Second To Fourth Digit Ratio

[Michael Scally MD]

This study will most likely have men all over examining their right hands. LMAO

Digit ratio, most commonly the ratio of the index to ring fingers in humans, is sexually dimorphic (males have lower values than females) with greater differences on their right hand. Ratios are determined early in development and remain relatively stable thereafter. Perhaps the popular appeal is the relative simplicity of the measure, and the fact that researchers interested in any number of behavioral or physiological traits correlated with hormone activity have adopted digit ratio as a convenient biomarker for prenatal androgen exposure. Over the past decade, the correlation of digit ratio with sexual behavior and other aspects of reproductive biology has been well documented and there is a growing list of traits with links to digit ratio, although the associations are less well established.

Amidst a flurry of 2D:4D publications, mostly indicative of positive findings, these criticisms were brought to light in a recent Asian Journal of Andrology report. The authors, Choi et al., provide convincing support for a relationship between digit ratio and penile length. The researchers measured right hand digits directly with calipers, averaging repeated measures to calculate digit ratio. Flaccid and stretched penile lengths were measured in anesthetized patients with a rigid ruler, by a second researcher blind to the digit measurements. Digit ratio was strongly (negatively) correlated with stretched penile length (P=0.024). Choi et al. concluded that higher prenatal androgen exposure is responsible for both the lower digit ratio and the longer penile length.


McQuade DB. Does digit ratio (2D:4D) predict penile length? Asian J Androl. http://www.nature.com/aja/journal/vaop/ncurrent/full/aja201181a.html / http://www.nature.com/aja/journal/vaop/ncurrent/pdf/aja201181a.pdf


Choi IH, Kim KH, Jung H, Yoon SJ, Kim SW, Kim TB. Second to fourth digit ratio: a predictor of adult penile length. Asian J Androl. http://www.nature.com/aja/journal/vaop/ncurrent/pdf/aja201175a.pdf

The second to fourth digit ratio (2D:4D) has been proposed as a putative biomarker for prenatal testosterone and covaries with the sensitivity of the androgen receptor (AR). Both prenatal testosterone and the AR play a central role in penile growth. In this study, we investigated the relationship between digit ratio and penile length.

Korean men who were hospitalized for urological surgery at a single tertiary academic centre were examined in this study, and 144 men aged 20 years or older who gave informed consent were prospectively enrolled. Right-hand second- and fourth-digit lengths were measured by a single investigator prior to measurement of penile length. Under anaesthesia, flaccid and stretched penile lengths were measured by another investigator who did not measure nor have any the information regarding the digit lengths.

Univariate and multivariate analysis using linear regression models showed that only height was a significant predictive factor for flaccid penile length (univariate analysis:r=0.185, P=0.026; multivariate analysis: r=0.172, P=0.038) and that only digit ratio was a significant predictive factor for stretched penile length (univariate analysis:r=?0.216, P=0.009; multivariate analysis: r=?0.201,P=0.024; stretched penile length=?9.201×digit ratio + 20.577).

Based on this evidence, we suggest that the digit ratio can predict adult penile size and that the effects of prenatal testosterone may in part explain the differences in adult penile length.

 

[biceps72]

Re: Second To Fourth Digit Ratio: A Predictor Of Adult Penile Length

r = pretty small

making r squared (coefficient of determination) quite small. Yes there is a "loose" relationship but damn loose!!!

 

[zkt]

Re: Second To Fourth Digit Ratio: A Predictor Of Adult Penile Length

r = pretty small

making r squared (coefficient of determination) quite small. Yes there is a "loose" relationship but damn loose!!!

P=0.009; multivariate analysis: Very weak correlation
[ame=http://en.wikipedia.org/wiki/Correlation_and_dependence]Correlation and dependence - Wikipedia, the free encyclopedia[/ame]

I didnt know you had a background in statistics.

 

[hardasnails1973]

Re: Second To Fourth Digit Ratio: A Predictor Of Adult Penile Length

They had this on a local morning TV talk show with regis and kelly. It was pretty hilarious!!

