages = 83–93|pmc = 2938584|year = 2009|last1 = Tobin|first1 = D. J.|pmid = 20927229|doi = 10.4103/0974-7753.58550 | doi-access=free }} The skin of face and hands has about twice the amount of pigment cells as unexposed areas of the body, as chronic exposure to the sun continues to stimulate melanocytes. The blotchy appearance of skin color in the face and hands of older people is due to the uneven distribution of pigment cells and to changes in the interaction between melanocytes and keratinocytes.

Women from some darker-skinned populations may have lighter skin than men so their bodies can absorb more vitamin D during pregnancy, which improves calcium absorption.

{{cite journal

|last1=Jablonski

|first1=Nina

|last2=Chaplin

|first2=George

|year=2000

|title=The evolution of human skin coloration |url=http://www.bgsu.edu/departments/chem/faculty/leontis/chem447/PDF_files/Jablonski_skin_color_2000.pdf

|url-status=dead

|journal=Journal of Human Evolution

|volume=39

|issue=1

|pages=57–106

|doi=10.1006/jhev.2000.0403

|pmid=10896812

|bibcode=2000JHumE..39...57J

|archive-url=https://web.archive.org/web/20150105164235/http://www.bgsu.edu/departments/chem/faculty/leontis/chem447/PDF_files/Jablonski_skin_color_2000.pdf

|archive-date=January 5, 2015}}

In light skinned populations, namely those of European descent, multiple different studies using up-to-date and robust statistical methods find that women have similar skin color as men.

It is unknown why skin color is sexually dimorphic in some populations. Prior to menopause, women may have darker skin than men due to the female sex hormone estrogen increasing skin pigmentation.

{{cite journal

|last=Frost

|first=Peter

|title=Human skin-color sexual dimorphism: A test of the sexual selection hypothesis

|journal=American Journal of Physical Anthropology

|volume=133

|issue=1

|date=2007

|pages=779-80; author reply 780-1

|issn=0002-9483

|doi=10.1002/ajpa.20555

|pmid=17326100

|quote=It is perhaps significant that this sex difference seems to disappear or even reverse itself when skin reflectance is close to the physiological maximum, notably in Dutch and Belgian subjects... Even after adolescence, age-related noise continues to muddy the data. Human skin may change more slowly during adulthood, but it does change. In particular, there is some evidence that skin color becomes less sexually dimorphic after 40, with some papers finding that women become non-significantly darker than men....}}

To the extent that women's skin is darker than men's results in lower rates of skin cancer in women than men.{{Cite web |title=Researchers discover genetic causes of higher melanoma risk in men |author= |work=ScienceDaily |date=21 July 2016 |access-date=15 February 2021 |url= https://www.sciencedaily.com/releases/2016/07/160721072753.htm |quote=Meanwhile, several studies have shown that female hormones promote the production of melanin, the pigment that protects the skin from the sun. Indeed, "estrogen could be the reason why women have a darker skin tone, even when the genotypes of both sexes are the same, meaning that their risk of skin cancer is lower. So much so that skin cancer is much more prevalent in men," explains Bárbara Hernando, fellow researcher at the Melanogen research group and coauthor of the study."}}

In populations where women have lighter skin than men, it has been hypothesized that the requirement for high amounts of calcium during pregnancy and lactation may be related to the dimorphism. Breastfeeding newborns, whose skeletons are growing, require high amounts of calcium intake from the mother's milk (about 4 times more than during prenatal development),{{cite journal|pmid=18689394 |last=Kovacs|first=Christine|title=Vitamin D in pregnancy and lactation: maternal, fetal, and neonatal outcomes from human and animal studies|journal=American Journal of Clinical Nutrition|year=2008|volume=88|issue=2|pages=520S–528S|doi=10.1093/ajcn/88.2.520S|doi-access=free}} part of which comes from reserves in the mother's skeleton.

Adequate vitamin D resources are needed to absorb calcium from the diet, and it has been shown that deficiencies of vitamin D and calcium increase the likelihood of various birth defects such as spina bifida and rickets. Natural selection may have led to females with lighter skin than males in some indigenous populations because women must get enough vitamin D and calcium to support the development of fetus and nursing infants and to maintain their own health. However, some authors have cast doubt on the theory that vitamin D synthesis is related to the sexual dimorphism of human skin color in these populations.{{cite journal | last1=Madrigal | first1=Lorena | last2=Kelly | first2=William | title=Human skin-color sexual dimorphism: A test of the sexual selection hypothesis | journal=American Journal of Physical Anthropology | volume=132 | issue=3 | date=2007 | issn=0002-9483 | doi=10.1002/ajpa.20453 | pages=470–482| pmid=16685728 |quote=Although Jablonski (2004) and Jablonski and Chaplin (2000) argued that production of vitamin D is the main evolutionary explanation for the origin of light skin in areas of solar radiation, others, such as Aoki (2002), were less convinced, still pointing to the lack of paleopathological evidence of rickets (Webb and Holick, 1988)...}}

