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Digit ratio

From Wikipedia - Reading time: 24 min
For the observation about the frequencies of leading digits of numbers, see Benford's law.

Hand with index finger being shorter than the ring finger, resulting in a small 2D:4D ratio.
Image shows the measurement procedure of dorsal digit length using vernier calipers. 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.

The digit ratio is the ratio taken of the lengths of different digits or fingers on a hand.

The most commonly studied digit ratio is that of the 2nd (index finger) and 4th (ring finger), also referred to as the 2D:4D ratio, measured on the palm side. It is proposed that the 2D:4D ratio indicates the degree to which an individual has been exposed to androgens during key stages of fetal 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 congenital adrenal hyperplasia.

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.[1] It has also been shown to vary considerably between racial groups[2] with males having, on average, lower 2D:4D ratio than females.[3]

Studies in this field have drawn criticism over questionable statistical significance and difficulties in reproducing their findings[4][5][6] as well as lack of high quality research protocols.[7]

Measurement

[edit]

The 2D:4D ratio is calculated by dividing the length of the index finger by the length of the ring finger of the same hand. Other digit ratios are also calculated similarly in the same hand.

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.[8] 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 are bent at 90 degrees to the palm) has also recently gained acceptance.[9][10] A study has shown that, compared to the palmar digit ratio, the dorsal digit ratio is a better indicator of bone digit ratio.[10] Furthermore, the palmar digit ratio is affected by the differential positioning of flexion creases.[11]

It has been alleged that, because academics have accepted a variety of techniques and equipment (such as calipers, radiography and photocopy), researchers record multiple measurements and report only those which have significant findings,[7] a form of reporting bias.

History of research

[edit]

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.[12] By 1930, statistically significant sex differences in digit ratio were established in a sample of 201 men and 109 women, [13] after which time the sex difference appears to have been largely forgotten or ignored.

In 1983, 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.[14] This was the first study to examine the correlation between digit ratio and a psychological trait within members of the same sex.[15] Wilson proposed that skeletal structure and personality were simultaneously affected by sex hormone levels in utero.[14]

In 1998, John T. Manning and colleagues reported the sex difference in digit ratios was present in two-year-old children[16] 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 stencils found in prehistoric European and Indonesian cave painting.[17][18][19]

Sexual dimorphism and age

[edit]

Studies measuring the 2D:4D of fetuses have found the ratio to be sexually dimorphic, being lower in males than females.[20][21]

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.[22] This has led the authors to suggest that digit ratio is also affected by postnatal development. Similarly, a 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.[23]

Sexual dimorphism is strongest in digit ratios involving digit 2 with palmar measurements.[24][25][26] However, when measured dorsally, digit ratios involving digit 5 showed strongest dimorphism, with women having shorter fifth digits on average.[9] Overall, dorsal digit ratios demonstrate stronger sexual dimorphism than palmar digit ratios,[9] including the palmar 2D:4D ratio that has been the basis of most study.[27] Moreover, compared to palmar digit ratio, dorsal digit ratio is a better indicator of bone digit ratio.[10] Thus, while most of the earlier research has focused on palmar 2D:4D ratio, study of other digit ratios is also promising.

A 2009 study in Biology Letters argues: "Sexual differences in 2D:4D are mainly caused by the shift along the common allometric 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",[28] which the authors claim may be the basis for the sex differences in 2D:4D and/or any putative hormonal influence on the ratios.

There has been no reliable correlation reported between 2D:4D and sex hormone levels in adulthood.[29][4] 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 level.[4]

Effect of prenatal hormones

[edit]

It has been proposed that 2D:4D ratio is affected by fetal exposure to sex hormones, in particular to testosterone and other androgens. Lower 2D:4D is found to correlate with higher prenatal androgen exposure.[30][29][31][32][33][34][35][36] Therefore digit ratio could be considered a proxy variable (indirect measure) for prenatal androgen exposure. Various studies suggest that 2D:4D is also influenced by prenatal estrogen exposure, and that it correlates negatively, not with prenatal testosterone alone, but with the testosterone-to-estrogen ratio.[37][8][20][38]

Prenatal hormone exposure can be measured via amniocentesis (usually performed between 14th and 20th weeks of pregnancy), maternal serum sampling and umbilical cord sampling at birth, the latter being a measure of exposure in late gestation. 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.[39]

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".[30] The formation of the digits in humans, in utero, is thought to occur by 13 weeks, and the bone-to-bone ratio is consistent from this point into an individual's adulthood.[40] 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 dizygotic twins 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).[41] However, an attempt to replicate these findings with a larger sample of dizygotic twins (867 individuals) found no differences in the variance or co-variance 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.[42]

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.[43]

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[37] found no association between prenatal testosterone and estrogen levels and 2D:4D in childhood.[44] Another paper also found no relationship between 2D:4D ratios and umbilical cord androgen and estrogen levels.[45] 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).[46]

Developmental disorders

[edit]

Women with congenital adrenal hyperplasia (CAH), who have elevated androgen levels before birth, have lower (more masculine) 2D:4D on average[31][32][47] along with other possible physiological effects such as an enlarged clitoris and shallow vagina.[48] Males with CAH also express lower digit ratios than controls.[31][32] Amniocentesis samples in males with CAH show that prenatal levels of testosterone are in the high-normal range and levels of the weaker androgen androstenedione are several fold higher than in controls,[49][50][51] indicating that males with CAH are exposed to greater prenatal concentrations of total androgens.

