Second to fourth digit ratio and male ability in sport: implications for sexual selection in humans

Butch-Femme Identity and Visuospatial Performance Among Lesbian and Bisexual Women in China

Lesbian and bisexual women who self-identify as "butch" show a masculine profile with regard to gender roles, gender nonconformity, and systemizing cognitive style, whereas lesbian and bisexual women who self-identify as "femme" show a corresponding feminine profile and those who self-identify as "androgynes" show an intermediate profile. This study examined the association between butch or femme lesbian or bisexual identity and visuospatial ability among 323 lesbian and bisexual women, compared to heterosexual women (n = 207) and men (n = 125), from multiple cities in China. Visuospatial ability was assessed using a Shepard and Metzler-type mental rotation task and Judgment of Line Angle and Position (JLAP) test on the Internet. Heterosexual men outperformed heterosexual women on both mental rotation and JLAP tasks. Lesbian and bisexual women outperformed heterosexual women on mental rotation, but not on JLAP. There were significant differences in mental rotation performance among women, with butch- and androgyne-identified lesbian/bisexual women outperforming femme-identified and heterosexual women. There were also significant differences in JLAP performance among women, with butch- and androgyne-identified lesbian/bisexual women and heterosexual women outperforming femme-identified lesbian/bisexual women. The butch-femme differences in visuospatial ability indicated an association between cognitive ability and butch-femme identity and suggest that neurobiological underpinnings may contribute to butch-femme identity although alternative explanations exist.

Digit ratio (2D:4D) and behavioral symptoms in primary-school aged boys

The second-to-forth digit length ratio (2D:4D) is considered to be a biomarker for intrauterine androgen levels. It is associated with adult and child mental health problems, primarily with behavioral symptoms and predominantly in males. Using a cross-sectional design, we examined whether 2D:4D was associated with conduct disorder (CD) symptoms in 138 primary-school aged children (54% boys, M_age = 7.70 years) and considered child sex as a moderating factor. Children's digit lengths were measured from hand scans and mothers rated the behavioral/emotional symptoms of their child. The regression analyses revealed that 2D:4D ratios were associated with behavioral symptoms in boys (β = -0.260, p = 0.026), but not in girls (β = -0.040, p = 0.762). Child emotional symptoms, analyzed as a control, were not significantly correlated with 2D:4D. In conclusion, prenatal brain hyperandrogenization - operationalized by the 2D:4D biomarker - could result in behavioral symptoms in boys at early school age, reflecting one predictor for early onset CD. Our data support the use of 2D:4D as a marker of prenatal androgen exposure.

Self-confidence, Overconfidence and Prenatal Testosterone Exposure: Evidence from the Lab

This paper examines whether foetal testosterone exposure predicts the extent of confidence and over-confidence in own absolute ability in adulthood. To study this question, we elicited incentive-compatible measures of confidence and over-confidence in the lab and correlate them with measures of right hand 2D:4D, used as as a marker for the strength of prenatal testosterone exposure. We provide evidence that men with higher prenatal testosterone exposure (i.e., low 2D:4D ratio) are less likely to set unrealistically high expectations about their own performance. This in turn helps them to gain higher monetary rewards. Men exposed to low prenatal testosterone levels, instead, set unrealistically high expectations which results in self-defeating behavior.

A Context Dependent Interpretation of Inconsistencies in 2D:4D Findings: The Moderating Role of Status Relevance

Whereas direct relationships between 2D:4D and dominance related attitudes or behavior often turn out to be weak, some literature suggests that the relation between 2D:4D and dominance is context-specific. That is, especially in status-challenging situations 2D:4D may be related to dominant behavior and its correlates. Based on this perspective, we interpret inconsistencies in the literature on the relation between 2D:4D and risk taking, aggression and dominance related outcomes and investigate in our empirical study how attitudes in low 2D:4D men may change as a function of the status relevance of the context. We provide evidence for the idea that status relevance of the particular situation at hand influences the attitude towards performance-enhancing means for low 2D:4D men, but not for high 2D:4D men. We argue that 2D:4D may be related to any behavior that is functional to attain status in a specific context. Implications for (economic) decision making are discussed.

Investigating Gender Differences under Time Pressure in Financial Risk Taking

There is a significant gender imbalance on financial trading floors. This motivated us to investigate gender differences in financial risk taking under pressure. We used a well-established approach from behavior economics to analyze a series of risky monetary choices by male and female participants with and without time pressure. We also used second to fourth digit ratio (2D:4D) and face width-to-height ratio (fWHR) as correlates of pre-natal exposure to testosterone. We constructed a structural model and estimated the participants' risk attitudes and probability perceptions via maximum likelihood estimation under both expected utility (EU) and rank-dependent utility (RDU) models. In line with existing research, we found that male participants are less risk averse and that the gender gap in risk attitudes increases under moderate time pressure. We found that female participants with lower 2D:4D ratios and higher fWHR are less risk averse in RDU estimates. Males with lower 2D:4D ratios were less risk averse in EU estimations, but more risk averse using RDU estimates. We also observe that men whose ratios indicate a greater prenatal exposure to testosterone exhibit a greater optimism and overestimation of small probabilities of success.

