Digit ratio - Knowledge

84: 76: 32: 641:). These high-runner mice exhibit increased 2D:4D in contradiction to the correlation between digit ratio and physical fitness in human beings, suggesting that 2D:4D may not be a clear proxy for prenatal androgen exposure in mice. The authors suggest that 2D:4D may more accurately reflect the effect of glucocorticoids or other factors that regulate any of various genes. 585:. This is especially problematic in cases where the relationship is likely to be weak, such as with prenatal testosterone. Furthermore, critics have pointed out that controlling for confounding variables is an impossible task due to the expanding list of confounding variables, including ethnicity, sex, and physical, medical or behavioral conditions. 330:

between 2D:4D ratios and umbilical cord androgen and estrogen levels. A large meta-analysis studying genomic correlations was unable to find evidence for 2D:4D being a marker for prenatal androgen exposure, but did not exclude the possibility given constraints in genomic knowledge (with 3.8% of the variance in 2D:4D ratio accounted for genetically).

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dimorphism than palmar digit ratios, including the palmar 2D:4D ratio that has been the basis of most study. Moreover, compared to palmar digit ratio, dorsal digit ratio is a better indicator of bone digit ratio. Thus, while most of the earlier research has focused on palmar 2D:4D ratio, study of other digit ratios is also promising.

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are bent at 90 degrees to the palm) has also recently gained acceptance. A study has shown that, compared to the palmar digit ratio, the dorsal digit ratio is a better indicator of bone digit ratio. Furthermore, the palmar digit ratio is affected by the differential positioning of flexion creases.

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The 2D:4D ratio has been associated with a variety of traits including academic ability, personality as well as physical attributes such as health outcomes. Lower (masculinized) 2D:4D ratios have been associated with higher mathematical ability as well as personality traits such as aggressiveness (in

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There has been no reliable correlation reported between 2D:4D and sex hormone levels in adulthood. Marta Kowal has suggested that testosterone levels are correlated with other factors (such as smoking, body weight and diet) that would impact the relationship between 2D:4D and an adult's testosterone

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However, when examining the extent of sexual dimorphism evident after birth, adults were found to demonstrate more dimorphism than children, who show the same extent of dimorphism as fetuses. This has led the authors to suggest that digit ratio is also affected by postnatal development. Similarly, a

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The digit length is typically measured on the palmar (ventral, "palm-side") hand, from the midpoint of the bottom crease to the tip of the finger. Measurement of the digits on the dorsal ("back-side") hand, from the tip of the finger to the proximal phalange-bone protrusion (which occurs when digits

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The 2D:4D ratio has been postulated to correlate with a range of physical and cognitive traits in childhood and adulthood, including personality traits, such as assertiveness in women, aggressiveness in men and cognitive abilities such as numerical skills. It has also been shown to vary considerably

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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). This variation is far larger than the differences between sexes; in Manning's

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Various findings have also challenged the general trend. One study of 66 children that attempted to replicate the findings of a frequently cited paper on the topic found no association between prenatal testosterone and estrogen levels and 2D:4D in childhood. Another paper also found no relationship

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A 2011 paper by Zhengui Zheng and Martin J. Cohn reports that "the 2D:4D ratio in mice is controlled by the balance of androgen to estrogen signaling during a narrow window of digit development". The formation of the digits in humans, in utero, is thought to occur by 13 weeks, and the bone-to-bone

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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. This was the first study to examine the correlation between digit ratio and a psychological trait within members of the

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A 2021 paper by James Smoliga, titled "Giving science the finger—is the second-to-fourth digit ratio (2D:4D) a biomarker of good luck? A cross sectional study" followed similar research methodologies adopted by others in the field and came to conclude that low digit ratio is associated with good

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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. By 1930, statistically significant sex differences in digit ratio were established in a sample of 201 men and 109 women, after

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found that the females in these pairings were born with significantly lower 2D:4D ratio, postulated to occur from exposure to excess androgens from their brothers in utero (the hormone-transfer theory). However, an attempt to replicate these findings with a larger sample of dizygotic twins (867

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ratio is consistent from this point into an individual's adulthood. If, during this period, the fetus is exposed to androgens (levels of which are usually far higher in male than female fetuses) the growth rate of the 4th digit is increased. In a 2006 study, digit ratio analysis of opposite-sex

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Though it is unclear why the digit ratio on the right hand should be more sensitive to prenatal hormones than that on the left hand, as indicated by the greater sex difference on the right than the left, these differences are not evident in dorsal measurements nor bone digit ratios, and it is

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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

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Sexual dimorphism is strongest in digit ratios involving digit 2 with palmar measurements. However, when measured dorsally, digit ratios involving digit 5 showed strongest dimorphism, with women having shorter fifth digits on average. Overall, dorsal digit ratios demonstrate stronger sexual

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line with non-zero intercept, which means 2D:4D necessarily decreases with increasing finger length, and the fact that men have longer fingers than women", which the authors claim may be the basis for the sex differences in 2D:4D and/or any putative hormonal influence on the ratios.

