Is 2D:4D digit ratio related to avowed religion? A study among Mongolian young males from Ulaanbaatar

BACKGROUND

The ratio of the second- (2D) to fourth (4D) digit lengths of hand (2D:4D) is a proxy marker of the relative testosterone and estrogen concentration during a relatively narrow period of fetal development that might affect behavioral and personality characteristics.

AIM

To estimate the differences in 2D:4D between different religious groups among a sample of young adult males in Mongolia.

METHODS

Two hundred and sixty-five Mongolian male students with mean age of 20.5 (SD = 1.7) years from different universities in Ulan Bator, were included in the study. Information on age, religious affiliation, marital status and parental education were obtained directly from each study participant. Digit lengths were measured from scanned images by using the ImageJ software 1.53 K. One-way analysis of variance was employed to evaluate whether they were significant differences in 2D:4D ratio between groups, along with Scheffe's post hoc comparison.

RESULTS

Study participants significantly differed in 2D:4D across religion. Left 2D:4D, but not the right, showed a significant difference between religions, with Muslims exhibiting the highest 2D:4D mean and the lowest DR-L .

CONCLUSION

Our study suggests that the 2D:4D ratio is related to the participants' religion. However, the distinctiveness of the Muslim students from study participants belonging to other religious groups in this study could also be related to ethnic differences, given that the students were Kazakhs. This is, to our knowledge, the only study looking at the relationship between the 2D:4D ratio and religious affiliation and, thus, further research is needed to confirm its results.

Effects of caste, birth season, and family income on digit ratios

OBJECTIVES

The contributions of latitude and ethnicity in the determination of cross-society differences in digit ratios are unclear. In India, different castes (endogamous groups) have been living in the same areas (villages or towns) for the last 1500 years and, therefore, these groups may have different gene pools without a latitude-related difference component. Thus, in the present study, we studied the effect of caste on digit ratios. We also studied the effects of sex, birth season, and family income on digit ratios.

METHODS

We selected a sample of 301 college students (age: M = 19.9 years, SD = 2.63) in Muzaffarnagar city of western Uttar Pradesh, India, and asked participants for information regarding their birth month, religion, caste, and monthly family income. We measured participants' dorsal and palmar digit lengths (of all fingers, except the thumb, in both hands) using vernier calipers of 0.01 mm accuracy.

RESULTS

Other backward castes (intermediate castes) had longer digit lengths than general castes (upper castes), scheduled castes (lower castes), and Muslims. However, there was no difference in digit ratios of caste groups (scheduled castes vs. other backward castes vs. general castes vs. Muslims) or specific castes (Chamar-Jatav vs. Jat vs. Pandit-Tyagi). Winter-born women had lower left dorsal 2D:4D and 3D:4D ratios than summer-born women. Family income was related to higher dorsal 2D:4D and 3D:4D ratios among women. Moreover, in dorsal digit ratios, sex difference (men < women) occurred in digit ratios constituting digit 5, whereas, in palmar digit ratios, sex difference occurred in digit ratios constituting digit 2.

CONCLUSIONS

The present study suggests that endogamy-led genetic difference in ethnic/caste groups is not a determinant, whereas birth season (i.e., the exposure to sunlight) and family income might be determinants of digit ratios. In addition, compared to palmar digit ratios, dorsal digit ratios are better markers of sexual dimorphism.

Relationship between parental consanguinity and digit ratios (2D:4D) among Turkish newborns in Sivas

OBJECTIVES

The aim of this study was to investigate the effects of parental consanguinity on the 2D:4D digit ratio of newborn infants, whose parents were the first cousins.

METHODS

The study included healthy and full-term newborn infants, delivered in a hospital, at the gestational ages from 37 to 41 weeks. A total of 225 newborns and their parents were included in the study. Of these 225 newborns; 100 were inbred and 125 were outbred infants. We used a Vernier caliper to measure the length of the second and fourth digits of the newborns (accuracy: 0.01 mm).

RESULTS

Controlling for education and number of pregnancies, male newborns had lower digit ratios than female newborns, for both left and right hands. There were, moreover, differences between inbred and outbred samples. We determined that inbreeding was related to a reduction in the digit ratios regardless of the side of the hand and the sex of the infant, showing a consistent tendency to appear more masculine. Interaction between marriage type*sex was highly significant.

CONCLUSIONS

Parental consanguinity appears to cause fetal masculinization of digit ratios by increasing fetal stress among Turkish newborns.

Hadza hunter-gatherer men do not have more masculine digit ratios (2D:4D)

OBJECTIVES

The ratio between the length of the second and the length of the fourth digit (2D:4D) is sexually dimorphic such that males of many species possess a lower ratio than females, particularly in the right hand. Still, men and women often exhibit overlapping 2D:4D ranges and the ratio is highly variable between populations. In order to further explore populational variability, we chose to analyze 2D:4D in the Hadza, a population of hunter-gatherers living in Tanzania.

MATERIALS AND METHODS

Data were collected separately by two researchers over the course of three years (1998, 2001, 2006) from 152 adult participants (male: n = 76, female: n = 76). Independent samples t-tests were used to explore sex differences, paired samples t-tests were used to explore directional effects within each sex, and linear regression and one-way ANOVA were used to test possible age effects.

RESULTS

In none of the years, or pooled (n = 152), did we find evidence that adult men have a lower 2D:4D than adult women. If anything, the data suggest that women in this population have a significantly lower right hand 2D:4D than men (P < 0.001, d = 0.57). In contrast, left hand 2D:4D did not exhibit a sex difference (P = 0.862, d = 0.03).

DISCUSSION

These findings challenge the current view that lower 2D:4D in men is a uniform characteristic of our species. Cross-populational variance in 2D:4D may be related to known patterns of hormonal variation resulting from both genetic and environmental mechanisms, though this relationship merits further investigation.