Spatial navigation related to the ratio of second to fourth digit length in women

2D:4D Digit Ratios in Adults with Gender Dysphoria: A Comparison to Their Unaffected Same-Sex Heterosexual Siblings, Cisgender Heterosexual Men, and Cisgender Heterosexual Women

We compared gender dysphoria (GD) patients and their same-sex siblings in terms of their 2D:4D ratios, which may reflect prenatal exposure to androgen, one of the possible etiological mechanisms underlying GD. Sixty-eight GD patients (46 Female-to-Male [FtM]; 22 Male-to-Female [MtF]), 68 siblings (46 sisters of FtMs; 22 brothers of MtFs), and 118 heterosexual controls (62 female; 56 male) were included in the study. FtMs were gynephilic and MtFs were androphilic. We found that 2D:4D ratios in the both right hand (p < .001) and the left hand (p = .003) were lower in male controls than in female controls. Regarding right hands, FtM GD patients had lower 2D:4D ratios than female controls (p < .001) but their ratios did not differ from those of their sisters or male controls. FtM GD patients had no significant difference in their left-hand 2D:4D ratios compared to their sisters or female and male controls. While there was no significant difference in right hands between FtM's sisters and male controls, left-hand 2D:4D ratios were significantly higher in FtM's sisters (p = .017). MtF GD patients had lower right-hand 2D:4D ratios than female controls (p <.001), but their right-hand ratios did not differ from those of their brothers and male controls. There was no significant difference in left-hand 2D:4D ratios between MtF GD patients, and their brothers, or female and male controls. FtM GD patients showed significantly masculinized right-hand 2D:4D ratios, while there was no evidence of feminization in MtF GD patients.

Is digit ratio (2D:4D) associated with the choice for the uniformed versus a civil study course by the Polish youth?

The 2nd to 4th digit ratio (2D:4D) is a sexually dimorphic trait determined by the relative balance of prenatal testosterone (T) and oestrogen during the intrauterine development of foetus. Males on average have relatively lower 2D:4D than women in population. Lower 2D:4D is very often linked with greater physical ability, strength, superior sporting performance and many personality traits and behaviours which are seen more among the males. Recently, lower 2D:4D were associated with military and police services among the Polish women. The objectives of this study were to examine whether 2D:4D differed between the students of a study course for future military service and a civil study course and whether sex difference in this ratio is present in both these groups. The cross sectional study included 50 boys and 42 girls enrolled in the uniformed course and other 56 boys and 50 girls of a general course in an upper-secondary School. The lengths of the second (2D) and fourth fingers (4D) of each hand were measured to have the 2D:4D ratio. Height and weight were also recorded. Overall, as well as among the civil course students, males showed significantly lower mean 2D:4D compared to the females. But there was no significant sex difference in digit ratio among the uniformed course students. Besides, the females under uniformed course showed lower 2D:4D than the females in civil course, whereas, the male uniformed students had similar or almost same 2D:4D values with the male civil course students. Increased prenatal testosterone exposure might have a role in determining the choice towards a challenging future occupation and such effect is perhaps more pronounced in women than in males.

2D:4D and spatial abilities: From rats to humans

Variance in spatial abilities are thought to be determined by in utero levels of testosterone and oestrogen, measurable in adults by the length ratio of the 2nd and 4th digit (2D:4D). We confirmed the relationship between 2D:4D and spatial performance using rats in two different tasks (paired-associate task and watermaze) and replicated this in humans. We further clarified anatomical and functional brain correlates of the association between 2D:4D and spatial performance in humans.