Mike,
Have there been actually studies done on figure length and athletic performance in childern ? I remember reading about this one time, but did not know how scientific valid it was.

 

[Jeton]

Re: Second To Fourth Digit Ratio: A Predictor Of Adult Penile Length

these finger length studies just point to a deeper tangle of associations. first, a 2d/4d ratio of <1 was correlated with being gay or lesbian, THEN it was correlated with being a str8 male or lesbian female. my index finger is 92-93% the length of my ring finger, ostensibly making me hyper heterosexual...which is exactly wrong, of course.

however, 4 years ago or so i DID do the Snoopy Happy Dance when i finally took a tailor's tape measure to myself....

...let's just say it's smarter than trying to use a carpenter's tape measure. i was very happy indeed.

 

[BBC3]

Re: Second To Fourth Digit Ratio: A Predictor Of Adult Penile Length

Am I misinterpreting? Because I had ofter heard it was a factor with the middle finger. BUT I think the study is referring to the POINTER and the RING finger. Thus stating that IF the length of your pointer finger is CLOSER to the length of you ring finger.... YOU HAVE A MONSTER COCK.

Did I miss something...

 

[Jeton]

Re: Second To Fourth Digit Ratio: A Predictor Of Adult Penile Length

Am I misinterpreting? Because I had ofter heard it was a factor with the middle finger. BUT I think the study is referring to the POINTER and the RING finger. Thus stating that IF the length of your pointer finger is CLOSER to the length of you ring finger.... YOU HAVE A MONSTER COCK.

Did I miss something...

i think it sez that the SHORTER ur index finger is compared to ur ring finger, the more testosterone u were exposed to in-utero....more t at that stage meaning more cock, n more machismo.

 

[GirlyMan]

Re: Second To Fourth Digit Ratio: A Predictor Of Adult Penile Length

So now every woman I meet will immediately know I have a little dick. ... great ... thanks. ... guess it's only fair 'cause I can see how big their boobs are,

 

[GirlyMan]

Re: Second To Fourth Digit Ratio: A Predictor Of Adult Penile Length

Am I misinterpreting? Because I had ofter heard it was a factor with the middle finger. BUT I think the study is referring to the POINTER and the RING finger. Thus stating that IF the length of your pointer finger is CLOSER to the length of you ring finger.... YOU HAVE A MONSTER COCK.

Yes, I think you are misinterpreting and my read is the same as Jeton's. The length of my index finger is almost the same as my ring finger. So the ratio is very close to 1.0 and I do indeed have a little dick. The shorter your index finger is compared to your ring finger, the bigger your dick. If your index finger is bigger than your ring finger then god help you. That's my read at least. ... unfortunately.

 

[biceps72]

Re: Second To Fourth Digit Ratio: A Predictor Of Adult Penile Length

P=0.009; multivariate analysis: Very weak correlation
Correlation and dependence - Wikipedia, the free encyclopedia

I didnt know you had a background in statistics.

ph.d in biometry actually

 

[DragonRider]

Re: Second To Fourth Digit Ratio: A Predictor Of Adult Penile Length

So now every woman I meet will immediately know I have a little dick. ... great ... thanks. ... guess it's only fair 'cause I can see how big their boobs are,

Well at least you aren't alone. It's a good thing I'm married. Now I understand why I never gort any attention when I was single.

 

[Michael Scally MD]

Second-To-Fourth Digit Ratio Predicts Facial Attractiveness In Men

The relative length of the second (index) and fourth (ring) fingers, or 2D:4D ratio, is sexually dimorphic in several species, with lower 2D:4D ratios for males than females in mammals, while in birds it appears to be the reverse. Although the precise genetic mechanism explaining this sexual dimorphism is still unclear, there is compelling evidence that in utero fetal testosterone and fetal oestrogen influence 2D:4D ratio in humans.

