Ring Finger Length Research Articles

Sex Differences in Directional Asymmetry of Digit Length and its Effects on Sex Differences in Digit Ratio (2D:4D)

Patterns of directional asymmetry in the length of index and ring finger (2D and 4D) may be sexually differentiated. Martin, Puts, and Breedlove (2008) found leftward bias, i.e., both a longer 2D and 4D in the left than in the right hand, more frequently in men, whereas rightward bias occurred more frequently in women. Further, rightward vs leftward bias seemed a substantial source of variation in digit ratio (2D:4D), a putative marker for prenatal androgen levels. Given the generally small effects, unreplicable results, and inconsistent findings of 2D:4D research, these findings potentially are important as the type of directional digit asymmetry could moderate or obfuscate real associations between 2D:4D and target traits. Based on six samples totaling about 3,000 individuals, the present study replicated the first finding of Martin, Puts, and Breedlove (2008): leftward bias was more frequent among men and rightward bias more frequent among women. This sex effect was small. However, the present study did not replicate the second finding of Martin, et al. (2008): relative to participants' sex the contributions of leftward vs rightward asymmetry to individual variation in 2D:4D were smaller by orders of magnitude and not significant. Implications of these findings for 2D:4D research are discussed.

Index and ring finger ratio—A new sex determinant in south Indian population

Identification of human remains is an imperative element of any medicolegal investigation, and a challenging task for forensic experts and physical anthropologists worldwide. Three hundred adult hands (150 males and 150 females) belonging to south Indian population were studied to investigate sexual dimorphism of the index and ring finger ratio. The index and ring finger ratio is derived by dividing the index finger length by ring finger length. The index and ring finger ratio is found to be higher in females. Index and ring finger ratio ≤0.9700 identified 80% of males for both hands, and ratio >0.9700 identified 74% females for the right hand and 78% for the left hand accurately. This study may prove useful to determine the sex of an isolated hand when it is subjected for medicolegal examination.

Human 2D (index) and 4D (ring) finger lengths and ratios: cross‐sectional data on linear growth patterns, sexual dimorphism and lateral asymmetry from 4 to 60 years of age

Human 2D : 4D ratios (measures of the relative lengths of index and ring fingers) attract considerable research interest because they exhibit sexual dimorphism and are associated with various morphological, physiological and behavioural traits as well as sporting abilities and medical conditions. In an attempt to identify potential confounding factors in such studies, we have examined how relative and absolute digit lengths vary with gender and tested whether they are influenced by age, right-left asymmetry and hand preference. Participants between 4 and 60 years of age were recruited from local educational sites. Hand photocopies and calliper measurement were used to obtain digit lengths. We employed linear regression analysis to examine the growth trajectories of individual digits, analyses of variance to isolate main and interaction effects of age, gender and hand preference, and paired t-tests to identify lateral asymmetries. Both digits exhibited biphasic growth with an early growth phase followed by a stable length phase. Digits in females attained their maximum length about 2.2 years (dextral subjects) or 5.1 years (sinistral subjects) earlier than those in males. Sexual dimorphism in 2D : 4D ratios was apparent by 4 years of age and age changes in ratios depended on gender, side and hand preference. Relative and absolute lengths displayed age, gender, hand-preference and age x gender interaction effects. Lengths tended to be greater in females in younger subjects and greater in males in older subjects. Ratios tended to be greater in sinistral subjects. In dextral subjects, significant lateral asymmetries in 2D lengths were seen at all ages but asymmetries in males and 4D lengths seemed to be age-dependent. We conclude that age, lateral asymmetry and hand preference are potential confounding factors and that future study designs should take account of these as well as other known confounders such as ethnicity, birth order, menstrual cycle phase and sexual preference.

