Testosterone and domain-specific risk: Digit ratios (2D:4D and rel2) as predictors of recreational, financial, and social risk-taking behaviors

Prenatal testosterone has important effects on brain organization and future behavior. The second-to-fourth digit length ratio (2D:4D), a proxy of prenatal testosterone exposure, has been linked to a wide variety of sexually differentiated dispositions and behaviors. We examine the relationship between digit length ratios (2D:4D and rel2, the length of the second finger relative to the sum of the lengths of all four fingers) and risk-taking behaviors across five domains: financial, social, recreational, ethical, and health. In a sub-sample of male Caucasians (ethnically homogeneous), lower rel2 was predictive of greater financial, social, and recreational risk-taking, whereas lower 2D:4D was predictive of greater risk-taking in two domains (social and recreational). In the full male sub-sample (ethnically heterogeneous), the only significant correlation was a negative association between 2D:4D and financial risk. A composite measure of risk-taking across all five domains revealed that both rel2 and 2D:4D were negatively correlated with overall risk-taking in both male sub-samples. No significant correlations were found in the female sub-samples. Finally, men were more risk-seeking than women across all five contexts.     

Social status, masculinity, and testosterone in young men

Among other things, sexual selection theory posits that in species with limited male parental investment, males should evolve biological mechanisms to competitively dominate or otherwise compete with one another. It is unclear whether such proposed mechanisms would influence status hierarchies in small human groups. We report the results of a study investigating possible effects of prenatal (index-to-ring finger length ratio or 2D:4D) and salivary testosterone, and masculine identification, on status among 71 male college students living in nine residential groups. The results indicate no role of either prenatal or salivary testosterone in maintaining status hierarchies in these groups. A possible explanation is that peer-assessed status in these groups was arrived at cooperatively rather than through dominance contests.     

Digit ratio (2D:4D), academic performance in computer science and computer-related anxiety

Being able to use information communication technology (ICT) effectively has become an essential element of participation within an increasingly digital culture. However, there are differences in participation within this digital culture. Prenatal testosterone exposure is thought to influence the development of numeric capabilities and relate to levels of anxiety, both of which contribute towards engagement with ICT. This study examined whether an index of prenatal exposure to testosterone, digit ratio (2D:4D), is related to successful involvement within a computer-technology context - performance in a Java programming course. Three studies (N = 73,75,65) identified a consistent negative correlation between 2D:4D digit ratio and attainment (r ≈ −0.2). A fourth study (N = 119) found that 2D:4D digit ratio positively correlated with two indices of computer-related anxieties, as well as anxiety sensitivity (r = 0.32/0.51). These results suggest that males and females who have been exposed to higher levels of testosterone within the womb perform better upon academic assessments of Java-related programming ability within computer science education, and have lower levels of computer-related anxieties outside computer science education. Thus, the 2D:4D index of prenatal testosterone exposure correlated with the two factors that directly impact upon ICT engagement, which is increasingly essential to effectively participate within educational and occupational environments.     

Investigating digit ratio (2D:4D) in a highly male‐dominated occupation: The case of firefighters

Voracek, M., Pum, U. & Dressler, S. G. (2009). Investigating digit ratio (2D:4D) in a highly male‐dominated occupation: The case of firefighters. Scandinavian Journal of Psychology, 51, 146–156. Second‐to‐fourth digit ratio (2D:4D), a widely studied putative marker for masculinization through prenatal androgen exposure, is lower (more masculinized) in athletes than in general population controls, and athletes with lower 2D:4D have higher sporting success. Occupations differ markedly in perceived masculinity and actual maleness (sex ratios), but these givens have not yet been picked up and utilized in 2D:4D research. Accordingly, this study extended existing accounts on 2D:4D in athletes to a novel approach: 2D:4D and possible relationships to a variety of candidate variables (demographic, fertility‐related, psychological, and other) were investigated in firefighters, a highly male‐dominated occupation. Contrary to expectation, 2D:4D in firefighters (N = 134) was not lower than in local male population controls. Lower 2D:4D corresponded to lower service ranks. Replicating previous findings either unequivocally or partly, lower 2D:4D was associated with larger family size, later sibling position, left‐handedness, and higher scores in the disinhibition component of sensation seeking. Not replicating prior evidence, 2D:4D was unrelated to body‐mass index, offspring sex ratio, and sporting performance level. Novel findings included low 2D:4D in those with low relationship satisfaction and in cigarette smokers, especially among heavy smokers. Absolute finger length, a positive correlate of pubertal‐adolescent androgen levels, was also considered. This marker showed negative associations with relationship consensus and satisfaction and positive ones with perceived quality of relationship alternatives and the experience seeking component of sensation seeking. The merits of this additional marker, relative to 2D:4D, for supplementing studies of possible sex‐hormonal effects on personality and directions for future inquiry along these lines are discussed.     

