Human

=== Biological variation ===
{{Main|Human genetic variation}}

[[File:Genetic Variation.jpg|upright=1.3|thumb|Changes in the number and order of genes (A–D) create genetic diversity within and between population.]]
There is biological variation in the human species{{snd}}with traits such as [[blood type]], [[genetic diseases]], [[Human skull|cranial features]], [[Human face|facial features]], [[organ systems]], [[eye color]], [[hair color]] and [[hair texture|texture]], [[Human height|height]] and [[Body shape|build]], and [[Human skin color|skin color]] varying across the globe. The typical height of an adult human is between {{Convert|1.4|and|1.9|m|ftin|abbr=on}}, although this varies significantly depending on sex, [[ethnic origin]], and family bloodlines.<ref>{{cite journal | vauthors = de Beer H | title = Observations on the history of Dutch physical stature from the late-Middle Ages to the present | journal = Economics and Human Biology | volume = 2 | issue = 1 | pages = 45–55 | date = March 2004 | pmid = 15463992 | doi = 10.1016/j.ehb.2003.11.001 }}</ref><ref name="adapt2">{{cite web | vauthors = O'Neil D |title=Adapting to Climate Extremes |url=https://anthro.palomar.edu/adapt/adapt_2.htm |work=Human Biological Adaptability |publisher=Palomar College |access-date=6 January 2013 |url-status=live |archive-url= https://web.archive.org/web/20130106211840/https://anthro.palomar.edu/adapt/adapt_2.htm |archive-date=6 January 2013 }}</ref> Body size is partly determined by genes and is also significantly influenced by environmental factors such as [[diet (nutrition)|diet]], exercise, and [[sleep pattern]]s.<ref>{{cite journal | vauthors = Rask-Andersen M, Karlsson T, Ek WE, Johansson Å | title = Gene-environment interaction study for BMI reveals interactions between genetic factors and physical activity, alcohol consumption and socioeconomic status | journal = PLOS Genetics | volume = 13 | issue = 9 | pages = e1006977 | date = September 2017 | pmid = 28873402 | pmc = 5600404 | doi = 10.1371/journal.pgen.1006977 | doi-access = free }}</ref>

There is evidence that populations have adapted genetically to various external factors. The genes that allow adult humans to [[Lactose tolerance|digest lactose]] are present in high frequencies in populations that have long histories of cattle domestication and are more dependent on [[cow milk]].<ref>{{cite journal | vauthors = Beja-Pereira A, Luikart G, England PR, Bradley DG, Jann OC, Bertorelle G, Chamberlain AT, Nunes TP, Metodiev S, Ferrand N, Erhardt G | display-authors = 6 | title = Gene-culture coevolution between cattle milk protein genes and human lactase genes | journal = Nature Genetics | volume = 35 | issue = 4 | pages = 311–313 | date = December 2003 | pmid = 14634648 | doi = 10.1038/ng1263 | s2cid = 20415396 }}</ref> [[Sickle cell anemia]], which may provide increased resistance to [[malaria]], is frequent in populations where [[malaria]] is endemic.<ref name="Hedrick 2011">{{cite journal | vauthors = Hedrick PW | title = Population genetics of malaria resistance in humans | journal = Heredity | volume = 107 | issue = 4 | pages = 283–304 | date = October 2011 | pmid = 21427751 | pmc = 3182497 | doi = 10.1038/hdy.2011.16 }}</ref><ref name="Weatherall 2008">{{cite journal | vauthors = Weatherall DJ | title = Genetic variation and susceptibility to infection: the red cell and malaria | journal = British Journal of Haematology | volume = 141 | issue = 3 | pages = 276–286 | date = May 2008 | pmid = 18410566 | doi = 10.1111/j.1365-2141.2008.07085.x | s2cid = 28191911 | doi-access = free }}</ref> Populations that have for a very long time inhabited specific climates tend to have developed specific [[phenotype]]s that are beneficial for those environments{{snd}}[[Allen's rule|short stature and stocky build in cold regions]], tall and lanky in hot regions, and with high lung capacities or other [[High-altitude adaptation in humans|adaptations at high altitudes]].