FURTHER EVIDENCE OF AN ASSOCIATION BETWEEN LOW SECOND-TO-FOURTH DIGIT RATIO (2D:4D) AND SELECTION FOR THE UNIFORMED SERVICES: A STUDY AMONG POLICE PERSONNEL IN WROCŁAW, POLAND

Males and females differ in their preference for occupations and sporting activities, and differ also in risk-taking attitudes. In addition to other explanations, prenatal hormone exposure has been implicated in these gender-associated differences. The ratio of the relative lengths of the second-to-fourth digits (2D:4D) is a proxy indicator of prenatal exposure to testosterone relative to oestrogen. The 2D:4D ratio has been found to be associated with choice of occupation, particularly among females. This study investigated whether 2D:4D differed between police officers and a control group of civilians in Wrocław, Poland. Participants were 147 male and 55 female police officers and 91 male and 75 female civilian controls. The police officers had to undergo rigorous physical ability tests during recruitment and their job bore relatively higher risk, whereas the controls had a normal civilian lifestyle. Height, weight, hand grip strength and lengths of the second and fourth digits were measured. Analyses of variance and covariance were employed to assess the significance of difference in digit ratio between groups (police officers and civilians) allowing for interaction with sex. The policewomen, compared with the female controls, were taller and had stronger hand grip strength, but had lower 2D:4D in the right hand and average 2D:4D of both hands. However, male and female police officers slightly differed only in the right hand digit ratio but not in the left hand ratio or the average for the two hands. However, the control group showed significant sex differences in all digit ratios with higher (feminine) mean values in females. The study provides further evidence that prenatal testosterone exposure, as reflected in the 2D:4D ratio, might have an association with choice of occupation, particularly among females.

Digit ratio (2D:4D) moderates the relationship between cortisol reactivity and self-reported externalizing behavior in young adolescent males

Although reduced cortisol reactivity to stress and increased circulating testosterone level are hypothesized to be associated with higher levels of externalizing behavior, empirical findings are inconsistent. One factor that may account for the heterogeneity in these relationships is prenatal testosterone exposure. This study examined whether the second-to-fourth digit ratio (2D:4D), a putative marker of prenatal testosterone exposure, moderates the relationships of testosterone and cortisol reactivity with externalizing behavior. Left and right hand 2D:4D and self-reported externalizing behavior were measured in a sample of 353 young adolescents (M age=11.92 years; 178 females; 79.7% African American). Saliva samples were collected before and after a stress task and later assayed for cortisol. Testosterone levels were determined from an AM saliva sample. 2D:4D interacted with cortisol reactivity to predict externalizing behavior in males, but not females. In males, low cortisol reactivity was associated with higher levels of aggression and rule-breaking behavior, but only among subjects with low 2D:4D (i.e., high prenatal testosterone). Findings suggest the importance of a multi-systems approach in which interactions between multiple hormones are taken into account. Furthermore, results demonstrate the importance of considering the organizational influence of prenatal testosterone in order to understand the activational influence of circulating hormones during adolescence.

The processing of object identity information by women and men

The study examined whether women excel at tasks which require processing the identity of objects information as has been suggested in the context of the well-known object location memory task. In a computer-simulated task, university students were shown simulated indoor and outdoor house scenes. After studying a scene the students were presented with two images. One was the original image and the other a modified version in which one object was either rotated by ninety degrees or substituted with a similar looking object. The participants were asked to indicate the original image. The main finding was that no sex effect was obtained in this task. The female and male students did not differ on a verbal ability test, and their 2D:4D ratios were found to be comparable.

Association between a marker for prenatal testosterone exposure and externalizing behavior problems in children

Prenatal androgen exposure has been associated with aggressive behavior in adults. It is less clear whether this association holds for childhood externalizing behavior. This study tests the hypothesis that increased prenatal androgen exposure is associated with aggressive behavior and attention problems in childhood. The ratio of the length of the second finger digit relative to the fourth digit, which is a marker for prenatal testosterone exposure, was assessed in 239 male and female fifth grade schoolchildren from Jintan, China, together with parent and teacher ratings of aggression and attention problems. Increased aggression and attention problems were both significantly associated with a lower ratio of the length of the second finger digit relative to the fourth digit ratios in boys but not girls. The effects remained significant after controlling for early adversity. These findings are the first to establish a relationship between an indirect indicator of fetal androgen exposure and any child psychopathology in Chinese children, and the observed effect size in boys was stronger than in male adults in Western studies. The results provide limited cross-cultural support for the importance of prenatal androgen exposure in contributing to the development of externalizing behavior problems in children, and they suggest that such effects may be specific to boys who may be relatively more vulnerable to early prenatal influences.