The Second to Fourth Digit Ratio in Elite and Non-Elite Greco-Roman Wrestlers

A low second-to-fourth digit ratio (2D:4D) has been reported to correlate with high performance and athletic potential of an individual in sport. It has been suggested that 2D:4D is a relatively weak predictor of strength and a stronger predictor of efficiency in aerobic exercise. Comparing extreme groups on a continuum of sports performance requiring high power (physical strength) output would be helpful to resolve this issue. Therefore, the purpose of the present study was to compare the 2D:4D ratio of world-class elite Greco-Roman wrestlers (n = 10) taking part in Olympic fitness camps in 2013 with the 2D:4D ratio of non-elite collegiate wrestlers (n = 20), and age-matched sedentary males (n = 40). The 2D:4D ratios of elite wrestlers were lower compared to non-elite athletes (p < 0.01, right hand d = 1.70, left hand d = 1.67) and the control group (p < 0.0001, right hand d = 3.16, left hand d = 2.00). No significant differences were noted among the groups for right - left 2D:4D. We concluded that 2D:4D may discriminate between non-elite and world-class wrestlers. We also suggest that a low 2D:4D ratio could be linked to performance potential in wrestlers. As such, 2D:4D may provide additional information, which is valuable in determining the potential athleticism of an individual, when it is used in conjunction with other measures.

Digit Ratio (2D:4D) Predicts Self-Reported Measures of General Competitiveness, but Not Behavior in Economic Experiments

The ratio of index finger length to ring finger length (2D:4D) is considered to be a putative biomarker of prenatal androgen exposure (PAE), with previous research suggesting that 2D:4D is associated with human behaviors, especially sex-typical behaviors. This study empirically examines the relationship between 2D:4D and individual competitiveness, a behavioral trait that is found to be sexually dimorphic. We employ two related, but distinct, measures of competitiveness, namely behavioral measures obtained from economic experiments and psychometric self-reported measures. Our analyses are based on two independent data sets obtained from surveys and economic experiments with 461 visitors of a shopping mall (Study I) and 617 university students (Study II). The correlation between behavior in the economic experiment and digit ratios of both hands is not statistically significant in either study. In contrast, we find a negative and statistically significant relationship between psychometric self-reported measures of competitiveness and right hand digit ratios (R2D:4D) in both studies. This relationship is especially strong for younger people. Hence, this study provides some robust empirical evidence for a negative association between R2D:4D and self-reported competitiveness. We discuss potential reasons why digit ratio may relate differently to behaviors in specific economics experiments and to self-reported general competitiveness.

2D:4D finger length ratio and radiographic hand osteoarthritis

To evaluate the association between the index and ring finger's (2D:4D) length ratio with the prevalence and severity of radiographic hand osteoarthritis (OA). A population-based sample included 802 males (mean age 46.98 ± 17.10 years) and 738 females (mean age 48.65 ± 16.62 years) who had participated in a Chuvashian skeletal aging study. Age, sex, basic demographics, anthropometric data and X-rays of both hands were acquired. Each hand was visually classified on X-ray as either type 1-index finger longer than the ring finger; type 2-index and ring finger equal in length; or type 3-index finger shorter than the ring finger. Hand OA was defined by the number of affected joints (Kellgren-Lawrence score ≥ 2) in both hands and the sum total of Kellgren-Lawrence scores (total OA score). After comparing the OA variables of individuals with different finger length ratio types (after adjustment for age and BMI) significant differences were found only in females between finger ratio types of the right hand in a number of affected joints (F = 3.153, p = 0.043) and finger ratio types of the left (F = 3.330, p = 0.036) and right (F = 2.397, p = 0.047) hands of the total OA score. Females with type 3 ratios had the highest adjusted values of hand OA parameters. We found that finger length ratios are associated with hand OA parameters. Females with a type 3 finger length pattern showed significantly higher hand OA values than those with types 1 and 2.

Relationships between the second to fourth digit ratio (2D:4D) and game-related statistics in semi-professional female basketball players

OBJECTIVE

Digit ratio (2D:4D) is a negative correlate of sports performance, although this relationship may be weak in open-skill sports such as basketball. The primary aim was to quantify relationships between 2D:4D and game-related statistics in semi-professional female basketball players. The secondary aim was to quantify the differences in mean 2D:4Ds between players based on their position in the starting lineup.

METHODS

Using a cross-sectional design, 64 female basketball players who competed in the South Australian Premier League were measured in-season for height, mass, and 2D:4D, with game-related statistics collected end-season. Partial correlations (adjusted for age and body mass index) were used to quantify relationships between right and left 2D:4Ds and game-related statistics. Unpaired t-tests were used to quantify differences in mean 2D:4Ds between starting and reserve players.

RESULTS

2D:4D was a substantial negative correlate of blocks, rebounds, and field-goal percentage; meaning, females with lower 2D:4Ds were generally better defensively as they recorded more blocks and rebounds, and were more efficient scorers, irrespective of their age and body size. Mean 2D:4D differed by position in the starting lineup, as females with lower 2D:4Ds were more likely to be in the starting lineup.

CONCLUSIONS

This study found evidence that 2D:4D was a correlate of performance in an open-skill sport. Female players with lower digit ratios tended to perform better in several aspects of basketball, especially defensively, and were more likely to be starters, suggesting they are the best players on the team in their positions. These results probably reflect the organizational benefits of prenatal testosterone.