<ref>{{cite journal| vauthors = Shelomi M, Zeuss D |date=5 April 2017|title=Bergmann's and Allen's Rules in Native European and Mediterranean Phasmatodea |journal=Frontiers in Ecology and Evolution|volume=5|doi=10.3389/fevo.2017.00025|s2cid=34882477|issn=2296-701X|doi-access=free|hdl=11858/00-001M-0000-002C-DD87-4|hdl-access=free}}</ref> Some populations have evolved highly unique adaptations to very specific environmental conditions, such as those advantageous to ocean-dwelling lifestyles and [[freediving]] in the [[Bajau]].<ref name="Ilardo2018">{{cite journal | vauthors = Ilardo MA, Moltke I, Korneliussen TS, Cheng J, Stern AJ, Racimo F, de Barros Damgaard P, Sikora M, Seguin-Orlando A, Rasmussen S, van den Munckhof IC, Ter Horst R, Joosten LA, Netea MG, Salingkat S, Nielsen R, Willerslev E | display-authors = 6 | title = Physiological and Genetic Adaptations to Diving in Sea Nomads | journal = Cell | volume = 173 | issue = 3 | pages = 569–580.e15 | date = April 2018 | pmid = 29677510 | doi = 10.1016/j.cell.2018.03.054 | doi-access = free }}</ref>

Human hair ranges in color from [[Red hair|red]] to [[blond]] to [[Brown hair|brown]] to [[Black hair|black]], which is the most frequent.<ref>{{cite journal|vauthors=Rogers AR, Iltis D, Wooding S|year=2004|title=Genetic variation at the MC1R locus and the time since loss of human body hair|journal=Current Anthropology|volume=45|issue=1|pages=105–08|doi=10.1086/381006|s2cid=224795768}}</ref> Hair color depends on the amount of [[melanin]], with concentrations fading with increased age, leading to [[Grey hair|grey]] or even white hair. Skin color can range from [[Dark skin|darkest brown]] to [[Light skin|lightest peach]], or even nearly white or colorless in cases of [[albinism]].<ref name="roberts1">{{cite book| vauthors = Roberts D |title=Fatal Invention|publisher=The New Press|year=2011|location=London & New York}}</ref> It tends to vary [[Clinal variation|clinally]] and generally correlates with the level of [[Ultraviolet|ultraviolet radiation]] in a particular geographic area, with darker skin mostly around the equator.<ref name="jabl04">{{cite journal|vauthors=Nina J|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}}</ref> Skin darkening may have evolved as protection against ultraviolet solar radiation.<ref>{{cite journal | vauthors = Jablonski NG, Chaplin G | title = Colloquium paper: human skin pigmentation as an adaptation to UV radiation | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 107 | issue = Supplement_2 | pages = 8962–8968 | date = May 2010 | pmid = 20445093 | pmc = 3024016 | doi = 10.1073/pnas.0914628107 | bibcode = 2010PNAS..107.8962J | doi-access = free }}</ref> Light skin pigmentation protects against depletion of [[vitamin D]], which requires [[sunlight]] to make.<ref>{{cite journal | vauthors = Jablonski NG, Chaplin G | title = The evolution of human skin coloration | journal = Journal of Human Evolution | volume = 39 | issue = 1 | pages = 57–106 | date = July 2000 | pmid = 10896812 | doi = 10.1006/jhev.2000.0403 | url = https://www.bgsu.edu/departments/chem/faculty/leontis/chem447/PDF_files/Jablonski_skin_color_2000.pdf | archive-url = https://web.archive.org/web/20120114203210/https://www.bgsu.edu/departments/chem/faculty/leontis/chem447/PDF_files/Jablonski_skin_color_2000.pdf | archive-date = 14 January 2012 }}</ref> Human skin also has a capacity to darken (tan) in response to exposure to ultraviolet radiation.<ref>{{cite journal | vauthors = Harding RM, Healy E, Ray AJ, Ellis NS, Flanagan N, Todd C, Dixon C, Sajantila A, Jackson IJ, Birch-Machin MA, Rees JL | display-authors = 6 | title = Evidence for variable selective pressures at MC1R | journal = American Journal of Human Genetics | volume = 66 | issue = 4 | pages = 1351–1361 | date = April 2000 | pmid = 10733465 | pmc = 1288200 | doi = 10.1086/302863 }}</ref><ref>{{cite book | vauthors = Robin A | date = 1991 | title = Biological Perspectives on Human Pigmentation | location = Cambridge | publisher = Cambridge University Press }}</ref>[[File:Seti1a.jpg|thumb|A [[Berbers|Libyan]], a [[Nubians|Nubian]], a [[Syrian people|Syrian]], and an [[Egyptians|Egyptian]], drawing by an unknown artist after a mural of the tomb of [[Seti I]]]]

