Digit ratio (2D:4D) and aggregate personality scores across nations: Data from the BBC internet study

The purpose of this study was to consider relationships between digit ratio (2D:4D, a putative correlate of prenatal sex steroids) and aggregate personality scores across nations. Differences in national personality scores may be influenced by such factors as prevalence of the parasite Toxoplasma gondii, latitude and economics, and variation in 2D:4D has also been linked to prevalence of T. gondii and to latitude. Here we report associations of mean 2D:4D per country and latitude, gross domestic product (GDP), T. gondii prevalence and personality profiles in 23 nations of an internet study. 2D:4D was not related to latitude or to T. gondii, but was related to GDP (women only). With regard to national personality scores, 2D:4D was not related to masculinity but there were significant positive relationships of 2D:4D with uncertainty avoidance in men and women and with neuroticism in men. Male 2D:4D was significantly related to uncertainty avoidance and neuroticism independent of T. gondii, whereas female 2D:4D was not significantly related to uncertainty avoidance or neuroticism after controlling for the effect of T. gondii and GDP. We conclude that nations with high male 2D:4D (low prenatal testosterone, high prenatal oestrogen) have high scores for uncertainty avoidance and neuroticism.     

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.     

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.     

Individual differences in women's perceptions of other women's dominance

Recent research on men's dominance perception suggests that the extent to which men perceive masculine men to be more dominant than relatively feminine men is negatively correlated with measures of their own dominance. In the current studies, we investigated the relationship between indices of women's own dominance and their perceptions of other women's facial dominance. Women's own height and scores on a dominance questionnaire were negatively correlated with the extent to which they perceived masculine women to be more dominant than relatively feminine women. In follow‐up studies, we observed similar individual differences when (i) women separately judged other women's social and physical dominance, suggesting that individual differences in women's dominance perceptions generalize across two different types of dominance judgment and (ii) we assessed the perceivers' dominance indirectly by using a questionnaire that measures the extent to which women view interactions with other women in competitive terms. These findings present new evidence that the extent to which people perceive masculine individuals to be more dominant than relatively feminine individuals is negatively correlated with measures of their own dominance and suggest that competition and conflict among women may have shaped individual differences in women's dominance perception. Copyright © 2011 John Wiley & Sons, Ltd.     

Digit ratio (2D:4D) and Cattell's personality traits

The ratio between second and fourth finger (2D:4D) is sexually dimorphic; it is lower in men than in women. Studies using broad personality domains yielded correlations of 2D:4D with neuroticism, extraversion or agreeableness, but the obtained results have been inconsistent. We correlated 2D:4D of 184 women and 101 men with their scores in Cattell's 16 Personality Factor (16PF) Questionnaire. We found women with a higher (more ‘feminine’) right hand 2D:4D to score lower in emotional stability and social boldness and higher in privateness. Mediator analysis showed emotional stability to be probably primarily correlated with 2D:4D and to act as a mediator between 2D:4D and social boldness. Privateness appears to be mediated by an even more complex path. We discuss the usefulness of primary‐level personality questionnaires and mediator analyses in the investigation of psycho‐morphological associations. Copyright © 2007 John Wiley & Sons, Ltd.     

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.     

Second to fourth digit ratio and numerical competence in children

The ratio between the 2nd and 4th fingers (2D:4D)-a potential proxy for prenatal testosterone (T) exposure-shows a sex difference, with males usually having lower mean values; the latter potentially indicates higher prenatal T exposure. We studied relations between 2D:4D and competencies in the domains of counting, number knowledge, and visual-number representation in 73 children aged 6-11 years. Significant negative correlations between numerical performance in all of these areas and right and left hand 2D:4D ratios were found for boys but not girls. To the extent that 2D:4D ratios reflects prenatal exposure to T, the implications are (i) high prenatal T may be associated with better performance on some basic numerical measures for boys, and (ii) prenatal exposure to T may affect boys and girls differently with respect to some numerical competencies.     

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.     

Effect of Prenatal Androgen on Adult Personality: Greater Openness with More Female-Typical 2D:4D Digit Ratios

One hundred seven university community participants (71 female, 36 male) were evaluated on the five personality factors (NEO-FFI), and finger lengths were measured to determine the ratio of the second to fourth digit (2D:4D). It is well-established that 2D:4D ratios are an index of prenatal androgenic activity. Sex differences were found such that the men had lower 2D:4D ratios than the women for both the left and right hands, and the women indicated greater Neuroticism than the men, as reported by others. Most interestingly, greater Openness was significantly associated with more female-typical (higher) 2D:4D ratios for the entire sample. This was significant for the male sample alone, and was found at a trend level in the female sample alone.     

