Digit Length Ratio Research Articles

Are 2D:4D finger-length ratios an indicator of androgenetic alopecia in males?

BACKGROUNDAlthough the pathogenesis of androgenetic alopecia is not completely understood, the roles of genetic susceptibility and androgens are well-known. A lower ratio of the second digit (index finger = 2D) to the fourth digit (ring finger = 4D) length has been hypothesized to reflect prenatal androgen exposure and/or higher sensitivity to androgens.OBJECTIVESTo determine the relationship between the second to fourth digit length ratio and androgenetic alopecia.METHODSFinger length measurements were made by a digital vernier calliper. Androgenetic alopecia severity was assessed using the Hamilton-Norwood scale. Subjects with an androgenetic alopecia score of grade III or more were included in the study.RESULTSA total of 189 males with androgenetic alopecia and 171 healthy controls were enrolled in the study. The age range of participants was 19-65 years. The 2D:4D ratios in patients with androgenetic alopecia were significantly lower than those of healthy controls for the right hand; however, no significant difference was found for the left hand. Average 2D:4D ratios in androgenetic alopecia patients were also lower than in controls. No significant relationship was observed between androgenetic alopecia severity and 2D:4D ratios.CONCLUSIONOur data support the anatomical evidence of in utero androgen exposure and/or an individual’s sensitivity to androgens in patients with androgenetic alopecia. Furthermore, the right hand 2D:4D ratio might be an indicator of androgenetic alopecia development.

Second-to-fourth digit length ratio as a measure of harm avoidance

Research on the associations between the ratio of second-to-fourth digit lengths (2D:4D ratio) and psychological variables could be a useful method of confirming sex hormone effects on human behavior tendencies. This study investigated the correlations between the 2D:4D ratio and characteristics of temperament and character in an urban community population. We hypothesized that the 2D:4D ratio correlates more strongly with temperament than with character. A total of 728 healthy adults (330 men and 398 women) ranging in age from 20 to 45years were tested. Subjects completed the Temperament and Character Inventory (TCI) and were examined by measuring the 2D:4D ratio using a direct measurement method. Correlations between the 2D:4D ratio and psychological characteristics were explored. For women only, significant positive correlations with the 2D:4D ratio were found in the TCI-Temperament dimension (TCI-T), particularly in the two subscales of harm avoidance scale. Women with higher 2D:4D ratios had higher fear of uncertainly scores (rpartial=0.206, p=0.028) and shyness with strangers scores (rpartial=0.252, p=0.024). The 2D:4D ratio shows stronger correlations with temperament than with character. A higher 2D:4D ratio of woman is expected to indicate harm avoidance.

Mixed Sex Effects on the Second-to-Fourth Digit Ratio of Túngara Frogs (Engystomops pustulosus) and Cane Toads (Rhinella marina).

Sexual dimorphism in the ratio of digit lengths has been correlated to behavioral, physiological, and morphological traits in a variety of taxa. While sexual dimorphism in the second-to-fourth digit length ratio (2D:4D) is a well-established indicator of prenatal androgen exposure in mammals, investigations into the patterns of 2D:4D and the drivers of such variation in other taxa are lacking. We used linear mixed effects models to gain a mechanistic understanding of the factors that drive variation in the scaling relationship between the lengths of the second and fourth digits in two species of anurans: túngara frogs (Engystomops pustulosus) and cane toads (Rhinella marina). We found evidence for sexual dimorphism of the 2D:4D scaling relationship on the front feet of túngara frogs, with female frogs having a larger ratio than males resulting from a relatively longer second digit on females. To our knowledge, this mammal-like pattern of sex differences in digit ratio has not yet been reported for anurans. However, given the reduced number of digits on the front feet of anurans, and uncertainty about which digit was lost during evolutionary history, this apparent sexual dimorphism in the front feet of túngara frogs should be treated with caution. In contrast, we found no evidence of sexual dimorphism in 2D:4D on either the front or rear feet of cane toads. This study highlights ambiguities in 2D:4D across taxa and suggests that further research is needed to evaluate the effect of androgens on 2D:4D in animals other than placental mammals.

