A comparison of measurement methods and sexual dimorphism for digit ratio (2D:4D) in Han ethnicity

The association and underlying mechanism of the digit ratio (2D:4D) in hypospadias

The second-to-fourth digit (2D:4D) ratio is thought to be associated with prenatal androgen exposure. However, the relationship between the 2D:4D ratio and hypospadias is poorly understood, and its molecular mechanism is not clear. In this study, by analyzing the hand digit length of 142 boys with hypospadias (23 distal, 68 middle, and 51 proximal) and 196 controls enrolled in Shanghai Children's Hospital (Shanghai, China) from December 2020 to December 2021, we found that the 2D:4D ratio was significantly increased in boys with hypospadias ( P < 0.001) and it was positively correlated with the severity of the hypospadias. This was further verified by the comparison of control mice and prenatal low testosterone mice model obtained by knocking out the risk gene (dynein axonemal heavy chain 8 [ DNAH8 ]) associated with hypospadias. Furthermore, the discrepancy was mainly caused by a shift in 4D. Proteomic characterization of a mouse model validated that low testosterone levels during pregnancy can impair the growth and development of 4D. Comprehensive mechanistic explorations revealed that during the androgen-sensitive window, the downregulation of the androgen receptor (AR) caused by low testosterone levels, as well as the suppressed expression of chondrocyte proliferation-related genes such as Wnt family member 5a ( Wnt5a ), Wnt5b , Smad family member 2 ( Smad2 ), and Smad3 ; mitochondrial function-related genes in cartilage such as AMP-activated protein kinase ( AMPK ) and nuclear respiratory factor 1 ( Nrf-1 ); and vascular development-related genes such as myosin light chain ( MLC ), notch receptor 3 ( Notch3 ), and sphingosine kinase 1 ( Sphk1 ), are responsible for the limitation of 4D growth, which results in a higher 2D:4D ratio in boys with hypospadias via decreased endochondral ossification. This study indicates that the ratio of 2D:4D is a risk marker of hypospadias and provides a potential molecular mechanism.

DSD/intersex: historical context and current perspectives

Intersex/Disorders/Differences of sex development conditions have been recognized for millennia. An organized approach was adopted in the 1960-70s using the philosophy that gender identity was fluid and malleable. Consequences of this approach were the lack of disclosure, stigmatization, and excessive surgery to "normalize" the genitalia. Often this led to quality of life issues for those patients. There have been many modifications in approach since then to avoid the problems noted. There is consensus on many of these changes (e.g. disclosure) but continued controversy on others (e.g. the benefits of early surgery). This review summarizes the historical context and the current areas of consensus and controversy.

To What Extent are Prenatal Androgens Involved in the Development of Male Homosexuality in Humans?

Endocrine variations, including possibly reduced exposure to androgens, may contribute to the development of male homosexuality, with animal models demonstrating same-sex mate preference with altered exposure during prenatal or early postnatal development. As similar studies in humans are impossible, indirect physical and cognitive measures of androgen exposure are used. Some studies suggest that physical measures affected by prenatal androgens, including the index-to-ring finger ratio, growth indices, and facial structure, are more "feminine" in gay men. Gay men also exhibit significant childhood gender non-conformity and a "feminized" anatomical and functional brain pattern in sexual arousal, as well as domains such as language, visuospatial skills and hemispheric relationships. However, many of these results are equivocal and may be confounded by other factors. Research has also been hampered by inconsistencies in the reporting of sexual orientation and the potentially unrepresentative populations of gay men studied, while additional complexities pertaining to gender conformity and sexual role may also influence results.

Can Digit Ratio (2D:4D) Be Indicative of Predispositions to Autoimmune Thyroid Diseases in Women - Hashimoto Thyroiditis and Graves' Disease?

