Human

=== Genetics ===
{{Main|Human genetics}}[[File:Human karyotype with bands and sub-bands.png|thumb|A graphical representation of the standard human [[karyotype]], including both the female (XX) and male (XY) sex chromosomes (bottom right), as well as the [[human mitochondrial genetics|mitochondrial genome]] (shown to scale as "MT" at bottom left). {{further|Karyotype}}]]

Like most animals, humans are a [[ploidy|diploid]] and [[eukaryote|eukaryotic]] species. Each [[somatic cell]] has two sets of 23 [[chromosome]]s, each set received from one parent; [[gamete]]s have only one set of chromosomes, which is a mixture of the two parental sets. Among the 23 pairs of chromosomes, there are 22 pairs of [[autosome]]s and one pair of [[sex-determination system|sex chromosomes]]. Like other mammals, humans have an [[XY sex-determination system]], so that females have the sex chromosomes XX and males have XY.<ref name="Therman1980">{{cite book | vauthors = Therman E |title=Human Chromosomes: Structure, Behavior, Effects |date=1980 |publisher=[[Springer Science+Business Media|Springer US]] |pages=112–124 |isbn=978-1-4684-0109-7 |doi=10.1007/978-1-4684-0107-3|s2cid=36686283 }}</ref> [[Gene]]s and [[Environment (biophysical)|environment]] influence human biological variation in visible characteristics, physiology, disease susceptibility and mental abilities. The exact influence of [[Environment (biophysical)|genes and environment]] on certain traits is not well understood.<ref>{{cite journal | vauthors = Edwards JH, Dent T, Kahn J | title = Monozygotic twins of different sex | journal = Journal of Medical Genetics | volume = 3 | issue = 2 | pages = 117–123 | date = June 1966 | pmid = 6007033 | pmc = 1012913 | doi = 10.1136/jmg.3.2.117 }}</ref><ref>{{cite journal | vauthors = Machin GA | title = Some causes of genotypic and phenotypic discordance in monozygotic twin pairs | journal = American Journal of Medical Genetics | volume = 61 | issue = 3 | pages = 216–228 | date = January 1996 | pmid = 8741866 | doi = 10.1002/(SICI)1096-8628(19960122)61:3<216::AID-AJMG5>3.0.CO;2-S }}</ref>

While no humans{{snd}}not even [[monozygotic twins]]{{snd}}are genetically identical,<ref>{{cite journal | vauthors = Jonsson H, Magnusdottir E, Eggertsson HP, Stefansson OA, Arnadottir GA, Eiriksson O, Zink F, Helgason EA, Jonsdottir I, Gylfason A, Jonasdottir A, Jonasdottir A, Beyter D, Steingrimsdottir T, Norddahl GL, Magnusson OT, Masson G, Halldorsson BV, Thorsteinsdottir U, Helgason A, Sulem P, Gudbjartsson DF, Stefansson K | display-authors = 6 | title = Differences between germline genomes of monozygotic twins | journal = Nature Genetics | volume = 53 | issue = 1 | pages = 27–34 | date = January 2021 | pmid = 33414551 | doi = 10.1038/s41588-020-00755-1 | s2cid = 230986741 }}</ref> two humans on average will have a genetic similarity of 99.5%-99.9%.<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=Between any two humans, the amount of genetic variation{{snd}}biochemical individuality{{snd}}is about 0.1%.}}</ref><ref>{{cite journal | vauthors = Levy S, Sutton G, Ng PC, Feuk L, Halpern AL, Walenz BP, Axelrod N, Huang J, Kirkness EF, Denisov G, Lin Y, MacDonald JR, Pang AW, Shago M, Stockwell TB, Tsiamouri A, Bafna V, Bansal V, Kravitz SA, Busam DA, Beeson KY, McIntosh TC, Remington KA, Abril JF, Gill J, Borman J, Rogers YH, Frazier ME, Scherer SW, Strausberg RL, Venter JC | display-authors = 6 | title = The diploid genome sequence of an individual human | journal = PLOS Biology | volume = 5 | issue = 10 | pages = e254 | date = September 2007 | pmid = 17803354 | pmc = 1964779 | doi = 10.1371/journal.pbio.0050254 | doi-access = free }}</ref> This makes them more [[Human genetic variation|homogeneous]] than other great apes, including chimpanzees.