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Sexually differentiated digit ratios of the hand (2D:4D and other) are currently widely studied, owing to their presumed role as a retrospective diagnostic window into prenatal androgen action. This study was only the second one (following McFadden & Shubel, 2002) to examine all 6 possible finger-length ratios (excluding the thumb) and all 10 possible toe-length ratios (including the big toe). Data from a sample of 59 male and 69 female Austrian adults (M age =27 yr., SD = 7.9) were collected. Replicating the prior study, the majority of toe-length ratios exhibited significant sex differences, which was similar to finger-length ratios, but of weaker effect size. Ipsilateral correlations of toe-length and finger-length ratios were largely absent, except for those of corresponding or adjacent length ratios of the right body side among women. However, these associations were directionally opposite, such that among women, feminized finger-length ratios corresponded to masculinized toe-length ratios. Foot preference (among both sexes) and wearing of toe rings (among women) were not correlates of toe-length ratios. Discussed are implications of these findings for digit ratio research, along with ideas for further inquiry on this topic. [ABSTRACT FROM AUTHOR]

Findings regarding within-sex associations of digit ratio (2D:4D), a putative pointer to long-lasting effects of prenatal androgen action, and sexually differentiated personality traits have generally been inconsistent or unreplicable, suggesting that effects in this domain, if any, are likely small. In contrast to evidence from Wilson's important 1983 study, a forerunner of modern 2D:4D research, two recent studies in 2005 and 2008 by Freeman, et al. and Hampson, et a!. showed assertiveness, a presumably male-typed personality trait, was not associated with 2D:4D; however, these studies were clearly statistically underpowered. Hence this study examined this question anew, based on a large sample of 491 men and 627 women. Assertiveness was only modestly sexually differentiated, favoring men, and a positive correlate of age and education and a negative correlate of weight and Body Mass Index among women, but not men. Replicating the two prior studies, 2D:4D was throughout unrelated to assertiveness scores. This null finding was preserved with controls for correlates of assertiveness, also in nonparametric analysis and with tests for curvilinear relations. Discussed are implications of this specific null finding, now replicated in a large sample, for studies of 2D:4D and personality in general and novel research approaches to proceed in this field. [ABSTRACT FROM AUTHOR]

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]

A scientometric analysis of modern research on the second-to-fourth digit ratio (2D:4D), a widely studied putative marker for prenatal androgen action, is presented. In early 2009, this literature totalled more than 300 publications and, since its initiation in 1998, has grown at a rate slightly faster than linear. Key findings included evidence of publication bias and citation bias, incomplete coverage and outdatedness of existing reviews, and a dearth of meta-analyses in this field. 2D:4D research clusters noticeably in terms of researchers, institutions, countries, and journals involved. Although 2D:4D is an anthropometric trait, most of the research has been conducted at psychology departments, not anthropology departments. However, 2D:4D research has not been predominantly published in core and specialized journals of psychology, but rather in more broadly scoped journals of the behavioral sciences, biomedical social sciences, and neurosciences. Total citation numbers of 2D:4D papers for the most part were not larger than their citation counts within 2D:4D research, indicating that until now, only a few 2D:4D studies have attained broader interest outside this specific field. Comparative citation analyses show that 2D:4D research presently is commensurate in size and importance to evolutionary psychological jealousy research, but has grown faster than the latter field. In contrast, it is much smaller and has spread more slowly than research about the Implicit Association Test. Fifteen conjectures about anticipated trends in 2D:4D research are outlined, appendixed by a first-time bibliography of the entirety of the published 2D:4D literature. [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]

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 differcntiated 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. [ABSTRACT FROM AUTHOR]

Twin and family study findings indicate a substantial heritability of digit ratio (2D:4D), a putative marker for the masculinizing effects of prenatal androgen exposure. Functional polymorphisms of the X-linked androgen receptor gene, i.e., androgen sensitivity, contribute somewhat to the expression of 2D:4D in men, but otherwise the genetics of 2D:4D is unknown. This study investigated differences in 2D:4D by self-reported ABO blood type and Rhesus factor, two easily collectible genetic traits, in two samples (combined N= 1,273). Effects of blood groups on 2D:4D were small and not significant in all tests in both samples; however, two consistent patterns emerged across samples. Of the ABO types, AB had the lowest right-hand 2D:4D, the highest left-hand 2D:4D, and the lowest right-minus-left difference in 2D:4D, and Rhesus factor Rh- had higher left-hand 2D:4D and lower right-minus-left difference in 2D:4D than Rh+. If replicable, this may suggest genes contributing to the expression of 2D:4D reside in the vicinity of the gene loci (chromosomal locations: 9q34.2 and 1p36.11) of these blood groups or pleiotropic effects of the blood-group genes. [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]