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In 1998, John T. Manning and colleagues reported the sex difference in digit ratios was present in two-year-old children 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.

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Pang S, Levine LS, Cederqvist LL, Fuentes M, Riccardi VM, Holcombe JH, et al. (August 1980). "Amniotic fluid concentrations of delta 5 and delta 4 steroids in fetuses with congenital adrenal hyperplasia due to 21 hydroxylase deficiency and in anencephalic fetuses".

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due to a dysfunctional gene for the androgen receptor present as women and have greater digit ratios on average, as would be predicted if androgenic hormones affect digit ratios. This finding suggests that the sex difference in digit ratios may be unrelated to the

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Researcher Marta Kowal states: "One of the general limitations of studies on the digit ratios is the high number of degrees of freedom within the 2D:4D (the right, left, and right minus left 2D:4D). Running many analyses with different predictors

527:." Subsequent researchers failed to replicate their findings, and criticised Manning and Fink for publishing papers that fail under scrutiny despite the urgent need for high quality science during the pandemic that informs medical decisions. 130:

development. A lower ratio has been associated with higher androgen exposure, which would be the physiological norm for males but may also occur in some exceptional circumstances in females. The latter include developmental disorders such as

376:) have greater digit ratios, though there have also been reports of failure in replicating this finding. Men with less sensitive androgen receptors may compensate for this by secreting more testosterone via reduced inhibitory feedback on 2715: 766:

Manning JT, Barley L, Walton J, Lewis-Jones DI, Trivers RL, Singh D, et al. (May 2000). "The 2nd:4th digit ratio, sexual dimorphism, population differences, and reproductive success. evidence for sexually antagonistic genes?".

3077:"Part of the interindividual variation in serum testosterone levels in healthy men reflects differences in androgen sensitivity and feedback set point: contribution of the androgen receptor polyglutamine tract polymorphism" 465:) has been found to lower the 2D:4D ratio in offspring, 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. 485:

Prenatal androgen exposure has been implicated as a determinant in left-handedness, though contradictory and inconclusive findings have been reported concerning an association between 2D:4D and left-hand dominance. Kumar

2974:"Profiling steroid hormones in amniotic fluid of midpregnancy by routine stable isotope dilution/gas chromatography-mass spectrometry: reference values and concentrations in fetuses at risk for 21-hydroxylase deficiency" 2936:

Dörr HG, Sippell WG (January 1993). "Prenatal dexamethasone treatment in pregnancies at risk for congenital adrenal hyperplasia due to 21-hydroxylase deficiency: effect on midgestational amniotic fluid steroid levels".

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study of people from Poland found statistically significant variation in 2D:4D between age groups (children, young adults and adults) for both males and females in the left hand, but only for women with the right hand.

501:. The prenatal sex hormone ratio (indicated by 2D:4D) was associated with similar alterations to both male and female face shapes in utero, though the effect was three times more pronounced in males than in females. 439:

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. A 2008 study by Lu

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Researchers have raised concerns that, although the general trend points towards a correlation between digit ratio and early androgen exposure, many results have not been statistically significant.

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Rivas MP, Moreira LM, Santo LD, Marques AC, El-Hani CN, Toralles MB (2014). "New studies of second and fourth digit ratio as a morphogenetic trait in subjects with congenital adrenal hyperplasia".

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Voracek M (February 2009). "Comparative study of digit ratios (2D:4D and other) and novel measures of relative finger length: testing magnitude and consistency of sex differences across samples".

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Wong WI, Hines M (February 2016). "Interpreting digit ratio (2D:4D)-behavior correlations: 2D:4D sex difference, stability, and behavioral correlates and their replicability in young children".

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Talarovicová A, Krsková L, Blazeková J (January 2009). "Testosterone enhancement during pregnancy influences the 2D:4D ratio and open field motor activity of rat siblings in adulthood".

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Studies in this field have drawn criticism over questionable statistical significance and difficulties in reproducing their findings as well as lack of high quality research protocols.