A new means of measuring index/ring finger (2D:4D) ratio and its association with gender and hand preference

Relative finger length can predict a person's gender or their hand preference. We measured finger length using a new “tubes” test, which required participants to slide a clear plastic tube over their fingers and read the length from an attached mm scale. Data collected from 600 students demonstrated that the right fingers are longer than the left for dextrals, but not for non-dextrals. Examination of the relative length of the index and ring fingers revealed a clear gender effect. There was also an effect of hand preference on index/ring finger ratio whereby non-dextrals showed a more masculine pattern compared to dextrals. For non-dextrals, prenatal exposure to high testosterone levels may have caused both a shift away from dextrality and a more masculine pattern of finger ratio. In the second experiment, finger length was measured by the tubes test and by photocopying the hands in 124 undergraduates. The tubes test yielded a longer estimate of ring finger length compared to the photocopy method. Despite this, there was a strong correlation between the tests and both showed an association with gender. Finally, test–retest scores for 45 participants showed a high level of reliability for absolute and relative finger measures. We conclude that the tubes technique provides an effective and easy-to-use means of measuring finger length, which can be administered in a classroom setting.

Index to ring finger length ratio and the risk of osteoarthritis

To determine the relationship between the index to ring finger (2D:4D) length ratio and the risk of knee and hip osteoarthritis (OA). We conducted a case-control study, in which cases with persistent symptoms and radiographic evidence of knee or hip OA were compared with controls with no symptoms and no radiographic evidence of knee or hip OA. Hand radiographs were visually classified as type 1 (index finger longer than the ring finger), type 2 (index finger equal to the ring finger), or type 3 (index finger shorter than the ring finger). The 2D:4D phalangeal and metacarpal length ratios were measured separately. The odds ratio (OR) and 95% confidence interval (95% CI) were calculated and adjusted for possible confounding factors using a logistic regression model. Of 2,049 cases, 1,013 had radiographic evidence of knee OA and 995 had hip OA. Of 1,123 controls, 836 had no knee OA and 1,050 had no hip OA. The type 3 finger pattern was associated with knee OA (OR 1.94, 95% CI 1.54-2.44), and the risk was greater in women (OR 3.05, 95% CI 2.08-4.47) than in men (OR 1.45, 95% CI 1.08-1.95). There was a dose-response relationship between both 2D:4D phalangeal and metacarpal length ratios and the risk of knee OA. The risk of hip OA was inconsistent. Compared with types 1 and 2, the type 3 "male" pattern 2D:4D length ratio is associated with OA, especially knee OA. The risk is independent of other major OA risk factors.

Sex-specific relationship between digit ratio (2D:4D) and romantic jealousy

The ratio of index finger length to ring finger length (2D:4D) is an index of prenatal androgen exposure. In a study with 71 female and 52 male undergraduate students, we assessed the relationship between 2D:4D and jealousy with respect to various dimensions of rival characteristics. Following the presentation of a jealousy-evoking scenario, participants rated the extent to which they would feel jealous if the rival possessed various characteristics (some which have been found to be more jealousy evoking for men, others which have been found to be more jealousy evoking for women). Men with higher, more feminine 2D:4D reacted more jealously toward more socially dominant rivals. Women with lower, more masculine 2D:4D reacted more jealously toward more physically attractive rivals. These results show that the level of prenatal testosterone affects which rival characteristics elicit the highest level of jealousy, which are different for men and women.

Second to fourth digit ratios and the implicit gender self-concept

Intersexual and intrasexual variation in the ratio of index and ring finger lengths (2D:4D) is thought to be a marker of fetal androgen and estrogen levels. Thus, 2D:4D ratios have been expected to be associated with the development of the gender self-concept (masculinity vs. femininity). These associations have, however, proven to be empirically rather small and lower than expected. By arguing that early developmental events more greatly influence implicit as compared with explicit self-concepts, we hypothesized that 2D:4D ratios might be associated with the implicit gender self-concept – assessed using an Implicit Association Test – as opposed to the self-reported explicit gender self-concept. Results showed that the implicit gender self-concept indeed significantly correlated with 2D:4D ratios for men, whereas these measures were dissociated for women. In contrast and as expected, we found only small correlations between 2D:4D ratios and the explicit gender self-concept for both sexes.