<ref name="REGWG2005">{{cite journal | vauthors = ((Race, Ethnicity, and Genetics Working Group)) | title = The use of racial, ethnic, and ancestral categories in human genetics research | journal = American Journal of Human Genetics | volume = 77 | issue = 4 | pages = 519–532 | date = October 2005 | pmid = 16175499 | pmc = 1275602 | doi = 10.1086/491747 }}</ref><ref name="oxf">{{cite web|title=Chimps show much greater genetic diversity than humans|url=https://www.ox.ac.uk/media/news_stories/2012/120302.html|url-status=dead|archive-url=https://web.archive.org/web/20131218091207/https://www.ox.ac.uk/media/news_stories/2012/120302.html|archive-date=18 December 2013|access-date=13 December 2013|work=Media|publisher=University of Oxford}}</ref> This small variation in human DNA compared to many other species suggests a [[population bottleneck]] during the [[Late Pleistocene]] (around 100,000 years ago), in which the human population was reduced to a small number of breeding pairs.<ref name="Harpending1998">{{cite journal | vauthors = Harpending HC, Batzer MA, Gurven M, Jorde LB, Rogers AR, Sherry ST | title = Genetic traces of ancient demography | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 95 | issue = 4 | pages = 1961–1967 | date = February 1998 | pmid = 9465125 | pmc = 19224 | doi = 10.1073/pnas.95.4.1961 | bibcode = 1998PNAS...95.1961H | doi-access = free }}</ref><ref name="Jorde1997">{{cite journal | vauthors = Jorde LB, Rogers AR, Bamshad M, Watkins WS, Krakowiak P, Sung S, Kere J, Harpending HC | display-authors = 6 | title = Microsatellite diversity and the demographic history of modern humans | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 94 | issue = 7 | pages = 3100–3103 | date = April 1997 | pmid = 9096352 | pmc = 20328 | doi = 10.1073/pnas.94.7.3100 | bibcode = 1997PNAS...94.3100J | doi-access = free }}</ref> The forces of [[natural selection]] have continued to operate on human populations, with evidence that certain regions of the [[genome]] display [[directional selection]] in the past 15,000 years.<ref name="urlNYT">{{cite news| vauthors = Wade N |date=7 March 2007|title=Still Evolving, Human Genes Tell New Story|newspaper=The New York Times|url=https://www.nytimes.com/2006/03/07/science/07evolve.html|url-status=live|access-date=13 February 2012|archive-url=https://web.archive.org/web/20120114232231/https://www.nytimes.com/2006/03/07/science/07evolve.html|archive-date=14 January 2012}}</ref>

The [[human genome]] was first sequenced in 2001<ref>{{cite journal | vauthors = Pennisi E | author-link=Elizabeth Pennisi | title = The human genome | journal = Science | volume = 291 | issue = 5507 | pages = 1177–1180 | date = February 2001 | pmid = 11233420 | doi = 10.1126/science.291.5507.1177 | s2cid = 38355565 }}</ref> and by 2020 hundreds of thousands of genomes had been sequenced.<ref>{{cite journal | vauthors = Rotimi CN, Adeyemo AA | title = From one human genome to a complex tapestry of ancestry | journal = Nature | volume = 590 | issue = 7845 | pages = 220–221 | date = February 2021 | pmid = 33568827 | doi = 10.1038/d41586-021-00237-2 | bibcode = 2021Natur.590..220R | s2cid = 231882262 }}</ref> In 2012 the [[International HapMap Project]] had compared the genomes of 1,184 individuals from 11 populations and identified 1.6 million [[single nucleotide polymorphisms]].