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Alžbeta Talarovičová and collaborators found in rats that elevated testosterone during the prenatal period can influence 4D length, the 2D:4D ratio, and open field motor activity.

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Pratt TC, Turanovic JJ, Cullen FT (22 September 2016). "Revisiting the Criminological Consequences of Exposure to Fetal Testosterone: A Meta-Analysis of the 2D:4D Digit Ratio".

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Lust JM, Geuze RH, Van de Beek C, Cohen-Kettenis PT, Bouma A, Groothuis TG (2011). "Differential effects of prenatal testosterone on lateralization of handedness and language".

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McCormick CM, Carré JM (April 2020). "Facing off with the phalangeal phenomenon and editorial policies: A commentary on Swift-Gallant, Johnson, Di Rita and Breedlove (2020)".

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Hilgard J, Engelhardt CR, Rouder JN, Segert IL, Bartholow BD (April 2019). "Null Effects of Game Violence, Game Difficulty, and 2D:4D Digit Ratio on Aggressive Behavior".

306:. A 2024 meta-analysis has suggested that digit ratio may be related to amniotic fluid testosterone levels, but not umbilical cord levels, requiring further validation. 1977:

Hönekopp J, Bartholdt L, Beier L, Liebert A (May 2007). "Second to fourth digit length ratio (2D:4D) and adult sex hormone levels: new data and a meta-analytic review".

342:(CAH), who have elevated androgen levels before birth, have lower (more masculine) 2D:4D on average along with other possible physiological effects such as an enlarged 5312: 508:

in the expected direction. In other words, women with a greater anogenital distance, indicating greater prenatal androgen exposure, had a smaller digit ratio. Ronalds

2389:"Clinical review: Anogenital distance or digit length ratio as measures of fetal androgen exposure: relationship to male reproductive development and its disorders" 2129:

Okten A, Kalyoncu M, Yariş N (December 2002). "The ratio of second- and fourth-digit lengths and congenital adrenal hyperplasia due to 21-hydroxylase deficiency".

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Pruszkowska-Przybylska, Paulina; Kobus, Magdalena; Żądzińska, Elżbieta; Rosset, Iwona; Pruszkowska, Milena; Kuczyński, Wojciech; Sitek, Aneta (21 December 2023).

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Kumar S, Voracek M, Singh M (February 2021). "The effects of hand preference and sex on right-left asymmetry in dorsal digit lengths among adults and children".

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Ventura T, Gomes MC, Pita A, Neto MT, Taylor A (February 2013). "Digit ratio (2D:4D) in newborns: influences of prenatal testosterone and maternal environment".

497:(2004) found that men with low 2D:4D ratios (indicating high testosterone) and women with high 2D:4D ratios (indicating high estrogen) express greater levels of 3756:

Coyne SM, Manning JT, Ringer L, Bailey L (2007). "Directional asymmetry (right–left differences) in digit ratio (2D: 4D) predict indirect aggression in women".

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Brown WM, Hines M, Fane BA, Breedlove SM (December 2002). "Masculinized finger length patterns in human males and females with congenital adrenal hyperplasia".

3226:, Klump KL (February 2008). "Genetic and environmental influences on 2D:4D finger length ratios: a study of monozygotic and dizygotic male and female twins". 593:. Smoliga would later go on to label the field as pseudoscience. In a response, John T. Manning criticized the researchers for not controlling for ethnicity. 547:). Direct effects of sex hormones on bone growth might be responsible, either by regulation of Hox genes in digit development or independently of such genes. 53: 4534:"No credible evidence for links between 2D:4D and COVID-19 outcomes: A probabilistic perspective on digit ratio, ACE variants, and national case fatalities" 4207:"No credible evidence for links between 2D:4D and COVID-19 outcomes: A probabilistic perspective on digit ratio, ACE variants, and national case fatalities" 921: 5031: 1513:

Nelson E, Manning J, Sinclair A (2006). "News Using the length of the 2nd to 4th digit ratio (2D:4D) to sex cave art hand stencils: Factors to consider".

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Williams TJ, Pepitone ME, Christensen SE, Cooke BM, Huberman AD, Breedlove NJ, et al. (March 2000). "Finger-length ratios and sexual orientation".

2781:"Genome-wide association study identifies nine novel loci for 2D:4D finger ratio, a putative retrospective biomarker of testosterone exposure in utero" 5266:

Romano M, Leoni B, Saino N (February 2006). "Examination marks of male university students positively correlate with finger length ratios (2D:4D)".

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have reported that hand preference is most strongly associated with 3D:4D digit ratios and that the effect is reversed between children and adults.