A greater (more feminine) digit ratio occurs for men with Klinefelter's syndrome, who have reduced testosterone secretion throughout life compared to their fathers or to controls.[34]

Digit ratio in men may correlate with genetic variation in the androgen receptor gene.[52] Men with genes that produce androgen receptors that are less sensitive to testosterone (because they have more CAG repeats) have greater digit ratios, though there have also been reports of failure in replicating this finding.[53] Men with less sensitive androgen receptors may compensate for this by secreting more testosterone via reduced inhibitory feedback on gonadotropins.[54] Thus, it is not clear that 2D:4D would be expected to correlate with CAG repeats, even if it accurately reflects prenatal androgen.

XY individuals with androgen insensitivity syndrome 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 Y chromosome per se.[55]

Geographic and ethnic variation

[edit]

Several studies have presented evidence that digit ratios are heritable.[56][57]

Manning and colleagues have reported that 2D:4D ratios vary greatly between different ethnic groups. In a study of Han, Berber, Uygur and 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).[2][58] This variation is far larger than the differences between sexes; in Manning's words, "There's more difference between a Pole and a Finn, than a man and a woman."[59]

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.[60] A 2008 study by Lu et al. found that the mean values of 2D:4D of the Hui and the Han in Ningxia were lower than those in European countries like Britain.[61]

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.[62][63]

Consanguineous parentage (inbreeding) has been found to lower the 2D:4D ratio in offspring,[64] 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.[65]

Cognitive and physical traits

[edit]

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 males), assertiveness (in females) and reduced agreeableness.[1][66][67] Males with higher (feminized) ratios are reported to be more at risk of low sperm counts, heart disease, obesity, metabolic syndrome and depression than those with lower ratios.[68][69][70] Females with higher ratios are more at risk of eating disorders, anxiety and depression.[71]

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.[72][73][74] Kumar et al. have reported that hand preference is most strongly associated with 3D:4D digit ratios and that the effect is reversed between children and adults.[75]

Fink et al. (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 facial symmetry.[76] 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.[77]

In a non-clinical sample of women, digit ratio correlated with anogenital distance in the expected direction. In other words, women with a greater anogenital distance, indicating greater prenatal androgen exposure, had a smaller digit ratio.[78] Ronalds et al. (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.[79]

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 case fatality rates with COVID-19, and suggested that this may be used to "identify for whom it would be advisable to exercise social distancing."[80] Subsequent researchers failed to replicate their findings,[81][6] 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.[6]

Explanation of the digit ratio effect

[edit]

The mechanisms by which prenatal hormones influence digit ratio are not clearly understood. Traits such as otoacoustic emissions and arm-to-trunk length ratio are also influenced by prenatal hormones, and it is postulated that Hox genes responsible for both digit and penis development play an important role in affecting these multiple traits (pleiotropy).[82] 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.

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,[83] these differences are not evident in dorsal measurements[84] nor bone digit ratios,[85][21][86] and it is possible that right-left differences in palmar 2D:4D may be attributed to differential placing of flexion creases.[11]

Criticism

[edit]

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

  1. Weaknesses in the statistical significance of numerous findings.[87][88][89]
  2. Irreproducibility of findings in many instances, with some studies reporting contradictory results.[90][5][91][92][93]
  3. Lack of a clear cause-and-effect relationship between digit ratio and traits.[94][88][7]

Concerning the evidence for causal relationships, the reliability of digit ratio as a proxy variable has come under scrutiny.[5][94][87] Some studies that investigate the relationship between a trait and an unobservable variable fail to consider possible confounding variables.[95] This is especially problematic in cases where the relationship is likely to be weak, such as with prenatal testosterone.[96][92][87] 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,[58][97] and physical, medical or behavioral conditions.[98]

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 luck.[7] This result is attributed to chance and presented as an illustration of the reproducibility crisis. Smoliga would later go on to label the field as pseudoscience.[99] In a response, John T. Manning criticized the researchers for not controlling for ethnicity.[100]

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 increases the chances of finding allegedly significant results."[4]

Other animals

[edit]
  • Dennis McFadden and collaborators have demonstrated sexual dimorphism in hind limb digit ratio in a number of great apes, including gorillas and chimpanzees.[25]
  • Emma Nelson and Susanne Shultz are currently investigating how 2D:4D relates to primate mating strategies and the evolution of human sociality.[101]
  • Nancy Burley's research group has demonstrated sexual dimorphism in zebra finches, and found a correlation between digit ratio in females and the strength of their preference for sexually selected traits in males.[102]
  • 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.[103]
  • Peter L. Hurd, Theodore Garland Jr., and their students have examined hindlimb 2D:4D in lines of mice selectively bred for high voluntary wheel-running behavior (see experimental evolution). 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.[104]
  • In pheasants, the ratio of the 2nd to 4th digit of the foot has been shown to be influenced by manipulations of testosterone in the egg.[105]
  • Studies in mice indicate that prenatal androgen influences 2D:4D primarily by promoting growth of the fourth digit.[30]