FURTHER EVIDENCE OF AN ASSOCIATION BETWEEN LOW SECOND-TO-FOURTH DIGIT RATIO (2D:4D) AND SELECTION FOR THE UNIFORMED SERVICES: A STUDY AMONG POLICE PERSONNEL IN WROCŁAW, POLAND

Males and females differ in their preference for occupations and sporting activities, and differ also in risk-taking attitudes. In addition to other explanations, prenatal hormone exposure has been implicated in these gender-associated differences. The ratio of the relative lengths of the second-to-fourth digits (2D:4D) is a proxy indicator of prenatal exposure to testosterone relative to oestrogen. The 2D:4D ratio has been found to be associated with choice of occupation, particularly among females. This study investigated whether 2D:4D differed between police officers and a control group of civilians in Wrocław, Poland. Participants were 147 male and 55 female police officers and 91 male and 75 female civilian controls. The police officers had to undergo rigorous physical ability tests during recruitment and their job bore relatively higher risk, whereas the controls had a normal civilian lifestyle. Height, weight, hand grip strength and lengths of the second and fourth digits were measured. Analyses of variance and covariance were employed to assess the significance of difference in digit ratio between groups (police officers and civilians) allowing for interaction with sex. The policewomen, compared with the female controls, were taller and had stronger hand grip strength, but had lower 2D:4D in the right hand and average 2D:4D of both hands. However, male and female police officers slightly differed only in the right hand digit ratio but not in the left hand ratio or the average for the two hands. However, the control group showed significant sex differences in all digit ratios with higher (feminine) mean values in females. The study provides further evidence that prenatal testosterone exposure, as reflected in the 2D:4D ratio, might have an association with choice of occupation, particularly among females.

Does the index-to-ring finger length ratio (2D:4D) differ in amyotrophic lateral sclerosis (ALS)? Results from an international online case-control study

OBJECTIVES

The ratio of the length of the index finger (2D) to the ring finger (4D) (2D:4D) has been reported to be lower (ie, 2D<4D) in people with amyotrophic lateral sclerosis (ALS) than non-ALS controls. This has led to suggestions that exposure to increased prenatal testosterone, which also lowers this ratio, could be a risk factor for ALS. In an attempt to test this hypothesis, we examined 2D:4Ds from large numbers of patients with ALS and controls.

SETTING

An online multilingual questionnaire enabling respondents to measure their own index and ring finger lengths.

PARTICIPANTS

Of the initial 949 respondents, 572 remained for analysis after elimination for inability to straighten fingers, not answering the question, statistical outliers and aged <40 years. Respondents remaining for analysis were 202 patients with ALS (125 males, 77 females) and 370 non-ALS controls (112 males, 258 females).

RESULTS

Unpaired t-tests with 95% CIs were used to assess differences in mean 2D:4Ds. Males had significantly lower mean 2D:4Ds than females, in both ALS and control groups, for both left and right hands. No significant differences were found in 2D:4Ds between ALS and control groups, in either males or females, for either left or right hands. Receiver operating characteristic curves showed no power for 2D:4Ds to predict ALS status in either males or females.

CONCLUSIONS

2D:4Ds did not differ between patients with ALS and controls in this study. This was despite the dataset being large enough to confirm the established finding of lower 2D:4Ds in males compared with females. These findings do not support the hypothesis that exposure to increased prenatal testosterone is a risk factor for ALS. A putative lower 2D:4D has been proposed to explain the link between ALS and exercise, but our results indicate that other exercise-related factors are more likely to explain this association.

Low second to fourth digit ratio in Dupuytren disease

The ratio of the lengths of the second and fourth digits (2D:4D) has been described as reflecting endogenous prenatal androgen exposure. In general, 2D:4D is lower in men than in women and has potential as a biomarker or predictor for various diseases, athletic ability, and academic performance. Dupuytren disease has digital flexion contractures and is known to predominate in men, but the pathogenesis of the disease remains unclear. To clarify the relationships between Dupuytren disease and endogenous androgens, we performed a retrospective analysis of hand radiographs to investigate 2D:4D in Dupuytren disease. The study included male patients with Dupuytren disease (n = 22) and a control group (n = 18) of male patients with carpal tunnel syndrome. Only unaffected hands, without contractures or osteoarthritis, were evaluated for the purpose of radiographic assessment. The lengths of the phalanx and metacarpal bones in the second and fourth digits were measured by 2 independent observers who each performed 2 sets of measurements separated by a minimum 1-week interval. The 2D:4D was calculated separately for the phalanges and metacarpals, and a combined (phalanx + metacarpal) 2D:4D was also calculated. The reliability of the observer measurements was established using the intraclass correlation coefficient, and both the intra- and interobserver reliability showed excellent agreement. We found that compared with control group, the Dupuytren disease group had significantly lower phalanx and combined 2D:4D. These findings suggest that endogenous prenatal androgens could contribute to the development of Dupuytren disease, leading to its characteristic clinical presentation predominantly in men and affecting the ulnar rays.

The 2D : 4D Digit Ratio as a Biomarker for Autism Spectrum Disorder

It has been suggested that the second (2D, index finger) to fourth (4D, ring finger) digit ratio, 2D : 4D, may be a biomarker for the risk of developing autism. The aim of the current study was to determine the usefulness of the 2D : 4D digit ratio as biomarker for autistic traits. N = 401 healthy young volunteers participated in the study. For both hands, digit lengths were measured using digital Vernier calipers. In addition to demographics, the Autism Spectrum Quotient (AQ) questionnaire was completed, comprised of five subscales, assessing “social insights and behavior,” “attention switching,” “communication,” “imagination,” and “attention to detail.” Overall, no significant correlations were observed between the AQ total score, its subscales, and the 2D : 4D digit ratio. For women, the left hand 2D : 4D digit ratio correlated significantly with the subscale score “communication” (r = −0.142; p = 0.036). For men, a significant positive correlation was found between the left 2D : 4D digit ratio and the total AQ score (r = 0.157; p = 0.042) and AQ subscale “attention switching” (r = 0.182; p = 0.017). In conclusion, gender specific associations between the 2D : 4D digit ratio and specific autism traits were observed, which were stronger in men than in women. Future studies should be conducted in patients that are formally diagnosed with autism.