Androgens such as testosterone are also involved in the development and maintenance of secondary sexual characters, and thereby in mate choice. Because maintaining a high level of testosterone is costly for males, those that display enhanced sexual characters without suffering too much from immunosuppression are considered high-quality males. Therefore, women should ultimately increase their reproductive success by choosing mates displaying testosterone-dependent sexual traits. In humans, men with higher levels of circulating testosterone have voices with lower fundamental frequency and more masculine faces, two traits that are preferred by women when they become sexually mature.

Since the growth of the fourth finger is dependent on the level of prenatal androgen, and since some authors have hypothesized a positive correlation between prenatal and adult testosterone levels, 2D:4D ratios might correlate negatively with some other testosterone-dependent traits. If these traits such as vocal and facial features are sexually selected, then measures of 2D:4D should be a good predictor of men’s attractiveness.

In this study, researchers investigated, in three sensory modalities involved in human mate choice (voice, body odour and face), whether second-to-fourth digit ratio of left and right hands, and digit ratio difference between the two hands (Dr2l), can predict male masculinity and attractiveness. They predicted that 2D:4D ratio and Dr2l would be negatively correlated with face, voice and odour masculinity and attractiveness, as evaluated by females. As voice frequency and face symmetry influence women’s preference for men (deeper voices are preferred; symmetrical faces are more attractive), they also measured these two factors and linked them to 2D:4D ratios. Finally, they controlled for the use of hormonal contraceptives by the female raters, since this could alter women’s preference for various male features, such as body odour, face and voice.

Their main finding is that right hand 2D:4D and Dr2l are significant predictors of attractiveness, but not masculinity of male faces, whether they are considered as short-term or long-term potential partners. Right hand 2D:4D also predicts perceived facial symmetry. The link between 2D:4D and facial attractiveness is consistent with previous studies investigating either self-evaluated attractiveness or men’s attractiveness rated by women. This illustrates a female preference for men with a low 2D:4D ratio possibly driven by the fact that these have more symmetrical faces. Such a preference might have evolved because it increases females’ reproductive success by gaining benefits from partners who are physically more robust and who have more ejaculates that are fertile.


Ferdenzi C, Lemaitre J-Fo, Leongomez JD, Roberts SC. Digit ratio (2D:4D) predicts facial, but not voice or body odour, attractiveness in men. Proceedings of the Royal Society B: Biological Sciences 2011;278(1724):3551-7. Digit ratio (2D:4D) predicts facial, but not voice or body odour, attractiveness in men

There is growing evidence that human second-to-fourth digit ratio (or 2D:4D) is related to facial features involved in attractiveness, mediated by in utero hormonal effects. The present study extends the investigation to other phenotypic, hormone-related determinants of human attractiveness: voice and body odour. Pictures of faces with a neutral expression, recordings of voices pronouncing vowels and axillary odour samples captured on cotton pads worn for 24 h were provided by 49 adult male donors. These stimuli were rated on attractiveness and masculinity scales by two groups of 49 and 35 females, approximately half of these in each sample using hormonal contraception. Multivariate regression analyses showed that males' lower (more masculine) right 2D:4D and lower right-minus-left 2D:4D (Dr?l) were associated with a more attractive (and in some cases more symmetrical), but not more masculine, face. However, 2D:4D and Dr?l did not predict voice and body odour masculinity or attractiveness. The results were interpreted in terms of differential effects of prenatal and circulating testosterone, male facial shape being supposedly more dependent on foetal levels (reflected by 2D:4D ratio), whereas body odour and vocal characteristics could be more dependent on variation in adult circulating testosterone levels.