The sexes also differ in how their skin color changes over time. Women's pigmentation in certain parts of their body, such as the areola and nipples, changes throughout the menstrual cycle and during pregnancy. Between 50 and 70% of pregnant women will develop the "mask of pregnancy", which refers to the browning and yellowing of the cheeks, upper lips, and forehead that occurs during pregnancy. This is caused by increases in estrogen, and it can also develop in women who take birth control pills or due to hormone replacement therapy.{{cite journal |last1=Costin|first1=G. E.|title=Human skin pigmentation: Melanocytes modulate skin color in response to stress|journal=FASEB Journal|year=2007 |volume=21|issue=4|pages=976–994|pmid=17242160|last2=Hearing|first2=V. J. |doi=10.1096/fj.06-6649rev |doi-access=free |s2cid=10713500}}

Uneven pigmentation of some sort affects most people, regardless of bioethnic background or skin color. Skin may either appear lighter, or darker than normal, or lack pigmentation at all; there may be blotchy, uneven areas, patches of brown to gray discoloration or freckling. Apart from blood-related conditions such as jaundice, carotenosis, or argyria, skin pigmentation disorders generally occur because the body produces either too much or too little melanin.

{{Main|Depigmentation}}

Some types of albinism affect only the skin and hair, while other types affect the skin, hair and eyes, and in rare cases only the eyes. All of them are caused by different genetic mutations. Albinism is a recessively inherited trait in humans where both pigmented parents may be carriers of the gene and pass it down to their children. Each child has a 25% chance of being albino and a 75% chance of having normally pigmented skin.Cummings (2011). Human Heridity Principles and Issues. Cengage 9th edition. Retrieved 2014-02-16. One common type of albinism is oculocutaneous albinism or OCA, which has many subtypes caused by different genetic mutations.

Albinism is a serious problem in areas of high sunlight intensity, leading to extreme sun sensitivity, skin cancer, and eye damage.

Albinism is more common in some parts of the world than in others, but it is estimated that 1 in 70 humans carry the gene for OCA.

The most severe type of albinism is OCA1A, which is characterized by complete, lifelong loss of melanin production, other forms of OCA1B, OCA2, OCA3, OCA4, show some form of melanin accumulation and are less severe. The four known types of OCA are caused by mutations in the TYR, OCA2, TYRP1, and SLC45A2 genes.

Albinos often face social and cultural challenges (even threats), as the condition is often a source of ridicule, racism, fear, and violence. Many cultures around the world have developed beliefs regarding people with albinism. Albinos are persecuted in Tanzania by witchdoctors, who use the body parts of albinos as ingredients in rituals and potions, as they are thought to possess magical power.BBC (27 July 2008). "Tanzania Albinos Targeted Again". BBC News (online edition). Retrieved 2010-01-03.

File:P. Sathasivam.jpg, P. Sathasivam, has vitiligo.]]

Vitiligo is a condition that causes depigmentation of sections of skin. It occurs when melanocytes die or are unable to function. The causes of vitiligo are not clear, but research suggests several possibilities, including autoimmune reactions, genetic make-up, oxidative stress, and neural or viral causes.{{cite journal |last1=Halder |first1=RM |last2=Chappell |first2=JL |title=Vitiligo update |journal=Seminars in Cutaneous Medicine and Surgery |volume=28 |issue=2 |pages=86–92 |year=2009 |pmid=19608058 |doi=10.1016/j.sder.2009.04.008|doi-broken-date=19 January 2025 }} The incidence worldwide is less than 1%.{{cite journal |title=Genetic epidemiology of vitiligo: multilocus recessivity cross-validated |journal=American Journal of Human Genetics |volume=55 |issue=5 |pages=981–90 |year=1994 |pmid=7977362 |pmc=1918341 |last1=Nath |first1=S. K. |last2=Majumder |first2=P. P. |last3=Nordlund |first3=J. J.}} Individuals affected by vitiligo sometimes suffer psychological discomfort because of their appearance.

Increased melanin production, also known as hyperpigmentation, can be a few different phenomena:

• Melasma describes the darkening of the skin. A type of Melasma is Chloasma, the skin discolorations caused by hormones. These hormonal changes are usually the result of pregnancy, birth control pills or estrogen replacement therapy.
• Solar lentigo, also known as "liver spots" or "senile freckles", refers to darkened spots on the skin caused by aging and the sun. These spots are quite common in adults with a long history of unprotected sun exposure.

Aside from sun exposure and hormones, hyperpigmentation can be caused by skin damage, such as remnants of blemishes, wounds or rashes.Cutis, August 2005, pp 19–23 This is especially true for those with darker skin tones.

The most typical cause of darkened areas of skin, brown spots or areas of discoloration is unprotected sun exposure. Once incorrectly referred to as liver spots, these pigment problems are not connected with the liver.

On lighter to medium skin tones, solar lentigenes emerge as small- to medium-sized brown patches of freckling that can grow and accumulate over time on areas of the body that receive the most unprotected sun exposure, such as the back of the hands, forearms, chest, and face. For those with darker skin colors, these discolorations can appear as patches or areas of ashen-gray skin.