See also

[edit]

References

[edit]
  1. ^ a b Jeevanandam S, Muthu PK (2016). "2D:4D Ratio and its Implications in Medicine". Journal of Clinical and Diagnostic Research. 10 (12): CM01–CM03. doi:10.7860/JCDR/2016/21952.9000. PMC 5296424. PMID 28208851.
  2. ^ a b 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?". Evolution and Human Behavior. 21 (3): 163–183. Bibcode:2000EHumB..21..163M. doi:10.1016/S1090-5138(00)00029-5. PMID 10828555.
  3. ^ Nayak, Satheesha B.; Nair, Dhiviah; Ravi, Vimal; Aithal, Ashwini P. (20 September 2018). "A comparative study on digit ratio and hand patterns of three ethnic races of Malaysia". Egyptian Journal of Forensic Sciences. 8 (1): 56. doi:10.1186/s41935-018-0087-1. ISSN 2090-5939.
  4. ^ a b c d Kowal M, Sorokowski P, Żelaźniewicz A, Nowak J, Orzechowski S, Żurek G, et al. (June 2020). "No relationship between the digit ratios (2D:4D) and salivary testosterone change: Study on men under an acute exercise". Scientific Reports. 10 (1): 10068. Bibcode:2020NatSR..1010068K. doi:10.1038/s41598-020-66915-9. PMC 7308391. PMID 32572079.
  5. ^ a b c Leslie M (2019). "Talk to the hand. Scientists try to debunk idea that finger length can reveal personality and health". Science. doi:10.1126/science.aay2735. S2CID 241187298. Archived from the original on 10 October 2021. Retrieved 1 October 2021.
  6. ^ a b c Jones AL, Satchell LP, Jaeger B, Schild C (September 2020). "(Mis-)understanding COVID-19 and digit ratio: Methodological and statistical issues in Manning and Fink (2020)". Early Human Development. 148: 105095. doi:10.1016/j.earlhumdev.2020.105095. PMC 7256504. PMID 32499091.
  7. ^ a b c d Smoliga JM, Fogaca LK, Siplon JS, Goldburt AA, Jakobs F (December 2021). "Giving science the finger-is the second-to-fourth digit ratio (2D:4D) a biomarker of good luck? A cross sectional study". BMJ. 375: e067849. doi:10.1136/bmj-2021-067849. PMC 8672321. PMID 34911738.
  8. ^ a b Mayhew TM, Gillam L, McDonald R, Ebling FJ (November 2007). "Human 2D (index) and 4D (ring) digit lengths: their variation and relationships during the menstrual cycle". Journal of Anatomy. 211 (5): 630–638. doi:10.1111/j.1469-7580.2007.00801.x. PMC 2375787. PMID 17764524.
  9. ^ a b c Kumar S, Voracek M, Singh M (6 March 2017). "Sexual Dimorphism in Digit Ratios Derived from Dorsal Digit Length among Adults and Children". Frontiers in Endocrinology. 8: 41. doi:10.3389/fendo.2017.00041. PMC 5337486. PMID 28321205.
  10. ^ a b c Auger J, Eustache F (August 2011). "Second to fourth digit ratios, male genital development and reproductive health: a clinical study among fertile men and testis cancer patients". International Journal of Andrology. 34 (4 Pt 2): e49–e58. doi:10.1111/j.1365-2605.2010.01124.x. PMID 21091719.
  11. ^ a b Kumar S, Voracek M, Singh M (2 August 2019). "Differential Placing of Flexion Creases Contributes to Sex Differences in the Second-to-Fourth Digit Ratio (2D:4D)". Frontiers in Endocrinology. 10: 537. doi:10.3389/fendo.2019.00537. PMC 6688535. PMID 31428058.
  12. ^ Baker F (1888). "Anthropological Notes on the Human Hand". American Anthropologist. A1: 51–76. doi:10.1525/aa.1888.1.1.02a00040.
  13. ^ Ruggles G (1930). "Human finger types". The Anatomical Record. 46 (2): 199–204. doi:10.1002/ar.1090460210. S2CID 83821071.
  14. ^ a b Wilson GD (1983). "Finger-length as an index of assertiveness in women". Personality and Individual Differences. 4: 111–112. doi:10.1016/0191-8869(83)90061-2.
  15. ^ Wilson G (2010). "Fingers to feminism: The rise of 2D:4D". Quarterly Review. 4: 25–32.
  16. ^ Manning JT, Scutt D, Wilson J, Lewis-Jones DI (November 1998). "The ratio of 2nd to 4th digit length: a predictor of sperm numbers and concentrations of testosterone, luteinizing hormone and oestrogen". Human Reproduction. 13 (11): 3000–3004. doi:10.1093/humrep/13.11.3000. PMID 9853845.
  17. ^ Snow DR (2006). "Sexual dimorphism in Upper Palaeolithic hand stencils". Antiquity. 80 (308): 390–404. doi:10.1017/S0003598X00093704. S2CID 16301395.
  18. ^ Chazine JM, Noury A (2008). "Sexual Determination of Hand Stencils on the Main Panel of the Gua Masri II Cave (East-Kalimantan/Borneo – Indonesia)". International Newsletter on Rock Art. 28: 16–22. Archived from the original on 31 January 2019. Retrieved 30 January 2019.