Meindl K, Windhager S, Wallner B, Schaefer K. Second-to-fourth digit ratio and facial shape in boys: the lower the digit ratio, the more robust the face. Proceedings of the Royal Society B: Biological Sciences. Second-to-fourth digit ratio and facial shape in boys: the lower the digit ratio, the more robust the face

During human ontogeny, testosterone has powerful organizational and activational effects on the male organism. This has led to the hypothesis that the prenatal environment (as studied through the second-to-fourth digit ratio, 2D : 4D) is not only associated with robust adult male faces that are perceived as dominant and masculine, but also that there is an activational step during puberty. To test the latter, we collected digit ratios and frontal photographs of right-handed Caucasian boys (aged 4–11 years) along with age, body height and body weight. Using geometric morphometrics, we show a significant relationship between facial shape and 2D : 4D before the onset of puberty (explaining 14.5% of shape variation; p = 0.014 after 10 000 permutations, n = 17). Regression analyses depict the same shape patterns as in adults, namely that the lower the 2D : 4D, the smaller and shorter the forehead, the thicker the eyebrows, the wider and shorter the nose, and the larger the lower face. Our findings add to previous evidence that certain adult male facial characteristics that elicit attributions of masculinity and dominance are determined very early in ontogeny. This has implications for future studies in various fields ranging from social perception to life-history strategies.

 

[Michael Scally MD]

Garcia-Cruz E, Huguet J, Piqueras M, Ribal MJ, Alcaraz A. Second to fourth digit ratio, adult testosterone level and testosterone deficiency. BJU Int 2012;109(2):266-71. Second to fourth digit ratio, adult testosterone level and testosterone deficiency - Garc[]a-Cruz - 2011 - BJU International - Wiley Online Library

OBJECTIVES: The ratio of the second and fourth finger lengths (2D/4D) is related to intrauterine exposure to testosterone. The relationship between 2D/4D and adult hormonal pattern is controversial. The aim of our study was to determine if there was a relationship between adult serum testosterone levels and the 2D/4D ratio.

PATIENTS AND METHODS: We prospectively recruited 204 consecutive patients referred for transrectal prostate biopsy between January 2008 and June 2009. The same physician performed clinical examinations, 2D/4D measurements and the transrectal biopsy in all cases. Cut-off points of 231 and 346 ng/dL testosterone (8 and 12 nmol/L) were used. 2D/4D determination was done with a vernier calliper on the left hand. The hormonal profile (testosterone and sexual hormone binding globulin) of the patients was determined between 7.00 am and 11.00 am. Age, weight, height, body mass index, toxic habits, digital rectal examination, prostate-specific antigen and 2D and 4D measurements were recorded prospectively.

RESULTS: The mean age was 67 +/- 7 years and the mean testosterone level was 413 +/- 18 ng/dL (14.33 +/- 0.62 nmol/L). The percentages of patients with testosterone <231 ng/dL (8 nmol/L) and testosterone <346 ng/dL (12 nmol/L) were 6.1 and 30.6 respectively. Univariate analysis showed that low 2D/4D ratios were related to higher levels of testosterone (B=-741.98; beta=-0.165, P= 0.045) and also with low prevalence of biochemical hypogonadism (testosterone <346 ng/dL). Mean 2D/4D ratio in patients with testosterone >346 ng/dL was lower than in patients with testosterone <346 ng/dL (2D/4D 0.97 +/- 0.037 vs 0.99 +/- 0.043 depending on their hormonal status, P= 0.05). High 2D/4D ratio was associated with low testosterone serum levels (P= 0.046).

CONCLUSIONS: The 2D/4D ratio is related to adult testosterone levels and the presence of testosterone deficiency syndrome. Patients with high 2D/4D ratios have lower testosterone levels and higher risk of testosterone deficiency syndrome.

 

[pinkman]

This is all very depressing stuff. I wonder when they start screening male fetuses for short ringfingers to abort them before birth.

 

[Michael Scally MD]

Lu H, Huo ZH, Liu YJ, Shi ZY, Zhao JL. Correlations between digit ratio and infertility in Chinese men. Early Hum Dev. ScienceDirect.com - Early Human Development - Correlations between digit ratio and infertility in Chinese men

BACKGROUND: Digit ratio, especially second to fourth digit ratio (2D:4D) is lower in men than in women. The ratios of digit may be established in utero and is negatively correlated with sperm counts and testosterone in men and positively correlated with estrogen in men and women. AIM: To study whether the digit ratio (especially 2D:4D) are associated with the a+b ratio of sperm number in Chinese populations.