Hashimoto thyroiditis and Graves' disease are autoimmune thyroid diseases which occur much more frequently in women than in men. Estrogen receptors are found in the thyroid gland and can modulate the gland's function. Digit ratio (2D:4D) is thought to be a negative correlate of prenatal testosterone and a positive correlate of prenatal estrogen. This study aimed to examine a relationship between right and left 2D:4D in women with Hashimoto thyroiditis and Graves' disease. The cross-sectional study included 106 women with autoimmune thyroid disease: 73 women diagnosed with Hashimoto thyroiditis and 33 women with Graves' disease, together with 70 healthy women as controls. Second and fourth digit length, weight, height were measured directly, and 2D:4D and BMI were calculated. Compared to controls, right and left 2D:4D were significantly higher in women with Hashimoto thyroiditis and lower in women with Graves' disease, the effects were higher for right 2D:4D. The mean length of right 4D was significantly lower in the examined women with Hashimoto thyroiditis than in Graves' disease. Higher right and left 2D:4D in women with Hashimoto thyroiditis suggests that prenatal exposure to high levels of estrogens relative to testosterone may play a role in the development of this disease. Lower right and left 2D:4D in women with Graves' disease suggest a role of high prenatal androgens relative to estrogens in Graves' disease pathogenesis.

The effects of hand preference and sex on right-left asymmetry in dorsal digit lengths among adults and children

BACKGROUND

Right-hand preference is related to stronger right-directional asymmetry in the length of proximal upper-limb bones, although the relationships of hand preference with directional asymmetry in phalangeal bone lengths are not known. Furthermore, dorsal digit length is an easy-to-measure, faithful proxy of X-rayed phalangeal bone length (which is costly and difficult to measure).

AIM

To study the effects of hand preference, sex, and age on right-left (R-L) asymmetry in dorsal digit lengths.

METHODS

We measured all dorsal digit lengths (except the thumb) in comparable numbers of left-handers and right-handers in samples of adults (N = 151, age: M = 22.6 years, SD = 3.3) and children (N = 65, age: M = 5.0 years, SD = 1.0).

RESULTS

Right-handers and adults had stronger right-directional asymmetry in digit lengths than left-handers and children. A Bayesian analysis yielded an 'extremely strong likelihood' of no sex differences in the R-L asymmetry of dorsal digit lengths 2 and 4.

CONCLUSIONS

The effects of hand preference, sex, and age on R-L asymmetry appear to be similar for phalangeal bone length and other (proximal) upper-limb bone lengths. Two distinct biologic mechanisms (i.e., a general right-directional asymmetry mechanism and a handedness-related directional asymmetry mechanism) may contribute to observed R-L asymmetry in limbs. Fingertip fat and bone digit length do not seem to contribute to sex differences in the R-L asymmetry (Dr-l) of the widely studied second-to-fourth digit ratio (2D:4D).

No evidence for a difference in 2D:4D ratio between youth with elevated prenatal androgen exposure due to congenital adrenal hyperplasia and controls

The second-to-fourth digit ratio (2D:4D) has been associated with sexual dimorphism, with a lower 2D:4D in males. A large body of research has relied on the 2D:4D as a proxy for prenatal androgen exposure, and includes reports of relationships between 2D:4D and a wide range of human traits. Here, we examine the validity of the 2D:4D proxy by studying the association between 2D:4D and classical Congenital Adrenal Hyperplasia (CAH) due to 21-hydroxylase deficiency, a condition characterized by excessive prenatal exposure to androgens during most of the gestational period. To this end, we retrospectively examine 513 serial radiographs of the left hand obtained clinically in 90 youth with classical CAH (45 female) and 70 control youth (31 female). Replicating previous reports, we observe associations of the 2D:4D with sex (lower 2D:4D in males) and age (increase of 2D:4D through development). However, we find no evidence for differences in 2D:4D between CAH and controls (full sample: β = -0.001 (-0.008, 0.006); females: β = -0.004 [-0.015, 0.007]; males: β = 0.001, [-0.008, 0.011]). Although our findings do not rule out a small association between the 2D:4D and CAH, they cast doubt on the usefulness of the 2D:4D as a biomarker for prenatal androgen exposure in behavioral research.