There is relatively little variation between human geographical populations, and most of the variation that occurs is at the individual level.<ref name="roberts1" /><ref name="hgp">{{cite web|title=The Science Behind the Human Genome Project|url=https://www.ornl.gov/sci/techresources/Human_Genome/project/info.shtml|url-status=dead|archive-url=https://web.archive.org/web/20130102065343/https://www.ornl.gov/sci/techresources/Human_Genome/project/info.shtml|archive-date=2 January 2013|access-date=6 January 2013|work=Human Genome Project|publisher=US Department of Energy|quote=Almost all (99.9%) nucleotide bases are exactly the same in all people.}}</ref><ref name="enr1">{{cite web| vauthors = O'Neil D | title=Ethnicity and Race: Overview|url=https://anthro.palomar.edu/ethnicity/ethnic_1.htm#return_from_ethnic_identity_question|url-status=live|archive-url=https://web.archive.org/web/20130106212622/https://anthro.palomar.edu/ethnicity/ethnic_1.htm#return_from_ethnic_identity_question|archive-date=6 January 2013|access-date=6 January 2013|publisher=Palomar College}}</ref> Much of human variation is continuous, often with no clear points of demarcation.<ref name="pmid15507998">{{cite journal | vauthors = Keita SO, Kittles RA, Royal CD, Bonney GE, Furbert-Harris P, Dunston GM, Rotimi CN | title = Conceptualizing human variation | journal = Nature Genetics | volume = 36 | issue = 11 Suppl | pages = S17-20 | date = November 2004 | pmid = 15507998 | doi = 10.1038/ng1455 | doi-access = free }}</ref><ref name="vary02">{{cite web|title=Models of Classification|url=https://anthro.palomar.edu/vary/vary_2.htm|url-status=dead|archive-url=https://web.archive.org/web/20130106212400/https://anthro.palomar.edu/vary/vary_2.htm|archive-date=6 January 2013|access-date=6 January 2013|work=Modern Human Variation|publisher=Palomar College|vauthors=O'Neil D}}</ref><ref>{{cite journal|vauthors=Jablonski N|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}}</ref><ref name="Palmie2007">{{cite journal|vauthors=Palmié S|date=May 2007|title=Genomics, divination, 'racecraft'|journal=American Ethnologist|volume=34|issue=2|pages=205–222|doi=10.1525/ae.2007.34.2.205}}</ref> Genetic data shows that no matter how population groups are defined, two people from the same population group are almost as different from each other as two people from any two different population groups.<ref>{{cite web|title=Genetic – Understanding Human Genetic Variation|url=https://science.education.nih.gov/supplements/nih1/genetic/guide/genetic_variation1.htm|url-status=dead|archive-url=https://web.archive.org/web/20130825143543/https://science.education.nih.gov/supplements/nih1/genetic/guide/genetic_variation1.htm|archive-date=25 August 2013|access-date=13 December 2013|work=Human Genetic Variation|publisher=National Institute of Health (NIH)|quote=In fact, research results consistently demonstrate that about 85 percent of all human genetic variation exists within human populations, whereas about only 15 percent of variation exists between populations.