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Voracek M, Pietschnig J, Nader IW, Stieger S (September 2011). "Digit ratio (2D:4D) and sex-role orientation: Further evidence and meta-analysis".

354:. Amniocentesis samples in males with CAH show that prenatal levels of testosterone are in the high-normal range and levels of the weaker androgen 323:

of same-sex and opposite-sex pairings to support the theory, though it did confirm female 2D:4D to be significantly higher than male as expected.

2430:"Relationship between the 2D : 4D and prenatal testosterone, adult level testosterone, and testosterone change: Meta-analysis of 54 studies" 512:(2002) showed that men who had an above average placental weight and a shorter neonatal crown-heel length had higher 2D:4D ratios in adult life. 2610: 2528:

van Anders SM, Vernon PA, Wilbur CJ (March 2006). "Finger-length ratios show evidence of prenatal hormone-transfer between opposite-sex twins".

1192:"Second to fourth digit ratios, male genital development and reproductive health: a clinical study among fertile men and testis cancer patients" 4121:

Ronalds G, Phillips DI, Godfrey KM, Manning JT (June 2002). "The ratio of second to fourth digit lengths: a marker of impaired fetal growth?".

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Manning JT, Churchill AJ, Peters M (April 2007). "The effects of sex, ethnicity, and sexual orientation on self-measured digit ratio (2D:4D)".

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Emma Nelson and Susanne Shultz are currently investigating how 2D:4D relates to primate mating strategies and the evolution of human sociality.

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has come under scrutiny. Some studies that investigate the relationship between a trait and an unobservable variable fail to consider possible

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Garn SM, Burdi AR, Babler WJ, Stinson S (November 1975). "Early prenatal attainment of adult metacarpal-phalangeal rankings and proportions".

3690:"Sexual dimorphism in ratio of second and fourth digits and its relationship with metabolic syndrome indices and cardiovascular risk factors" 358:

are several fold higher than in controls, indicating that males with CAH are exposed to greater prenatal concentrations of total androgens.

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Lutchmaya S, Baron-Cohen S, Raggatt P, Knickmeyer R, Manning JT (April 2004). "2nd to 4th digit ratios, fetal testosterone and estradiol".

3402: 1404:"The ratio of 2nd to 4th digit length: a predictor of sperm numbers and concentrations of testosterone, luteinizing hormone and oestrogen" 3436:

Loehlin JC, McFadden D, Medland SE, Martin NG (December 2006). "Population differences in finger-length ratios: ethnicity or latitude?".

4661:"A variant in LIN28B is associated with 2D:4D finger-length ratio, a putative retrospective biomarker of prenatal testosterone exposure" 515:

In 2020, a paper by John T Manning and Bernhard Fink reported that at the national level, high mean male 2D:4D was associated with high

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Manning JT, Bundred PE, Newton DJ, Flanagan BF (2003). "The second to fourth digit ratio and variation in the androgen receptor gene".

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and depression than those with lower ratios. Females with higher ratios are more at risk of eating disorders, anxiety and depression.

380:. Thus, it is not clear that 2D:4D would be expected to correlate with CAG repeats, even if it accurately reflects prenatal androgen. 40: 559:

The credibility of research into the relationship between digit ratios and traits has been subject to criticism for various reasons.

91:. The hand is placed on the edge of a table so that fingers are rested on table while making an angle of 90 degrees to the palm. 624:, and found a correlation between digit ratio in females and the strength of their preference for sexually selected traits in males. 3272:

Manning JT, Stewart A, Bundred PE, Trivers RL (November 2004). "Sex and ethnic differences in 2nd to 4th digit ratio of children".

637:, and their students have examined hindlimb 2D:4D in lines of mice selectively bred for high voluntary wheel-running behavior (see 1728: 4886:"Adult digit ratio (2D:4D) is not related to umbilical cord androgen or estrogen concentrations, their ratios or net bioactivity" 2742:"Adult digit ratio (2D:4D) is not related to umbilical cord androgen or estrogen concentrations, their ratios or net bioactivity" 5062: 291:

exposure, and that it correlates negatively, not with prenatal testosterone alone, but with the testosterone-to-estrogen ratio.

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Hampson E, Sankar JS (2012). "Re-examining the Manning hypothesis: androgen receptor polymorphism and the 2D: 4D digit ratio".

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same sex. Wilson proposed that skeletal structure and personality were simultaneously affected by sex hormone levels in utero.

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Hönekopp J, Watson S (September 2010). "Meta-analysis of digit ratio 2D:4D shows greater sex difference in the right hand".

