Assessment Of 2D:4D ratios amongst federal polytechnic Ekowe students, Bayelsa State, Nigeria

Humans, primates, birds and reptiles have demonstrated sexually dimorphism in the length of their 2nd and 4th digits otherwise known as 2D:4D, with males on the average having lower values than females. This difference has been associated with the differential exposure of prenatal testosterone relative to estrogen during intrauterine life. This present study assesses the 2d:4d ratio amongst students of the federal Polytechnic Ekowe, Bayelsa state of Nigeria. A total of 299 students (males n=150 and females n=149) participated in the study. The length of 2nd and 4th digits were measured with digital Vernier caliper from the basal crease to the tip of the finger, and 2nd digit length (2D) was divided by 4th digit (4D) to obtain 2D:4D ratio. The results of this study showed no significant difference between 2D right and left and 4D right and left for same sex (0.98±0.04 and 0.98±0.04 for males and 0.96±0.05 and 0.96±0.05 for female). Sexual dimorphism exits between sexes which is an indication that prenatal hormones have played a fundamental role on humans, during developmental stages.

Digit ratio (2D:4D) researchers on 2D:4D research: An expert survey

Research into the second-to-fourth digit ratio (2D:4D), an assumed negative correlate of prenatal testosterone, has grown substantially over the past decade, so interim stocktaking of this field seems appropriate. Forty-four (38% of all) corresponding authors of 2D:4D articles participated in an expert opinion survey, indicating their perceptions of 2D:4D research (top insights/achievements, gaps/desiderata, problems/pitfalls, prospects/expectations). Major themes emerging from these researchers’ content-analyzed survey responses included: calls for a general framework and research integration; for more theoretical rigor, experimental evidence, longitudinal studies, and animal research; and for measurement, methodology, study design, and data analysis standards in 2D:4D research. Mentioned high-priority issues of 2D:4D research, needed to be addressed and solved, included: lacking validation studies of 2D:4D (what it actually indexes, why it is influenced by prenatal hormones, including elucidation of its genetics), small effects, inconsistent or unreplicable findings, prevalence of correlational or underpowered studies, publication bias, and sparseness of meta-analyses.

Digit ratio, a proposed marker of the prenatal hormone environment, is not associated with prenatal sex steroids, anogenital distance, or gender-typed play behavior in preschool age children

Prenatal hormones have been proposed as key factors impacting child development as well as long-term health and disease. Digit ratio (the ratio of the lengths of the second to fourth digits; 2D:4D) has been proposed as a sexually dimorphic, noninvasive marker of prenatal androgen exposure that can be reliably measured in children and adults. To date, few longitudinal pregnancy cohort studies have examined childhood digit ratio in relation to other relevant measures including prenatal hormones and androgen-sensitive outcomes. To augment the current literature on this topic, we measured right-hand digit ratio in 4-year-old children participating in The Infant Development and the Environment Study, a multicenter longitudinal cohort study that has been following mother–child dyads since the first trimester of pregnancy (n = 321). We assessed sex differences in digit ratio and fit multivariable linear regression models to examine digit ratio in relation to: (1) child sex; (2) maternal sex steroid hormone concentrations in early pregnancy; (3) newborn anogenital distance, another proposed measure of sensitivity to prenatal androgens; and (4) gender-typical play behavior as measured by the Preschool Activities Inventory (PSAI) at age 4. We observed no sex difference in digit ratio; the mean 2D:4D was 0.97 ± 0.05 mm in both sexes. Furthermore, digit ratio was not associated with maternal sex steroid concentrations in early pregnancy, anogenital distance in either sex, or PSAI scores in either sex in covariate-adjusted models. In conclusion, we observed no evidence that early childhood digit ratio was associated with child sex or hormone-sensitive measures in this cohort.

No association between sex steroids and handedness in humans

There is ongoing debate about the effect of prenatal hormones on the lateralisation of the developing brain. In humans, there are conflicting theories of how testosterone during development should affect lateralisation. Empirical studies linking prenatal and postnatal testosterone levels to handedness (a proxy for lateralisation) are similarly mixed. In the largest study of the phenomenon to date (n = 9708), I find that, contrary to the prediction of current theories, the testosterone and oestradiol levels of left- and mixed-handed individuals are no different to those of right-handers. This has implications for studies that show elevated risk of hormonal-related mental and physical disorders in left-handed individuals. It also raises questions about whether serum steroid hormone levels are effective proxies for prenatal hormones. To the extent that they are, these results suggest that prenatal steroid hormones may not significantly influence lateralisation of the human brain.

The sociobiological development and arousal of implicit motives: The emergence of a growth-and-prune model of motive development and the continued linkage of hormones and motives throughout the life span

Background: Research points to three groups of interrelationships of hormones with implicit motives. The first two are organizational: First, prenatal hormones (e.g., testosterone) may provide a biological basis for initial development of the implicit power motive (and probably other motives), as the 2D:4D ratio was associated with this motive in three samples when considering activity inhibition, a marker for functional right-hemispheric brain lateralization. After this biological basis has been pruned to varying degrees by parental demands in early childhood, a second organizational phase seems to modulate implicit motives: The interaction between the power motive and activity inhibition was also related to facial width-to-height ratio, a likely marker of pubertal testosterone, when aggregating two samples. We speculate that after this second phase, peers further trim the power motive to varying degrees. The third pathway is activational and its strength may depend on the outcomes of the two organizational phases: For example, higher progesterone around ovulation entails higher affiliation motivation in the luteal phase and testosterone responses after winning or losing dominance contests are scaled by power motive strength. Conclusions: We propose a tentative life-span model of the relationship between steroid hormones and implicit motives in which two growth-and-prune phases lay the foundation for arousal effects later in life. Future research may corroborate this model via (1) testing the associations of motives with organizational hormone effects using other markers like anogenital distance, (2) exploring social influences on motive development during adolescence, and (3) including saliva sampling in all studies involving motive arousal.

Why Does Digit Ratio Research Fail to Give Any Implication Regarding the Organizational Effect of Prenatal Androgen?

The digit ratio is a putative biomarker for evaluating the organizational effects of prenatal testosterone. This evaluation was performed by relating postnatal traits to digit ratio. We examined the relationship among digit ratio, depression, and positive/negative affect. A total of 335 university students who completed a set of questionnaires had both of their hands scanned, and the digit ratios were measured using a computer program. All the studied variables were insignificantly related to the right-hand digit ratio. The variables remained insignificant even when the data for males and females were analyzed separately. Furthermore, a meta-analysis, including a previous study combined with current data, showed no association between digit ratio and depression, although the current sample size of 355 could detect r = 0.2 at α = 0.05, and β = 0.2. The lack of association between digit ratio and depression was common, and the present results corroborated those of previous studies, which showed no association between digit ratio and depression. This nil result would be least likely attributable to an inadequate sample size, considering that the current sample size of 335 allowed the detection of r = 0.2 at α = 0.05 and β = 0.2, nor idiosyncratic results, given that the meta-analysis with previous relevant studies also concluded the same results. We extensively reviewed the relevant literature and evaluated the use of digit ratio as a biomarker for prenatal testosterone exposure in seven different perspectives. Nearly all the analysis showed the problems of using digit ratio as a biomarker for evaluating the organizational effect of prenatal hormones.