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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.

Over the past decade, the second-to-fourth digit ratio (2D:4D), a putative biomarker for the organizational (permanent) effects of prenatal androgens on the human brain, body, and behavior, has received extensive research attention in psychology. This account makes more widely accessible the contributions of the German psychologist, Hans-Dieter Rösler, an early, for a long time unnoticed, predecessor of modern 2D:4D research. In the mid-1950s, Rösler collected a massive sample of hand outline drawings, totalling nearly 7,000 individuals, ranging in age from 1 mo. to 70 yr. With regard to the distal finger-extent pattern, Rösler differentiated radial (longer index than ring finger), ulnar (reversed pattern), and intermediate hand types, which reflect higher (more female-typical), lower (more male-typical), and intermediate 2D:4D, respectively. Here is summarized Rösler's research. In a series of investigations into the hand types, he reported on their anatomical bases, unsuitability for paternity testing, developmental changes, heritability, sex, side, and occupational group differences, and associations with left-handedness, manual dexterity, mental retardation, and clinodactyly. Based on new data from 313 male and 316 female adults, hand type is further shown to be only a weak proxy of actual 2D:4D, leaving 75% of the interindividual variation in 2D:4D unexplained. Notwithstanding these shortcomings of the hand-type method, Rösler's work from the 1950s still has the potential to inform modern 2D:4D research, as it contains a multitude of testable hypotheses not yet picked up by current research.

Preliminary evidence suggests that within-sex individual variation in the length ratio of the index finger to the ring finger (2D:4D), a putative marker of prenatal androgen levels, may be more strongly or consistently related to implicit measures (Implicit Association Test, IAT) than to corresponding explicit (self-report) measures of candidate personality traits. The underlying logic is that the non-introspective TAT may reflect earlier and inaccessible experiences, whereas introspective self-reports reflect more recent and necessarily accessible experiences. Associations of 2D:4D and absolute finger length (a marker of pubertal-adolescent androgen levels) with implicit versus explicit aggression measures (TAT vs. Buss-Perry Aggression Questionnaire and a feeling thermometer) were examined in two samples with identical procedures (Ns= 244 and 233). Attesting to procedural validity and data typicality, several experiments of related research were replicated in both samples, including sex differences in 2D:4D and theory compliant interrelations among psychometric measures. However, no theory compliant, reliable, or replicable associations of 2D:4D or finger length with implicit or explicit aggression measures resulted. These nil findings cast doubt on hypothesized advantages of implicitly (over explicitly) measured target traits for 2D:4D research. More generally, they add to a growing number of replication failures in this area. [ABSTRACT FROM AUTHOR]

Summary-Digit ratios, such as the frequently studied second-to-fourth digit ratio (2D:4D), are already sexually differentiated in utero, postnatally fairly stable, and thus commonly held as possible markers for prenatal androgen levels. Based on six independent samples, totaling 381 male and 420 female subjects from different age bands, this study investigated the magnitude and cross-sample consistency of sex differences in all six possible digit ratios (2D:3D, 2D:4D, 2D:5D, 3D:4D, 3D:5D, 4D:5D) and in four novel relative finger-length measures (the ratio of a given finger to the sum of all four fingers) that were recently suggested by Loehlin, Medland, and Martin as possibly superior to digit ratios for discriminating between the sexes. However, based on the magnitude of sex effects and observed measurement repeatabilities, these novel measures were not superior to digit ratios. Across samples, among digit ratios the traditionally used 2D:4D never yielded the largest sex effect, 2D:5D was the most and 2D:3D the least sexually differentiated. Sex differences were generally larger for digit ratios calculated from nonadjacent than from adjacent fingers. Compared with females, males' relative finger length was clearly lower for 2D, somewhat lower for 3D, somewhat higher for 4D, and clearly higher for 3D. This gradient suggests mediolaterally arranged developmental fields that act sexually differentiated on fingerlength expression. Implications of these findings for further digit ratio research are discussed. [ABSTRACT FROM AUTHOR]

Different methods for measuring the second-to-fourth digit ratio (2D:4D), a putative marker for prenatal androgen exposure, may lead to varying values of 2D:4D. Specifically, it has been hypothesized that fingertip fat pads may be differentially deformed when taking palm images (photocopies or flatbed scans), but not when fingers are measured directly, thus yielding lower 2D:4D values from image-based measurements rather than direct ones. A measurement protocol for fingertip size is unavailable, as are data on finger and sex differences in this trait. Introducing such a protocol, this study found very large finger differences in adult fingertip size (largest for 4D, smaller for 3D and 5D, smallest for 2D), large side differences (larger in the left than in the right hand of right-handed subjects), but only small and not significant sex differences. Fingertip size was unrelated to image-based 2D:4D measurements, suggesting that fingertip size and the extent of finger and sex differences there- in are unlikely to explain discrepant 2D:4D values obtained from image-based versus direct measurements. [ABSTRACT FROM AUTHOR]

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. Pre-natal 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 épée 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. [ABSTRACT FROM AUTHOR]