  19. ^ 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". Before Farming. 2006: 1–7. doi:10.3828/bfarm.2006.1.6.
  20. ^ a b Malas MA, Dogan S, Evcil EH, Desdicioglu K (July 2006). "Fetal development of the hand, digits and digit ratio (2D:4D)". Early Human Development. 82 (7): 469–475. doi:10.1016/j.earlhumdev.2005.12.002. PMID 16473482.
  21. ^ a b Galis F, Ten Broek CM, Van Dongen S, Wijnaendts LC (February 2010). "Sexual dimorphism in the prenatal digit ratio (2D:4D)". Archives of Sexual Behavior. 39 (1): 57–62. doi:10.1007/s10508-009-9485-7. PMC 2811245. PMID 19301112.
  22. ^ Galis, Frietson; Ten Broek, Clara M. A.; Van Dongen, Stefan; Wijnaendts, Liliane C. D. (February 2010). "Sexual Dimorphism in the Prenatal Digit Ratio (2D:4D)". Archives of Sexual Behavior. 39 (1): 57–62. doi:10.1007/s10508-009-9485-7. ISSN 0004-0002. PMC 2811245. PMID 19301112.
  23. ^ Pruszkowska-Przybylska, Paulina; Kobus, Magdalena; Żądzińska, Elżbieta; Rosset, Iwona; Pruszkowska, Milena; Kuczyński, Wojciech; Sitek, Aneta (21 December 2023). "The age difference in 2D:4D among the Polish population: An exploratory study". Anthropological Review. 86 (4): 99–110. doi:10.18778/1898-6773.86.4.08. hdl:11089/49401. ISSN 2083-4594. Archived from the original on 3 January 2024. Retrieved 25 December 2023.
  24. ^ Loehlin JC, Medland SE, Martin NG (April 2009). "Relative finger lengths, sex differences, and psychological traits". Archives of Sexual Behavior. 38 (2): 298–305. doi:10.1007/s10508-007-9303-z. PMID 18340520. S2CID 12340685.
  25. ^ a b McFadden D, Shubel E (December 2002). "Relative lengths of fingers and toes in human males and females". Hormones and Behavior. 42 (4): 492–500. doi:10.1006/hbeh.2002.1833. PMID 12488115. S2CID 1360679.
  26. ^ 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". Perceptual and Motor Skills. 108 (1): 83–93. doi:10.2466/pms.108.1.83-93. PMID 19425449. S2CID 10076143.
  27. ^ Hönekopp J, Watson S (September 2010). "Meta-analysis of digit ratio 2D:4D shows greater sex difference in the right hand". American Journal of Human Biology. 22 (5): 619–630. doi:10.1002/ajhb.21054. PMID 20737609. S2CID 29503255.
  28. ^ Kratochvíl L, Flegr J (October 2009). "Differences in the 2nd to 4th digit length ratio in humans reflect shifts along the common allometric line". Biology Letters. 5 (5): 643–646. doi:10.1098/rsbl.2009.0346. PMC 2781964. PMID 19553247.
  29. ^ a b 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". Psychoneuroendocrinology. 32 (4): 313–321. doi:10.1016/j.psyneuen.2007.01.007. PMID 17400395. S2CID 44238240.
  30. ^ a b c Zheng Z, Cohn MJ (September 2011). "Developmental basis of sexually dimorphic digit ratios". Proceedings of the National Academy of Sciences of the United States of America. 108 (39): 16289–16294. doi:10.1073/pnas.1108312108. PMC 3182741. PMID 21896736.
  31. ^ a b c Brown WM, Hines M, Fane BA, Breedlove SM (December 2002). "Masculinized finger length patterns in human males and females with congenital adrenal hyperplasia". Hormones and Behavior. 42 (4): 380–386. doi:10.1006/hbeh.2002.1830. PMID 12488105. S2CID 8886238.
  32. ^ a b c 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". Early Human Development. 70 (1–2): 47–54. doi:10.1016/s0378-3782(02)00073-7. PMID 12441204.
  33. ^ 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". American Journal of Human Biology. 26 (4): 559–561. doi:10.1002/ajhb.22545. PMID 24668932. S2CID 7711519.
  34. ^ a b Manning JT, Kilduff LP, Trivers R (January 2013). "Digit ratio (2D:4D) in Klinefelter's syndrome". Andrology. 1 (1): 94–99. doi:10.1111/j.2047-2927.2012.00013.x. PMID 23258636. S2CID 4503281.
  35. ^ 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". Early Human Development. 89 (2): 107–112. doi:10.1016/j.earlhumdev.2012.08.009. hdl:10400.17/772. PMID 23017880.
  36. ^ McIntyre MH (February 2006). "The use of digit ratios as markers for perinatal androgen action". Reproductive Biology and Endocrinology. 4: 10. doi:10.1186/1477-7827-4-10. PMC 1409789. PMID 16504142.
  37. ^ a b Lutchmaya S, Baron-Cohen S, Raggatt P, Knickmeyer R, Manning JT (April 2004). "2nd to 4th digit ratios, fetal testosterone and estradiol". Early Human Development. 77 (1–2): 23–28. doi:10.1016/j.earlhumdev.2003.12.002. PMID 15113628.