Cerebral laterality for language is related to adult salivary testosterone levels but not digit ratio (2D:4D) in men: A functional transcranial Doppler ultrasound study

The adequacy of three competing theories of hormonal effects on cerebral laterality are compared using functional transcranial Doppler sonography (fTCD). Thirty-three adult males participated in the study (21 left-handers). Cerebral lateralization was measured by fTCD using an extensively validated word generation task. Adult salivary testosterone (T) and cortisol (C) concentrations were measured by luminescence immunoassay and prenatal T exposure was indirectly estimated by the somatic marker of 2nd to 4th digit length ratio (2D:4D). A significant quadratic relationship between degree of cerebral laterality for language and adult T concentrations was observed, with enhanced T levels for strong left hemisphere dominance and strong right hemisphere dominance. No systematic effects on laterality were found for cortisol or 2D:4D. Findings suggest that higher levels of T are associated with a relatively attenuated degree of interhemispheric sharing of linguistic information, providing support for the callosal and the sexual differentiation hypotheses rather than the Geschwind, Behan and Galaburda (GBG) hypothesis.

The relationship between second-to-fourth digit (2D:4D) ratios and problematic and pathological Internet use among Turkish university students

Background and aims The ratio of the second and fourth fingers (2D:4D ratio) is a sexually dimorphic trait, with men tending to have lower values than women. This ratio has been related to prenatal testosterone concentrations and addictive behaviors including problematic video-gaming. We aimed to investigate the possible association between 2D:4D ratios and Internet addiction and whether such a relationship would be independent of impulsivity. Methods A total of 652 university students (369 women, 283 men), aged 17-27 years, were enrolled in the study. Problematic and pathological Internet use (PPIU) was assessed using the Internet Addiction Test (IAT). The participants also completed the Barratt Impulsiveness Scale (version 11; BIS-11) and had their 2D:4D ratios measured. Results 2D:4D ratios were not significantly different in women with PPIU and in those with adaptive Internet use (AIU). Men with PPIU exhibited lower 2D:4D ratios on both hands when compared with those with AIU. Correlation analysis revealed that 2D:4D ratios on both hands were negatively correlated with IAT scores among men, but not among women. The multiple linear regression analysis revealed that age, duration of weekly Internet use, impulsiveness, and 2D:4D ratios on the right hand were independently associated with IAT scores among men, and impulsivity did not mediate the relationship between 2D:4D ratios and PPIU. Conclusions For men, 2D:4D ratios on the right hand were inversely correlated with Internet addiction severity even after controlling for individual differences in impulsivity. These findings suggest that high prenatal testosterone levels may contribute to the occurrence of PPIU among men.

Digit Ratio (2D:4D), Lateral Preferences, and Performance in Fencing

The second to fourth digit ratio (2D:4D) is a sexually dimorphic trait (men tend to have lower values than women) and a likely biomarker for the organizational (permanent) effects of prenatal androgens on the human brain and body. Prenatal testosterone, as reflected by 2D:4D, has many extragenital effects, including its relevance for the formation of an efficient cardiovascular system. Previous research, reviewed here, has therefore investigated possible associations of 2D:4D with sport performance. Several studies found more masculinized digit ratio patterns (low 2D:4D values or a negative right-minus-left difference in 2D:4D) to be related to high performance in running, soccer, and skiing. The present research tested this hypothesis in a sample of 54 tournament fencers, predominantly from Austria. For men, negative right-left differences in 2D:4D corresponded significantly to better current as well as highest national fencing rankings, independent of training intensity and fencing experience. The mean 2D:4D values of these fencers were significantly lower and the proportion of left-handers was elevated relative to the local general population. For the right hand, the ratio was somewhat lower in male sabre fencers than in male 6pke and foil fencers combined and significantly lower in left-handed compared to right-handed fencers. Although nonsignificant due to low statistical power, effect sizes suggested that crossed versus congruent hand-eye and hand-foot preferences might also be related to fencing performance. The present findings add to the evidence that 2D:4D might be a performance indicator for men across a variety of sports.

Finger Length Ratio (2D:4D) in Central India and an Attempt to Verify Fraternal Birth Order Effect: A Population Based Cross-Sectional Study

INTRODUCTION

A normal physiology of a human being is not mere a series of functions occurring with specific intensities and timing. There are lot of factors that may change the normal physiological activity within normal limits. Finger length ratio is one of the markers of intrauterine androgen exposure and it is debated and contradicted by many authors. Digit ratio varies among the ethnicities. Many Indian studies show that there is considerable difference in finger length ratio in different population. Data regarding Central India was not found on extensive search.

AIM

To find out the finger length ratio and explore the birth order effect on finger length ratio among the first two successive born in the said population.