Digit ratio (2D:4D), a putative marker for prenatal androgen levels, and absolute finger length, a marker for pubertal androgen action, were not associated with wearing of wedding rings in a sample of 150 male and 199 female married individuals. This failure to replicate associations previously reported by Manning was true for both men and women, self-reported and spousal ring-wearing behavior, and one's own and spousal 2D:4D or absolute finger lengths. Supplemental findings included sex differences and age effects in the prevalence of wearing wedding rings (more frequent in women and the younger than in men and the older) and a sex bias when ring-wearing behavior within couples was discordant (men more frequently did not wear their wedding ring when their wives did than vice versa). Discussed are implications of the current findings and directions for future research into possible associations of 2D:4D with other aspects of body ornamentation. [ABSTRACT FROM AUTHOR]

Sex and side differences in relative thumb length of children and adolescents have been reported by prior researchers. These findings mirror those reported for the second-to-fourth digit ratio (2D:4D), a likely biomarker for the organizational (permanent) effects of prenatal androgens on the human brain and body. The present study investigated relative thumb length, in particular, its associations with all possible digit ratios (2D:3D, 2D:4D, 2D5D, 3D:4D, 3D5D, and 4D5D), in a sample of young adults (60 men and 64 women). Relative thumb length was less precisely measurable than direct or image-based finger-length measurements, as used in digit ratio research. There were no significant sex or side differences in relative thumb length. Contrary to expectation, thumb size was not positively correlated with any digit ratios. Relative thumb length appears to be developmentally unstable (decreases during childhood and adolescence). Additional findings, such as the magnitude ranking of sex differences in digit ratios and the comparability of direct versus image-based finger-length measurements, are also discussed. [ABSTRACT FROM AUTHOR]

The second-to-fourth digit ratio (2D:4D) is sexually dimorphic in humans, such that men on average have a lower 2D:4D than women. This somatic trait has been proposed as a biomarker for the organizational (permanent) effects of prenatal testosterone on the brain and behavior. Over the past few years, an accumulating research program has shown 2D:4D to be related to a multitude of sex-dependent, hormonally influenced psychological and behavioral traits. The present study investigated the 2D:4D ratio of 44 men and 70 women from 36 identical and 21 fraternal twin pairs. Both basic and advanced approaches for estimating heritability concordantly suggested that the trait is substantially heritable. The best-fitting Structural equation model indicated that the contributions to individual differences in 2D:4D are 81% additively genetic, 19% nonshared environmental, and 0% shared environmental. Supplemental analyses showed that, consistent with a prediction from sex-hormone transfer theory, women from opposite-sex fraternal twin pairs had significantly lower (more male-typical) 2D:4D than women from same-sex fraternal twin pairs. Directions for research are discussed, such as investigating possible influences of the sex chromosomes on the expression of 2D:4D. Further family studies will be needed to test whether the transmission mode of 2D:4D is consistent with X-linked or Y-linked inheritance. The study of sex chromosome aberrations should indicate whether the presence of additional X or Y chromosomes is associated with 2D:4D levels. [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]

Summary: The number of sexual partners per individual (NSP) is an important component of sexual behaviour. Here, we report two studies concerning the relationship between a probable negative correlate of prenatal testosterone, the ratio of the length of 2nd and 4th digits (2D:4D), and NSP in men. The right hand 2D:4D ratio appears to be more strongly related to prenatal testosterone than does the left hand. Accordingly we found: (a) in a sample of 99 German heterosexual male undergraduates right hand 2D:4D (but not left hand 2D:4D) was significantly negatively associated with reported lifetime NSP. The relationship between NSP and 2D:4D was independent of free testosterone, but free testosterone also showed a weak positive association with NSP (b) in a sample of 79 heterosexual and 95 homosexual Austrian men we found a significant negative association between right hand 2D:4D (but not left hand 2D:4D) and reported NSP in past year for heterosexual but not for homosexual men. The association in heterosexuals was independent of age, years of education, occupation and relationship status. We conclude that male NSP is likely to be influenced by the long-term organisational effects of prenatal testosterone. The relationship between NSP and 2D:4D appears to be confined to heterosexual men. [Copyright &y& Elsevier]

Augmenting and supplementing the arguments of Crespi & Badcock (C&B), I show that digit ratio (2D:4D), a putative marker of prenatal androgen action, indeed appears differentially altered in autism-spectrum disorders (lower/masculinized) versus schizophrenic-spectrum disorders (higher/feminized). Consistent with C&B's framework, some evidence (substantial heritability, assortative mating, sex-specific familial transmission) points to possible sex chromosome and imprinted genes effects on 2D:4D expression. [ABSTRACT FROM AUTHOR]