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Lindová J, Hrušková M, Pivoňková V, Kuběna A, Flegr J (June 2008). "Digit ratio (2D:4D) and Cattell's personality traits".

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Luxen MF, Buunk BP (2005). "Second-to-fourth digit ratio related to verbal and numerical intelligence and the Big Five".

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Malas MA, Dogan S, Evcil EH, Desdicioglu K (July 2006). "Fetal development of the hand, digits and digit ratio (2D:4D)".

1030:"Giving science the finger-is the second-to-fourth digit ratio (2D:4D) a biomarker of good luck? A cross sectional study" 860:"No relationship between the digit ratios (2D:4D) and salivary testosterone change: Study on men under an acute exercise" 3048:

Hampson E, Sankar JS (2012). "Re-examining the Manning hypothesis: androgen receptor polymorphism and the 2D:4D ratio".

648:, the ratio of the 2nd to 4th digit of the foot has been shown to be influenced by manipulations of testosterone in the 283:. Lower 2D:4D is found to correlate with higher prenatal androgen exposure. Therefore digit ratio could be considered a 5353: 1480:"Sexual Determination of Hand Stencils on the Main Panel of the Gua Masri II Cave (East-Kalimantan/Borneo – Indonesia)" 1750:

Loehlin JC, Medland SE, Martin NG (April 2009). "Relative finger lengths, sex differences, and psychological traits".

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gene. Men with genes that produce androgen receptors that are less sensitive to testosterone (because they have more

287:(indirect measure) for prenatal androgen exposure. Various studies suggest that 2D:4D is also influenced by prenatal 2583:"No effects of prenatal hormone transfer on digit ratio in a large sample of same- and opposite-sex dizygotic twins" 1236:"Differential Placing of Flexion Creases Contributes to Sex Differences in the Second-to-Fourth Digit Ratio (2D:4D)" 478:. Males with higher (feminized) ratios are reported to be more at risk of low sperm counts, heart disease, obesity, 655:

Studies in mice indicate that prenatal androgen influences 2D:4D primarily by promoting growth of the fourth digit.

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possible that right-left differences in palmar 2D:4D may be attributed to differential placing of flexion creases.

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Manning and colleagues have reported that 2D:4D ratios vary greatly between different ethnic groups. In a study of

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Hönekopp J, Watson S (2010). "Meta-analysis of digit ratio 2D:4D shows greater sex difference in the right hand".

384: 5023: 974:"(Mis-)understanding COVID-19 and digit ratio: Methodological and statistical issues in Manning and Fink (2020)" 455:

geographical differences in 2D:4D ratio were caused by genetic pool differences, not by geographical latitude.

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Manning JT, Peters M (2009). "Digit ratio (2D:4D) and hand preference for writing in the BBC Internet Study".

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Dennis McFadden and collaborators have demonstrated sexual dimorphism in hind limb digit ratio in a number of

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Bailey Allison A, Hurd PL (2005). "Depression in men is associated with more feminine finger length ratios".

1927:"Differences in the 2nd to 4th digit length ratio in humans reflect shifts along the common allometric line" 1082:"Human 2D (index) and 4D (ring) digit lengths: their variation and relationships during the menstrual cycle" 543:

responsible for both digit and penis development play an important role in affecting these multiple traits (

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The mechanisms by which prenatal hormones influence digit ratio are not clearly understood. Traits such as

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Fink B, Manning JT, Neave N, Grammer K (March 2004). "Second to fourth digit ratio and facial asymmetry".

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side. It is proposed that the 2D:4D ratio indicates the degree to which an individual has been exposed to

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McFadden D, Shubel E (December 2002). "Relative lengths of fingers and toes in human males and females".

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It has been alleged that, because academics have accepted a variety of techniques and equipment (such as

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Galis, Frietson; Ten Broek, Clara M. A.; Van Dongen, Stefan; Wijnaendts, Liliane C. D. (February 2010).

2876: 2582: 922:"Talk to the hand. Scientists try to debunk idea that finger length can reveal personality and health" 362: 4385:"A comparison of measurement methods and sexual dimorphism for digit ratio (2D:4D) in Han ethnicity" 3450: 2673:"Digit ratio (2D:4D) and amniotic testosterone and estradiol: an attempted replication of Lutchmaya 365:, who have reduced testosterone secretion throughout life compared to their fathers or to controls. 2210:

Manning JT, Kilduff LP, Trivers R (January 2013). "Digit ratio (2D:4D) in Klinefelter's syndrome".