Sex and modulatory menstrual cycle effects on sleep related memory consolidation

The benefit of sleep in general for memory consolidation is well known. The relevance of sleep characteristics and the influence of hormones are not well studied. We explored the effects of a nap on memory consolidation of motor (finger-tapping-task) and verbal (associated-word-pairs) tasks in following settings: A: young, healthy males and females during early-follicular phase (n=40) and B: females during mid-luteal and early-follicular phase in the menstrual cycle (n=15). We found a sex and in women a menstrual cycle effect on memory performance following a nap. Men performed significantly better after a nap and women did so only in the mid-luteal phase of their menstrual cycle. Only the men and the women in their mid-luteal phase experienced a significant increase in spindle activity after learning. Furthermore, in women estrogen correlated significantly with the offline change in declarative learning and progesterone with motor learning. The ratio of the 2nd and 4th digit, which has been associated to fetal sex hormones and cognitive sex differences, significantly predicted the average performance of the female subjects in the learning tasks. Our results demonstrate that sleep-related memory consolidation has a higher complexity and more influencing factors than previously assumed. There is a sex and menstrual cycle effect, which seems to be mediated by female hormones and sleep spindles. Further, contrary to previous reports, consolidation of a simple motor task can be induced by a 45 min NREM sleep nap, thus not dependent on REM sleep.

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.

Digit ratio predicts sense of direction in women

The relative length of the second-to-fourth digits (2D:4D) has been linked with prenatal androgen in humans. The 2D:4D is sexually dimorphic, with lower values in males than females, and appears to correlate with diverse measures of behavior. However, the relationship between digit ratio and cognition, and spatial cognition in particular, has produced mixed results. In the present study, we hypothesized that spatial tasks separating cue conditions that either favored female or male strategies would examine this structure-function correlation with greater precision. Previous work suggests that males are better in the use of directional cues than females. In the present study, participants learned a target location in a virtual landscape environment, in conditions that contained either all directional (i.e., distant or compass bearing) cues, or all positional (i.e., local, small objects) cues. After a short delay, participants navigated back to the target location from a novel starting location. Males had higher accuracy in initial search direction than females in environments with all directional cues. Lower digit ratio was correlated with higher accuracy of initial search direction in females in environments with all directional cues. Mental rotation scores did not correlate with digit ratio in either males or females. These results demonstrate for the first time that a sex difference in the use of directional cues, i.e., the sense of direction, is associated with more male-like digit ratio.

Organizing effects of testosterone and economic behavior: not just risk taking

Recent literature emphasizes the role that testosterone, as well as markers indicating early exposure to T and its organizing effect on the brain (such as the ratio of second to fourth finger, ), have on performance in financial markets. These results may suggest that the main effect of T, either circulating or in fetal exposure, on economic behavior occurs through the increased willingness to take risks. However, these findings indicate that traders with a low digit ratio are not only more profitable, but more able to survive in the long run, thus the effect might consist of more than just lower risk aversion. In addition, recent literature suggests a positive correlation between abstract reasoning ability and higher willingness to take risks. To test the two hypotheses of testosterone on performance in financial activities (effect on risk attitude versus a complex effect involving risk attitude and reasoning ability), we gather data on the three variables in a sample of 188 ethnically homogeneous college students (Caucasians). We measure a digit ratio, abstract reasoning ability with the Raven Progressive Matrices task, and risk attitude with choice among lotteries. Low digit ratio in men is associated with higher risk taking and higher scores in abstract reasoning ability when a combined measure of risk aversion over different tasks is used. This explains both the higher performance and higher survival rate observed in traders, as well as the observed correlation between abstract reasoning ability and risk taking. We also analyze how much of the total effect of digit ratio on risk attitude is direct, and how much is mediated. Mediation analysis shows that a substantial part of the effect of T on attitude to risk is mediated by abstract reasoning ability.