{{See also|Sun tanning}}

File:Skin tanning.JPG.]]

Melanin in the skin protects the body by absorbing solar radiation. In general, the more melanin there is in the skin the more solar radiation can be absorbed. Excessive solar radiation causes direct and indirect DNA damage to the skin and the body naturally combats and seeks to repair the damage and protect the skin by creating and releasing further melanin into the skin's cells. With the production of the melanin, the skin color darkens, but can also cause sunburn. The tanning process can also be created by artificial UV radiation.

There are two different mechanisms involved. Firstly, the UVA-radiation creates oxidative stress, which in turn oxidizes existing melanin and leads to rapid darkening of the melanin, also known as IPD (immediate pigment darkening). Secondly, there is an increase in production of melanin known as melanogenesis.{{cite journal |title=Melanogenesis: a photoprotective response to DNA damage? |journal=Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis |volume=571 |issue=1–2 |pages=121–132 |year=2005 |pmid=15748643 |doi=10.1016/j.mrfmmm.2004.11.016|last1=Agar |first1=N |last2=Young |first2=A. R.|bibcode=2005MRFMM.571..121A }} Melanogenesis leads to delayed tanning and first becomes visible about 72 hours after exposure. The tan that is created by an increased melanogenesis lasts much longer than the one that is caused by oxidation of existing melanin. Tanning involves not just the increased melanin production in response to UV radiation but the thickening of the top layer of the epidermis, the stratum corneum.

A person's natural skin color affects their reaction to exposure to the sun. Generally, those who start out with darker skin color and more melanin have better abilities to tan. Individuals with very light skin and albinos have no ability to tan.{{cite book|last=Fitzpatrick|first=T. B.|title=Fitzpatrick's Dermatology in General Medicine|year=2003|publisher=McGraw-Hill|location=New York|pages=819–825|chapter=Normal skin color and general considerations of pigmentary disorders}} The biggest differences resulting from sun exposure are visible in individuals who start out with moderately pigmented brown skin: the change is dramatically visible as tan lines, where parts of the skin which tanned are delineated from unexposed skin.

Modern lifestyles and mobility have created mismatch between skin color and environment for many individuals. Vitamin D deficiencies and UVR overexposure are concerns for many. It is important for these people individually to adjust their diet and lifestyle according to their skin color, the environment they live in, and the time of year. For practical purposes, such as exposure time for sun tanning, six skin types are distinguished following Fitzpatrick (1975), listed in order of decreasing lightness:

{{Main|Fitzpatrick scale}}

The following list shows the six categories of the Fitzpatrick scale in relation to the 36 categories of the older von Luschan scale:{{cite book|first=Nina|last=Jablonski|editor-first1=Michael P. |editor-last1=Muehlenbein|title=Human Evolutionary Biology|date=2010|publisher=Cambridge University Press|isbn=978-0-521-87948-4|page=177|url=https://books.google.com/books?id=1VXX1jkhPH8C |access-date=24 May 2016}}{{cite web|title=Fitzpatrick Skin Type |url=http://www.arpansa.gov.au/pubs/RadiationProtection/FitzpatrickSkinType.pdf |publisher=Australian Radiation Protection and Nuclear Safety Agency |access-date=24 May 2016 |url-status=dead |archive-url= https://web.archive.org/web/20160331085655/http://www.arpansa.gov.au///pubs/RadiationProtection/FitzpatrickSkinType.pdf |archive-date=31 March 2016}}

Dark skin with large concentrations of melanin protects against ultraviolet light and skin cancers; light-skinned people have about a tenfold greater risk of dying from skin cancer, compared with dark-skinned persons, under equal sunlight exposure. Furthermore, UV-A rays from sunlight are believed to interact with folic acid in ways that may damage health.{{cite journal |last1=Vorobey |first1=P |last2=Steindal |first2=AE |last3=Off |first3=MK |last4=Vorobey |first4=A |last5=Moan |first5=J |title=Influence of human serum albumin on photodegradation of folic acid in solution |journal=Photochemistry and Photobiology |volume=82 |issue=3 |pages=817–22 |year=2006 |pmid=16454580 |doi=10.1562/2005-11-23-RA-739|s2cid=36351333 }} In a number of traditional societies the sun was avoided as much as possible, especially around noon when the ultraviolet radiation in sunlight is at its most intense. Midday was a time when people stayed in the shade and had the main meal followed by a nap, a practice similar to the modern siesta.