<ref>{{cite journal | vauthors = Altshuler DM, Gibbs RA, Peltonen L, Altshuler DM, Gibbs RA, Peltonen L, Dermitzakis E, Schaffner SF, Yu F, Peltonen L, Dermitzakis E, Bonnen PE, Altshuler DM, Gibbs RA, de Bakker PI, Deloukas P, Gabriel SB, Gwilliam R, Hunt S, Inouye M, Jia X, Palotie A, Parkin M, Whittaker P, Yu F, Chang K, Hawes A, Lewis LR, Ren Y, Wheeler D, Gibbs RA, Muzny DM, Barnes C, Darvishi K, Hurles M, Korn JM, Kristiansson K, Lee C, McCarrol SA, Nemesh J, Dermitzakis E, Keinan A, Montgomery SB, Pollack S, Price AL, Soranzo N, Bonnen PE, Gibbs RA, Gonzaga-Jauregui C, Keinan A, Price AL, Yu F, Anttila V, Brodeur W, Daly MJ, Leslie S, McVean G, Moutsianas L, Nguyen H, Schaffner SF, Zhang Q, Ghori MJ, McGinnis R, McLaren W, Pollack S, Price AL, Schaffner SF, Takeuchi F, Grossman SR, Shlyakhter I, Hostetter EB, Sabeti PC, Adebamowo CA, Foster MW, Gordon DR, Licinio J, Manca MC, Marshall PA, Matsuda I, Ngare D, Wang VO, Reddy D, Rotimi CN, Royal CD, Sharp RR, Zeng C, Brooks LD, McEwen JE | display-authors = 6 | title = Integrating common and rare genetic variation in diverse human populations | journal = Nature | volume = 467 | issue = 7311 | pages = 52–58 | date = September 2010 | pmid = 20811451 | doi = 10.1038/nature09298 | pmc = 3173859 | bibcode = 2010Natur.467...52T }}</ref> African populations harbor the highest number of private genetic variants. While many of the common variants found in populations outside of Africa are also found on the African continent, there are still large numbers that are private to these regions, especially [[Oceania]] and [[the Americas]].<ref name="Bergstrom2020" /> By 2010 estimates, humans have approximately 22,000 genes.<ref name=Pertea2010>{{cite journal | vauthors = Pertea M, Salzberg SL | title = Between a chicken and a grape: estimating the number of human genes | journal = Genome Biology | volume = 11 | issue = 5 | page = 206 | year = 2010 | pmid = 20441615 | pmc = 2898077 | doi = 10.1186/gb-2010-11-5-206 | doi-access = free }}</ref> By comparing [[mtDNA|mitochondrial DNA]], which is inherited only from the mother, geneticists have concluded that the last female common ancestor whose [[genetic marker]] is found in all modern humans, the so-called [[mitochondrial Eve]], must have lived around 90,000 to 200,000 years ago.<ref name="pmid3025745">{{cite journal | vauthors = Cann RL, Stoneking M, Wilson AC | title = Mitochondrial DNA and human evolution | journal = Nature | volume = 325 | issue = 6099 | pages = 31–36 | year = 1987 | pmid = 3025745 | doi = 10.1038/325031a0 | bibcode = 1987Natur.325...31C | s2cid = 4285418 }}</ref><ref>{{cite journal | vauthors = Soares P, Ermini L, Thomson N, Mormina M, Rito T, Röhl A, Salas A, Oppenheimer S, Macaulay V, Richards MB | display-authors = 6 | title = Correcting for purifying selection: an improved human mitochondrial molecular clock | journal = American Journal of Human Genetics | volume = 84 | issue = 6 | pages = 740–759 | date = June 2009 | pmid = 19500773 | pmc = 2694979 | doi = 10.1016/j.ajhg.2009.05.001}}</ref><ref>{{Cite web|url=https://www.leeds.ac.uk/news/article/245/new_molecular_clock_aids_dating_of_human_migration_history|title=University of Leeds &#124; News > Technology > New 'molecular clock' aids dating of human migration history|date=20 August 2017|archive-url=https://web.archive.org/web/20170820230218/https://www.leeds.ac.uk/news/article/245/new_molecular_clock_aids_dating_of_human_migration_history|archive-date=20 August 2017}}</ref><ref name="poz">{{cite journal | vauthors = Poznik GD, Henn BM, Yee MC, Sliwerska E, Euskirchen GM, Lin AA, Snyder M, Quintana-Murci L, Kidd JM, Underhill PA, Bustamante CD | display-authors = 6 | title = Sequencing Y chromosomes resolves discrepancy in time to common ancestor of males versus females | journal = Science | volume = 341 | issue = 6145 | pages = 562–565 | date = August 2013 | pmid = 23908239 | pmc = 4032117 | doi = 10.1126/science.1237619 | bibcode = 2013Sci...341..562P }}</ref>