Changes in spatial cognition and brain activity after a single dose of testosterone in healthy women

Studies have consistently shown that males perform better than females on several spatial tasks. Animal and human literature suggests that sex hormones have an important role in both establishing and maintaining this difference. The aim of the present study was to examine the effects of exogenous testosterone on spatial cognition and brain activity in healthy women. A cross-sectional, double-blind, randomized, placebo-controlled study was performed in 42 healthy young women who either received one dose of 0.5mg sublingual testosterone or placebo. They then learned a virtual environment and performed navigation tasks during functional magnetic resonance imaging (fMRI). Subsequently, their knowledge of the virtual environment, self-reported navigation strategy, and mental rotation abilities were measured. The testosterone group had improved representations of the directions within the environment and performed significantly better on the mental rotation task compared to the placebo group, but navigation success and navigation strategy were similar in the two groups. Nevertheless, the testosterone group had significantly increased activity within the medial temporal lobe during successful navigation compared to the placebo group, and a positive correlation between testosterone load and medial temporal lobe activity was found. Fetal testosterone levels, measured as second-to-fourth digit length ratio, interacted significantly with parahippocampal activity and tended towards giving higher mental rotation task scores. These results demonstrated that testosterone had a limited effect pertaining specifically to spatial cognition involving 3D-visualization in healthy women, while complex behaviors such as navigation, relying more on learned strategies, were not altered despite increased neuronal activity in relevant brain regions.

Digit ratios in two lacertid lizards: sexual dimorphism and morphological and physiological correlates

Digit length ratio (primarily 2D:4D) has become increasingly popular as a possible biomarker of intrauterine steroid exposure in the human medical, social and psychological literature. Human males tend to have lower digit ratios than females, and individuals with low ratios tend to excel in physical performance, especially in endurance-related sports. Because early limb development is evolutionarily conservative, it has been speculated that these trends should also be visible in other tetrapod vertebrates. However, studies on non-human vertebrates are scant, and their results suggest that sexual dimorphism in digit ratios and the associations with physical performance are much more intricate and taxon-specific than presumed. In this study, we compared digit ratios of two Podarcis lizards among sexes, colour morphs and species. We also tested for associations with three performance characteristics that are of ecological relevance. Both species examined exhibit male-larger sexual dimorphism in digit ratio. 2D:4D, 3D:4D and 2D:3D ratios are tightly correlated within the manus and the pes, but less so between manus and pes. In the colour polymorphic species P. melisellensis, the yellow morph exhibits higher dimorphism than the orange and white morphs. Digit ratios did not correlate with individual performance for sprint speed or endurance, but within males of P. melisellensis, individuals with higher digit ratios correlated positively with head size and bite force. We conclude that digit ratios in lizards deserve attention, because they exhibit sexual dimorphism and correlate with ecologically relevant morphological and performance variables. As lizard species differ widely in mating systems, reproductive mode, habitat use and locomotor behaviour, they seem excellent model animals for studying patterns in digit length ratios.

Sex differences in mental rotation and how they add to the understanding of autism.

The most consistent cognitive sex differences have been found in the visuo-spatial domain, using Mental Rotation (MR) tasks. Such sex differences have been suggested to bear implications on our understanding of autism spectrum disorders (ASD). However, it is still debated how the sex difference in MR performance relates to differences between individuals with ASD compared to typically developed control persons (TD). To provide a detailed exploration of sex differences in MR performance, we studied rotational (indicated by slopes) and non-rotational aspects (indicated by intercepts) of the MR task in TD individuals (total N = 50). Second-to-fourth digit length ratios (2D:4D) were measured to investigate the associations between prenatal testosterone and performance on MR tasks. Handedness was assessed by the use of the Edinburgh Handedness Inventory in order to examine the relation between handedness and MR performance. In addition, we investigated the relation of spatial to systemising abilities, both of which have been associated with sex differences and with ASD, employing the Intuitive Physics Test (IPT). Results showed a male advantage in rotational aspects of the MR task, which correlated with IPT results. These findings are in contrast to the MR performance of individuals with ASD who have been shown to outperform TD persons in the non-rotational aspects of the MR task. These results suggest that the differences in MR performance due to ASD are different from sex-related differences in TD persons, in other words, ASD is not a simple and continuous extension of the male cognitive profile into the psychopathological range as the extreme male brain hypothesis (EMB) of ASD would suggest.