}}</ref><ref name="goodman1">{{cite web| vauthors = Goodman A |title=Interview with Alan Goodman|url=https://www.pbs.org/race/000_About/002_04-background-01-07.htm|url-status=live|archive-url=https://web.archive.org/web/20121029063805/https://www.pbs.org/race/000_About/002_04-background-01-07.htm|archive-date=29 October 2012|access-date=6 January 2013|work=Race Power of and Illusion|publisher=PBS}}</ref><ref>{{cite book| vauthors = Marks J |year=2010|chapter=Ten facts about human variation |title=Human Evolutionary Biology| veditors = Muehlenbein M |location=New York|publisher=Cambridge University Press|url=https://personal.uncc.edu/jmarks/pubs/tenfacts.pdf|url-status=dead|archive-url=https://web.archive.org/web/20120415012646/https://personal.uncc.edu/jmarks/pubs/tenfacts.pdf|archive-date=15 April 2012|access-date=5 September 2013}}</ref> Dark-skinned populations that are found in Africa, Australia, and South Asia are not closely related to each other.<ref name="jablo04">{{cite journal|vauthors=Nina J|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|quote=genetic evidence [demonstrate] that strong levels of natural selection acted about 1.2 mya to produce darkly pigmented skin in early members of the genus Homo}}</ref><ref>{{cite web|title=Overview|url=https://anthro.palomar.edu/vary/vary_1.htm|url-status=dead|archive-url=https://web.archive.org/web/20121105101522/https://anthro.palomar.edu/vary/vary_1.htm|archive-date=5 November 2012|access-date=6 January 2013|work=Modern Human Variation|publisher=Palomar College|vauthors=O'Neil D}}</ref>

Genetic research has demonstrated that human populations native to the [[African continent]] are the most genetically diverse<ref name="Jorde2000">{{cite journal | vauthors = Jorde LB, Watkins WS, Bamshad MJ, Dixon ME, Ricker CE, Seielstad MT, Batzer MA | title = The distribution of human genetic diversity: a comparison of mitochondrial, autosomal, and Y-chromosome data | journal = American Journal of Human Genetics | volume = 66 | issue = 3 | pages = 979–988 | date = March 2000 | pmid = 10712212 | pmc = 1288178 | doi = 10.1086/302825 }}</ref> and genetic diversity decreases with migratory distance from Africa, possibly the result of [[Evolutionary bottleneck|bottlenecks]] during human migration.<ref name="sciencedaily.com">{{cite web |date=19 July 2007 |title=New Research Proves Single Origin Of Humans In Africa |url=https://www.sciencedaily.com/releases/2007/07/070718140829.htm |website=[[Science Daily]] |access-date=5 September 2011 |url-status=live |archive-url=https://web.archive.org/web/20111104103559/https://www.sciencedaily.com/releases/2007/07/070718140829.htm |archive-date=4 November 2011 }}</ref><ref>{{cite journal | vauthors = Manica A, Amos W, Balloux F, Hanihara T | title = The effect of ancient population bottlenecks on human phenotypic variation | journal = Nature | volume = 448 | issue = 7151 | pages = 346–348 | date = July 2007 | pmid = 17637668 | pmc = 1978547 | doi = 10.1038/nature05951 | author-link3 = Francois Balloux | bibcode = 2007Natur.448..346M }}</ref> These non-African populations acquired new genetic inputs from local [[Interbreeding between archaic and modern humans|admixture with archaic populations]] and have much greater variation from [[Neanderthals]] and [[Denisovans]] than is found in Africa,<ref name="Bergstrom2020">{{cite journal | vauthors = Bergström A, McCarthy SA, Hui R, Almarri MA, Ayub Q, Danecek P, Chen Y, Felkel S, Hallast P, Kamm J, Blanché H, Deleuze JF, Cann H, Mallick S, Reich D, Sandhu MS, Skoglund P, Scally A, Xue Y, Durbin R, Tyler-Smith C | display-authors = 6 | title = Insights into human genetic variation and population history from 929 diverse genomes | journal = Science | volume = 367 | issue = 6484 | pages = eaay5012 | date = March 2020 | pmid = 32193295 | pmc = 7115999 | doi = 10.1126/science.aay5012 |quote=Populations in central and southern Africa, the Americas, and Oceania each harbor tens to hundreds of thousands of ''private'', common genetic variants. Most of these variants arose as new mutations rather than through archaic introgression, except in Oceanian populations, where many private variants derive from Denisovan admixture.}}</ref> though Neanderthal admixture into African populations may be underestimated.