Approximately 10% of the variance in skin color occurs within regions, and approximately 90% occurs between regions.{{cite journal|title=Apportionment of global human genetic diversity based on craniometrics and skin color |year=2002|last=Relethford|first=J. H.|journal=American Journal of Physical Anthropology|issue=4 |volume=118|pages=393–8|pmid=12124919|doi=10.1002/ajpa.10079|citeseerx=10.1.1.473.5972|s2cid=8717358 }} Because skin color has been under strong selective pressure, similar skin colors can result from convergent adaptation rather than from genetic relatedness; populations with similar pigmentation may be genetically no more similar than other widely separated groups. Furthermore, in some parts of the world where people from different regions have mixed extensively, the connection between skin color and ancestry has substantially weakened.{{cite journal|title=Implications of correlations between skin color and genetic ancestry for biomedical research|journal=Nature Genetics|volume=36 |issue=11|year=2004 |pages=S54–S60 |doi=10.1038/ng1440|pmid=15508005|last1=Parra|first1=E. J.|last2=Kittles|first2=R. A. |last3=Shriver|first3=M. D. |s2cid=13712615|doi-access=free}} In Brazil, for example, skin color is not closely associated with the percentage of recent African ancestors a person has, as estimated from an analysis of genetic variants differing in frequency among continent groups.{{cite journal|title=Color and genomic ancestry in Brazilians |year=2003|journal=Proceedings of the National Academy of Sciences |issue=1|volume=100|pages=177–182 |doi=10.1073/pnas.0126614100|pmc=140919|pmid=12509516 |last1=Parra|first1=F. C.|last2=Amado|first2=R. C. |last3=Lambertucci|first3=J. R.|last4=Rocha|first4=J. |last5=Antunes|first5=C. M.|last6=Pena|first6=S. D. J. |bibcode=2003PNAS..100..177P |doi-access=free}}

In general, people living close to the equator are highly darkly pigmented, and those living near the poles are generally very lightly pigmented. The rest of humanity shows a high degree of skin color variation between these two extremes, generally correlating with UV exposure. The main exception to this rule is in the New World, where people have only lived for about 10,000 to 15,000 years and show a less pronounced degree of skin pigmentation.

In recent times, humans have become increasingly mobile as a consequence of improved technology, domestication, environmental change, strong curiosity, and risk-taking. Migrations over the last 4000 years, and especially the last 400 years, have been the fastest in human history and have led to many people settling in places far away from their ancestral homelands. This means that skin colors today are not as confined to geographical location as they were previously.

{{Main|Discrimination based on skin color}}

File:Felix von Luschan Skin Color chart.svg]]

According to classical scholar Frank Snowden, skin color did not determine social status in ancient Egypt, Greece or Rome. These ancient civilizations viewed relations between the major power and the subordinate state as more significant in a person's status than their skin colors.{{cite book|last=Snowden|first=Frank M. |author-link=Frank M. Snowden Jr.|title=Blacks in Antiquity: Ethiopians in the Greco-Roman Experience|url=https://books.google.com/books?id=37MTRCr9oAUC|year=1970|publisher=Harvard University Press|isbn=978-0-674-07626-6}}{{Page needed|date=February 2021}}

Some social groups favor specific skin coloring. The preferred skin tone varies by culture and has varied over time. A number of indigenous African groups, such as the Maasai, associated pale skin with being cursed or caused by evil spirits associated with witchcraft. They would abandon their children born with conditions such as albinism and showed a sexual preference for darker skin.[http://allafrica.com/stories/200909101054.html Africa: Dispelling Myths about Albinism] {{webarchive|url= https://web.archive.org/web/20110622125145/http://allafrica.com/stories/200909101054.html |date=2011-06-22 }}, Pambazuka News, 10 September 2009

Many cultures have historically favored lighter skin for women. Before the Industrial Revolution, inhabitants of the continent of Europe preferred pale skin, which they interpreted as a sign of high social status. The poorer classes worked outdoors and got darker skin from exposure to the sun, while the upper class stayed indoors and had light skin. Hence light skin became associated with wealth and high position.{{cite web|first= Karl|last= Kruszelnicki|title= News in Science: Skin Colour 1|date= March 1, 2001|publisher= abc.net.au|access-date= May 25, 2014|url= http://www.abc.net.au/science/articles/2001/03/01/249992.htm?site=science/greatmomentsinscience |archive-url= https://web.archive.org/web/20131228122132/http://www.abc.net.au/science/articles/2001/03/01/249992.htm?site=science%2Fgreatmomentsinscience|archive-date= December 28, 2013 |url-status=live}} Women would put lead-based cosmetics on their skin to whiten their skin tone artificially.{{cite journal |last1=Agredano |title=Accessibility to air travel correlates strongly with increasing melanoma incidence |journal= Melanoma Research |date=February 2006 |volume=16 |issue=1 |pmid=16432460 |pages=77–81 |doi= 10.1097/01.cmr.0000195696.50390.23 |s2cid=6462810}} However, when not strictly monitored, these cosmetics caused lead poisoning.