MATERIALS AND METHODS

We conducted a survey on 1500 volunteer persons (800 male and 700 female) over two years of time. We measured the length of the index finger (2D) and ring finger (4D) of both the hands and asked about their birth order history to find out the digit ratio for Central India population and any existing correlation of the same with birth order. T Test and Analysis of Variance (ANOVA) were used for the measure of significance and difference among the groups. The p< 0.05 was considered to be significant.

RESULTS

Our study reports that, study population mean for right hand 2D:4D ratio was 0.976 (SD±0.031) and for left hand it was found to be 0.969 (SD±0.035). For males, mean finger length ratio for right hand was 0.967 (SD±0.033) and 0.963 (SD±0.037) for left hand. In females the mean Finger length ratio was 0.982 (SD±0.027) for right hand and 0.974 (SD±0.034) for the left hand respectively. Finger length ratio was found to be significantly less (p=0.03) in males for right hand. No significant (p=0.24) difference was observed for left hand. When assessed fraternal birth order effect among the eldest, second born with elder brother and second born with elder sister groups, no significant (p>0.05) variation for finger length ratio of right and left hands observed in both male and female population.

CONCLUSION

Our study reports that the finger length ratio (2D:4D) for Central India population did not show significant association between finger length ratio and fraternal birth order among the first two successive born.

Assessment of the 2D:4D ratio in aggression-related injuries in children attending a paediatric emergency department

BACKGROUND

The 2D:4D ratio is a sexually dimorphic trait. A lower ratio is correlated with sporting prowess, successful financial trading, risk taking behaviour, aggression, and aggression-related injuries, such as the fifth metacarpal fractures.

AIMS

We aimed to assess if the ratio correlates to skeletally immature patient aggression.

METHODS

Radiology reports were searched for the terms "5th metacarpal" or "boxer". Of 537 X-rays, 142 had fractures. The mechanism of injury was recorded in 102 patients, differentiating aggressive and non-aggressive injury groups. Bone age and chronological age were recorded.

RESULTS

A clear male preponderance for aggression was identified with only 60% of non-aggressive injuries occurring in males compared to 95% in the aggression group (p < 0.001). Patients with aggression injuries were older chronologically (14.6 vs 12.7, p < 0.001) and by bone age (14.5 vs 13.0, p < 0.001). For male patients, there was no difference in the 2D:4D ratio (p = 0.94); however, for females, the difference was significant (p = 0.04).

CONCLUSIONS

Aggression injuries occur at an older age and are more common in males. In the female cohort, there was a distinct difference in digit ratio.

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.

Digit ratio (2D:4D), testosterone, cortisol, aggression, personality and hand-grip strength: Evidence for prenatal effects on strength

BACKGROUND

Digit ratio (2D:4D) is a putative marker for prenatal testosterone and is correlated with performance in many sports. Low 2D:4D has been linked to strength but the evidence is mixed and strength is also influenced by mass, testosterone, and behavioural factors. It has been hypothesised that the 2D:4D-strength correlation may be strongest in challenge conditions when short-term changes occur in steroid hormones.

AIMS

We tested this suggestion in men.

STUDY DESIGN

We used a cross-over study design with a challenge (an aggressive video of rugby tackles) and control (a blank screen) condition.

SUBJECTS

89 healthy men.

OUTCOME MEASURES

Finger lengths (2nd and 4th for both hands), hand-grip strength (HGS), testosterone (T), cortisol (C), aggression (Buss-Perry Aggression Questionnaire) and personality type (Ten Item Personality Measure). In both conditions participants provided saliva samples (for hormone assays).

RESULTS

In the challenge condition there was a highly significant increase in HGS, and modest changes in T, physical aggression and emotional stability. HGS correlated negatively with left hand 2D:4D. In a multiple regression, left hand 2D:4D was negatively related to HGS and emotional stability was positively related to HGS. In the control condition HGS was not correlated with 2D:4D. In a multiple regression, BMI, physical aggression, and emotional stability were significantly related to HGS.

CONCLUSIONS

2D:4D is a negative correlate of strength in challenge situations. This finding may in part explain associations between 2D:4D and sports performance.

CAN BODY PROPORTIONS SERVE AS A PREDICTOR OF RISK-TAKING BEHAVIOURS IN WOMEN AND MEN?

The second to fourth digit ratio (2D:4D) is claimed to be a biomarker of prenatal sex steroids. This study compared 2D:4D and waist-hip ratio (WHR) in men and women with nose deformity caused by injuries suggesting risky behaviour with those of unaffected controls. This kind of facial trauma was accepted as an indicator of risk-taking behaviour. The study involved 100 patients (50 women aged 30.74±8.09 years and 50 men aged 30.98±10.86 years) who underwent rhinoplasty due to nose trauma in a hospital in Łódź, Poland, in 2015. For comparison purposes, a control sample of 70 women (aged 23.03±3.36 years) and 70 men (aged 22.87±3.46 years) was recruited. In both groups the following measurements were taken: body height, waist and hip circumferences, II and IV digit lengths and body weight. The results showed that women and men who had suffered nose injury had significantly higher values of WHR than controls. The 2D:4D in women with post-traumatic nose deformity was significantly different than the ratio in control women (p<0.0001) and presented the male pattern. It is concluded that in women risky behaviours seem to be associated with prenatal sex hormone influence, while differences in WHR suggest that this tendency is also related to postnatal hormonal factors. Risky behaviours in men should be linked to postnatal hormonal changes rather than to increased prenatal androgen exposure.