Effects of prenatal exposure to polybrominated diphenyl ethers (PBDEs) on the second to fourth digit ratio in children aged 4 years

BACKGROUND

The second to fourth digit ratio (2D:4D) is assumed to be a biomarker of prenatal sex steroid exposure, correlating negatively with prenatal testosterone and positively with prenatal estrogen. The ratio has been suggested to be influenced by endocrine disrupting chemicals (EDCs). However, evidence regarding effects of prenatal exposure to polybrominated diphenyl ethers (PBDEs) on 2D:4D of children was sparse.

OBJECTIVES

We investigated the associations between prenatal exposure to PBDEs and 2D:4D of children aged 4 years.

METHODS

Participants were mother-child pairs from the Shanghai-Minhang Birth Cohort Study (S-MBCS) which enrolled pregnant women at 12-16 weeks of gestation from April to December 2012. Nine PBDE congeners in venous umbilical cord plasma of 340 children were measured. Digit lengths were measured using a vernier caliper in children aged 4 years and 2D:4D for left and right hands and average 2D:4D value of both hands were calculated. A total of 281 children (160 boys and 121 girls) who had data on both 2D:4D and PBDE concentrations were included in the final analysis. Associations between prenatal PBDE exposures and 2D:4D were investigated using multiple linear regression models.

RESULTS

Among the nine congeners, BDE-47 had the highest detection rate of 86.12% with the highest median concentration of 0.20 ng/ml lipid. Five PBDE congeners with detection rates greater than or close to 50% (BDE-28, -47, -99, -100 and -153) and Σ₅PBDEs (the sum of them) were included in final analysis. For girls, a consistent pattern for the positive associations between prenatal PBDE exposures and 2D:4D of children was observed mainly for the left hand, where those in the highest exposure groups had higher 2D:4D compared to the lowest exposure groups (a feminizing effect), with statistically significant associations observed for BDE-47 (β = 0.0247, 95% confidence interval (CI): 0.0017, 0.0477), -100 (β = 0.0264, 95% CI: 0.0087, 0.0441) and Σ₅PBDEs (β = 0.0201, 95% CI: 0.0027, 0.0374). For boys, compared with the lowest exposure groups, statistically significantly higher (feminized) 2D:4D for both hands was observed in those with the highest exposure levels of BDE-100 (β = 0.0147, 95% CI: 0.0005, 0.0289 for the left hand; β = 0.0182, 95% CI: 0.0046, 0.0318 for the right hand) and those with the middle and the highest exposure levels of BDE-153 (middle vs. undetected, β = 0.0215, 95% CI: 0.0072, 0.0358 for the left hand; β = 0.0155, 95% CI: 0.0015, 0.0295 for the right hand; highest vs. undetected, β = 0.0162, 95% CI: 0.0017, 0.0307 for the left hand; β = 0.0152, 95% CI: 0.0011, 0.0294 for the right hand).

CONCLUSIONS

Our study provides preliminary evidence that prenatal exposure to PBDEs might be associated with higher 2D:4D in boys and girls.

Usefulness of measurement of proximal phalanx length by using ultrasonography in newborn infants