Colonization and enslavement was a cause of discrimination due to skin color and racism.{{cite web|first= Ron |last= Hall |title= The Psychogenesis of Color Based Racism: Implications of Projection for Dark-Skinned Puertorriqueños|access-date= 2012-09-25 |url= http://www.jsri.msu.edu/RandS/research/irr/rr21.pdf|archive-date= January 6, 2011|archive-url= https://web.archive.org/web/20110106160600/http://www.jsri.msu.edu/RandS/research/irr/rr21.pdf |work=Julian Samora Research Institute, Michigan State University |year=1997}} Slavery in the Americas led to the perception that lighter-skinned African-Americans were more intelligent and cooperative. Such lighter-skinned individuals had a greater likelihood of receiving preferential treatment from overseers and for opportunities for higher education.{{cite news|url= http://www.sptimes.com/2003/08/31/Columns/The_paper_bag_test.shtml |title=The Paper Bag Test |newspaper=St. Petersburg Times |date=2003-08-31 |access-date=2014-03-23 |url-status=live |archive-url= https://web.archive.org/web/20130806113724/http://www.sptimes.com/2003/08/31/Columns/The_paper_bag_test.shtml |archive-date=2013-08-06}} The preference for fair skin remained prominent until the end of the Gilded Age, but racial stereotypes about worth and beauty persisted throughout the 20th century.{{cite news|first1=Jill |last1=Nelson |title=Straight, No Chaser—How I Became a Grown-Up Black Woman— WHO'S THE FAIREST OF THEM ALL? |work=The New York Times |year=1997 |url= http://comminfo.rutgers.edu/professional-development/childlit/books/Straight.PDF |access-date=2009-11-06 |url-status=live |archive-url= https://web.archive.org/web/20110510212534/http://comminfo.rutgers.edu/professional-development/childlit/books/Straight.PDF |archive-date=2011-05-10}}

A preference for fair or lighter skin continues in some countries, including Latin American countries where whites form a minority.{{cite news|url= http://www.post-gazette.com/lifestyle/2006/12/26/Documentary-studies-renew-debate-about-skin-color-s-impact/stories/200612260092|title= Documentary, Studies Renew Debate About Skin Color's Impact|work= Pittsburgh Post-Gazette|date= 2006-12-26|access-date= 2014-03-23|url-status= live|archive-url= https://web.archive.org/web/20140130034050/http://www.post-gazette.com/lifestyle/2006/12/26/Documentary-studies-renew-debate-about-skin-color-s-impact/stories/200612260092|archive-date= 2014-01-30}} In Brazil, a dark-skinned person is more likely to experience discrimination.{{cite news|url= http://www.miamiherald.com/multimedia/news/afrolatin/part5/index.html|title= Racism Takes Many Hues|work= Miami Herald|date= 2007-08-24|access-date= 2014-03-23|url-status= live|archive-url= https://web.archive.org/web/20130223175545/http://www.miamiherald.com/multimedia/news/afrolatin/part5/index.html|archive-date= 2013-02-23}}

Significant exceptions to a preference for lighter skin started to appear in Western culture in the mid-20th century.{{cite book|last1= Singer |first1= Merrill |first2= Hans |last2= Beyer |author-link= Merrill Singer|title= Killer Commodities: Public Health and the Corporate Production of Harm|url= https://books.google.com/books?id=64xpa-rhHLgC&q=sun+tan+lower+class&pg=PA151|access-date= 2009-09-11 |date= 28 July 2008|publisher= AltaMira Press|isbn= 978-0-7591-0979-7|page= 151|quote= Harris investigated the history of the parasol... everywhere ordinary people were forbidden to protect themselves with such devices "pallid skin became a marker of upper-class status". At the beginning of the 20th Century, in the United States, lighter-skinned people avoided the sun... Tanned skin was considered lower class.}} Though sun-tanned skin was once associated with the sun-exposed manual labor of the lower class, the associations became dramatically reversed during this time—a change usually credited to the trendsetting Frenchwoman Coco Chanel (1883–1971) presenting tanned skin as fashionable, healthy, and luxurious.{{cite book|last= Koskoff|first= Sharon |title= Art Deco of the Palm Beaches|url= https://books.google.com/books?id=RHdeo6uvlfYC&q=%22Coco%20Chanel%22%20%22Josephine%20Baker%22%20tan&pg=PA2|access-date= 2009-09-11 |date= 28 May 2007|publisher= Arcadia Publishing|isbn= 978-0-7385-4415-1|page= 2|quote= In 1920s France, the caramel-skinned entertainer Josephine Baker became a Parisian idol. Concurrently, fashion designer Coco Chanel was "bronzed" while cruising on a yacht. A winter tan became a symbol of the leisure class and showed you could afford to travel to exotic climates.}}

Many people within the United States regard tanned skin as both more attractive and healthier than pale or very dark skin.{{cite journal|last1= Geller|first1= A. C.|last2= Colditz|first2= G.|last3= Oliveria|first3= S.|last4= Emmons|first4= K.|last5= Jorgensen|first5= C.|last6= Aweh|first6= G. N.|last7= Frazier|first7= A. L.|title= Use of Sunscreen, Sunburning Rates, and Tanning Bed Use Among More Than 10 000 US Children and Adolescents|journal= Pediatrics|date= 1 June 2002|volume= 109|issue= 6|pages= 1009–1014|doi= 10.1542/peds.109.6.1009|pmid= 12042536}}{{cite journal|url= http://www3.interscience.wiley.com/journal/119318887/abstract?CRETRY=1&SRETRY=0 |archive-url= https://archive.today/20130105060850/http://www3.interscience.wiley.com/journal/119318887/abstract?CRETRY=1&SRETRY=0 |url-status= dead |archive-date= 2013-01-05 |title= Effects of Suntan on Judgements of Healthiness and Attractiveness by Adolescents |journal= Journal of Applied Social Psychology |volume= 22 |issue= 2 |pages= 157–172 |date= 2006-07-31 |doi= 10.1111/j.1559-1816.1992.tb01527.x|last1= Broadstock |first1= Marita |last2= Borland |first2= Ron |last3= Gason |first3= Robyn }}{{cite journal|doi= 10.1111/j.1559-1816.1993.tb01039.x|url= http://www3.interscience.wiley.com/journal/119292742/abstract |archive-url= https://archive.today/20130105084812/http://www3.interscience.wiley.com/journal/119292742/abstract |url-status= dead |archive-date= 2013-01-05 |title= The Social Psychology of Tanning and Sunscreen Use: Self-Presentational Motives as a Predictor of Health Risk |journal= Journal of Applied Social Psychology |volume= 23 |issue= 17 |pages= 1390–1406 |date= 2006-07-31|last1= Leary |first1= Mark R. |last2= Jones |first2= Jody L.}} Pale skin has become associated with indoor office-work while tanned skin has become associated with increased leisure time, sportiness and good health that comes with wealth and higher social status. Studies have also emerged indicating that the degree of tanning is directly related to how attractive a young woman is.{{cite journal |last1= Leary |first1= Mark R. |last2= Jones |first2= Jody L. |title= The Social Psychology of Tanning and Sunscreen Use: Self-Presentational Motives as a Predictor of Health Risk |journal= Journal of Applied Social Psychology |volume= 23 |pages= 1390–406 |year= 1993 |doi= 10.1111/j.1559-1816.1993.tb01039.x |issue= 17}}

{{cite journal

|title = Fact or wishful thinking? Biased expectations in "I think I look better when I'm tanned"

|journal = American Journal of Health Behavior

|volume = 32

|issue = 3

|year = 2008

|pages = 243–52

|url = https://www.ethicshare.org/node/425236

|pmid = 18067464

|last1 = Banerjee

|first1 = S. C.

|last2 = Campo

|first2 = S

|last3 = Greene

|first3 = K

|url-status = live

|archive-url = https://web.archive.org/web/20140324020512/https://www.ethicshare.org/node/425236

|archive-date = 2014-03-24

|doi = 10.5993/AJHB.32.3.2

}}

{{Main|Skin whitening}}

File:Skin Bleaching is everywhere.jpg soaps]]

In South Asia, society regards fair skin as more attractive and associates dark skin with lower class status. This results in a massive market for skin-whitening creams.{{cite news |last= Sidner |first= Sara |title= Skin whitener advertisements labeled racist |publisher= CNN |date= 9 September 2009 |url= http://www.cnn.com/2009/WORLD/asiapcf/09/09/india.skin/index.html |quote= 'We always have a complex towards a white skin, towards foreign skin or foreign hair,' Jawed Habib says. Habib should know. He owns a chain of 140 salons located in India and across the world. 'We Indian people, we Asian people are more darker, so we want to look more fair.' … A marketing study found sales for skin whitening creams have jumped more than 100 percent in rural India and sales for male grooming products are increasing 20 percent annually. |access-date= 2009-09-11 |url-status= live |archive-url= https://web.archive.org/web/20090912195424/http://www.cnn.com/2009/WORLD/asiapcf/09/09/india.skin/index.html |archive-date= 12 September 2009 }} Fairer skin-tones also correlate to higher caste-status in the Hindu social order—although the system is not based on skin tone.{{cite news |title= Caste: Racism in all but name? |url= http://articles.timesofindia.indiatimes.com/2009-04-26/special-report/28005708_1_caste-based-discrimination-caste-discrimination-dalit-human-rights |archive-url= https://web.archive.org/web/20130522205451/http://articles.timesofindia.indiatimes.com/2009-04-26/special-report/28005708_1_caste-based-discrimination-caste-discrimination-dalit-human-rights |url-status= dead |archive-date= 22 May 2013 |location= New Delhi |first= Shobhan |last= Saxena |date= 26 April 2009 |work= The Times of India |access-date= 2012-09-20}} Actors and actresses in Indian cinema tend to have light skin tones, and Indian cinematographers have used graphics and intense lighting to achieve more "desirable" skin tones.{{cite news |title= Has skin whitening in India gone too far? |url= https://www.bbc.co.uk/news/magazine-18268914 |work= BBC News |location= London |first= Rajini |last= Vaidyanathan |date= 5 June 2012 |access-date= 2012-09-20 |url-status= live |archive-url= https://web.archive.org/web/20120906041844/http://www.bbc.co.uk/news/magazine-18268914 |archive-date= 6 September 2012 }} Fair skin tones are advertised as an asset in Indian marketing.{{cite news |title= In India's Huge Marketplace, Advertisers Find Fair Skin Sells |url= https://www.washingtonpost.com/wp-dyn/content/article/2008/01/26/AR2008012601057.html |newspaper= Washington Post |location= Washington DC |first= Rama |last= Lakshmi |date= 27 January 2008 |access-date= 2012-09-20 |url-status= live |archive-url= https://web.archive.org/web/20131010072059/http://www.washingtonpost.com/wp-dyn/content/article/2008/01/26/AR2008012601057.html |archive-date= 10 October 2013 }}

In 2013, 77% of Nigerian women, 52% of Senegalese women, and 25% of Malian women were using lightening products.{{Cite news |last1=Fihlani |first1=Pumza |date=January 2013 |title=Africa: Where black is not really beautiful |work=BBC News |url=https://www.bbc.com/news/world-africa-20444798}}{{Cite journal |last1=Jacobs |first1=Meagan |last2=Levine |first2=Susan |last3=Abney |first3=Kate |last4=Davids |first4=Lester |year=2016 |title=Fifty shades of African lightness: A bio-psychosocial review of the global phenomenon of skin lightening practices |journal=Journal of Public Health in Africa |volume=7 |issue=2 |page=552 |doi=10.4081/jphia.2016.552 |pmc=5345401 |pmid=28299156}} In 2020, Der Spiegel reported that in Ghana, "When You Are Light-Skinned, You Earn More", and that "[s]ome pregnant women take tablets in the hopes that it will lead their child to be born with fair skin. Some apply bleaching lotion [...] to their babies, in the hopes that it will improve their child's chances."{{cite web |surname=Backhaus |given=Anne |date=2020-06-16 |title=Skin Bleaching in Ghana: "When You Are Light-Skinned, You Earn More" |url=https://www.spiegel.de/international/world/skin-bleaching-in-ghana-when-you-are-light-skinned-you-earn-more-a-3a46c628-23b2-4d05-9d32-6cb6deeb4a5a |url-status=live |archive-url=https://web.archive.org/web/20201001234949/https://www.spiegel.de/international/world/skin-bleaching-in-ghana-when-you-are-light-skinned-you-earn-more-a-3a46c628-23b2-4d05-9d32-6cb6deeb4a5a-amp |archive-date=2020-10-01 |website=Spiegel International |publisher=Der Spiegel |surname2=Okunmwendia |given2=Ella |department=Global Societies}}

Skin-whitening products have remained popular over time, often due to historical beliefs and perceptions about fair skin. Sales of skin-whitening products across the world grew from $40 billion to $43 billion in 2008.{{cite news|url= http://news.medill.northwestern.edu/chicago/news.aspx?id=161243 |title= Bleaching Creams: Fade to Beautiful? |publisher= Northwestern University |date= 2010-03-10 |url-status= dead |access-date= 2014-03-23 |archive-url= https://web.archive.org/web/20110720014201/http://news.medill.northwestern.edu/chicago/news.aspx?id=161243 |archive-date= July 20, 2011 }} In South and East Asian countries, people have traditionally seen light skin as more attractive, and a preference for lighter skin remains prevalent. In ancient China and Japan, for example, pale skin can be traced back to ancient drawings depicting women and goddesses with fair skin tones.{{citation needed|date=November 2017}} In ancient China, Japan, and Southeast Asia, pale skin was seen as a sign of wealth. Thus skin-whitening cosmetic products are popular in East Asia.{{cite news|url= http://edition.cnn.com/2002/WORLD/asiapcf/east/05/13/asia.whitening/|title= Skin Deep: Dying to be White|publisher= CNN|date= 2002-05-15|access-date= 2014-03-23|url-status= live|archive-url= https://web.archive.org/web/20100408132814/http://edition.cnn.com/2002/WORLD/asiapcf/east/05/13/asia.whitening/|archive-date= 2010-04-08}}

In 2010, four out of ten women surveyed in Hong Kong, Malaysia, the Philippines and South Korea used a skin-whitening cream, and more than 60 companies globally compete for Asia's estimated $18 billion market.[http://www.pri.org/world/asia/skin-whitening-big-business-asia.html Skin whitening big business in Asia] {{webarchive|url= https://web.archive.org/web/20100726034953/http://www.pri.org/world/asia/skin-whitening-big-business-asia.html |date=2010-07-26 }}. Pri.Org. Retrieved 2011-02-27. Changes in regulations in the cosmetic industry led to skin-care companies introducing harm-free skin lighteners. In Japan, the geisha have a reputation for their white-painted faces, and the appeal of the {{Nihongo|bihaku|美白}}, or "beautiful white", ideal leads many Japanese women to avoid any form of tanning.{{cite news |title= Japanese girls choose whiter shade of pale |url= https://www.theguardian.com/japan/story/0,7369,1185335,00.html |work= Guardian Unlimited |location= London |first= Nicole |last= Mowbray |date= 4 April 2004 |access-date= 2010-05-24}}