Digit ratio and faculty membership: Implications for the relationship between prenatal testosterone and academia

Digit ratio (length of index finger divided by length of ring finger) is an index of exposure to prenatal testosterone. Prenatal testosterone slows the growth rate of the left side of the brain while enhancing growth of the right side. Right hemisphere processing is associated with better visual-spatial and mathematical abilities, as is digit ratio. Thus, traditional sex differences in visual-spatial and mathematical abilities can be attributed to differences in exposure to prenatal testosterone, indexed by a sex dimorphic pattern in digit ratio (female=1.00, male=0.98 for UK samples). Additionally, the digit ratio is a marker for within-sex variance in visual-spatial ability. This study examines the digit ratio of an academic sample. No sex differences are found and there is a significant difference between the Science Faculty and Social Science Faculty. Social Scientists of both sexes have a ratio consistent with the male norm (0.98) whilst Scientists have a digit ratio consistent with the female norm (1.00). These results are discussed in terms of the lower normal range of male testosterone being associated with highest visual spatial abilities. Relationships with fertility and Dyslexia are also identified.

Radiographic 2D:4D index in females: no relation to anthropometric, behavioural, nutritional, health-related, occupational or fertility variables

BackgroundThe ratio of index finger to ring finger length (2D:4D index) may be an indicator of gonadal hormone exposure, because the differentiation of gonads, fingers and toes is influenced by the same HOXA and HOHD genes. Some previous studies have found significant associations between the 2D:4D index and sexual, psychological or behavioural variables. We studied the usability of the radiographic 2D:4D index as a potential predictor of several features in a large female sample.Methods271 female dentists and 219 teachers (age 45 – 63 years) had their hands radiographed and their right 2nd and 4th fingers measured from the base of the bony proximal phalanxes to the tip of the distal phalanxes to define the radiographic 2D:4D index. The study subjects were classified into two distinctly separate clusters (by using cluster analysis with the K-means algorithm) in each of the following dimensions: anthropometric (including four items), behavioural (five items), nutritional (five items), health-related (seven items), occupational (Karasek job control and job demand scores) and fertility (four items).ResultsThe radiographic 2D:4D index ranged from 0.845 to 0.981 (mean 0.925, SD 0.021). The intraclass correlation between three radiographers' measurements (31 cases) was 0.971. No differences concerning the 2D:4D index were found between clusters 1 and 2 in any studied dimension, nor did any of the items in clusters have relations with the 2D:4D index when tested separately with bivariate tests.ConclusionDespite the ideal set-up of the measuring possibilities in a relatively large radiographic material the variables currently studied were not dependent on the length of finger bones. It can therefore be questioned whether any real associations between the bony 2D:4D index in adult life and (direct or indirect) hormone dependent effects exist. There may be a publication bias explaining that mostly positive findings have been the previously reported. However, the associations of the 2D:4D index with various features, if present, may be related to the soft parts of fingers rather than to the length of bones.

Length of index and ring fingers differentially influence sexual attractiveness of men’s and women’s hands

Humans show intra- and intersexual variation in second (2D) relative to fourth (4D) finger length, men having smaller 2D:4D ratio, possibly because of differential exposure to sex hormones during fetal life. The relations between 2D:4D and phenotypic traits including fitness components reported by several studies may originate from the organizational effects that sex hormones have on diverse organs and their concomitant effect on 2D:4D. Evolutionary theory posits that sexual preferences are adaptations whereby choosy individuals obtain direct or genetic indirect benefits by choosing a particular mate. Since sex hormones influence both fitness and 2D:4D, hand sexual attractiveness should depend on 2D:4D, a hypothesis tested only in one correlational study so far. We first presented hand computer images to undergraduates and found that opposite-sex hands with long 2D and 4D were considered more sexually attractive. When we experimentally manipulated hand images by increasing or decreasing 2D and/or 4D length, women preferred opposite-sex hands that had been masculinized by elongating 4D, whereas men avoided masculinized opposite-sex right hands with shortened 2D. Hence, consensus exists about which hands are attractive among different opposite-sex judges. Finger length may signal desirable sex hormone-dependent traits or genetic quality of potential mates. Psychological mechanisms mediating hand attractiveness judgments may thus reflect adaptations functioning to provide direct or indirect benefits to choosy individuals. Because the genetic mechanisms that link digit development to sex hormones may be mediated by Hox genes which are conserved in vertebrates, present results have broad implications for sexual selection studies also in nonhuman taxa.