The purpose of this study was to compare digit lengths and proximal phalanx lengths in newborn infants by using ultrasonography (USG) and to examine sex differences between the ratio of the second digit (2D) and fourth digit (4D) of digit length and that of proximal phalanx length and the associations of digit length and proximal phalanx length with birth weight and birth height. Sixty newborn infants (28 males and 32 females) were recruited. Digit lengths were measured by using a transparent ruler and proximal phalanx lengths were measured by using USG. There were significant correlations between digit length and proximal phalanx length in the left and right hands. There was no significant correlation between 2D:4D ratios of digit lengths and 2D:4D ratios of proximal phalanx lengths measured by using USG. In males, birth height was significantly associated with right fourth proximal phalanx length and with left second and fourth proximal phalanx lengths. Birth weight was significantly associated with proximal phalanx length in males. Proximal phalanx length measured by using USG was significantly associated with digit length in newborn infants. Hormonal exposure before birth may be involved in the associations of proximal phalanx length with birth weight and height in males.Impact statementWhat is already known on this subject? The ratio of the second digit (2D) and fourth digit (4D) has been used postnatally to provide a retrospective indication of the foetal hormonal environment. Digit lengths have been measured by using a direct method, photocopies, digital scans and radiographs, but the results of a study on measurement of digit lengths by using ultrasonography (USG) have not been reported.What do the results of this study add? Proximal phalanx length measured by using USG was significantly associated with digit length in newborn infants. In males, birth height was significantly associated with right fourth proximal phalanx length and with left second and fourth proximal phalanx lengths. Birth weight was significantly associated with proximal phalanx length in males.What are the implications of these findings for clinical practice and/or further research? Measurement of proximal phalanx length by using USG may be useful for a study on gender differences in foetal development and the foetal hormonal environment. Hormonal exposure before birth may be involved in the associations of proximal phalanx length with birth weight and height in males.

The associations between left-hand digit ratio (2D:4D) and puberty characteristics among Chinese girls

BACKGROUND

The aim of this study was to analyse the associations of left-hand digit ratio (2D:4D), digit length and puberty characteristics to show the role of prenatal hormones in development among Chinese girls.

METHOD

A total of 318 Chinese girls aged 8-15 years were recruited using a stratified cluster sampling method. The index finger (2D), ring finger (4D) of the left hand, oestradiol and testosterone were measured, and age at menarche (AAM), breast (high and low) and pubic hair (high and low) development were recorded.

RESULTS

Girls who had experienced menarche had longer left digits (2D and 4D) and higher oestradiol, testosterone than those who had not. The high breast group had longer digits (2D and 4D), and higher oestradiol than the low breast group. With regard to pubic hair development, the high group had high 2D:4D, longer 2D and higher oestradiol, testosterone than the low group. After adjusting for oestradiol and testosterone, 4D length was positively related to occurrence of menarche. In addition, 2D and 2D:4D were significantly correlated with pubic hair development after adjusting for oestradiol, respectively.

CONCLUSION

Prenatal hormone level may be related to the development of puberty characteristics among Chinese girls.

Associations between digit ratio (2D4D), mood, and autonomic stress response in healthy men

The ratio between the length of the second (index) and the fourth (ring) finger (2D4D) is a putative biomarker of prenatal testosterone (T) exposure, with higher exposure leading to a smaller ratio. 2D4D has further been linked to mental and somatic disorders. Healthy male Swiss recruits (N = 245; M_age = 20.30 years) underwent a psychosocial stress test. Mood and salivary alpha-amylase (sAA) were assessed before and after the stress test, while heart rate (HR) and heart rate variability (HRV) were measured continuously. Additionally, 2D4D (right: R2D4D; left: L2D4D) was determined and divided into quartile groups. Correlation analysis showed no associations between R/L2D4D and outcome measures. Comparing calculated quartiles for R2D4D, subjects in the lowest R2D4D quartile expressed trendwise (p < 0.10) lower positive and higher negative affect, significantly elevated sAA activity (p < 0.05), but no HR and HRV differences at baseline as compared to subjects in the upper three quartiles. With regard to acute stress, subjects in the lowest as compared to subjects in the upper three R2D4D quartiles showed a higher increase of negative affect and a stronger cardiac response (p < 0.05), but no alterations in positive affect and sAA activity. Young healthy men in the lowest R2D4D quartile revealed a more negative affect and increased physiological activity at baseline and in response to acute stress. An exposure to high levels of prenatal T might constitute a risk factor potentially increasing vulnerability to stress-related disorders in men.