<ref name="pmid32004458">{{cite journal | vauthors = Chen L, Wolf AB, Fu W, Li L, Akey JM | title = Identifying and Interpreting Apparent Neanderthal Ancestry in African Individuals | journal = Cell | volume = 180 | issue = 4 | pages = 677–687.e16 | date = February 2020 | pmid = 32004458 | pmc = | doi = 10.1016/j.cell.2020.01.012 | s2cid = 210955842 | doi-access = free }}</ref> Furthermore, recent studies have found that populations in [[sub-Saharan Africa]], and particularly [[West Africa]], have ancestral genetic variation which predates modern humans and has been lost in most non-African populations. Some of this ancestry is thought to originate from admixture with an [[Interbreeding between archaic and modern humans#Archaic African hominins|unknown archaic hominin]] that diverged before the split of Neanderthals and modern humans.<ref name="Bergstrom2020a">{{cite journal | vauthors = Bergström A, McCarthy SA, Hui R, Almarri MA, Ayub Q, Danecek P, Chen Y, Felkel S, Hallast P, Kamm J, Blanché H, Deleuze JF, Cann H, Mallick S, Reich D, Sandhu MS, Skoglund P, Scally A, Xue Y, Durbin R, Tyler-Smith C | display-authors = 6 | title = Insights into human genetic variation and population history from 929 diverse genomes | journal = Science | volume = 367 | issue = 6484 | pages = eaay5012 | date = March 2020 | pmid = 32193295 | pmc = 7115999 | doi = 10.1126/science.aay5012 |quote=An analysis of archaic sequences in modern populations identifies ancestral genetic variation in African populations that likely predates modern humans and has been lost in most non-African populations.}}</ref><ref name="Durvasula2020">{{cite journal | vauthors = Durvasula A, Sankararaman S | title = Recovering signals of ghost archaic introgression in African populations | journal = Science Advances | volume = 6 | issue = 7 | pages = eaax5097 | date = February 2020 | pmid = 32095519 | pmc = 7015685 | doi = 10.1126/sciadv.aax5097 | bibcode = 2020SciA....6.5097D |quote=Our analyses of site frequency spectra indicate that these populations derive 2 to 19% of their genetic ancestry from an archaic population that diverged before the split of Neanderthals and modern humans.}}</ref>

Humans are a [[Gonochorism|gonochoric]] species, meaning they are divided into male and female [[sex]]es.<ref>{{Cite book|url={{GBurl|id=z4pXRaZAkdkC|q=humans are dioecious genetics|p=75}}|title=Genetics: A Conceptual Approach|vauthors=Pierce BA|date=2012|publisher=Macmillan|isbn=978-1-4292-3252-4|pages=75|language=en|access-date=30 July 2022}}</ref><ref>{{Cite book|vauthors=Muehlenbein MP|url={{GBurl|id=1VXX1jkhPH8C|q=humans are dioecious biology|pg=PT57}}}|title=Human Evolutionary Biology|date=29 July 2010|publisher=Cambridge University Press|isbn=978-0-521-87948-4|veditors=Jones J|page=74|language=en|access-date=30 July 2022}}</ref><ref>{{Cite book|vauthors=Fusco G, Minelli A|url={{GBurl|id=AKGsDwAAQBAJ|q=homo sapiens gonochoric|p=304}}|title=The Biology of Reproduction|date=10 October 2019|publisher=Cambridge University Press|isbn=978-1-108-49985-9|page=304|language=en|access-date=30 July 2022}}</ref> The greatest degree of genetic [[Sex differences in humans|variation exists between males and females]]. While the [[nucleotide diversity|nucleotide]] genetic variation of individuals of the same sex across global populations is no greater than 0.1%–0.5%, the genetic difference between [[Man|males]] and [[woman|females]] is between 1% and 2%. Males on average are 15% heavier and {{Convert|15|cm|in|abbr=on|lk=off|0}} taller than females.