Prenatal exposure to sex hormones predicts gratitude intervention use. Examination of digit ratio,motivational beliefs,and online activities

Men are less grateful than women and less likely to intentionally enhance gratitude via interventions. Yet, little is known if sex differences in gratitude result from biological influences such as prenatal testosterone and estrogen levels – hormones that control the development of sex-specific characteristics. In two studies, we examined how sex and second-to-fourth digit ratio (2D:4D) – an indicator of prenatal sex hormones exposure – predicts gratitude intervention use. In the first study, we tested whether lower 2D:4D (i.e., higher masculinization) would suppress gratitude intervention use. Contrary to expectations, after controlling for sex, women and men with more male-type fingers were more motivated and likely to complete the intervention. In the second study, we replicated these findings using a larger sample and different 2D:4D metric. Our research suggests that motivation towards gratitude interventions is facilitated by female sex and masculinity. These findings provide initial evidence for the biological grounding of individual differences in gratitude behavior.     

Reliability of 2D:4D measurements using a direct method suitable for clinical settings

The second to fourth digit ratio (2D:4D) indicates androgen exposure during early development. Numerous methods are used in the assessment of 2D:4D, however, some are not reliable enough and others are difficult to perform in large epidemiological studies. We assessed the reliability of 2D:4D using a direct method with a caliper, and compared it with a computer-assisted analysis on scanned images. Both methods were moderately correlated, but the scan method produced slightly lower 2D:4D. The main source of variation was differences between subjects (real variation). Reliability was higher among men and among younger participants. All reliability coefficients were higher than 0.8 when three repeated measurements were averaged. Our results suggest that reliability is influenced by participants’ characteristics. Digit ratios determined directly with calipers are reliable when repeated measurements are averaged.     

An interactionist perspective on the relation between 2D:4D and behavior: An overview of (moderated) relationships between 2D:4D and economic decision making

The present paper gives an overview of recent research on the association between 2D:4D and different types of economic behavior. Particular attention is given to the importance of context dependence of relationships between 2D:4D and economic as well as other, social, behavior. Patterns of results are discussed from the perspective that 2D:4D might serve as a biological marker of dispositional dominance. This overview hopes to stimulate research from an interactionist perspective which focuses at relationships between 2D:4D and behavior that only appear when specific situational pressures interact with individual differences in 2D:4D.     

Lack of correlation between digit ratio (2D:4D) and Baron-Cohen’s “Reading the Mind in the Eyes” test, empathy, systemising, and autism-spectrum quotients in a general population sample

The second-to-fourth digit ratio (2D:4D) is sexually differentiated and is a likely biomarker for the organisational (permanent) effects of prenatal testosterone on the human brain. Recent research has highlighted a possible role of prenatal testosterone levels in both the etiology of autism-spectrum disorders and in sex and individual differences in cognitive styles of the normal mind (Baron-Cohen’s Extreme Male Brain Theory of Autism and Empathising/Systemising Theory). Importantly, autistic children present lower (hypermasculinised) 2D:4D than healthy controls. Based on these accounts, we investigated the relation of 2D:4D with Baron-Cohen’s measures of empathising (“Reading the Mind in the Eyes” test, RMET; Empathy Quotient, EQ), systemising (Systemising Quotient, SQ), and autistic-like traits (Autism-Spectrum Quotient, AQ) in the general population (N = 423 Austrian adults). Whereas sex differences into the expected direction and of expected size were obtained for all variables and internal scale consistencies tallied to retrievable reference values, 2D:4D was unrelated to RMET, EQ, SQ, and AQ scores. Candidate explanations for this lack of correlation might be possible developmental timing differences in the expression of 2D:4D and empathising/systemising, qualitative (as opposed to quantitative) functional differences between the normal and the autistic mind, or the suboptimal psychometric properties of the measures.     