The ratios of 2nd to 4th digit may be a predictor of schizophrenia in male patients.

The production of androgens (mostly testosterone) during the early fetal stage is essential for the differentiation of the male brain. Some authors have suggested a relationship between androgen exposure during the prenatal period and schizophrenia. These two separate relationships suggest that digit length ratios are associated with schizophrenia in males. The study was performed in a university hospital between October 2012 and May 2013. One hundred and three male patients diagnosed with schizophrenia according to DSM-IV using SCID-I, and 100 matched healthy males, were admitted to the study. Scale for the Assessment of Positive Symptoms (SAPS), Scale for the Assessment of Negative Symptoms (SANS) and Brief Psychiatric Rating Scale (BPRS) were used to assess schizophrenia symptoms. The second digit (2D) and fourth digit (4D) asymmetry index (AI), and the right- and left-hand 2D:4D ratios were calculated. All parametric data in the groups were compared using an independent t-test. The predictive power of the AI was estimated by receiver operating characteristics analysis. The 2D:4D AI was statistically significantly lower in the patient group than the healthy control comparison group. There were significant differences between the schizophrenia and the control groups in respect of left 2D:4D and right 2D:4D. There was no correlation between AI, left, or right 2D:4D, BPRS, or SAPS in the schizophrenia group. However, there was a negative correlation between left 2nd digit (L2D):4D and the SANS score. Our findings support the view that the 2D:4D AI can be used as a moderate indicator of schizophrenia. Even more simply, the right or left 2D:4D can be used as an indicator. L2D:4D could indicate the severity of negative symptoms.

Validation of digit-length ratio (2D:4D) assessments on the basis of DXA-derived hand scans.

BackgroundThe second-to-fourth digit-length ratio (2D:4D) may be a correlate of prenatal sex steroids, and it has been linked to sporting prowess. The aim of the study was to validate dual-energy X-ray-absorptiometry (DXA) as a technique to assess 2D:4D in soccer players under 15 years of age (U-15).MethodsPaired X-ray and DXA scans of the left hands of 63 male U-15 elite soccer players (age: 14.0 ± 0.3 years) were performed, and 2D:4D was then compared between the two techniques. The 2D:4D measurements were performed twice by two blinded raters. Intrarater and interrater reliability, as well as agreement between the X-ray and the DXA assessments, were tested.ResultsIntrarater reliabilities of both raters using X-ray with intraclass correlation coefficients (ICCs) of 0.97 and 0.90 were excellent. Using DXA, the ICCs were 0.90 and 0.91 thus also showing excellent reliability. Interrater reliabilities were excellent using both the X-ray (ICC of 0.94) and the DXA (ICC of 0.90), assessments respectively. Bland-Altman plots demonstrated that the 2D:4D ratios of the two raters did not differ significantly between the X-ray and the DXA assessments. The standard errors of estimate were 0.01 for both techniques. The 95% limits of agreement of ±0.018 (±2.0%) and ±0.023 (±2.6%), respectively, were within the acceptable tolerance of 5%, and showed very good agreement.ConclusionDXA offered a replicable technique for assessing 2D:4D in youth soccer players. Therefore, the DXA technique seems to be an alternative method for evaluating 2D:4D in youth sports.

Penile length, digit length, and anogenital distance according to birth weight in newborn male infants.

