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.     

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.     

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 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.     

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.     

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.     

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.     

2D:4D in men is related to aggressive dominance but not to sociable dominance

It has been shown that a smaller ratio between the length of the second and fourth digit (2D:4D) is an indicator of the exposure to prenatal testosterone (T). This study measured the 2D:4D of men and assessed dominance as a personality trait to investigate indirectly if the exposure to prenatal T is related to a dominant personality later in life. Results showed that men had a more aggressive dominant personality when having a more masculine (lower) 2D:4D, while there was no relationship between sociable dominance and 2D:4D. Findings from this study indicate that it is important to distinguish different forms of dominance since other studies failed to find relationships between dominance and 2D:4D.     

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.     

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.     

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.     

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.     

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.     

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.     

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.