METHODS: Photocopies of the two hands of 268 men (controls: 72; patients: 196) and seminal parameters of masturbatory semen samples were collected.

RESULTS: The mean values of digit ratio of the controls and the patients all presented a trend as 2D:3D<2D:4D<3D:4D<2D:5D<4D:5D<3D:5D; the patients have higher mean values than controls; significant variances of 2D:3D, 3D:4D (left: P<0.05; right: P</=0.05) and 2D:4D (left: P<0.001; right: P<0.01) were found between two groups; there was a higher percentage of 2D>4D in the patients; the relationship between 2D:4D and a+b ratio of sperm number in the patients was significant (P<0.001).

CONCLUSION: Digit ratio, especially 2D:4D in the left hand maybe one of the important markers of infertility in men for early diagnosis.

 

[Michael Scally MD]

Zhang C, Dang J, Pei L, et al. Relationship of 2D:4D finger ratio with androgen receptor CAG and GGN repeat polymorphism. Am J Hum Biol. Relationship of 2D:4D finger ratio with androgen receptor CAG and GGN repeat polymorphism - Zhang - 2012 - American Journal of Human Biology - Wiley Online Library

OBJECTIVES: The relative length of the second-to-fourth digits (2D:4D) has been linked with prenatal androgen in humans. A recent study shows that the 2D:4D ratio in mice is controlled by the balance of androgen to estrogen signaling during a narrow window of digit development. Androgen receptor (AR) activity is higher in digit 4 than in digit 2, and inactivation of AR decreases growth of digit 4, which causes a higher 2D:4D ratio. At the molecular level, the effect of androgens is mediated through the activation of AR. The CAG/GGN repeat polymorphisms of the AR gene are associated with AR activity. Here, we investigate the effect of CAG/GGN repeat polymorphisms in AR on 2D:4D in Chinese.

METHODS: Digit lengths of the second and fourth fingers were measured from photocopies of the ventral surface of the hand and by actual finger measurements. We genotyped AR polymorphisms by ABI 3730 DNA analyzer.

RESULTS: We found that left hand 2D:4D ratio was longer than that of the right hand both in males and in females. We failed to find any relationship between CAG / GGN alleles and the left hand, right hand, right minus left-hand or mean hand 2D:4D ratios (all, r < 0.20, P > 0.05).

CONCLUSIONS: In this study, we first found that the left hand 2D:4D ratio was longer than that of the right hand in both males and females. However, we found that both CAG and GGN alleles were not associated with the left hand, right hand, right minus left-hand or mean hand 2D:4D ratios.

 

[Michael Scally MD]

Perciavalle V, Di Corrado D, Petralia MC, Gurrisi L, Massimino S, Coco M. The second-to-fourth digit ratio correlates with aggressive behavior in professional soccer players. Mol Med Rep. The second-to-fourth digit ratio correlates with aggressive behavior in professional soccer players

The aim of this study was to test the hypothesis that high levels of testosterone during prenatal life, testified by a low second-to-fourth digit ratio (2D:4D), as well as in adulthood affect the aggressive behavior of professional soccer players. Using 18 male professional players from a first level Italian Soccer Team we calculated: i) the 2D:4D ratio of the right hand, ii) the number of yellow and red cards per game, iii) the mean salivary testosterone concentration (Sal/T) and iv) the handling of aggressive impulses as assessed by the Picture Frustration test (PFT). Soccer players with a lower 2D:4D ratio had a higher number of fouls per game. A significant negative correlation was observed between Sal/T and 2D:4D ratio, as well as between 2D:4D ratio and the aggressiveness of players. By contrast, a significant positive correlation of Sal/T and fouls/game score and PFT was detected. No significant correlation was detected between 2D:4D or Sal/T and the playing position of players. Results of this study revealed that in professional soccer players, aggressive behavior, with the consequent increased risk of fouls during the game, is more likely to occur in individuals with high testosterone levels, not only in adulthood, but also during their intrauterine life.

 

[Michael Scally MD]

Ellis L, Hoskin AW. Criminality and the 2D:4D Ratio: Testing the Prenatal Androgen Hypothesis. Int J Offender Ther Comp Criminol. Criminality and the 2D:4D Ratio: Testing the Prenatal Androgen Hypothesis

A decade old theory hypothesizes that brain exposure to androgens promotes involvement in criminal behavior. General support for this hypothesis has been provided by studies of postpubertal circulating levels of testosterone, at least among males. However, the theory also predicts that for both genders, prenatal androgens will be positively correlated with persistent offending, an idea for which no evidence currently exists. The present study used an indirect measure of prenatal androgen exposure-the relative length of the second and fourth fingers of the right hand (r2D:4D)-to test the hypothesis that elevated prenatal androgens promote criminal tendencies later in life for males and females. Questionnaires were administered to 2,059 college students in Malaysia and 1,291 college students in the United States. Respondents reported their r2D:4D relative finger lengths along with involvement in 13 categories of delinquent and criminal acts. Statistically significant correlations between the commission of most types of offenses and r2D:4D ratios were found for males and females even after controlling for age. It is concluded that high exposure to androgens during prenatal development contributes to most forms of offending following the onset of puberty.

 

[Michael Scally MD]

Honekopp J. Digit ratio (2D:4D) and male facial attractiveness: New data and a meta-analysis. Evol Psychol 2013;11(5):944-52. Digit ratio (2D:4D) and male facial attractiveness: New data and a meta-analysis | Evolutionary Psychology

Digit ratio (2D:4D) appears to correlate negatively with prenatal testosterone (T) effects in humans. As T probably increases facial masculinity, which in turn might be positively related to male facial attractiveness, a number of studies have looked into the relationship between 2D:4D and male facial attractiveness, showing equivocal results. Here, I present the largest and third largest samples so far, which investigate the relationship between 2D:4D and male facial attractiveness in adolescents (n = 115) and young men (n = 80). I then present random-effects meta-analyses of the available data (seven to eight samples, overall n = 362 to 469). These showed small (r approximately -.09), statistically non-significant relationships between 2D:4D measures and male facial attractiveness. Thus, 2D:4D studies offer no convincing evidence at present that prenatal T has a positive effect on male facial attractiveness. However, a consideration of confidence intervals shows that, at present, a theoretically meaningful relationship between 2D:4D and male facial attractiveness cannot be ruled out either.

 

[Michael Scally MD]

Honekopp J. No Evidence that 2D:4D is Related to the Number of CAG Repeats in the Androgen Receptor Gene. Front Endocrinol (Lausanne) 2013;4:185. Frontiers | No Evidence that 2D:4D is Related to the Number of CAG Repeats in the Androgen Receptor Gene | Frontiers in Pediatric Endocrinology

The length ratio of the second to the fourth digit (2D:4D) is a putative marker of prenatal testosterone (T) effects. The number of CAG repeats (CAGn) in the AR gene is negatively correlated with T sensitivity in vitro. Results regarding the relationship between 2D:4D and CAGn are mixed but have featured prominently in arguments for and against the validity of 2D:4D. Here, I present random-effects meta-analyses on 14 relevant samples with altogether 1904 subjects. Results were homogeneous across studies. Even liberal estimates (upper limit of the 95% CI) were close to zero and therefore suggested no substantial relationship of CAGn with either right-hand 2D:4D, left-hand 2D:4D, or the difference between the two. However, closer analysis of the effects of CAGn on T dependent gene activation in vitro and of relationships between CAGn and T dependent phenotypic characteristics suggest that normal variability of CAGn has mostly no, very small, or inconsistent effects. Therefore, the lack of a clear association between CAGn and 2D:4D has no negative implications for the latter's validity as a marker of prenatal T effects.