Differential Placing of Flexion Creases Contributes to Sex Differences in the Second-to-Fourth Digit Ratio (2D:4D)

The present research examined whether differential placing of the basal flexion creases contributes to the occurrence of sex differences in digit ratio (2D:4D) derived from palmar digit lengths. The ratio of palmar-to-dorsal digit length, a measure of the placing of the basal flexion crease in the finger, was derived for the digits 2 and 4 of the right hand in two independent samples (Study I: N = 100; Study II: N = 200), in accordance with discovery-replication sample approach. The results show that men have lower palmar-to-dorsal digit ratios than women, and this effect is significantly stronger for digit 2 than for digit 4. Thus, the present study supports the likelihood that differential placing of flexion creases in the digits contributes to the occurrence of sex differences in palmar 2D:4D. In addition (Study II), the measurement procedure assessing the placing of flexion creases was validated. In conclusion, this evidence highlights potential conceptual shortcomings and technical limitations in the measurement conventions and methods currently employed in the field of 2D:4D research.

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

The ratio of the length of the index finger to that of the ring finger (2D:4D) is sexually dimorphic and is commonly used as a non-invasive biomarker of prenatal androgen exposure. Most association studies of 2D:4D ratio with a diverse range of sex-specific traits have typically involved small sample sizes and have been difficult to replicate, raising questions around the utility and precise meaning of the measure. In the largest genome-wide association meta-analysis of 2D:4D ratio to date (N = 15 661, with replication N = 75 821), we identified 11 loci (9 novel) explaining 3.8% of the variance in mean 2D:4D ratio. We also found weak evidence for association (β = 0.06; P = 0.02) between 2D:4D ratio and sensitivity to testosterone [length of the CAG microsatellite repeat in the androgen receptor (AR) gene] in females only. Furthermore, genetic variants associated with (adult) testosterone levels and/or sex hormone-binding globulin were not associated with 2D:4D ratio in our sample. Although we were unable to find strong evidence from our genetic study to support the hypothesis that 2D:4D ratio is a direct biomarker of prenatal exposure to androgens in healthy individuals, our findings do not explicitly exclude this possibility, and pathways involving testosterone may become apparent as the size of the discovery sample increases further. Our findings provide new insight into the underlying biology shaping 2D:4D variation in the general population.

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

The ratio of the length of the index finger to that of the ring finger (2D:4D) is sexually dimorphic and is commonly used as a non-invasive biomarker of prenatal androgen exposure. Most association studies of 2D:4D ratio with a diverse range of sex-specific traits have typically involved small sample sizes and have been difficult to replicate, raising questions around the utility and precise meaning of the measure. In the largest genome-wide association meta-analysis of 2D:4D ratio to date (N = 15 661, with replication N = 75 821), we identified 11 loci (9 novel) explaining 3.8% of the variance in mean 2D:4D ratio. We also found weak evidence for association (β = 0.06; P = 0.02) between 2D:4D ratio and sensitivity to testosterone [length of the CAG microsatellite repeat in the androgen receptor (AR) gene] in females only. Furthermore, genetic variants associated with (adult) testosterone levels and/or sex hormone-binding globulin were not associated with 2D:4D ratio in our sample. Although we were unable to find strong evidence from our genetic study to support the hypothesis that 2D:4D ratio is a direct biomarker of prenatal exposure to androgens in healthy individuals, our findings do not explicitly exclude this possibility, and pathways involving testosterone may become apparent as the size of the discovery sample increases further. Our findings provide new insight into the underlying biology shaping 2D:4D variation in the general population.

The association between digit ratio (2D:4D) and the first spermatorrhea among Chinese boys

BACKGROUND

The second-to-fourth digit ratio (2D:4D) is a marker of prenatal hormone exposure, which is negatively correlated with prenatal androgen and positively correlated with prenatal estrogen. The study was to analyze the association between 2D:4D and the first spermatorrhea to indirectly show the possible role of prenatal hormone during puberty development among boys.

METHOD

The total of 367 boys aged 8-15 years were enrolled by using the stratified cluster sampling method. The variables of index finger (2D), ring finger (4D), height, weight, waist circumference (WC), skinfold thickness, testosterone and estradiol were measured, and the age at the first spermatorrhea was surveyed.