Sexual orientation and spatial position effects on selective forms of object location memory

Prior research has demonstrated robust sex and sexual orientation-related differences in object location memory in humans. Here we show that this sexual variation may depend on the spatial position of target objects and the task-specific nature of the spatial array. We tested the recovery of object locations in three object arrays (object exchanges, object shifts, and novel objects) relative to veridical center (left compared to right side of the arrays) in a sample of 35 heterosexual men, 35 heterosexual women, and 35 homosexual men. Relative to heterosexual men, heterosexual women showed better location recovery in the right side of the array during object exchanges and homosexual men performed better in the right side during novel objects. However, the difference between heterosexual and homosexual men disappeared after controlling for IQ. Heterosexual women and homosexual men did not differ significantly from each other in location change detection with respect to task or side of array. These data suggest that visual space biases in processing categorical spatial positions may enhance aspects of object location memory in heterosexual women.

Digit ratio (2D:4D) is associated with traffic violations for male frequent car drivers

Digit ratio (2D:4D) is a putative marker of prenatal hormone exposure. A lower digit ratio has been suggested as an index of higher testosterone relative to estrogen exposure during prenatal development. Digit ratio has been associated with a variety of psychological sex-dimorphic variables, including spatial orientation, aggression, or risk-taking behavior. The present study aimed to relate digit ratio to traffic violations for a male sample (N = 77) of frequent car drivers. Digit ratio was assessed via printout scans of the hand, and traffic offense behavior was assessed via self-reported penalty points as registered by the Central Register of Traffic Offenders in Germany. In addition, social desirability and sensation seeking were recorded. Results showed that digit ratio was inversely related to penalty point entries, suggesting more traffic violations for individuals with higher prenatal testosterone exposure. Sensation seeking was positively associated with traffic violations, but there was no relationship between sensation seeking and digit ratio, proposing additive effects of both variables. The results suggest that prenatal androgen exposure might be related to traffic violations for frequent car drivers.

Scientometric analysis and bibliography of digit ratio (2D:4D) research, 1998-2008

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.

Anxiety, sex-linked behaviors, and digit ratios (2D:4D)

The second to fourth (2D:4D) digit ratio, a sexually dimorphic, phenotypic characteristic putatively associated with perinatal androgen action, has been used to evaluate the hypothesized relation between prenatal hormonal factors and a variety of sexually dimorphic behaviors, including sex-linked psychopathology. Smaller digit ratios, suggestive of stronger perinatal androgen action, have been associated with male-linked disorders (e.g., autism), and larger digit ratios, suggestive of weaker perinatal androgen action, have been associated with female-linked disorders (e.g., depression and eating disorders). To evaluate the possible relation between digit ratio and another traditionally female-linked disorder, anxiety, 2D:4D ratios were measured in a non-clinical sample (58 men, 52 women). Participants also completed a battery of anxiety and gender role measures and performed two spatial/cognitive tasks typically showing a male advantage (mental rotation and targeting) and two tasks typically showing a female advantage (location memory and spatial working memory). Men with a more feminine pattern of sex-linked traits and behaviors (including digit ratios) reported greater anxiety. In contrast, greater anxiety in women was associated with both female-typical and male-typical traits and behaviors, but and no significant association between digit ratio and anxiety was found. This pattern of results suggests that the development of anxiety is multiply determined, with contributing factors varying by sex.

Spatial ability and prenatal androgens: meta-analyses of congenital adrenal hyperplasia and digit ratio (2D:4D) studies

Hormonal manipulations indicate that early androgens organize sex differences in spatial ability in laboratory rats. In humans, spatial ability is also sexually dimorphic, and information about the effects of prenatal androgens on spatial ability can be obtained from studies of congenital adrenal hyperplasia (CAH) and the ratio of the second and fourth finger lengths (2D:4D). CAH is characterized by prenatal overproduction of adrenal androgens and several lines of evidence suggest that 2D:4D reflects prenatal androgen exposure. Some studies have found that these proxy measures of prenatal androgens predict spatial ability, others have found no significant relationship, and yet others have obtained results in the opposite direction. In light of these mixed findings, we conducted meta-analyses of published literature and unpublished results to determine if, across studies, either of these indicators of prenatal androgens predicts performance on spatial tasks that show a male advantage. In addition, we applied a trim and fill analysis to the data in search of asymmetry that might be an indication of publication bias. Results indicated that females with CAH perform better on these spatial tasks, and CAH males perform worse, than do controls. Little or no relationship exists between 2D:4D and spatial ability. Implications for possible hormonal contributions and the developmental timing of sex differences in spatial cognition are discussed.

On the relation between 2D:4D and sex-dimorphic personality traits

Several personality traits, including aggressiveness and sensation seeking, have been hypothesized to be influenced by prenatal androgen exposure, though evidence for this proposition is limited. We investigated whether individual differences in aggressiveness, sensation seeking, and several prosocial personality traits can be predicted from differences in the 2D:4D digit ratio, a putative marker of prenatal androgen activity. A total of 164 undergraduates (87 men, 77 women) completed self-report measures of physical and verbal aggression, as well as a standardized measure of sensation seeking, and five scales to assess empathy, nurturance, expressivity/femininity, instrumentality/masculinity, and assertiveness. Two sex-dimorphic tests of spatial ability also were included. Men had a lower 2D:4D ratio than women, confirming the typical sex difference in digit proportions. Significant sex differences were observed on 10 of the 11 personality scales purported to show sex differences and on both tests of spatial ability. The 2D:4D ratio was a significant predictor of scores on three of the four aggression subscales, total aggression, thrill and adventure seeking, and total sensation-seeking, in the sample as a whole and in women. In men, correlations with 2D:4D were significant only for total sensation-seeking and verbal aggression. In both sexes, lower 2D:4D ratios were associated with increased aggressiveness and sensation seeking. For the spatial tests, there was no evidence of any association with 2D:4D in either men or women. The 2D:4D digit ratio may be a valid, though weak, predictor of selective sex-dependent traits that are sensitive to testosterone.

Visuospatial performance on an internet line judgment task and potential hormonal markers: sex, sexual orientation, and 2D:4D

We investigated whether performance on a visuospatial line judgment task, the Judgment of Line Angle and Position-15 test (JLAP-15), showed evidence of sensitivity to early sex steroid exposure by examining how it related to sex, as well as to sexual orientation and 2D:4D digit ratios. Participants were drawn from a large Internet study with over 250,000 participants. In the main sample (ages 12-58 years), males outperformed females on the JLAP-15, showing a moderate effect size for sex. In agreement with a prenatal sex hormone hypothesis, line judgment accuracy in adults related to 2D:4D and sexual orientation, both of which are postulated to be influenced by early steroids. In both sexes, better visuospatial performance was associated with lower (more male-typical) digit ratios. For men, heterosexual participants outperformed homosexual/bisexual participants on the JLAP-15 and, for women, homosexual/bisexual participants outperformed heterosexual participants. In children aged 8-10 years, presumed to be a largely prepubertal group, boys also outperformed girls. These findings are consistent with the hypothesis that visuospatial ability is influenced by early sex steroids, although they do not rule out alternative explanations or additional influences. More broadly, such results support a prenatal sex hormone hypothesis that degree of androgen exposure may influence the neural circuitry underlying cognition (visuospatial ability) and sexual orientation as well as aspects of somatic (digit ratio) development.

Digit Ratio (2D:4D) and Lateralization for Basic Numerical Quantification

Abstract. The ratio between the second and fourth fingers (2D:4D) is supposed to serve as a putative indicator of prenatal testosterone (PT). Significant associations between 2D:4D, children's basic numerical ability, and the Spatial Numerical Associations of Response Codes (SNARC) effect have recently been reported. The present study explored potential relationships between 2D:4D and the basic numerical ability of subitizing (the rapid enumeration of small quantities) in 80 right-handed adult volunteers. Participants completed a short battery of computerized subitizing and color recognition control tasks with both left and right hands, independently (order counterbalanced). Findings revealed a significant interaction between sex and 2D:4D on reaction time differences for right vs. left hand responses to the subitizing task. While 2D:4D in women showed a significant negative association with a right-hand advantage for the task, a nonsignificant trend in the opposite direction was observed for men. Results are discussed with respect to the possible effect of PT on sex differences in lateralization for basic quantification.

Associations among gender-linked toy preferences, spatial ability, and digit ratio: evidence from eye-tracking analysis

Eye-tracking technology was used to monitor eye-movements in 64 adults (age range, 18-22 years) during simultaneous presentation of "masculine" and "feminine" toys. Women and men who showed more visual fixations on male-typical toys compared to female-typical toys had significantly better targeting ability and smaller (i.e., more masculine) digit ratios, a putative marker of prenatal androgen levels. In contrast, individuals with visual preferences for female-typical or male-typical toys did not differ in mental rotations ability and in their retrospective reports of childhood gender-linked activities. The finding that targeting ability and digit ratios varied according to visual preferences for gender-linked toys suggests that prenatal androgens promote enduring preferences for male-typical objects and indicate further that some gender-linked traits vary according to the direction of a visual preference for gender-linked toys. Visual preferences derived from eye-tracking, therefore, may be a useful supplement to current measures of psychosexual differentiation in hormone-behavior research, particularly because eye-movements are not dependent on verbal abilities or subjective evaluations of behavior.

Digit ratio (2D:4D) and the spatial representation of magnitude

Digit ratio (as a putative indicator of prenatal androgen exposure) is related to a range of sexually dimorphic abilities, including spatial skills and mathematical ability. This study examined a phenomenon known as the SNARC effect (Spatial Numerical Association of Response Codes), which is taken as evidence of a mental representation of magnitude along a left-right-oriented number line, with low magnitudes associated with the left side of space, and high numbers with the right side of space. Participants made a parity judgement of numbers with responses made with a left key to odd numbers and a right key to even numbers. This was reversed for a second block of trials. Response times to numbers one to nine with both the right and left hand were calculated, and regression analyses conducted to analyse whether lower magnitudes were responded to faster with the left hand and higher magnitudes with the right hand. Participants with lower (more masculine) digit ratios on the right hand showed a stronger SNARC effect compared to participants with high digit ratios. This pattern of results was also found when the analyses were conducted separately for men and women. Results from left hand digit ratios indicated that only low digit ratio females showed a significant SNARC effect. These findings add to a growing literature on the relationship between digit ratio and cognitive abilities; in this case, simple cognitive representations that are accessed automatically rather than complex skills such as mental rotation or "mathematics" where a variety of solution strategies may be utilised.

Examination marks of male university students positively correlate with finger length ratios (2D:4D)

Intersexual and intrasexual variation in second to fourth digit length (2D:4D) in humans may result from differential exposure to fetal testosterone. 2D:4D predicts several physiological, psychological and performance traits in adulthood. These relationships may reflect the 'pleiotropic' effects of testosterone on development of digits and diverse organ systems, which are expressed in adulthood. We hypothesized that 2D:4D also predicts academic success of students. 2D:4D of right hand positively predicted examination marks of males from two three-year degree courses (TYDCs). Marks of females did not covary with 2D:4D. Males from the two TYDCs differed in 2D:4D. The present results thus add to the rapidly accumulating literature on 2D:4D showing correlations with phenotypic traits in humans. If testosterone affects 2D:4D and intellectual performance, our results suggest that testosterone levels are under stabilizing selection because of effects on performance traits documented in previous studies and antagonistic effects on intellectual performance (present study).

Sex differences in a human analogue of the Radial Arm Maze: the "17-Box Maze Test"

This study investigated sex differences in spatial memory using a human analogue of the Radial Arm Maze: a revision on the Nine Box Maze originally developed by called the 17-Box Maze Test herein. The task encourages allocentric spatial processing, dissociates object from spatial memory, and incorporates a within-participants design to provide measures of location and object, working and reference memory. Healthy adult males and females (26 per group) were administered the 17-Box Maze Test, as well as mental rotation and a verbal IQ test. Females made significantly fewer errors on this task than males. However, post hoc analysis revealed that the significant sex difference was specific to object, rather than location, memory measures. These were medium to large effect sizes. The findings raise the issue of task- and component-specific sexual dimorphism in cognitive mapping.