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Irreproducibility of findings in many instances, with some studies reporting contradictory results.

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2D:4D digit ratios have been used alongside other methods in an attempt to understand Palaeolithic

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and arm-to-trunk length ratio are also influenced by prenatal hormones, and it is postulated that

4158:"Understanding COVID-19: Digit ratio (2D:4D) and sex differences in national case fatality rates" 858:

Kowal M, Sorokowski P, Żelaźniewicz A, Nowak J, Orzechowski S, Żurek G, et al. (June 2020).

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Fink B, Grammer K, Mitteroecker P, Gunz P, Schaefer K, Bookstein FL, Manning JT (October 2005).

2634:"Digit ratio (2D:4D) and prenatal/perinatal sex hormones: A response to Manning and Fink (2017)" 5348: 3445: 3414: 638: 351: 5085: 3175:"The big finger: the second to fourth digit ratio is a predictor of sporting ability in women" 2870: 1136:"Sexual Dimorphism in Digit Ratios Derived from Dorsal Digit Length among Adults and Children" 523:, and suggested that this may be used to "identify for whom it would be advisable to exercise 5368: 3532:

Ozener B, Hurd PL, Duyar I (2014). "Inbreeding is associated with lower 2D: 4D digit ratio".

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Manning JT, Kilduff LP, Trivers R (2013). "Digit ratio (2D: 4D) in Klinefelter's syndrome".

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Hand with index finger being shorter than the ring finger, resulting in a small 2D:4D ratio.

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Medland SE, Zayats T, Glaser B, Nyholt DR, Gordon SD, Wright MJ, et al. (April 2010).

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Hollier LP, Keelan JA, Jamnadass ES, Maybery MT, Hickey M, Whitehouse AJ (February 2015).

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Hollier LP, Keelan JA, Jamnadass ES, Maybery MT, Hickey M, Whitehouse AJ (February 2015).

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Burley NT (May 2006). "An eye for detail: selective sexual imprinting in zebra finches".

4074:"Stability of proposed biomarkers of prenatal androgen exposure over the menstrual cycle" 3075:

Crabbe P, Bogaert V, De Bacquer D, Goemaere S, Zmierczak H, Kaufman JM (September 2007).

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Warrington NM, Shevroja E, Hemani G, Hysi PG, Jiang Y, Auton A, et al. (June 2018).

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Nayak, Satheesha B.; Nair, Dhiviah; Ravi, Vimal; Aithal, Ashwini P. (20 September 2018).

691: 665: 505: 5224: 4001: 3931:"Effects of hand preference on digit lengths and digit ratios among children and adults" 3666: 3320: 3026: 875: 812:"A comparative study on digit ratio and hand patterns of three ethnic races of Malaysia" 780: 5291: 5243: 5208: 5189: 5146: 5130: 5000: 4975: 4956: 4861: 4837:"A comprehensive allometric analysis of 2nd digit length to 4th digit length in humans" 4836: 4817: 4736: 4685: 4660: 4641: 4558: 4533: 4511: 4458: 4433: 4409: 4384: 4365: 4322: 4279: 4231: 4206: 4182: 4157: 4098: 4073: 4049: 4024: 3958: 3844: 3819: 3706: 3689: 3674: 3603: 3576: 3557: 3514: 3471: 3383: 3340: 3251: 3199: 3174: 3150: 3125: 3106: 3061: 2805: 2780: 2707: 2563: 2465: 2326: 2299: 2235: 2189: 2106: 2053: 2026: 2002: 1951: 1926: 1907: 1864: 1821: 1775: 1688: 1664: 1631: 1607: 1582: 1460: 1335: 1262: 1235: 1162: 1135: 1106: 1081: 1054: 1029: 998: 973: 937: 892: 859: 740: 715: 590: 516: 479: 230: 4134: 4009: 3034: 2142: 788: 577:

Concerning the evidence for causal relationships, the reliability of digit ratio as a

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and umbilical cord sampling at birth, the latter being a measure of exposure in late

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argues: "Sexual differences in 2D:4D are mainly caused by the shift along the common

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of the same hand. Other digit ratios are also calculated similarly in the same hand.

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between racial groups with males having, on average, lower 2D:4D ratio than females.