RESULTS

The average age at the first spermatorrhea was 12.15 years. The 2D:4D was not related to first spermatorrhea, circulating testosterone in boys (P > 0.05), however, was positively correlated with circulating estradiol (P < 0.05). The direct association (OR value) between 4D, average of index finger and ring finger (AIR) and first spermatorrhea were 2.79 and 2.29, and the mediating effect (OR value) of which were 1.95 and 2.01 by testosterone, accounting for 41.18% and 46.73% of the total effect, respectively. The 2D, MIDRL, lean body mass (LBM) were indirectly related to first spermatorrhea by testosterone, the mediating effects (OR value) were 2.11, 1.71 and 2.41, respectively.

CONCLUSION

The prenatal androgen exposure may be directly and indirectly related to first spermatorrhea. In addition, the high prenatal estrogen exposure may be indirectly associated with first spermatorrhea by testosterone.

Overall trends vs. individual trajectories in the second-to-fourth digit (2D:4D) and metacarpal (2M:4M) ratios during puberty and adolescence

OBJECTIVES

The second-to-fourth digit ratio (2D:4D ratio) can be assumed a valid indicator of sexual differentiation, provided that it is stable once it develops, or eventual changes remain uniform in a respective cohort throughout ontogenesis. The main goal of this study was to determine whether the metacarpal 2M:4M and the digit 2D:4D ratio change during the period of pubertal/adolescent growth.

MATERIALS AND METHODS

The metacarpals and digits were measured on radiographs of left hands in the sample of 328 individuals (96 pairs of male and 68 pairs of female twins) from the Wrocław Longitudinal Study of Twins (1967-1983). Five consecutive annual measurements were done for each individual within a 4-year-interval somewhere between 7 and 18 years of age. Age-related changes in both ratios were studied using a set of mixed-effects linear models. Three types of correlation coefficients were used for assessment of stability between repeated measurements at different ages.

RESULTS

An overall decrease in the average 2M:4M ratio was observed, attributable to a much larger extent to males than to females. On the contrary, a slight overall increase in the average 2D:4D ratio was observed, attributable to a much larger extent to females than to males. The rank order of the ratios remained highly stable within the monitored period (the correlation coefficient mostly ranged between 0.85 and 0.95). In spite of these findings, we recorded significant intraindividual changes in both ratios. In some individuals the 2D:4D ratio can undergo changes comparable to average sex differences and much higher than average age-related changes.

DISCUSSION

Relatively slight overall changes in digit ratio in puberty and adolescence themselves are not inconsistent with the use of the 2D:4D ratio as an indirect marker of prenatal sexual differentiation. Nevertheless, individual changes in the ratios varied substantially in this study and differed from the average trends. Future studies should focus on the nature of interindividual developmental differences in the digit and metacarpal ratios.

Sexual Dimorphism in Digit Ratios Derived from Dorsal Digit Length among Adults and Children

Sexual dimorphism in ventrally measured digit ratios (2D:4D and other) has been related to prenatal sex-hormone levels. In the present series of three studies, we measured all digit lengths (excluding the thumb) on the dorsal, rather than the ventral, side of left and right hands and investigated the sexual dimorphism in digit ratios in three independent samples, two of them comprising adults (Study I, N = 104; Study II, N = 154), and one further, comprising kindergarten children (Study III, N = 64). Results show that men have lower digit-ratio values compared to women in digit ratios that include digit 5 as one of the constituents of the ratio (i.e., the 4D:5D, 3D:5D, and 2D:5D ratios). Boys have lower values compared to girls for the 4D:5D and 3D:5D ratios, and there is a similar trend of sexual dimorphism in the 2D:5D ratio. Thus, based on the evidence from dorsally measured digit ratios, the present findings from three samples are consistent with the idea that early sex-hormonal effects might be stronger for digit ratios involving digit 5, as compared to the classic, and frequently studied, ventrally measured 2D:4D ratio.

