Inbreeding is associated with lower 2D: 4D digit ratio

Abstract

Our results suggest that consanguineous marriages are associated with a fetal environment that influences morphological development and may have associated behavioral sequelae.

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

“…Our present data show that consanguinity of the parents is related to lower and more masculine 2D:4D ratios, confirming the results of our previous study on adults (Özener et al, ). Remarkably, we found that infants of mothers with higher educational level had higher digit ratio.…”

“…If digit ratio is indeed a valid indicator of the developmental stability and susceptibility to stress via its relationship with fetal exposure to sex steroids, we can anticipate that inbreeding may affect the digit ratio (a proxy marker of prenatal sex steroid exposure). We have previously shown that (Özener et al, ) across hands and sex, consanguineous parentage is consistently associated with lower, more masculine, digit ratios in Turkish adults. This previous study demonstrates the indirect effects of inbreeding depression on prenatal steroids in adult subjects.…”

“…Moreover, as the pregnancy number increased, digit ratios of the newborns significantly became masculine. In our previous study (Özener et al, ), we determined that the income level and digit ratio in adults are negatively correlated. On the other hand, one of the weaknesses of our study is the lack of finger measurements of the parents.…”

“…It has recently been suggested that digit ratio may be considered to indicate an individual's developmental instability and susceptibility to stress through its association with prenatal sexual steroids (Fink, Manning, Neave, & Grammer, ; Özener, Hurd, & Duyar, ; Ronalds, Phillips, Godfrey, & Manning, ). These studies suggest that environmental and genetic influences on fetal development also influence testosterone and estrogen levels.…”

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

“…However, the pattern of reported results is contradictory, that is, a study at a specific locale has reported a positive relationship between family income and 2D:4D ratio (Ozener et al, 2014), whereas an Internet‐based large international study has reported a negative relationship (Manning et al, 2021). Interestingly, Ozener et al (2014) have suggested that the stress, induced by lower socioeconomic status, leads to heightened prenatal testosterone levels and lower digit ratios, whereas Manning et al (2021) have suggested that maternally induced epigenetic response mediates the relationship of family income with lower digit ratios. Thus, because of the prior contradictory findings and explanations, in the present study, we tested the effect of family income on digit ratios without any specific hypothesis.…”