5295: 5279: 5193: 5150: 4960: 4740: 4645: 4515: 4326: 4283: 3561: 3518: 3255: 3110: 2567: 2006: 1911: 1868: 1779: 1464: 1339: 5358: 5275: 5238: 5228: 5173: 5122: 4995: 4987: 4940: 4905: 4897: 4856: 4848: 4801: 4763: 4720: 4680: 4672: 4625: 4590: 4553: 4545: 4495: 4453: 4445: 4404: 4396: 4349: 4306: 4263: 4226: 4218: 4177: 4169: 4130: 4093: 4085: 4044: 4036: 4005: 3942: 3903: 3868: 3839: 3831: 3792: 3765: 3738: 3701: 3670: 3635: 3598: 3588: 3541: 3498: 3475: 3455: 3387: 3367: 3324: 3281: 3235: 3194: 3186: 3145: 3137: 3088: 3057: 3030: 2985: 2946: 2910: 2841: 2800: 2792: 2753: 2691: 2645: 2594: 2545: 2537: 2500: 2492: 2441: 2400: 2361: 2321: 2311: 2270: 2262: 2239: 2219: 2193: 2173: 2138: 2110: 2090: 2048: 2038: 1990: 1986: 1946: 1938: 1891: 1848: 1825: 1805: 1759: 1710: 1700: 1659: 1643: 1602: 1594: 1552: 1522: 1452: 1415: 1365: 1327: 1298: 1257: 1247: 1203: 1157: 1147: 1101: 1093: 1049: 1041: 993: 985: 929: 887: 879: 823: 784: 735: 727: 88: 20: 4267: 3930: 589:

luck. This result is attributed to chance and presented as an illustration of the

5363: 5233: 4835:

Lolli L, Batterham AM, Kratochvíl L, Flegr J, Weston KL, Atkinson G (June 2017).

4574: 3688:

Oyeyemi BF, Iyiola OA, Oyeyemi AW, Oricha KA, Anifowoshe AT, Alamukii NA (2014).

3489:

Xu Y, Zheng Y (6 May 2015). "The digit ratio (2D:4D) in China: A meta-analysis".

1303: 1286: 681: 670: 498: 355: 311: 246: 194:

which time the sex difference appears to have been largely forgotten or ignored.

5319: 5177: 5086:"Evolution of Primate Social Systems: Implications for Hominin Social Evolution" 4805: 4724: 4499: 4486:

Voracek M, Kossmeier M, Tran US (2019). "Which Data to Meta-Analyze, and How?".

2541: 1479: 1420: 1403: 4676: 4594: 4432:

Robertson J, Zhang W, Liu JJ, Muir KR, Maciewicz RA, Doherty M (January 2008).

3769: 3742: 3639: 3575:

Tadmouri GO, Nair P, Obeid T, Al Ali MT, Al Khaja N, Hamamy HA (October 2009).

3223: 2598: 2031:

Proceedings of the National Academy of Sciences of the United States of America

1705: 1689:"The age difference in 2D:4D among the Polish population: An exploratory study" 883: 578: 429: 284: 182: 83: 4909: 4400: 4089: 3907: 3459: 3371: 3239: 2950: 2695: 1763: 1647: 1598: 1456: 828: 811: 5342: 4952: 4775: 4629: 4602: 4507: 4434:"Radiographic assessment of the index to ring finger ratio (2D:4D) in adults" 3190: 2830:"High fetal testosterone and sexually dimorphic cerebral networks in females" 2606: 2453: 1724: 1655: 1252: 1152: 837: 649: 630: 475: 458: 425: 377: 295: 218: 177:), researchers record multiple measurements and report only those which have 4767: 2846: 2829: 2496: 2043: 1852: 1045: 933: 19:

For the observation about the frequencies of leading digits of numbers, see

5287: 5252: 5185: 5142: 5024:"Faculty Spotlight: James M. Smoliga | Tufts University School of Medicine" 5009: 4917: 4870: 4852: 4813: 4732: 4694: 4637: 4567: 4467: 4418: 4361: 4318: 4240: 4191: 4142: 4107: 4058: 4040: 3954: 3915: 3880: 3804: 3715: 3612: 3593: 3553: 3510: 3467: 3379: 3336: 3293: 3247: 3208: 3159: 3102: 2999: 2990: 2973: 2855: 2814: 2765: 2703: 2657: 2559: 2461: 2414: 2373: 2335: 2316: 2284: 2231: 2185: 2150: 2102: 2094: 2062: 1998: 1960: 1942: 1903: 1860: 1817: 1809: 1771: 1673: 1616: 1564: 1526: 1271: 1217: 1171: 1115: 1063: 1007: 901: 796: 749: 389: 276: 214: 151: 111: 4275: 3820:"Second to fourth digit ratio, handedness and testicular germ cell tumors" 2958: 2922: 2914: 2514: 1686: 1429: 1331: 75: 3173:

Paul SN, Kato BS, Hunkin JL, Vivekanandan S, Spector TD (December 2006).

