Editing Digit ratio (section)

==History of research==
Various reports in the scientific literature of the late 1800s noted that a greater proportion of men have shorter index fingers than ring fingers as compared to women.<ref name="Ecker A 1875 68–74">{{cite journal |volume=A1|doi=10.1525/aa.1888.1.1.02a00040 |title=Anthropological Notes on the Human Hand |journal=American Anthropologist |pages=51–76 |year=1888 | vauthors = Baker F |doi-access=free }}</ref> By 1930, statistically significant sex differences in digit ratio were established in a sample of 201 men and 109 women, <ref name="Ruggles_1930">{{cite journal |doi=10.1002/ar.1090460210 |title=Human finger types |journal=The Anatomical Record |volume=46 |issue=2 |pages=199–204 |year=1930 | vauthors = Ruggles G |s2cid=83821071 }}</ref> after which time the sex difference appears to have been largely forgotten or ignored.

In 1983, [[Glenn Wilson (psychologist)|Glenn Wilson]] of [[King's College London]] published a study examining the correlation between assertiveness in women and their digit ratio, which found that women with a lower 2D:4D ratio reported greater assertiveness.<ref name="Wilson_1983">{{cite journal |doi=10.1016/0191-8869(83)90061-2 |title=Finger-length as an index of assertiveness in women |journal=Personality and Individual Differences |volume=4 |pages=111–112 |year=1983 | vauthors = Wilson GD }}</ref> This was the first study to examine the correlation between digit ratio and a psychological trait within members of the same sex.<ref>{{Cite journal | vauthors = Wilson G | year = 2010 | title = Fingers to feminism: The rise of 2D:4D | url = https://archive.org/details/sim_michigan-quarterly-review_winter-2010_49_1/page/25 | journal = Quarterly Review | volume = 4 | pages = 25–32 }}</ref> Wilson proposed that skeletal structure and personality were simultaneously affected by sex hormone levels in utero.<ref name="Wilson_1983"/>

In 1998, John T. Manning and colleagues reported the sex difference in digit ratios was present in two-year-old children<ref name="Manning_1998">{{cite journal | vauthors = Manning JT, Scutt D, Wilson J, Lewis-Jones DI | title = The ratio of 2nd to 4th digit length: a predictor of sperm numbers and concentrations of testosterone, luteinizing hormone and oestrogen | journal = Human Reproduction | volume = 13 | issue = 11 | pages = 3000–3004 | date = November 1998 | pmid = 9853845 | doi = 10.1093/humrep/13.11.3000 | doi-access = free }}</ref> and further developed the idea that the index was a marker of prenatal sex hormones. Since then, research on the topic has burgeoned around the world.

2D:4D digit ratios have been used alongside other methods in an attempt to understand Palaeolithic [[hand stencil]]s found in prehistoric European and Indonesian [[cave painting]].<ref>{{cite journal |doi=10.1017/S0003598X00093704 |title=Sexual dimorphism in Upper Palaeolithic hand stencils |url=https://archive.org/details/sim_antiquity_2006-06_80_308/page/390 |journal=Antiquity |volume=80 |issue=308 |pages=390–404 |year=2006 |vauthors = Snow DR |s2cid=16301395 }}</ref><ref>{{cite journal |vauthors=Chazine JM, Noury A |title=Sexual Determination of Hand Stencils on the Main Panel of the Gua Masri II Cave (East-Kalimantan/Borneo – Indonesia) |journal=International Newsletter on Rock Art |volume=28 |pages=16–22 |url=https://hal.archives-ouvertes.fr/hal-00342551 |year=2008 |access-date=30 January 2019 |archive-date=31 January 2019 |archive-url=https://web.archive.org/web/20190131093148/https://hal.archives-ouvertes.fr/hal-00342551 |url-status=live }}</ref><ref name="Nelson_2006">{{cite journal | vauthors = Nelson E, Manning J, Sinclair A |doi=10.3828/bfarm.2006.1.6 |title=News Using the length of the 2nd to 4th digit ratio (2D:4D) to sex cave art hand stencils: Factors to consider |journal=Before Farming |volume=2006 |pages=1–7 |year=2006 }}</ref>