PurposeAnogential distance (AGD) and the 2:4 digit length ratio appear to provide a reliable guide to fetal androgen exposure. We intended to investigate the current status of penile size and the relationship between penile length and AGD or digit length according to birth weight in Korean newborn infants.Materials and MethodsBetween May 2013 and February 2014, among a total of 78 newborn male infants, 55 infants were prospectively included in this study. Newborn male infants with a gestational age of 38 to 42 weeks and birth weight>2.5 kg were assigned to the NW group (n=24) and those with a gestational age<38 weeks and birth weight<2.5 kg were assigned to the LW group (n=31). Penile size and other variables were compared between the two groups.ResultsStretched penile length of the NW group was 3.3±0.2 cm, which did not differ significantly from that reported in 1987. All parameters including height, weight, penile length, testicular size, AGD, and digit length were significantly lower in the LW group than in the NW group. However, there were no significant differences in AGD ratio or 2:4 digit length ratio between the two groups.ConclusionsThe penile length of newborn infants has not changed over the last quarter century in Korea. With normal penile appearance, the AGD ratio and 2:4 digit length ratio are consistent irrespective of birth weight, whereas AGD, digit length, and penile length are significantly smaller in newborns with low birth weight.

2D:4D values are associated with mathematics performance in business and economics students

Prenatal testosterone has organizational effects on adult cognition. The second-to-fourth digit length ratio, which is a proxy of prenatal testosterone exposure, has been linked to a wide variety of sexually differentiated behaviors. We analyze the association between academic performance and the second-to-fourth digit ratio among students at the Faculty of Business and Economics of the University of Granada (Spain). In a sample of 516 freshmen (304 women), we find an inverted U-shaped relationship between digit ratio and mathematics grades. Males and females show the same pattern. Participants with both high and low digit ratios earn lower grades in mathematics, while participants which have intermediate digit ratios achieve the highest grades in mathematics. We also find that there is no statistically significant relationship between the digit ratio and the average grades earned by students in other courses except mathematics taken in the first semester at the Faculty of Business and Economics.

Anthropometrics related to the performance of a sample of male swimmers.

The main purpose of the present investigation of 21 elite male swimmers was to assess whether the Ape Index (the ratio between the individual's arm span and height) and/or the second-to-fourth digit length ratio (2D:4D), i.e., the ratio between the length of the second and the fourth fingers of the right hand, are associated with the performance of high-level swimmers, when mood and/or executive function are covaried. The results showed no statistically significant correlation between the Ape Index and 2D:4D ratio, performance, executive function, or mood. In contrast, statistically significant correlations were found between 2D:4D ratio and performance, executive function, and mood. Regressions indicated that 2D:4D ratio and not Ape Index is related to the performances of a sample of male swimmers.

Environmental levels of oestrogenic and antiandrogenic compounds feminize digit ratios in male rats and their unexposed male progeny

Digit length ratios, especially the second-to-fourth digit ratio (2D : 4D), are associated with various pathological and behavioural conditions in many species including humans and are dependent upon prenatal androgen to oestrogen balance. It is unknown whether digit ratios are modified by environmental exposure to ubiquitous endocrine disruptors. We studied the effect on adult male Wistar rat digit ratios of a gestational exposure to the oestrogenic and antiandrogenic compounds bisphenol A (BPA), genistein and vinclozolin, in low doses, and in combination with investigating in parallel a possible sexual dimorphism of this trait. We also investigated the effects on the male progeny not exposed during gestation. X-rays were taken of the left and right forepaws, and 2D-5D proximal to distal phalanx distances were measured by a standardized procedure based on semi-automatic image analysis. We provide evidence that there is a sexual dimorphism of digit ratios in the Wistar rat, and we found that BPA alone or in combination with genistein and vinclozolin significantly feminized digit ratios in male rats. Intriguingly, significant feminization of digit ratios was also found in the unexposed male progeny of males that had been exposed to compound mixtures. In conclusion, prenatal environmental levels of endocrine-active substances permanently disrupt digit ratios. Digit ratio measurement in adults is thus a promising biomarker of prenatal exposure to low-dose endocrine disruptors in rodents, with potential implications for future studies in humans.

Alcohol and nicotine intake and prenatal level of androgens measured by digit ratio

The purpose of this study was to examine the associations between using unhealthy substances and the digit ratio (2nd to 4th digit length ratio, 2D:4D) which is supposed to indicate the prenatal testosterone level. The subjects were 455 students, 225 women and 230 men. Participants declared their frequency of smoking and alcohol drinking. There was no significant difference in digit ratios between subjects regularly using both nicotine and alcohol and those who took none of them. When analyzing the two substances separately, there was no relationship between 2D:4D and alcohol drinking, whereas left hand 2D:4D was positively related to smoking only for women (nonsignificant trend was observed for right hand). Contrary to the previous study, our results indicate that there is no relationship between 2D:4D and alcohol drinking. There is, however, a subtle influence of prenatal testosterone levels for cigarette smoking habits in the case of women.