3141: 3093: 3076: 2796: 2550: 2505: 2405: 2388: 1443:

Snow DR (2006). "Sexual dimorphism in Upper Palaeolithic hand stencils".

1356:

Wilson GD (1983). "Finger-length as an index of assertiveness in women".

1028:

Smoliga JM, Fogaca LK, Siplon JS, Goldburt AA, Jakobs F (December 2021).

621: 404: 400:

Several studies have presented evidence that digit ratios are heritable.

373: 320: 272: 174: 170: 155: 115: 4991: 2275: 5134: 4310: 3545: 3502: 2445: 2177: 1895: 1715: 675: 611: 544: 462: 444: 299: 298:(usually performed between 14th and 20th weeks of pregnancy), maternal 251: 3124:

Berenbaum SA, Bryk KK, Nowak N, Quigley CA, Moffat S (November 2009).

5126: 3872: 3328: 2351: 853: 851: 849: 847: 540: 416: 303: 178: 123: 5207:

Yan RH, Malisch JL, Hannon RM, Hurd PL, Garland T (September 2008).

4944: 1581:

Galis F, Ten Broek CM, Van Dongen S, Wijnaendts LC (February 2010).

620:

Nancy Burley's research group has demonstrated sexual dimorphism in

3401:

Lu H, Huo ZH, Shi ZY, Peng L, Dang J, Jiao HY, et al. (2008).

645: 520: 343: 316: 288: 280: 166: 87:

Image shows the measurement procedure of dorsal digit length using

3858: 3403:"Study on the digit ratio of Hui and Han ethnic groups in Ningxia" 2300:"The use of digit ratios as markers for perinatal androgen action" 1629: 1580: 844: 229:

Studies measuring the 2D:4D of fetuses have found the ratio to be

3818:

Trabert B, Graubard BI, Erickson RL, Zhang Y, McGlynn KA (2013).

2972:

Wudy SA, Dörr HG, Solleder C, Djalali M, Homoki J (August 1999).

448: 412: 408: 4254:

Dickman S (March 1997). "HOX gene links limb, genital defects".

3306: 857: 563:

Weaknesses in the statistical significance of numerous findings.

31: 5209:"Selective breeding for a behavioral trait changes digit ratio" 3074: 1402:

Manning JT, Scutt D, Wilson J, Lewis-Jones DI (November 1998).

599:

increases the chances of finding allegedly significant results.

504:

In a non-clinical sample of women, digit ratio correlated with

368:

Digit ratio in men may correlate with genetic variation in the

347: 100: 4930: 2733: 765: 4883: 4834: 4615: 4580: 4120: 2739: 1976: 1401: 268: 127: 5163: 3817: 3435: 3271: 3012: 2827: 2778: 2670: 1080:

Mayhew TM, Gillam L, McDonald R, Ebling FJ (November 2007).

972:

Jones AL, Satchell LP, Jaeger B, Schild C (September 2020).

150:

The 2D:4D ratio is calculated by dividing the length of the

5084:

Shultz S, Opie C, Nelson E, Atkinson QD, Dunbar RI (2014).

4022: 2899: 1383:

Wilson G (2010). "Fingers to feminism: The rise of 2D:4D".

1027: 119: 104: 3687: 3172: 1542: 1079: 451:

were lower than those in European countries like Britain.

361:

A greater (more feminine) digit ratio occurs for men with

110:

The most commonly studied digit ratio is that of the 2nd (

4658: 3123: 2671:

Richards G, Browne WV, Constantinescu M (December 2021).

971: 5322:

Digit Ratio: A Pointer to Fertility, Behavior and Health

5083: 3755: 2163: 2027:"Developmental basis of sexually dimorphic digit ratios" 530: 118:), also referred to as the 2D:4D ratio, measured on the 3987: 3574: 2971: 2080: 1632:"Sexual Dimorphism in the Prenatal Digit Ratio (2D:4D)" 1583:"Sexual dimorphism in the prenatal digit ratio (2D:4D)" 4078:

Journal of Developmental Origins of Health and Disease

3357: 3221: 2684:

Journal of Developmental Origins of Health and Disease

2527: 2482: 350:. Males with CAH also express lower digit ratios than 5115:

Evolution; International Journal of Organic Evolution

4431: 3782: 2209: 1512: 267:

It has been proposed that 2D:4D ratio is affected by

5206: 4753: 4485: 3081: