Editing Digit ratio (section)

==Geographic and ethnic variation==
Several studies have presented evidence that digit ratios are heritable.<ref name="Paul_2006">{{cite journal | vauthors = Paul SN, Kato BS, Hunkin JL, Vivekanandan S, Spector TD | title = The big finger: the second to fourth digit ratio is a predictor of sporting ability in women | journal = British Journal of Sports Medicine | volume = 40 | issue = 12 | pages = 981–983 | date = December 2006 | pmid = 17008344 | pmc = 2577466 | doi = 10.1136/bjsm.2006.027193 }}</ref><ref>{{cite journal | vauthors = Gobrogge KL, Breedlove SM, Klump KL | title = Genetic and environmental influences on 2D:4D finger length ratios: a study of monozygotic and dizygotic male and female twins | url = https://archive.org/details/sim_archives-of-sexual-behavior_2008-02_37_1/page/112 | journal = Archives of Sexual Behavior | volume = 37 | issue = 1 | pages = 112–118 | date = February 2008 | pmid = 18074216 | doi = 10.1007/s10508-007-9272-2 | author2-link = Marc Breedlove | s2cid = 41921265 }}</ref>

Manning and colleagues have reported that 2D:4D ratios vary slightly between different ethnic groups. In a study of [[Han Chinese|Han]], [[Berbers|Berber]], [[Uyghurs|Uygur]] and [[Jamaicans|Jamaican]] children, Manning ''et al.'' found that Han children had the highest mean values of 2D:4D (0.954±0.032). They were followed by the Berbers (0.950±0.033), then the Uygurs (0.946±0.037) and the Jamaican children had the lowest mean 2D:4D (0.935±0.035).<ref name="Manning_2000">{{cite journal | vauthors = Manning JT, Barley L, Walton J, Lewis-Jones DI, Trivers RL, Singh D, Thornhill R, Rohde P, Bereczkei T, Henzi P, Soler M, Szwed A | display-authors = 6 | title = The 2nd:4th digit ratio, sexual dimorphism, population differences, and reproductive success. evidence for sexually antagonistic genes? | journal = Evolution and Human Behavior | volume = 21 | issue = 3 | pages = 163–183 | date = May 2000 | pmid = 10828555 | doi = 10.1016/S1090-5138(00)00029-5 | bibcode = 2000EHumB..21..163M }}</ref><ref name="Manning_2004">{{cite journal | vauthors = Manning JT, Stewart A, Bundred PE, Trivers RL | title = Sex and ethnic differences in 2nd to 4th digit ratio of children | journal = Early Human Development | volume = 80 | issue = 2 | pages = 161–168 | date = November 2004 | pmid = 15500996 | doi = 10.1016/j.earlhumdev.2004.06.004 }}</ref> This variation is far larger than the differences between sexes; in Manning's words, "There's more difference between a [[Polish people|Pole]] and a [[Finnish people|Finn]], than a man and a woman."<ref name=pmid10761903>{{cite journal | vauthors = Williams TJ, Pepitone ME, Christensen SE, Cooke BM, Huberman AD, Breedlove NJ, Breedlove TJ, Jordan CL, Breedlove SM | display-authors = 6 | title = Finger-length ratios and sexual orientation | journal = Nature | volume = 404 | issue = 6777 | pages = 455–456 | date = March 2000 | pmid = 10761903 | doi = 10.1038/35006555 | s2cid = 205005405 | bibcode = 2000Natur.404..455W }}</ref>

In 2007, Manning ''et al.'' reported further evidence of ethnic variation in mean 2D:4D, with higher ratios for Whites, non-Chinese Asians and Middle-Easterners, and lower ratios in Chinese and Black samples.<ref>{{cite journal | vauthors = Manning JT, Churchill AJ, Peters M | title = The effects of sex, ethnicity, and sexual orientation on self-measured digit ratio (2D:4D) | url = https://archive.org/details/sim_archives-of-sexual-behavior_2007-04_36_2/page/223 | journal = Archives of Sexual Behavior | volume = 36 | issue = 2 | pages = 223–233 | date = April 2007 | pmid = 17373585 | doi = 10.1007/s10508-007-9171-6 | s2cid = 2042042 }}</ref> A 2008 study by Lu ''et al.'' found that the mean values of 2D:4D of the [[Hui people|Hui]] and the Han in [[Ningxia]] were lower than those in European countries like Britain.<ref>{{Cite journal | vauthors = Lu H, Huo ZH, Shi ZY, Peng L, Dang J, Jiao HY, Zhu YS, Zhong HJ, Chen YT | display-authors = 6 | title = Study on the digit ratio of Hui and Han ethnic groups in Ningxia. | journal = Acta Anatomica Sinica | date = 2008 | volume = 39 | issue = 2 | pages = 267 | url = http://en.cnki.com.cn/Article_en/CJFDTOTAL-JPXB200802033.htm | access-date = 7 November 2016 | archive-date = 7 November 2016 | archive-url = https://web.archive.org/web/20161107221950/http://en.cnki.com.cn/Article_en/CJFDTOTAL-JPXB200802033.htm | url-status = dead }}</ref>

Two studies explored the question of whether geographical differences in 2D:4D ratios were caused by gene pool differences or whether some environmental variable associated with latitude might be involved (e.g., exposure to sunlight or different day-length patterns). The conclusions were that geographical differences in 2D:4D ratio were caused by genetic pool differences, not by geographical latitude.<ref>{{cite journal | vauthors = Loehlin JC, McFadden D, Medland SE, Martin NG | title = Population differences in finger-length ratios: ethnicity or latitude? | url = https://archive.org/details/sim_archives-of-sexual-behavior_2006-12_35_6/page/739 | journal = Archives of Sexual Behavior | volume = 35 | issue = 6 | pages = 739–742 | date = December 2006 | pmid = 16688484 | doi = 10.1007/s10508-006-9039-1 | s2cid = 4763807 | citeseerx = 10.1.1.579.6269 }}</ref><ref>{{cite journal | vauthors = Xu Y, Zheng Y | title = The digit ratio (2D:4D) in China: A meta-analysis | journal = American Journal of Human Biology | volume = 27 | issue = 3 | pages = 304–309 | date = 6 May 2015 | pmid = 25284473 | doi = 10.1002/ajhb.22639 | s2cid = 40725875 }}</ref>

[[Consanguinous|Consanguineous]] parentage ([[inbreeding]]) has been found to lower the 2D:4D ratio in offspring,<ref>{{cite journal | vauthors = Ozener B, Hurd PL, Duyar I | title = Inbreeding is associated with lower 2D: 4D digit ratio | journal = American Journal of Human Biology | volume = 26 | issue = 2 | pages = 183–188 | year = 2014 | pmid = 24288299 | doi = 10.1002/ajhb.22491 | s2cid = 23618195 }}</ref> which may account for some of the geographical and ethnic variation in 2D:4D ratios, as consanguinity rates depend on, among others, religion, culture, and geography.<ref>{{cite journal | vauthors = Tadmouri GO, Nair P, Obeid T, Al Ali MT, Al Khaja N, Hamamy HA | title = Consanguinity and reproductive health among Arabs | journal = Reproductive Health | volume = 6 | pages = 17 | date = October 2009 | pmid = 19811666 | pmc = 2765422 | doi = 10.1186/1742-4755-6-17 | doi-access = free }}</ref>