Anogenital Distance or Digit Length Ratio as Measures of Fetal Androgen Exposure: Relationship to Male Reproductive Development and Its Disorders

Male reproductive disorders evident at birth or in young adulthood are remarkably common. They are hypothesized to comprise a testicular dysgenesis syndrome (TDS), with a fetal origin involving mild androgen deficiency. Testing this hypothesis requires "seeing back in time." Two ways have been proposed: measurement of anogenital distance (AGD), or measurement of the 2:4 digit length ratio. This review assesses the evidence that they reflect fetal androgen exposure and might be used to provide insight into the origin of TDS disorders. Supporting evidence for AGD derives from rat experimental studies that identified a fetal masculinization programming window, within which androgen action determines adult reproductive organ size, TDS disorders, and AGD. In humans, AGD is positively correlated to testis size, sperm count/fertility, penis length, and T levels, consistent with rat experimental data. The 2:4 digit ratio also shows associations with these parameters, but inconsistently between studies; evidence that the 2:4 digit ratio accurately reflects fetal androgen exposure is also equivocal. AGD appears to provide a reliable guide to fetal androgen exposure, although available data are limited. The next steps are to: standardize AGD measurement; obtain age-specific population data; and use AGD to evaluate the importance of fetal androgens in determining reproductive disorders and variation in testis/penis size and sperm count in the normal population. These studies should identify what, if any, clinical applications of AGD measurement are feasible--for example, its ability to predict adult-onset reproductive function and disorders.

The Path to Glory Is Paved With Hierarchy

Two experiments examined the psychological and biological antecedents of hierarchical differentiation and the resulting consequences for productivity and conflict within small groups. In Experiment 1, which used a priming manipulation, hierarchically differentiated groups (i.e., groups comprising 1 high-power-primed, 1 low-power-primed, and 1 baseline individual) performed better on a procedurally interdependent task than did groups comprising exclusively either all high-power-primed or all low-power-primed individuals. There were no effects of hierarchical differentiation on performance on a procedurally independent task. Experiment 2 used a biological marker of dominance motivation (prenatal testosterone exposure as measured by a digit-length ratio) to manipulate hierarchical differentiation. The pattern of results from Experiment 1 was replicated; mixed-testosterone groups achieved greater productivity than did groups comprising all high-testosterone or all low-testosterone individuals. Furthermore, intragroup conflict mediated the productivity decrements for the high-testosterone but not the low-testosterone groups. This research suggests possible directions for future research and the need to further delineate the conditions and types of hierarchy under which hierarchical differentiation enhances rather than undermines group effectiveness.

Patterns of Second‐to‐Fourth Digit Length Ratios (2D:4D) in Two Species of Frogs and Two Species of Lizards at La Selva, Costa Rica

It is now well documented that androgen and estrogen signaling during early development cause a sexual dimorphism in second-to-fourth digit length ratio (2D:4D). It is also well documented that males of mammalian species have a smaller 2D:4D than females. Although there are discrepancies among 2D:4D studies in birds, the consensus is that birds exhibit the opposite pattern with males having a larger 2D:4D than females. The literature currently lacks substantial information regarding the phylogenetic pattern of this trait in amphibians and reptiles. In this study, we examined 2D:4D in two species of frogs (Oophaga pumilio and Craugastor bransfordii) and two species of lizards (Anolis humilis and Anolis limifrons) to determine the existence and the pattern of the sexual dimorphism. Male O. pumilio and C. bransfordii displayed larger 2D:4D than females in at least one of their two forelimbs. Male A. humilis had larger 2D:4D than females in both hindlimbs, but smaller 2D:4D than females in both forelimbs. Male A. limifrons may also have smaller 2D:4D than females in the right forelimb. Finally, digit ratios were sometimes positively related to body length, suggesting allometric growth. Overall, our results support the existence of the 2D:4D sexual dimorphism in amphibians and lizards and add to the knowledge of 2D:4D trait patterning among tetrapods.

Comparison of all hand digit length ratios in left- and right-handed individuals

To compare and detect possible differences between the digit length and digit length ratios in left- and right-handed female and male students. One of the cerebral hemispheres is dominant over the other. Knowing a person’s dominant hemisphere can be a useful guide in some personal activities. Materials and methods: Digit lengths (D) of the students were measured, followed by calculating the ratio of each digit to the others (1D:2D, 1D:3D, 1D:4D, 1D:5D, 2D:3D, 2D:4D, 2D:5D, 3D:4D, 3D:5D, and 4D:5D). Results: In males, no significant difference was found between digit lengths and digit length ratios. Among left-handed females, the fifth digit length was significantly longer. The 2D:5D, 3D:5D, and 4D:5D ratios were significantly smaller in their left hands, which indicated that the fifth digit was longer in left-handed females. Conclusion: The results of this study suggest that left-handed women could be especially successful in sports that require grasping a ball. This criterion should be considered for left-handed women while selecting athletes.

The Path to Glory is Paved with Hierarchy: When Hierarchical Differentiation Increases Group Effectiveness

Two experiments examined the psychological and biological antecedents of hierarchical differentiation and the resulting consequences for productivity and conflict within small groups. In Experiment 1, which used a priming manipulation, hierarchically differentiated groups (i.e., groups comprising 1 high-power-primed, 1 low-power-primed, and 1 baseline individual) performed better on a procedurally interdependent task than did groups comprising exclusively either all high- power or all low-power individuals. There were no effects of hierarchical differentiation on performance on a procedurally independent task. Experiment 2 used a biological marker of dominance motivation (prenatal testosterone exposure as measured by a digit-length ratio) to manipulate hierarchical differentiation. The pattern of results from Experiment 1 was replicated; mixed-testosterone groups achieved greater productivity than did groups comprising all high-testosterone or all low-testosterone individuals. Furthermore, intragroup conflict mediated the productivity decrements for the high- testosterone but not the low testosterone groups. This research suggests possible directions for future research and the need to further delineate the conditions and types of hierarchy under which hierarchical differentiation enhances rather than undermines group effectiveness.

Testosterone, financial risk-taking, and pathological gambling.

The current review article considers the relationship between testosterone and pathological gambling (PG). Recent evidence suggests that high-testosterone individuals have a greater appetite for financial risk-taking and are more likely to succumb to certain impulsivity-related pathologies. Further, two markers of androgenization have recently been shown to be predictive of financial risk-taking propensity, namely second-to-fourth digit length ratio and facial masculinity. Given that financial risktaking propensity and PG susceptibility share neurobiological and phenomenological similarities, it is argued in this review that circulating testosterone levels, second-tofourth digit length ratio, and facial masculinity may be predictors of PG susceptibility. Potential caveats and future research avenues are discussed.

Second to fourth digit ratio and the sporting success of sumo wrestlers

The second (index finger) to fourth (ring finger) digit length ratio (2D:4D) is known to be a putative marker of prenatal exposure to testosterone. It has been reported that fetal and adult testosterone may be critical for development of physical and mental traits such as cardiovascular system, reaction time, aggressiveness and masculinity. Testosterone-driven attributes are associated with success in male-to-male physical competition, which may be proxied by ability in sports. Many researchers have found that 2D:4D is sexually dimorphic and is a negative correlate of athletic performance. This study aims to investigate the associations of 2D:4D with measures of power as another possible testosterone-associated trait using ability in sumo wrestling as a proxy for male physical competitiveness. The measures of sumo performance comprised the sumo ranks and winning percentages of 142 Japanese professional sumo wrestlers. We found that sumo wrestlers with low 2D:4D had higher sumo ranks and better winning records. The significant negative associations between 2D:4D and the athletic prowess of sumo wrestlers provide further evidence of the possible link between high testosterone levels and muscle strength. The relatively small effect sizes found in this study, however, imply that 2D:4D may be a weaker predictor for sports requiring explosive power than for those requiring endurance.