Fetal exposure to androgens,as indicated by digit ratios (2D:4D), increases men’s agreeableness with women

The ratio of the length of the second finger, or digit, to the fourth finger (2D:4D) is influenced by fetal exposure to androgens; a smaller ratio indicates greater androgen exposure. We used event contingent recording to investigate the relation between the 2D:4D ratio and social behavior. Participants completed multiple records of their behavior in events in naturalistic settings; records included information about situational features such as the gender of the person with whom the person was interacting. Men were more agreeable towards women than men; this effect was significantly greater in those with smaller 2D:4D ratios. Men with smaller 2D:4D ratios were also less quarrelsome towards women than towards men. The 2D:4D ratio did not influence social behavior in women. The hormonal environment in which the male fetal brain develops may influence adult social behavior in specific contexts.     

Digit ratio (2D:4D) and sensation seeking: New data and meta-analysis

Previously reported associations between low (male-typical) digit ratio (2D:4D), a putative pointer to prenatal testosterone exposure, and high (male-typical) sensation seeking have been inconsistent across studies (alternately present for men, women, either sex, or neither). Addressing this question again in three new studies (N = 198, 188, 1118) produced similarly erratic findings. Meta-analysis of the entire literature (13 studies with nearly 3000 individuals, including unpublished accounts) showed that the current cumulative evidence does not support any negative correlations between 2D:4D and sensation seeking traits. The only significant meta-analytical finding was for right-hand 2D:4D and the experience seeking facet of sensation seeking in both sexes, but this effect accounted for merely 0.4% attributable variance, and moreover was directionally opposite to expectation (i.e., a positive correlation). Discussed are inherent limitations of narrow-scoped approaches (such as via 2D:4D) for elucidating the biological bases of individual difference variables with evidentially intricate neurochemical underpinnings (such as sensation seeking).     

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.     

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.     

Relationships between digit ratio (2D:4D) and sex-typed play behavior in pre-school children

Juvenile play shows sex differences in animals and humans. Animal studies and a recent study in humans suggest that testosterone exposure during early development plays a key role. Here we report on the relationship between children’s sex-typed play behavior and digit ratio (2D:4D), a putative negative correlate of prenatal testosterone. 2D:4D and sex-typed play behavior as assessed by parents were negatively correlated in a sample of 83 pre-school boys but not in a sample of 93 girls. This finding lends some support to the ideas that early testosterone has a masculinising effect upon sex-typed play behavior in humans and that 2D:4D is a valuable tool for studying effects of early testosterone on human behavior.     

The role of sex hormones and of 2D:4D ratio in individual differences in cognitive abilities

The present study aimed at investigating the role of sex hormones in individual differences in cognitive abilities. This was achieved by a combination of two methods, reflecting 2 critical periods of hormonal secretion: prenatal, based on the 2D:4D ratio, and postnatal, based on circulating hormone levels. Both methods were tested in 39 men and 41 women, who completed a battery of 6 cognitive tasks. Results showed significant sex differences on the mental rotation task, with men outperforming women. A positive correlation was found between testosterone and performance on the mental rotation task for the combined sample (men and women). A significant interaction was found between sex and estrogen on mental rotation task. Findings also revealed a significant interaction between sex and right hand 2D:4D ratio on different memory tasks. Findings regarding between- and within-sex differences in cognition are discussed in light of the organisational and activational effects of sex hormones.     

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.     

Social dominance orientation and climate change denial: The role of dominance and system justification

Extending previous research, we examined whether the relation between social dominance orientation (SDO) and climate change denial reflects group-based dominance (SDO and nature dominance) or general system justification. Moreover, we examined whether the relation between personality (domineering and empathy) and denial is mediated by group-based dominance variables. The results showed that the group-based dominance variables reduce the effect of system justification on denial to nonsignificant. Also, social dominance and nature dominance explain unique parts of the variance in denial. Moreover, path analyses showed that the relations between empathy and system justification with denial are mediated by both of the group-based dominance variables, while the relation between domineering and denial is mediated only by SDO. Together, these results suggest that denial is driven partly by dominant personality and low empathy, and partly by motivation to justify and promote existing social and human-nature hierarchies. We conclude by suggesting that climate change mitigation efforts could be more successful if framed as being clearly beneficial for everybody and nonthreatening to existing social order.     

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.     

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

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

The 2nd to 4th digit ratio (2D:4D) and eating disorder diagnosis in women

Eating disorders are more common in females than in males and are believed to be caused, in part, by biological and hormonal factors. Digit ratio or 2D:4D (the ratio of the 2nd to the 4th digit) is considered to be a proxy for prenatal testosterone (PT) and prenatal oestrogen (PE) exposure. However, how 2D:4D may be related to type of eating pathology is unknown. The relationship between 2D:4D and eating disorder diagnosis was investigated in recovered and currently eating disordered (n = 31) and control (n = 99) women. Mean 2D:4D ratio was significantly lower (indicating higher levels of PT and lower levels of PE) in anorexic (AN) compared to bulimic (BN) women, with controls intermediary. In eating disordered women, 2D:4D was positively and significantly related to current weight, lowest weight and current BMI, with strongest associations for right 2D:4D. Among women, low 2D:4D is related to AN and high 2D:4D to BN, suggesting a differential causal influence of prenatal sex hormones on later eating pathology.