Experimental manipulation of yolk testosterone affects digit length ratios in the ring-necked pheasant (Phasianus colchicus)

In humans, most of the mammals and one bird species studied so far, the relative length of individual digits is sexually dimorphic. Most studies of humans have been concerned with the ratio between second (2D) and fourth digits (4D), whereas some studies of humans and other mammals have also investigated other digit ratios. Inter- and intra-sexual variation in 2D:4D may depend on differential exposure to androgens during embryonic life, and the genetic mechanisms linking 2D:4D to androgens may be mediated by Hox genes. Because Hox genes are conserved in vertebrates, similar patterns of variation in digit ratios might be expected across vertebrate classes. The observation of correlations between digit ratios and physiological, psychological and performance traits in humans has generated interest in exploring the possibility that digit ratios are a marker of embryonic exposure to androgens, which have diverse consequences on several phenotypic traits. However, the hypothesis that digit ratios depend on androgen effects during development has never been tested experimentally. In this study, we increased testosterone concentration in ring-necked pheasant eggs and measured length ratios between the second, third and fourth digits of both feet in fully grown offspring. Females from testosterone-injected eggs had larger 2D:3D in the left foot, whereas this was not the case in males. The other digit ratios were unaffected by hormone treatment in both sexes. However, digit ratios showed no sexual dimorphism among controls. Thus, present results are consistent with the hypothesis that variation in testosterone levels during development affects digit ratios.

Digit ratio (2D:4D) and behavioral differences between inbred mouse strains

Digit ratio (2D:4D) is a trait, which is sexually differentiated in a variety of species. In humans, males typically have shorter second digits (2Ds) (index fingers) compared to fourth digits (4Ds) (ring fingers) whereas females' fingers are more equal in length. Smaller, more masculine, digit ratios are thought to be associated with higher prenatal testosterone levels, greater sensitivity to prenatal androgens or both. Men with more masculine digit ratios have shown increased ability, achievement and speed in sports and tend to report that they are more physically aggressive. Previous research has shown the same sexually differentiated pattern in the hind paws of laboratory mice as in human hands, males have lower 2D:4D than females. We measured hind paw digit ratio in mice of eight inbred strains. These measurements were made while blind to strain, sex and whether the paw was from the left or right side. We found large differences in digit ratio between the strains and suggest that inbred mice are a promising system for investigating the correlation between digit ratio and behavioral traits.

Finger length ratio (2D:4D) correlates with physical aggression in men but not in women

Finger length ratio (2D:4D) is a sexually dimorphic trait. Men have relatively shorter second digits (index fingers) than fourth digits (ring fingers). Smaller, more masculine, digit ratios are thought to be associated with either higher prenatal testosterone levels or greater sensitivity to androgens, or both. Men with more masculine finger ratios are perceived as being more masculine and dominant by female observers, and tend to perform better in a number of physical sports. We hypothesized that digit ratio would correlate with propensity to engage in aggressive behavior. We examined the relationship between trait aggression, assayed using a questionnaire, and finger length ratio in both men and women. Men with lower, more masculine, finger length ratios had higher trait physical aggression scores (r(partial) = -0.21, N = 134, P = 0.028). We found no correlation between finger length ratio and any form of aggression in females. These results are consistent with the hypothesis that testosterone has an organizational effect on adult physical aggression in men.

A Specific Sexual Orientation-Related Difference in Navigation Strategy

During spatial navigation, women typically navigate an environment using a landmark strategy, whereas men typically use an orientation strategy. To examine the as yet unknown effects of sexual orientation on these normative sex differences, this study required 80 healthy heterosexual and homosexual adult men and women to provide directions from experimental maps for 4 routes. The frequency and type of strategy used by each participant were computed. Expected sex differences were demonstrated, and a robust cross-sex shift was shown by homosexual men in using landmarks. This remained after controlling for differences in mental rotation, directional sense, and general intelligence. The findings may limit the number of putative neurodevelopmental pathways responsible for sex differences in navigation strategy utility.

