Sex differences in directional asymmetry of digit length and its effects on sex differences in digit ratio (2D:4D)

The relationship between 2D:4D ratio and postpartum adult female variables in a Ghanaian population

OBJECTIVES

Postpartum hematological and anthropometric assessment is a requirement for optimal maternal and child health. The study aimed to determine the relationship between the 2D:4D ratio and postpartum hematological and anthropometric variables in adult females.

METHODS

The study was cross-sectional from December 2020 to April 2021 involving 272 postpartum adult females, aged between 18 and 36 years. The right (2D:4DR) and the left (2D:4DL) digit ratios were measured using computer-assisted analysis. Fasting venous samples were collected at a median (interquartile range) of 111 (44-210) days postpartum and analyzed for total testosterone (TT), estradiol, sex hormone-binding globulin, and complete blood count.

RESULTS

The mean ± standard deviation 2D:4DR and 2D:4DL were 0.94 ± 0.04 and 0.93 ± 0.04, respectively. As expected, the TT (r = -0.198, p = .015) and the free androgen index (FAI: r = -0.186, p = .019) were inversely correlated with the 2D:4DL while free testosterone (FT%: r = -0.157, p = .038) was inversely correlated with the 2D:4DR. The absolute basophile count (BASO: r = -0.124, p = .040) and the Platelet-lymphocyte ratio (PLR: r = -0.153, p = .016) were inversely correlated with the 2D:4DL and the 2D:4DR respectively. In addition, the mean cell volume was inversely correlated with the 2D:4DR (r = -0.139, p = .024) and the 2D:4DL (r = -0.122, p = .045). Moreover, the 2D:4DR was inversely correlated with height (r = -0.164, p = .007). Unexpectedly, the red blood cell count (RBC: r = 0.138, p = .025) was positively correlated with the 2D:4DR.

CONCLUSION

There are significant relationships between the 2D:4D ratio and postpartum female variables. These findings are useful preliminary reference data for postpartum research and subsequent 2D:4D ratio studies.

Second to fourth (2D:4D) digit ratio and their relationships among a mother and child population in Ghana

The study aimed to determine the relationship between digit ratios among a mother–child population in Ghana. This was a cross-sectional study from December 2020 to April 2021 involving 272 mothers, their daughters (n = 132) and their sons (n = 140). The right (2D:4DR) and the left (2D:4DL) digit ratios were measured using computer-assisted analysis. The data were analysed in SPSS (v23) and GraphPad Prism (v8) at an alpha value of 0.05. The mean ± SD age of the mothers was 23.9 ± 3.67 years while the median (IQR) age of daughters was 116(54–240) days and sons, 134(54–240) days. The mean ± SD 2D:4DR were 0.94 ± 0.04, 0.91 ± 0.04 and 0.90 ± 0.04 respectively for mothers, daughters and sons. The mean ± SD 2D:4DL was 0.93 ± 0.04, for mothers, 0.92 ± 0.05 for daughters and 0.92 ± 0.05 for sons. The daughters and sons showed leftward asymmetry while the mothers showed rightward asymmetry in digit ratios. The 2D:4DR of sons was significantly lower than daughters (P = 0.031). There were negative correlations between the 2D:4DL and age of daughters (r = −0.182, P = 0.043) and sons (r = −0.221, P = 0.012). The 2D:4DR of mothers was positively correlated with that of daughters (r = 0.332, P = 0.000) and that of sons (r = 0.233, P = 0.008). There are significant relationships between digit ratios in a mother–child population.

Stature estimation for Saudi men based on different combinations of upper limb part dimensions

Estimating stature based on body/limb parts can help define the characteristics of unidentified bodies. The most studied upper limb part is the hand, although few studies have examined whether stature can be estimated using fingers plus other hand dimensions. Moreover, there is paucity in anthropometric studies that determined whether bilateral whole limb parts (e.g., arms, forearms, and hands) are related to stature among the living subjects.This prospective cross-sectional study aimed to evaluate the relationship between different upper limb measurements and the stature of Saudi men. Furthermore, I assessed whether upper limb asymmetry was present, and developed regression models to estimate stature based on different available measurements. Stature and 13 upper limb parameters were measured for 100 right-handed Saudi men who were 18 to 24 years old.All measurements were positively correlated with stature (P < .001), and the best single predictor was the bilateral ulnar length. Asymmetry was more pronounced in the hand measurements. A multiparameter model provided reasonable predictive accuracy (±3.77-5.68 cm) and was more accurate than single-parameter models. Inclusion of the right-side fingers improved the model's accuracy.This study developed potential models for estimating stature during the identification of bodies of Saudi men.

The effects of hand preference and sex on right-left asymmetry in dorsal digit lengths among adults and children

BACKGROUND

Right-hand preference is related to stronger right-directional asymmetry in the length of proximal upper-limb bones, although the relationships of hand preference with directional asymmetry in phalangeal bone lengths are not known. Furthermore, dorsal digit length is an easy-to-measure, faithful proxy of X-rayed phalangeal bone length (which is costly and difficult to measure).

AIM

To study the effects of hand preference, sex, and age on right-left (R-L) asymmetry in dorsal digit lengths.

METHODS

We measured all dorsal digit lengths (except the thumb) in comparable numbers of left-handers and right-handers in samples of adults (N = 151, age: M = 22.6 years, SD = 3.3) and children (N = 65, age: M = 5.0 years, SD = 1.0).

RESULTS

Right-handers and adults had stronger right-directional asymmetry in digit lengths than left-handers and children. A Bayesian analysis yielded an 'extremely strong likelihood' of no sex differences in the R-L asymmetry of dorsal digit lengths 2 and 4.

CONCLUSIONS

The effects of hand preference, sex, and age on R-L asymmetry appear to be similar for phalangeal bone length and other (proximal) upper-limb bone lengths. Two distinct biologic mechanisms (i.e., a general right-directional asymmetry mechanism and a handedness-related directional asymmetry mechanism) may contribute to observed R-L asymmetry in limbs. Fingertip fat and bone digit length do not seem to contribute to sex differences in the R-L asymmetry (Dr-l) of the widely studied second-to-fourth digit ratio (2D:4D).

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.