2D:4D Ratio and its Implications in Medicine

Digit ratios, especially 2D:4D ratio, a potential proxy marker for prenatal androgen exposure shows sexual dimorphism. Existing literature and recent research show accumulating evidence on 2D:4D ratio showing correlations with various phenotypic traits in humans. Ratio of 2D:4D is found to correlate negatively to testosterone and positively to oestrogen in the foetus. Interestingly, it is constant since birth and not influenced by the adult hormone levels. Usually, males have lower ratios when compared to females. Prenatal androgen exposure and therefore, digit ratios have been reported to be associated with numerical competencies, spatial skills, handedness, cognitive abilities, academic performance, sperm counts, personalities and prevalence of obesity, migraine, eating disorders, depression, myopia, autism etc. The authors have attempted to write a brief account on the digit ratios and the dimorphism observed in various physiological, psychological and behavioural traits. Also, the authors have discussed the relevant molecular basics and the methods of measurement of digit ratios.

Soccer players awarded one or more red cards exhibit lower 2D:4D ratios

Anatomical, cognitive and behavioral sex differences are widely recognized in many species. It has been proposed that some of these differences might result from the organizing effects of prenatal sex steroids. In humans, males usually exhibit higher levels of physical aggression and prowess. In this study, we analyze the relationship between second-to-fourth digit (2D:4D) ratios-a proxy for prenatal androgen levels-and foul play and sporting performance in a sample of junior soccer players from a professional Uruguayan soccer club. Our results show that the most aggressive players (i.e., those awarded one or more red cards) have a more masculine finger pattern (lower 2D:4D ratio), while no relationship could be found between sporting performance and 2D:4D ratios. The results are discussed in the context of previous findings. Aggr. Behav. 42:417-426, 2016. © 2015 Wiley Periodicals, Inc.

Putative Androgen Exposure and Sexual Orientation: Cross-Cultural Evidence Suggesting a Modified Neurohormonal Theory

INTRODUCTION

According to neurohormonal theory, prenatal androgens are key determinants of sexual orientation. As a reputed marker for prenatal androgens, the 2D:4D finger length ratio has been used in more than a dozen studies to test the hypothesis that prenatal androgens influence sexual orientation. Findings have been very inconsistent.

AIM

The present study sought to retest the hypothesis that 2D:4D and sexual orientation are related is a manner consistent with neurohormonal theory.

METHODS

A 2D:4D measure (of the right hand) along with four additional somatic markers of androgen exposure (height, physical strength, muscularity, and athletic ability) with samples of college students in Malaysia (N = 2,058) and the United States (N = 2,511). The five androgen measures were factor analyzed, resulting in a two-factor solution: Factor 1 consisted of strength, muscularity, and athletic ability (the muscular coordination factor), and Factor 2 was comprised of the r2D:4D and adult height (the bone growth factor).

MAIN OUTCOME MEASURES

Sexual orientation was measured by asking each respondent the extent to which they were sexually attracted to males and the extent to which they were sexually attracted to females, both on 11-point scales.

RESULTS

When the countries and sexes were analyzed separately, neither the r2D:4D measure nor Factor 2 correlated with sexual orientation to significant degrees. Instead, it was the muscular coordination factor that correlated the best. Support was found for the hypothesis that prenatal androgens influence sexual orientation, but the nature of these influences was more complex than neurohormonal theory predicted.

CONCLUSION

A modified theory is needed and presented to accommodate the results from this study.

Sexual dimorphism in finger length ratios and sex determination - A study in Indo-Mauritian population

Many studies have shown that the finger length ratios might be characteristic for sexual dimorphism. The aim of the study was to determine sexual dimorphism in finger length ratios among the representatives of the Indo-Mauritian population. The study group comprised of 200 healthy Indo-Mauritian people (100 male and 100 female) of the age ranged from 19 to 25 years. The lengths of second (2D), third (3D), forth (4D) and fifth (5D) finger of both hands were measured by using a vernier caliper. Our results indicate that all finger length ratios have significant sex differences (p-value < 0.05) except 2D:5D and 3D:5D. To conclude, 2D:4D ratio is the most decisive ratio (predictive accuracy = 0.61) which can demarcate between male and female.