  38. ^ Dean A, Sharpe RM (June 2013). "Clinical review: Anogenital distance or digit length ratio as measures of fetal androgen exposure: relationship to male reproductive development and its disorders". The Journal of Clinical Endocrinology and Metabolism. 98 (6): 2230–2238. doi:10.1210/jc.2012-4057. PMID 23569219.
  39. ^ Sorokowski, Piotr; Kowal, Marta (5 October 2023). "Relationship between the 2D : 4D and prenatal testosterone, adult level testosterone, and testosterone change: Meta-analysis of 54 studies". American Journal of Biological Anthropology. 183 (1): 20–38. doi:10.1002/ajpa.24852. ISSN 2692-7691. PMID 37795916. S2CID 263670473.
  40. ^ Garn SM, Burdi AR, Babler WJ, Stinson S (November 1975). "Early prenatal attainment of adult metacarpal-phalangeal rankings and proportions". American Journal of Physical Anthropology. 43 (3): 327–332. doi:10.1002/ajpa.1330430305. hdl:2027.42/37557. PMID 1211429.
  41. ^ van Anders SM, Vernon PA, Wilbur CJ (March 2006). "Finger-length ratios show evidence of prenatal hormone-transfer between opposite-sex twins". Hormones and Behavior. 49 (3): 315–319. doi:10.1016/j.yhbeh.2005.08.003. hdl:2027.42/83921. PMID 16143332. S2CID 17288420.
  42. ^ Medland SE, Loehlin JC, Martin NG (1 April 2008). "No effects of prenatal hormone transfer on digit ratio in a large sample of same- and opposite-sex dizygotic twins". Personality and Individual Differences. 44 (5): 1225–1234. doi:10.1016/j.paid.2007.11.017. ISSN 0191-8869. Archived from the original on 28 November 2012. Retrieved 10 June 2023.
  43. ^ Richards G (October 2017). "Digit ratio (2D:4D) and prenatal/perinatal sex hormones: A response to Manning and Fink (2017)". Early Human Development. 113: 75–76. doi:10.1016/j.earlhumdev.2017.09.004. PMID 28917583.
  44. ^ Richards G, Browne WV, Constantinescu M (December 2021). "Digit ratio (2D:4D) and amniotic testosterone and estradiol: an attempted replication of Lutchmaya et al. (2004)" (PDF). Journal of Developmental Origins of Health and Disease. 12 (6): 859–864. doi:10.1017/S2040174420001294. PMID 33472723. S2CID 231664924. Archived (PDF) from the original on 2 April 2022. Retrieved 23 March 2022.
  45. ^ Hollier LP, Keelan JA, Jamnadass ES, Maybery MT, Hickey M, Whitehouse AJ (February 2015). "Adult digit ratio (2D:4D) is not related to umbilical cord androgen or estrogen concentrations, their ratios or net bioactivity". Early Human Development. 91 (2): 111–117. doi:10.1016/j.earlhumdev.2014.12.011. PMID 25594498.
  46. ^ Warrington NM, Shevroja E, Hemani G, Hysi PG, Jiang Y, Auton A, et al. (June 2018). "Genome-wide association study identifies nine novel loci for 2D:4D finger ratio, a putative retrospective biomarker of testosterone exposure in utero". Human Molecular Genetics. 27 (11): 2025–2038. doi:10.1093/hmg/ddy121. PMC 5961159. PMID 29659830.
  47. ^ Ciumas C, Lindén Hirschberg A, Savic I (May 2009). "High fetal testosterone and sexually dimorphic cerebral networks in females". Cerebral Cortex. 19 (5): 1167–1174. doi:10.1093/cercor/bhn160. PMID 18854582.
  48. ^ McAnulty RD, Burnette MM (2006). Sex and sexuality. Vol. 1. Greenwood Publishing Group. p. 165. ISBN 9780313049194.
  49. ^ 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". The Journal of Clinical Endocrinology and Metabolism. 51 (2): 223–229. doi:10.1210/jcem-51-2-223. PMID 6447160.
  50. ^ 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". The Journal of Clinical Endocrinology and Metabolism. 76 (1): 117–120. doi:10.1210/jcem.76.1.8421074. PMID 8421074.
  51. ^ Wudy SA, Dörr HG, Solleder C, Djalali M, Homoki J (August 1999). "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". The Journal of Clinical Endocrinology and Metabolism. 84 (8): 2724–2728. doi:10.1210/jcem.84.8.5870. PMID 10443667.
  52. ^ Manning JT, Bundred PE, Newton DJ, Flanagan BF (2003). "The second to fourth digit ratio and variation in the androgen receptor gene". Evolution and Human Behavior. 24 (6): 399–405. Bibcode:2003EHumB..24..399M. doi:10.1016/S1090-5138(03)00052-7.