There are exceptions to this, with Japanese fashion trends such as ganguro emphasizing tanned skin. Skin whitening is also not uncommon in Africa,{{cite news|url= http://news.bbc.co.uk/2/hi/africa/718359.stm|title= The Heavy Cost of Light Skin|work= BBC News|date= 2000-04-18|access-date= 2014-03-23|url-status= live|archive-url= https://web.archive.org/web/20140323231534/http://news.bbc.co.uk/2/hi/africa/718359.stm|archive-date= 2014-03-23}}[http://www.scienceinafrica.co.za/2004/march/skinlightening.htm "Mirror mirror on the wall, who is the FAIREST of them all?" Skin lightening] {{webarchive|url= https://web.archive.org/web/20100910013826/http://www.scienceinafrica.co.za/2004/march/skinlightening.htm |date=2010-09-10 }}. Scienceinafrica.co.za. Retrieved 2011-02-27. and several research projects have suggested a general preference for lighter skin in the African-American community.[https://www.questia.com/library/1G1-143164170/color-counts-it-is-evident-that-differing-color Color Counts: "... it is evident that differing color holds considerable importance within the black community and is measurably influencing self-esteem, prestige, and marital status." |USA Today (Society for the Advancement of Education)] {{webarchive|url= https://web.archive.org/web/20140330120654/http://www.questia.com/library/1G1-143164170/color-counts-it-is-evident-that-differing-color |date=2014-03-30 }}. Retrieved 2012-09-25. In contrast, one study on men of the Bikosso tribe in Cameroon found no preference for attractiveness of females based on lighter skin color, bringing into question the universality of earlier studies that had exclusively focused on skin-color preferences among non-African populations.{{Cite journal|doi= 10.1007/s10508-006-9093-8|pmid= 17136587|title= Human Physique and Sexual Attractiveness: Sexual Preferences of Men and Women in Bakossiland, Cameroon|journal= Archives of Sexual Behavior|volume= 36|issue= 3|pages= 369–75|year= 2006|last1= Dixson|first1= Barnaby J.|last2= Dixson|first2= Alan F.|last3= Morgan|first3= Bethan|last4= Anderson|first4= Matthew J.|s2cid= 40115821}}

{{div col|colwidth=18em}}

• Afro-textured hair
• Carnation (heraldry)
• Color terminology for race
• Olive skin
• Complexion
• Eye color
• Health effects of sunlight exposure
• Human hair color
• Human physical appearance
• Human skin
• Race (human classification)

{{div col end}}

{{Reflist}}

{{refbegin|2|indent=yes}}

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• {{cite journal|last1=Rees |first1=J.L. |last2=Flanagan |first2=N |year=1999 |title=Pigmentation, melanocortins and red hair |journal=QJM |volume=92 |issue=3 |pages=125–31 |doi=10.1093/qjmed/92.3.125 |pmid=10326071 |doi-access=free}}
• {{cite journal|last1=Relethford |first1=JH |year=2000 |title=Human skin color diversity is highest in sub-Saharan African populations |journal=Human Biology; an International Record of Research |volume=72 |issue=5 |pages=773–80 |pmid=11126724}}
• {{cite book|last=Robins |first=AH |title=Biological Perspectives on Human Pigmentation |publisher=Cambridge University Press |year=1991 |isbn=0-521-36514-7}}
• {{cite news |last=Wade |first=Nicholas |date=August 19, 2003 |title=Why Humans and Their Fur Parted Ways |work=The New York Times |page=F1 |url=https://www.nytimes.com/2003/08/19/science/why-humans-and-their-fur-parted-ways.html}} Summary of clues to the saga in which humans evolved to lose their hair and had to adjust, including turning from light skin to dark skin, together with an estimation of the time when humans invented clothing.
• {{cite book|last1=Walters|first1=KA|last2=Roberts|first2=MS |title=Dermatologic, Cosmeceutic, and Cosmetic Development: Therapeutic and Novel Approaches |publisher=Informa Healthcare|year=2008|isbn=978-0-8493-7589-7 |location=New York}}
• {{cite book|ref={{harvid|Weller et al|2008}} |last1=Weller|first1=R|last2=Hunter|first2=J |last3=Savin |first3=J |last4=Dahl|first4=M|title=Clinical Dermatology|publisher=Blackwell Publishing|year=2008 |isbn=978-1-4051-4663-0 |edition=4th |location=Malden, MA |pages=268}}

{{refend}}

{{Commons category|Human skin color}}

• [http://news.bbc.co.uk/2/hi/health/4531966.stm "Key gene 'controls skin colour{{'"}}], BBC News. SLC24A5 gene controls up to 38% of the tonal range in people with mixed European and West African ancestry
• [https://www.pbs.org/wgbh/evolution/library/07/3/text_pop/l_073_04.html "The Biology of Skin Color: Black and White"]—PBS
• [https://www.youtube.com/watch?v=hFw8mMzH5YA "The Biology of Skin Color — HHMI BioInteractive Video"]—YouTube

{{Human Evolution}}

{{Skin colors}}

{{Authority control}}

Category:Human genetics

Category:Human physiology

color

Category:Skin physiology