Effects of two-year testosterone replacement therapy on cognition, emotions and quality of life in young and middle-aged hypogonadal men

The aim of the study was to examine the effects of two-year testosterone replacement therapy on cognitive functioning, emotional state and quality of life in young and middle-aged men with hypogonadotropic hypogonadism. Nineteen males diagnosed with hypogonadotropic hypogonadism participated in the study. Cognitive functions were assessed by Trail Making Test and Digit Span Test of Wechsler Adult Intelligence Scale. Emotional state was evaluated by Profile of Mood States. Quality of life was evaluated by WHO Brief Quality of Life Questionnaire. Changes after two-year testosterone replacement therapy were detected in Trail Making A (42.9 ± 22.3 vs. 36.2 ± 22.5, p = .050) and B (90.6 ± 55.3 vs. 65.6 ± 21.4, p = .025) tests, showing improvement in attention and visual scanning abilities, executive function and psychomotor speed, as well as in Digit Span Test forward score (5.4 ± 2.0 vs. 6.1 ± 2.6, p = .046), showing improvement in attention capacity and psychomotor speed. No significant differences were observed in emotional state and quality of life. In conclusion, beneficial effect in cognitive functioning (improved attention and visual scanning ability, executive function and psychomotor speed), but not in emotional state and quality of life, was observed in young and middle-aged hypogonadal men after two-year testosterone replacement therapy.

The Ratio of 2nd to 4th Digit Length in Korean Alcohol-dependent Patients

Objective

The ratio of 2nd to 4th digit length (2D:4D) is a sexually dimorphic trait. Men have a relatively shorter second digit than fourth digit. This ratio is thought to be influenced by higher prenatal testosterone level or greater sensitivity to androgen. The purpose of this study is to investigate the relationship between alcohol dependence and 2D:4D in a Korean sample and whether 2D:4D can be a biologic marker in alcohol dependence.

Methods

In this study, we recruited 87 male patients with alcohol dependence from the alcohol center of one psychiatric hospital and 52 healthy male volunteers who were all employees in the same hospital as controls. We captured images of the right and left hands of patients and controls using a scanner and extracted data with a graphics program. We measured the 2D:4D of each hand and compared the alcohol dependence group with the control group. We analyzed these ratios using an independent-samples t-test.

Results

The mean 2D:4D of patients was 0.934 (right hand) and 0.942 (left hand), while the mean 2D:4D of controls was 0.956 (right hand) and 0.958 (left hand). Values for both hands were significantly lower for patients than controls (p<0.001, right hand; p=0.004, left hand).

Conclusion

Patients who are alcohol dependent have a significantly lower 2D:4D than controls, similar to the results of previous studies, which suggest that a higher prenatal testosterone level in the gonadal period is related to alcoholism. Furthermore, 2D:4D is a possible predictive marker of alcohol dependence.

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.

Does human ejaculate quality relate to phenotypic traits?

A given man's phenotype embodies cues of his ancestral ability to effectively defend himself and his kin from harm, to survive adverse conditions, and to acquire status and mating opportunities. In this review, we explore the hypothesis that a man's phenotype also embodies cues to fertility or the probability that an ejaculate will fertilize ova. Female mate choice depends on the ability to discern the quality of a male reproductive partner through his phenotype, and male fertility may be among the traits that females have evolved to detect. A female who selects as mates males that deliver higher quality ejaculates will, on average, be more fecund than her competitors. Data on several non-human species demonstrate correlations between ejaculate quality and secondary sexual characteristics that inform female mate choice, suggesting that females may select mates in part on the basis of fertility. While the non-human literature on this topic has advanced, the human literature remains limited in scope and there is no clear consensus on appropriate methodologies or theoretical positions. We provide a comprehensive review and meta-analysis of this literature, and conclude by proposing solutions to the many issues that impede progress in the field. In the process, we hope to encourage interest and insight from investigators in other areas of human mating and reproductive biology. Am. J. Hum. Biol. 28:318-329, 2016. © 2015 Wiley Periodicals, Inc.

SEX DIFFERENCES IN DIGIT RATIO (2D:4D) AMONG MILITARY AND CIVIL COHORTS AT A MILITARY ACADEMY IN WROCŁAW, POLAND

The ratio of second-to-fourth digit length (2D:4D), which is generally higher in women compared with men, is a putative marker of prenatal testosterone (PT) exposure. Lower 2D:4D is linked with greater physical ability and strength, better sporting performance and a propensity towards jobs demanding greater physical ability. The objectives of this paper were to examine the sexual dimorphism in 2D:4D in both hands 1and compare this dimorphism in the students of military and civil courses at the General Kuściuszko Military Academy of Land Forces in Wrocław. The cross-sectional study compared 59 female and 118 male students from the military courses and 53 females and 64 male students from the civil courses. Besides calculating 2D:4D (2D/4D) for each hand, height and weight were also recorded. Physical fitness and endurance were assessed using Eurofit tests. Handgrip strength was measured using a standardized isometric dynamometer. In almost all physical tests, students in the military cohort showed highly significant greater physical ability and strength (e.g. handgrip strength) when compared with the civil cohort. Male participants had a significantly lower 2D:4D than females for each hand, as well as for the average value for both hands. The sexual dimorphism was, however, a little more pronounced in the right hand than in the left. Both sex and course type were significant predictors of 2D:4D. There were significant interactions between sex and the student type. Among females, but not in males, the military cohort had a significantly lower, i.e. more 'masculine', 2D:4D for the left hand and right hand and average for both hands (t=3.290, p<0.001) than the civil cohort. This was not the case in males. However, the sex difference in 2D:4D was only significant among the civil students, and not among the military cadets. In conclusion, higher PT exposure, as represented by a lower 2D:4D, among the Polish females might be an indicator of relatively increased physical ability and motivation to choose professions that require higher strength and endurance.