Relationships between digit ratio 2D:4D and self-reported aggression and risk taking in an online study

2D:4D, the length ratio of the second to the fourth digit, is a putative measure of prenatal testosterone, which may have effects on aggression and risk taking. Participants in a German online study (>1000 females, >1200 males) submitted their self-measured digit lengths and self-report measures on verbal and physical aggression and risk taking. For males, left-hand 2D:4D and verbal aggression correlated significantly (r = −.10, after correction for age and reduced reliability in self-measured 2D:4D), with other relationships being similar but non-significant. For females, no relationships between aggression and 2D:4D were found. Risk taking and right-hand 2D:4D correlated significantly in women (r = −.10, after correction for age and reduced reliability in self-measured 2D:4D); similar, but statistically non-significant, relationships were found in men. The result corroborates an emerging view that 2D:4D is negatively related to aggression in males and that 2D:4D is negatively related to risk taking. This tentatively points to effects of prenatal testosterone on these characteristics.     

Digit ratio (2D:4D) and sex-role orientation: Further evidence and meta-analysis

Three new studies (N = 132, 623, 1112) did not yield hypothesized associations between digit ratio (2D:4D), an assumed negative correlate of prenatal testosterone, and psychometrically measured sex-role orientation (positive association with femininity, negative ones with masculinity and masculinity-femininity difference scores) among heterosexuals of either sex. Meta-analysis of the pertinent literature (N = 6311, 28 studies from 10 countries, 46% unpublished) showed only men’s (but not women’s) left-hand (but not right-hand) 2D:4D reliably related as expected (positively) to femininity. This effect was tiny (0.14% attributable variance) and possibly non-robust (crucially dependent on one large study included). Hence, the cumulative evidence does not support systematic, robust, noteworthy within-sex correlations between 2D:4D and the masculinity/femininity personality dimensions.     

Meta-analysis of the relationship between digit-ratio 2D:4D and aggression

Males tend to be more aggressive than females and the organizational effects of prenatal testosterone (T) appear to contribute to this sex difference. Low second-to-fourth digit ratio (2D:4D) is thought to be a marker of high prenatal testosterone. For this reason, a number of studies have used 2D:4D to investigate a potential effect of prenatal T upon aggression in later life. Here we meta-analyse these studies to determine the true size of the relationship between 2D:4D and aggression. We find no evidence of 2D:4D better predicting aggression at different levels of risk nor do we find evidence for a relationship between 2D:4D and aggression in females. Regarding males we find some evidence of a small, negative relationship between 2D:4D and aggression (r ≈ −.06) and no indication that either hand would predict aggression better than the other. We contrast these findings with results regarding levels of aggression in females with elevated prenatal T levels due to Congenital Adrenal Hyperplasia and we discuss implications for 2D:4D research.     

Special issue preamble: Digit ratio (2D:4D) and individual differences research

The sexually differentiated second-to-fourth digit ratio (2D:4D) is currently frequently utilized in individual differences research as a putative indicator of the masculinizing brain organization effects of prenatal testosterone. This preamble introduces the journal special issue on this theme, entitled “Digit ratio (2D:4D) and individual differences research”. Notes regarding the background, history, and recent progress of 2D:4D research are provided, and the background of the special issue and the contents of its 11 research articles are briefly summarized.     