  53. ^ Hampson E, Sankar JS (2012). "Re-examining the Manning hypothesis: androgen receptor polymorphism and the 2D:4D ratio". Evol Hum Behav. 33 (5): 557–561. Bibcode:2012EHumB..33..557H. doi:10.1016/j.evolhumbehav.2012.02.003.
  54. ^ Crabbe P, Bogaert V, De Bacquer D, Goemaere S, Zmierczak H, Kaufman JM (September 2007). "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". The Journal of Clinical Endocrinology and Metabolism. 92 (9): 3604–3610. doi:10.1210/jc.2007-0117. PMID 17579205. S2CID 33761349.
  55. ^ Berenbaum SA, Bryk KK, Nowak N, Quigley CA, Moffat S (November 2009). "Fingers as a marker of prenatal androgen exposure". Endocrinology. 150 (11): 5119–5124. doi:10.1210/en.2009-0774. PMC 2775980. PMID 19819951.
  56. ^ Paul SN, Kato BS, Hunkin JL, Vivekanandan S, Spector TD (December 2006). "The big finger: the second to fourth digit ratio is a predictor of sporting ability in women". British Journal of Sports Medicine. 40 (12): 981–983. doi:10.1136/bjsm.2006.027193. PMC 2577466. PMID 17008344.
  57. ^ Gobrogge KL, Breedlove SM, Klump KL (February 2008). "Genetic and environmental influences on 2D:4D finger length ratios: a study of monozygotic and dizygotic male and female twins". Archives of Sexual Behavior. 37 (1): 112–118. doi:10.1007/s10508-007-9272-2. PMID 18074216. S2CID 41921265.
  58. ^ a b Manning JT, Stewart A, Bundred PE, Trivers RL (November 2004). "Sex and ethnic differences in 2nd to 4th digit ratio of children". Early Human Development. 80 (2): 161–168. doi:10.1016/j.earlhumdev.2004.06.004. PMID 15500996.
  59. ^ Williams TJ, Pepitone ME, Christensen SE, Cooke BM, Huberman AD, Breedlove NJ, et al. (March 2000). "Finger-length ratios and sexual orientation". Nature. 404 (6777): 455–456. Bibcode:2000Natur.404..455W. doi:10.1038/35006555. PMID 10761903. S2CID 205005405.
  60. ^ Manning JT, Churchill AJ, Peters M (April 2007). "The effects of sex, ethnicity, and sexual orientation on self-measured digit ratio (2D:4D)". Archives of Sexual Behavior. 36 (2): 223–233. doi:10.1007/s10508-007-9171-6. PMID 17373585. S2CID 2042042.
  61. ^ Lu H, Huo ZH, Shi ZY, Peng L, Dang J, Jiao HY, et al. (2008). "Study on the digit ratio of Hui and Han ethnic groups in Ningxia". Acta Anatomica Sinica. 39 (2): 267. Archived from the original on 7 November 2016. Retrieved 7 November 2016.
  62. ^ Loehlin JC, McFadden D, Medland SE, Martin NG (December 2006). "Population differences in finger-length ratios: ethnicity or latitude?". Archives of Sexual Behavior. 35 (6): 739–742. CiteSeerX 10.1.1.579.6269. doi:10.1007/s10508-006-9039-1. PMID 16688484. S2CID 4763807.
  63. ^ Xu Y, Zheng Y (6 May 2015). "The digit ratio (2D:4D) in China: A meta-analysis". American Journal of Human Biology. 27 (3): 304–309. doi:10.1002/ajhb.22639. PMID 25284473. S2CID 40725875.
  64. ^ Ozener B, Hurd PL, Duyar I (2014). "Inbreeding is associated with lower 2D: 4D digit ratio". American Journal of Human Biology. 26 (2): 183–188. doi:10.1002/ajhb.22491. PMID 24288299. S2CID 23618195.
  65. ^ Tadmouri GO, Nair P, Obeid T, Al Ali MT, Al Khaja N, Hamamy HA (October 2009). "Consanguinity and reproductive health among Arabs". Reproductive Health. 6: 17. doi:10.1186/1742-4755-6-17. PMC 2765422. PMID 19811666.
  66. ^ Luxen MF, Buunk BP (2005). "Second-to-fourth digit ratio related to verbal and numerical intelligence and the Big Five". Personality and Individual Differences. 39 (5): 959–966. doi:10.1016/j.paid.2005.03.016.
  67. ^ Hampson E, Sankar JS (2012). "Re-examining the Manning hypothesis: androgen receptor polymorphism and the 2D: 4D digit ratio". Evolution and Human Behavior. 33 (5): 557–561. Bibcode:2012EHumB..33..557H. doi:10.1016/j.evolhumbehav.2012.02.003.
  68. ^ Oyeyemi BF, Iyiola OA, Oyeyemi AW, Oricha KA, Anifowoshe AT, Alamukii NA (2014). "Sexual dimorphism in ratio of second and fourth digits and its relationship with metabolic syndrome indices and cardiovascular risk factors". Journal of Research in Medical Sciences. 19 (3): 234–239. PMC 4061645. PMID 24949031.
  69. ^ Bailey Allison A, Hurd PL (2005). "Depression in men is associated with more feminine finger length ratios". Personality and Individual Differences. 39 (4): 829–836. doi:10.1016/j.paid.2004.12.017.