Testing the prenatal androgen hypothesis: measuring digit ratios, sexual orientation, and spatial abilities in adults

The present study examined whether the following variables putatively associated with prenatal androgens are inter-related in women: spatial abilities, sexual orientation, and 2nd to 4th finger (digit) length ratio (2D:4D). Participants were 99 healthy premenopausal women tested in the menstrual phase of the ovarian cycle between 0800 and 0930 hr. Women completed the Kinsey scales of sexual orientation, and were either strictly heterosexual (HS; N=79) or not-strictly heterosexual (NHS; N=20). Photocopies of the two hands were collected, and participants completed the revised Vandenberg Mental Rotations test, the Paper Folding test, and a short version of the Guilford-Zimmerman Spatial Orientation Test. Results showed that NHS women exhibited superior spatial ability relative to HS women. No significant difference was found between the HS and NHS women in the 2D:4D digit ratio. There was no association between the digit ratio and spatial performance. These results support an association between increased spatial abilities and heteroflexible sexual orientation, which may possibly be mediated by high prenatal androgens.

Sexual dimorphism in metapodial and phalanges length ratios in the wood mouse

Relative length of metapodials and digits is sexually dimorphic in most primates and one rodent and one bird species studied so far. Recently, interest in digit ratios has increased because of their correlation with diverse physiological, psychological, and performance traits in humans. These correlations may reflect the effect of androgens during early ontogeny on digit development and their long-term organizational effects on extragenital organs. Inter- and intrasexual variation in digit ratios may be ultimately controlled by modulation of the expression of Hoxa and Hoxd genes. Since Hox genes are conserved in vertebrates, similar patterns of sex-related variation in length ratios may be expected across taxa. In fact, sexual dimorphism in length ratios has been documented for metapodials or digit bones in nonhuman vertebrates, but the specific pattern of sex-related variation varies considerably. However, no study has investigated sexual dimorphism in length ratios between all ray segments (metapodials plus phalanges) using osteometrical measures. In an outbred wild population of wood mice (Apodemus sylvaticus), we found extensive sex-related variation in ratios between osteometrical length of the phalanges, but not metatarsals, similar to that recorded on undissected digits of humans and laboratory mice. Most sexually dimorphic ratios involved the second digit. We found very weak evidence for directional asymmetry in length ratios. The present study shows that sex-related variation in length ratios between digit segments observed in mammals may actually depend on relative bone length. Hence, other species may be used to investigate the causal and semeiotic implications of variation in human digit ratios.

Digit length ratios predict reactive aggression in women, but not in men

Considerable evidence suggests that digit length and dermatoglyphic asymmetry patterns in the hand are affected by early exposure to androgens. Because androgens play an important role in sexual differentiation of morphological and behavioral traits, digit length patterns often display sex differences. When present, sex differences in digit lengths are more pronounced on the right side as compared to the left side. Moreover, the ratio of the second to fourth digit length (2D:4D) in the right hand is inversely correlated with testosterone (T) in men. Because T is implicated in agonistic behavior, 2D:4D may be used as a marker of androgen exposure and subsequent behavioral variation in adulthood. Consequently, we investigated the relationships among 2D:4D, directional asymmetry of 2D:4D (left hand 2D:4D minus right hand 2D:4D) as a variant of T, and human reactive aggression. One hundred young men (n = 51) and women (n = 49) participated in our experiments (mean age = 20.1 years). Participants called two noncompliant confederates to solicit donations for a fictitious charity organization and selected follow-up letters after the calls. The force exerted when hanging up the phone and the "tone" of the follow-up letters were used to assess reactive aggression. High aggression scores were associated with high directional asymmetry of 2D:4D and masculinized (low) right hand 2D:4D, only in females and under high provocation. Directional asymmetry of 2D:4D was positively correlated with T in males (pooled data, n = 97). Taken together, these data confirm the predominantly right-sided influence of androgens on digit length and suggest that digit length ratios may be associated with female reactive aggression when sufficient provocation is present.