Digit ratios and preferences for aggressive content in entertainment

Digit ratios (2D:4D) contain information concerning an individual’s propensity towards aggression. Our study adds the first clue to better understanding the relationship between 2D:4D and exposure to aggressive contents in entertainment products. Our findings suggest that individuals with low 2D:4D prefer aggressive contents such as action films, sports telecast, killing and achieving games, hip-hop music, and erotic video clips rather than do individuals with high 2D:4D. Also individuals with low 2D:4D tend to demonstrate less preference for romance films than individuals with high 2D:4D. In addition, we found that low 2D:4D was associated with a preference for sports instead of other genres of entertainment products. Therefore, 2D:4D (a putative correlate of prenatal sex steroids) helps us to better understand the rationale of individuals’ preferences for media violence.     

Is CAG sequence length in the androgen receptor gene correlated with finger-length ratio?

Manning, Bundred, Newton, and Flanagan reported a significant correlation of .29 in a sample of 50 British males between the length of a repeated sequence on the androgen receptor gene and 2D:4D finger-length ratio on the right hand. We report a 2nd failure to replicate this result. Ours was a sample of 182 Australian male twins studied for other purposes, for whom both measures were available. The result was a nonsignificant correlation of −.055. A similar result was obtained for female twins, and for comparisons within sibling pairs. Correlations are also reported for left hands and right-left differences--the last showed a weak tendency toward replication.     

Are occupational interests hormonally influenced? The 2D:4D-interest nexus

Occupational interests constitute a psychological variable with pronounced sex differences. Whereas males are more interested in things, females primarily take an interest in people. As various studies with mammals and humans documented the role of androgen exposure on sex-typical behavior, we assumed that androgen levels are associated with occupational interests. In our study, we used 2D:4D digit ratio as an indicator of prenatal androgen levels and finger lengths as an indicator of post-pubertal androgen levels. Occupational interests were measured with a standard interest inventory. We hypothesized that finger lengths and ratios indicating high androgen levels are associated with stronger interests in things and weaker interests in people. All measures were gathered using an online interest inventory thereby leading to sufficient statistical power (N = 8646). Results partly confirmed our hypotheses. We found significant correlations between finger lengths and interests in things for males. Moreover, in the case of males we identified significant correlations between finger lengths (positive) as well as digit ratios (negative) with realistic interests and significant correlations between finger lengths (negative) and social interests, which are a marker variable of the people-things dimension.     

Domain Specific Relationships of 2D:4D Digit Ratio in Risk Perception and Risk Behavior

The 2D:4D digit ratio (henceforth, 2D:4D) is accepted as a marker of prenatal testosterone, demonstrating gender differences. The present study reveals that 2D:4D shows not only gender differences but also individual differences in personality and risk-taking behavior. We measured individual participants’ 2D:4D, structural personality, and risk-taking attitude scores. The result of the current study replicates the gender difference in 2D:4D in previous researches. However, we found different aspects of the correlations among 2D:4D, personality, and risk-taking attitude. Path analyses indicated that 2D:4D passes through personality factors before reaching the risk-taking attitude, particularly in the financial domain activities of investing and gambling. Also we observed a specific relationship between right-hand 2D:4D and emotionality and between left-hand 2D:4D and agreeableness. Finally, we suggest multiple path models of 2D:4D and personality in risk taking depending on the domain.     

Masculinised brain and romantic jealousy: Examining the association between digit ratio (2D:4D) and between- and within-sex differences

We examined the relationship between second-to-fourth digit ratio (2D:4D), a correlate of prenatal testosterone exposure, and distress at sexual versus emotional infidelity in hypothetical scenarios of relationship threat. As predicted, a significant negative association was found between 2D:4D and greater distress at sexual infidelity for the whole sample (N = 179, females = 101). While this novel finding supports the view of romantic jealousy as a sexually-dimorphic adaptation, we explore reasons for the relatively weak association and discuss how underlying differences in brain structure could have influenced sex-specific behavioural capacities in romantic jealousy. We suggest a useful direction for future research will be to develop novel methods that facilitate the investigation of implicit emotional, rather than explicit cognitive, processes in response to pair-bond threat.