  70. ^ Coyne SM, Manning JT, Ringer L, Bailey L (2007). "Directional asymmetry (right–left differences) in digit ratio (2D: 4D) predict indirect aggression in women". Personality and Individual Differences. 43 (4): 865–872. doi:10.1016/j.paid.2007.02.010.
  71. ^ Manning JT, Kilduff LP, Trivers R (2013). "Digit ratio (2D: 4D) in Klinefelter's syndrome". Andrology. 1 (1): 94–99. doi:10.1111/j.2047-2927.2012.00013.x. PMID 23258636.
  72. ^ Trabert B, Graubard BI, Erickson RL, Zhang Y, McGlynn KA (2013). "Second to fourth digit ratio, handedness and testicular germ cell tumors". Early Human Development. 89 (7): 463–466. doi:10.1016/j.earlhumdev.2013.04.001. PMC 3684556. PMID 23623693.
  73. ^ 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". Neuropsychology. 25 (5): 581–589. doi:10.1037/a0023293. PMID 21500918.
  74. ^ Manning JT, Peters M (2009). "Digit ratio (2D:4D) and hand preference for writing in the BBC Internet Study". Laterality. 14 (5): 528–540. doi:10.1080/13576500802637872. PMID 19177258.
  75. ^ Kumar S, Singh M, Voracek M (December 2020). "Effects of hand preference on digit lengths and digit ratios among children and adults". Early Human Development. 151: 105204. doi:10.1016/j.earlhumdev.2020.105204. PMID 33059164. S2CID 222829822. Archived from the original on 17 May 2022. Retrieved 23 March 2022.
  76. ^ Fink B, Manning JT, Neave N, Grammer K (March 2004). "Second to fourth digit ratio and facial asymmetry". Evolution and Human Behavior. 25 (2): 125–32. Bibcode:2004EHumB..25..125F. doi:10.1016/S1090-5138(03)00084-9.
  77. ^ Fink B, Grammer K, Mitteroecker P, Gunz P, Schaefer K, Bookstein FL, Manning JT (October 2005). "Second to fourth digit ratio and face shape". Proceedings. Biological Sciences. 272 (1576): 1995–2001. doi:10.1098/rspb.2005.3179. PMC 1559906. PMID 16191608.
  78. ^ Barrett ES, Parlett LE, Swan SH (April 2015). "Stability of proposed biomarkers of prenatal androgen exposure over the menstrual cycle". Journal of Developmental Origins of Health and Disease. 6 (2): 149–157. doi:10.1017/S2040174414000646. PMC 5119464. PMID 25584807.
  79. ^ Ronalds G, Phillips DI, Godfrey KM, Manning JT (June 2002). "The ratio of second to fourth digit lengths: a marker of impaired fetal growth?". Early Human Development. 68 (1): 21–26. doi:10.1016/s0378-3782(02)00009-9. PMID 12191526.
  80. ^ Manning JT, Fink B (July 2020). "Understanding COVID-19: Digit ratio (2D:4D) and sex differences in national case fatality rates". Early Human Development. 146: 105074. doi:10.1016/j.earlhumdev.2020.105074. PMC 7224643. PMID 32419720.
  81. ^ Jones AL, Jaeger B, Schild C (January 2021). "No credible evidence for links between 2D:4D and COVID-19 outcomes: A probabilistic perspective on digit ratio, ACE variants, and national case fatalities". Early Human Development. 152: 105272. doi:10.1016/j.earlhumdev.2020.105272. PMC 7670914. PMID 33227636.
  82. ^ Dickman S (March 1997). "HOX gene links limb, genital defects". Science. 275 (5306): 1568. doi:10.1126/science.275.5306.1568. PMID 9072822. S2CID 33709778.
  83. ^ Hönekopp J, Watson S (2010). "Meta-analysis of digit ratio 2D:4D shows greater sex difference in the right hand". American Journal of Human Biology. 22 (5): 619–630. doi:10.1002/ajhb.21054. PMID 20737609. S2CID 29503255.
  84. ^ 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". Early Human Development. 153: 105293. doi:10.1016/j.earlhumdev.2020.105293. PMID 33340946. S2CID 229333079.
  85. ^ Xi H, Li M, Fan Y, Zhao L (February 2014). "A comparison of measurement methods and sexual dimorphism for digit ratio (2D:4D) in Han ethnicity". Archives of Sexual Behavior. 43 (2): 329–333. doi:10.1007/s10508-013-0179-9. PMC 3890058. PMID 24013635.
  86. ^ Robertson J, Zhang W, Liu JJ, Muir KR, Maciewicz RA, Doherty M (January 2008). "Radiographic assessment of the index to ring finger ratio (2D:4D) in adults". Journal of Anatomy. 212 (1): 42–48. doi:10.1111/j.1469-7580.2007.00830.x. PMC 2423386. PMID 18005121.
  87. ^ a b c Voracek M, Kossmeier M, Tran US (2019). "Which Data to Meta-Analyze, and How?". Zeitschrift für Psychologie. 227 (1). Hogrefe Publishing Group: 64–82. doi:10.1027/2151-2604/a000357. ISSN 2190-8370. S2CID 86788835.