Second-to-fourth digit ratio related to Verbal and Numerical Intelligence and the Big Five

Androgens influence individual differences in a predictable way: they “masculinise” people. The ratio of index finger length to ring finger length (2D:4D) is an index of prenatal androgen exposure. We related 2D:4D to Verbal Intelligence, Numerical Intelligence and the Big Five personality dimensions in a Dutch sample of 44 men and 37 women. We found a relation between right-hand 2D:4D and Verbal and Numerical Intelligence as well as Agreeableness ( R 2’s around .22), in a typical masculine pattern (low 2D:4D, low verbal intelligence, high numerical intelligence, and low agreeableness). We conclude 2D:4D is a valuable tool in the study of the determinants of individual differences.

Finger lengths, 2D:4D ratios, and their relation to gender-related personality traits and the Big Five

Finger lengths and the ratio of index finger to ring finger length (2D:4D) may be markers of gonadal hormone exposure. The current study investigated possible associations between absolute finger lengths, 2D:4D ratios, and gender-related personality traits in over 2000 participants. Regression analyses showed no associations between men's 2D:4D ratios and gender-related personality traits and weak associations between women's 2D:4D ratios and gender-related occupational preferences. Men's absolute finger lengths were weakly associated with self-ascribed masculinity, and women's absolute finger lengths were weakly associated with masculine occupational preferences. Big Five personality traits were assessed in a subsample of over 1000 participants. Analyses showed a weak positive association between 2D:4D and extraversion and a weak negative association between 2D:4D and openness to experience. Absolute finger lengths showed a weak negative association with agreeableness and a tendency to be associated with women's but not men's openness. Overall, associations between finger-length measures and personality were weak and inconsistent.

Do differences in sex hormones affect handwriting style? Evidence from digit ratio and sex role identity as determinants of the sex of handwriting

This study investigated whether there could be a biological determinant of the judged gender of handwriting. It further investigated the potential interplay between these variables and sex role identification. The biological marker used was 2D:4D digit ratio (of index to ring finger length) which is negatively associated with prenatal testosterone and positively with prenatal oestrogen. Handwriting samples of 120 participants (half of each sex) were presented on computer to be rated for gender by 20 raters. Feedback on accuracy was given after each trial. These raters accurately identified the gender of two thirds of the sample and the rated difference between the sexes was large ( d = 0.75). These ratings of handwriting gender correlated significantly with digit ratio and the femininity scale of the BSRI. A more conservative analysis this time within each sex found that women’s right hand digit ratio correlated with relative sexuality of handwriting, but there was no corresponding relationship for the males. These findings suggest that prenatal hormonal influences can affect later female handwriting performance and might even affect developmental inter-hemispheric differences, but do not appear to impact on males.

Sexual dimorphism in the 2D/4D ratio and its relation to mental rotation performance

A reliable sexual dimorphism exists for the 2D/4D ratio, where 2D denotes index finger length and 4D denotes ring finger length. Several reports suggest that this dimorphism is correlated with cognitive performance in domains where sex differences are observed, such as mental rotation performance. However, this study did not find a significant relation between these variables in a sample comprised of 237 males and 399 females. The actual values of the 2D/4D ratios in our almost exclusively Caucasian sample are lower than those reported for most Caucasian populations, and they are closer to values reported for Black African samples.

Sex differences in relative index and ring finger length

Sex differences in relative index and ring finger length