<ref name="Gustafsson">{{cite journal | vauthors = Gustafsson A, Lindenfors P | title = Human size evolution: no evolutionary allometric relationship between male and female stature | journal = Journal of Human Evolution | volume = 47 | issue = 4 | pages = 253–266 | date = October 2004 | pmid = 15454336 | doi = 10.1016/j.jhevol.2004.07.004 }}</ref><ref name="NHANES_III_data">{{cite journal | vauthors = Ogden CL, Fryar CD, Carroll MD, Flegal KM | title = Mean body weight, height, and body mass index, United States 1960–2002 | journal = Advance Data | volume = | issue = 347 | pages = 1–17 | date = October 2004 | pmid = 15544194 | doi = | url = https://www.cdc.gov/nchs/data/ad/ad347.pdf | archive-url = https://archive.wikiwix.com/cache/20110223153209/https://www.cdc.gov/nchs/data/ad/ad347.pdf |archive-date=23 February 2011 }}</ref> On average, men have about 40–50% more upper body strength and 20–30% more lower body strength than women at the same weight, due to higher amounts of muscle and larger muscle fibers.<ref>{{cite journal | vauthors = Miller AE, MacDougall JD, Tarnopolsky MA, Sale DG | title = Gender differences in strength and muscle fiber characteristics | journal = European Journal of Applied Physiology and Occupational Physiology | volume = 66 | issue = 3 | pages = 254–262 | year = 1993 | pmid = 8477683 | doi = 10.1007/BF00235103 | hdl-access = free | s2cid = 206772211 | hdl = 11375/22586 }}</ref> Women generally have a higher [[body fat]] percentage than men.<ref>{{Cite book | vauthors = Bredella MA |chapter=Sex Differences in Body Composition|date=2017 |title=Sex and Gender Factors Affecting Metabolic Homeostasis, Diabetes and Obesity |series=Advances in Experimental Medicine and Biology|volume=1043 |pages=9–27| veditors = Mauvais-Jarvis F |place=Cham |publisher=Springer International Publishing |doi=10.1007/978-3-319-70178-3_2 |pmid=29224088|isbn=978-3-319-70177-6 }}</ref> Women have [[Human skin color#Sexual dimorphism|lighter skin]] than men of the same population; this has been explained by a higher need for vitamin D in females during pregnancy and [[lactation]].<ref>{{cite journal | vauthors = Rahrovan S, Fanian F, Mehryan P, Humbert P, Firooz A | title = Male versus female skin: What dermatologists and cosmeticians should know | journal = International Journal of Women's Dermatology | volume = 4 | issue = 3 | pages = 122–130 | date = September 2018 | pmid = 30175213 | pmc = 6116811 | doi = 10.1016/j.ijwd.2018.03.002 }}</ref> As there are chromosomal differences between females and males, some X and Y chromosome-related conditions and [[Disease|disorders]] only affect either men or women.<ref>{{cite web|vauthors=Easter C|title=Sex Linked|url=https://www.genome.gov/genetics-glossary/Sex-Linked|access-date=18 April 2021|website=National Human Genome Research Institute|language=en|archive-date=14 April 2022|archive-url=https://web.archive.org/web/20220414183337/https://www.genome.gov/genetics-glossary/Sex-Linked|url-status=live}}</ref> After allowing for body weight and volume, the male voice is usually an [[octave]] deeper than the female voice.<ref>{{cite journal | vauthors = Puts DA, Gaulin SJ, Verdolini K | title = Dominance and the evolution of sexual dimorphism in human voice pitch. | journal = Evolution and Human Behavior | date = July 2006 | volume = 27 | issue = 4 | pages = 283–296 | doi = 10.1016/j.evolhumbehav.2005.11.003 | s2cid = 32562654 }}</ref> Women have a [[Sex differences in longevity|longer life span]] in almost every population around the world.<ref name="WHO">{{cite web | url = https://www.who.int/gender/documents/en/ | title = Gender, women, and health | archive-url = https://web.archive.org/web/20130625083240/https://www.who.int/gender/documents/en/ | archive-date=25 June 2013 | work = Reports from WHO 2002–2005 }}</ref> There are [[intersex]] conditions in the human population, however these are rare.<ref>{{Cite journal |last=Sax |first=Leonard |date=1 August 2002 |title=How common is lntersex? A response to Anne Fausto-Sterling |url=https://www.tandfonline.com/doi/full/10.1080/00224490209552139 |journal=The Journal of Sex Research |language=en |volume=39 |issue=3 |pages=174–178 |doi=10.1080/00224490209552139 |pmid=12476264 |s2cid=33795209 |issn=0022-4499}}</ref>