  88. ^ a b Jones AL, Jaeger B, Schild C (January 2021). "No credible evidence for links between 2D:4D and COVID-19 outcomes: A probabilistic perspective on digit ratio, ACE variants, and national case fatalities". Early Human Development. 152. Elsevier BV: 105272. doi:10.1016/j.earlhumdev.2020.105272. PMC 7670914. PMID 33227636.
  89. ^ Voracek M, Pietschnig J, Nader IW, Stieger S (September 2011). "Digit ratio (2D:4D) and sex-role orientation: Further evidence and meta-analysis". Personality and Individual Differences. 51 (4). Elsevier BV: 417–422. doi:10.1016/j.paid.2010.06.009. ISSN 0191-8869.
  90. ^ 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". Psychological Science. 30 (4). SAGE Publications: 606–616. doi:10.1177/0956797619829688. PMID 30843758. S2CID 73496727.
  91. ^ Medland SE, Zayats T, Glaser B, Nyholt DR, Gordon SD, Wright MJ, et al. (April 2010). "A variant in LIN28B is associated with 2D:4D finger-length ratio, a putative retrospective biomarker of prenatal testosterone exposure". American Journal of Human Genetics. 86 (4): 519–525. doi:10.1016/j.ajhg.2010.02.017. PMC 2850436. PMID 20303062.
  92. ^ a b 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". Hormones and Behavior. 78. Elsevier BV: 86–94. doi:10.1016/j.yhbeh.2015.10.022. PMID 26542674. S2CID 26592548.
  93. ^ 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". Criminology. 54 (4). Wiley: 587–620. doi:10.1111/1745-9125.12115. ISSN 0011-1384.
  94. ^ a b 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)". Hormones and Behavior. 120. Elsevier BV: 104710. doi:10.1016/j.yhbeh.2020.104710. PMID 32057822. S2CID 211112860.
  95. ^ Lolli L, Batterham AM, Kratochvíl L, Flegr J, Weston KL, Atkinson G (June 2017). "A comprehensive allometric analysis of 2nd digit length to 4th digit length in humans". Proceedings. Biological Sciences. 284 (1857): 20170356. doi:10.1098/rspb.2017.0356. PMC 5489719. PMID 28659446.
  96. ^ Hollier LP, Keelan JA, Jamnadass ES, Maybery MT, Hickey M, Whitehouse AJ (February 2015). "Adult digit ratio (2D:4D) is not related to umbilical cord androgen or estrogen concentrations, their ratios or net bioactivity". Early Human Development. 91 (2). Elsevier BV: 111–117. doi:10.1016/j.earlhumdev.2014.12.011. hdl:20.500.11937/48405. PMID 25594498.
  97. ^ Lindová J, Hrušková M, Pivoňková V, Kuběna A, Flegr J (June 2008). "Digit ratio (2D:4D) and Cattell's personality traits". European Journal of Personality. 22 (4). SAGE Publications: 347–356. doi:10.1002/per.664. ISSN 0890-2070. S2CID 18205251.
  98. ^ McQuade DB (September 2011). "Does digit ratio (2D:4D) predict penile length?". Asian Journal of Andrology. 13 (5). Medknow: 667–668. doi:10.1038/aja.2011.81. PMC 3739583. PMID 21725331.
  99. ^ "Faculty Spotlight: James M. Smoliga | Tufts University School of Medicine". medicine.tufts.edu. Archived from the original on 25 December 2023. Retrieved 25 December 2023.
  100. ^ Manning, John T. (11 June 2023). "The Big Finger Trumps the Lucky Jim Fallacy". The BMJ. Archived from the original on 11 June 2023. Retrieved 11 June 2023.
  101. ^ Shultz S, Opie C, Nelson E, Atkinson QD, Dunbar RI (2014). "Evolution of Primate Social Systems: Implications for Hominin Social Evolution". In Dunbar RI, Gamble C, Gowlett JA (eds.). Lucy to Language: The Benchmark Papers. OUP Oxford. pp. 317–405. ISBN 978-0-19-965259-4.
  102. ^ Burley NT (May 2006). "An eye for detail: selective sexual imprinting in zebra finches". Evolution; International Journal of Organic Evolution. 60 (5): 1076–1085. doi:10.1554/05-399.1. JSTOR 4095408. PMID 16817546. S2CID 28869542.
  103. ^ 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". Hormones and Behavior. 55 (1): 235–239. doi:10.1016/j.yhbeh.2008.10.010. PMID 19022257. S2CID 23727819.
  104. ^ Yan RH, Malisch JL, Hannon RM, Hurd PL, Garland T (September 2008). "Selective breeding for a behavioral trait changes digit ratio". PLOS ONE. 3 (9): e3216. Bibcode:2008PLoSO...3.3216Y. doi:10.1371/journal.pone.0003216. PMC 2528935. PMID 18797502.
  105. ^ Romano M, Leoni B, Saino N (February 2006). "Examination marks of male university students positively correlate with finger length ratios (2D:4D)". Biological Psychology. 71 (2): 175–182. doi:10.1016/j.biopsycho.2005.03.006. PMID 15978716. S2CID 39777964.
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