Hadza hunter-gatherer men do not have more masculine digit ratios (2D:4D)

OBJECTIVES

The ratio between the length of the second and the length of the fourth digit (2D:4D) is sexually dimorphic such that males of many species possess a lower ratio than females, particularly in the right hand. Still, men and women often exhibit overlapping 2D:4D ranges and the ratio is highly variable between populations. In order to further explore populational variability, we chose to analyze 2D:4D in the Hadza, a population of hunter-gatherers living in Tanzania.

MATERIALS AND METHODS

Data were collected separately by two researchers over the course of three years (1998, 2001, 2006) from 152 adult participants (male: n = 76, female: n = 76). Independent samples t-tests were used to explore sex differences, paired samples t-tests were used to explore directional effects within each sex, and linear regression and one-way ANOVA were used to test possible age effects.

RESULTS

In none of the years, or pooled (n = 152), did we find evidence that adult men have a lower 2D:4D than adult women. If anything, the data suggest that women in this population have a significantly lower right hand 2D:4D than men (P < 0.001, d = 0.57). In contrast, left hand 2D:4D did not exhibit a sex difference (P = 0.862, d = 0.03).

DISCUSSION

These findings challenge the current view that lower 2D:4D in men is a uniform characteristic of our species. Cross-populational variance in 2D:4D may be related to known patterns of hormonal variation resulting from both genetic and environmental mechanisms, though this relationship merits further investigation.

Development and implementation of algorithms for automatic and robust measurement of the 2D:4D digit ratio using image data

Early in the 20th century it could be observed that the finger lengths of second (2D) and fourth digit (4D) represents a sexually dimorphic feature, whereby in general the second digit is longer than the fourth digit for men and vice versa for women. In the early 1980s first studies could show a correlation between the 2D:4D ratio and the concentration of androgens one is exposed to during a short window within the prenatal development phase. Therefore, the 2D:4D digit ratio can serve as an additional marker for certain physiological and psychological traits like fertility, assertiveness, aggressiveness and alcohol addiction. Manual measurements are the established method to retrieve the finger lengths e.g. by using a ruler on printed scans of hands. For higher reliability these extremely time-consuming procedures have to be done multiple times. In this contribution two automated procedures are proposed to reduce the time for measurements whilst maintaining the accuracy. A deviation of maximal 2% from the manual measurement could be achieved for more than 75% of the 22 participants.

Bulbocavernosus muscle area measurement: a novel method to assess androgenic activity

Serum testosterone does not correlate with androgen tissue activity, and it is critical to optimize tools to evaluate such activity in males. Ultrasound measurement of bulbocavernosus muscle (BCM) was used to assess the relationship between the number of CAG repeats (CAGn) in the androgen receptor (AR) and the BCM size; the changes in the number of CAGn over age were also evaluated. Transperineal ultrasound measurement of the BCM was also performed. AR CAGn were determined by high performance liquid chromatography, and morning hormone levels were determined using immunoassays. Forty-eight men had CAG repeat analysis. Twenty-five were <30 years of age, mean 23.7 years (s.d. = 3.24) and 23 were >45 years of age, mean 53 years (s.d. = 5.58). The median CAGn was 21 (13-29). BCM area was greater when the number of CAGn were <18 as compared to the number of CAGn >24 (P = 0.04). There was a linear correlation between the number of CAGn and the BCM area R 2 = 16% (P = 0.01). In the 45 to 65-years-old group, a much stronger negative correlation (R 2 = 29%, P = 0.01) was noticed. In the 19 to 29-years-old group, no such correlation was found (R 2 = 4%, P = 0.36). In older men, the number of CAGn increased with age (R 2 = 32%, P = 0.01). The number of CAGn in the AR correlates with the area of the BCM. Ultrasound assessment of the BCM is an effective surrogate to evaluate end-organ activity of androgens. The number of CAGn may increase with age.

Digit ratio (2D:4D) and salivary testosterone, oestradiol and cortisol levels under challenge: Evidence for prenatal effects on adult endocrine responses

BACKGROUND

Digit ratio (2D:4D) is a marker for prenatal sex steroids and a correlate of sporting performance. This association may exist because low 2D:4D is linked to high prenatal levels of testosterone (T) and low oestrogens (E). It was recently suggested that low 2D:4D, and particularly low right-left 2D:4D (or Dr-l), is a marker for T changes in response to physical and aggressive challenges. If correct, this link may in part explain the association between 2D:4D and sports performance.

AIMS

We tested this hypothesis in adults.

STUDY DESIGN

Three experimental treatments were completed using a randomised, cross-over design; (i) cycle sprints plus an aggressive video (S+V), (ii) aggressive video plus cycle sprints (V+S), and (iii) a control session.

SUBJECTS

24 healthy adults (12 men and 12 women).

OUTCOME MEASURES

Salivary T, oestradiol (E2) and cortisol (C) levels were measured on six occasions across each session and pooled for analysis.

RESULTS

The S+V treatment was associated with a rise in T and C levels, and Dr-l was significantly and negatively correlated with T and E2 with these effects confined to men. The right 2D:4D and Dr-l were also negatively correlated with the T/C ratio and Dr-l negatively related to the E2/C ratio in men during the S+V treatment.

CONCLUSIONS

We suggest that the hormonal responses to a challenge are programmed by prenatal levels of T and E with possible links to sporting performance in adulthood.

Relationship Between Second to Fourth Digit Ratios and Benign Prostatic Hyperplasia in Aging Men

INTRODUCTION

Benign prostatic hyperplasia (BPH) is the most common prostate disease, characterized by benign enlargement of the prostate gland in aging men. Testosterone is said to be the major factor in development of BPH. The relative length of 2nd and 4th digit (2D:4D) is a marker for prenatal androgen exposure. A low 2D:4D ratio is associated with a high prenatal androgen exposure. The main objective of this study was to assess the causal relationship between the 2D:4D ratio and incidence of BPH.

MATERIALS AND METHODS

Thirty five patients with BPH were compared with 35 non BPH subjects and 35 controls recruited from general population for measures of 2D:4D ratio. BPH status was determined by clinical & radiological evaluation. Both hands of all the participants were scanned and their second and fourth digit lengths were measured and the ratio calculated.

RESULTS

In the present study, 2D:4D ratio was lower in BPH patients compared to non BPH subjects in both hands. Compared with controls, BPH patients had lower 2D:4D ratio in the right hand, but the difference between the groups in left hand 2D:4D ratios was not significant. Compared with controls, non BPH subjects had higher 2D:4D ratio in the left hand, but the difference between the groups in right hand 2D:4D ratios was not significant.

CONCLUSION

Results of the present study indicate that individuals with lower 2D:4D ratios are at a higher risk of developing BPH and those with higher 2D:4D ratios are at a lower risk of developing BPH compared to the general population.

Digit ratio (2D:4D) and physical fitness (Eurofit test battery) in school children

BACKGROUND

The relative lengths of the index finger to the ring finger (2D:4D) is sexually dimorphic and is thought to be a correlate of prenatal sex steroids (low 2D:4D=high prenatal testosterone and low prenatal oestrogen). In adults there have been reports that low 2D:4D is consistently associated with high sports performance.

AIMS

To investigate correlations between 2D:4D and fitness levels in children.

STUDY DESIGN

Right 2D:4D and body size were measured, in addition to flexibility, speed, endurance and strength (Eurofit tests).

SUBJECTS

922 boys and 835 girls (mean ages (years): 10.8 ± 1.01 and 10.07 ± 1.00 respectively).

OUTCOME MEASURES

height, mass, BMI, triceps and subscapular skinfolds, 20 m shuttle run, sit and reach, standing broad jump, hand grip strength, 10 × 5m sprint, and the sit and reach test.

RESULTS

Boys significantly outperformed the girls in the 10 × 5m sprints, the 20 m shuttle run, standing broad jump, and hand grip strength. In boys but not girls, 2D:4D was significantly negatively correlated with scores in all these tests except the standing broad jump. In girls but not boys, 2D:4D was significantly positively correlated to stature, mass, BMI and waist circumference.

CONCLUSIONS

It is suggested that high prenatal testosterone and low prenatal oestrogen (low 2D:4D) is implicated in high sprinting speed, endurance and hand grip strength in boys. In girls low prenatal testosterone and high prenatal oestrogen is associated with large body size.

Can persistence hunting signal male quality? A test considering digit ratio in endurance athletes

Various theories have been posed to explain the fitness payoffs of hunting success among hunter-gatherers. ‘Having’ theories refer to the acquisition of resources, and include the direct provisioning hypothesis. In contrast, ‘getting’ theories concern the signalling of male resourcefulness and other desirable traits, such as athleticism and intelligence, via hunting prowess. We investigated the association between androgenisation and endurance running ability as a potential signalling mechanism, whereby running prowess, vital for persistence hunting, might be used as a reliable signal of male reproductive fitness by females. Digit ratio (2D:4D) was used as a proxy for prenatal androgenisation in 439 males and 103 females, while a half marathon race (21km), representing a distance/duration comparable with that of persistence hunting, was used to assess running ability. Digit ratio was significantly and positively correlated with half-marathon time in males (right hand: r = 0.45, p<0.001; left hand: r = 0.42, p<0.001) and females (right hand: r = 0.26, p<0.01; left hand: r = 0.23, p = 0.02). Sex-interaction analysis showed that this correlation was significantly stronger in males than females, suggesting that androgenisation may have experienced stronger selective pressure from endurance running in males. As digit ratio has previously been shown to predict reproductive success, our results are consistent with the hypothesis that endurance running ability may signal reproductive potential in males, through its association with prenatal androgen exposure. However, further work is required to establish whether and how females respond to this signalling for fitness.

The processing of object identity information by women and men

The study examined whether women excel at tasks which require processing the identity of objects information as has been suggested in the context of the well-known object location memory task. In a computer-simulated task, university students were shown simulated indoor and outdoor house scenes. After studying a scene the students were presented with two images. One was the original image and the other a modified version in which one object was either rotated by ninety degrees or substituted with a similar looking object. The participants were asked to indicate the original image. The main finding was that no sex effect was obtained in this task. The female and male students did not differ on a verbal ability test, and their 2D:4D ratios were found to be comparable.