No association between two candidate markers of prenatal sex hormones: Digit ratios (2D:4D and other) and finger‐ridge counts

Abstract

The second-to-fourth digit ratio (2D:4D), putatively indexing prenatal androgen levels retrospectively, has become increasingly popular as an easily applied measure in research into the prenatal sex-hormonal bases of behavior, health, and disease. However, its validity has not yet been conclusively demonstrated and in fact is currently debated, because validation tests of 2D:4D with other, prenatally established, presumed markers for prenatal sex-hormone action have yielded mixed evidence or still are unavailable. Hence, the associations of 2D:4D with finger-ridge counts, one such further under-researched marker, were examined in this study. In a sample of 75 male and 75 female normal healthy adults, the six possible finger-length ratios of the human hand (from 2D:3D to 4D:5D, including the classic 2D:4D ratio) were ascertained with two commonly used measurement methods (imaged-based vs. fingers measured directly), along with two traditional dermatoglyphic traits (total and absolute finger-ridge counts). Sex differences in finger-length ratios (lower in men) generally were of moderate size (about .5 SD units), whereas those in finger-ridge counts (higher in men) were small to negligible (about .2 SD units). Within-sex analysis did not indicate theory compliant (i.e., negative) correlations between these two sets of traits that were consistent, noteworthy, or reliable. Finger-length ratios and finger-ridge counts are ontogenetically overlapping in their prenatal formation and anatomically adjacent. Hence, possible temporal and localized sex-hormonal effects in prenatal life are unlikely to account for their nonassociation. The current findings cast some doubt on the validity of these retrospective pointers to prenatal androgen levels.

Early-to-Mid Gestation Fetal Testosterone Increases Right Hand 2D∶4D Finger Length Ratio in Polycystic Ovary Syndrome-Like Monkeys

“…Origins of digit length ratios are not as straightforward as initially proposed by Manning and colleagues [3], [4], [61], [91]. Our monkey results may help to explain why associations of 2D∶4D with developmental outcomes in humans are more pronounced than the magnitude of sex differences in 2D∶4D [62], [92], as well as the substantial variations in 2D∶4D between different human populations [58], [62]. As genetically-determined sex of an individual [93], together with gestational stage at fetal T exposure (from exogenous or endogenous sources) and its duration, may all influence how 2D∶4D manifests after birth, our monkey results call into question the widespread use of 2D∶4D as an associated fetal T biomarker implicating gestational T exposure with pathological [3], [10], [11], [18], [19] or other outcomes [3], [59], [61], [62].…”

The relationship between the second to fourth digit ratio and acne vulgaris

“…Prenatal androgens levels increase at the end of the first trimester and affect a number of organ systems . A number of studies have evaluated the putative impact of prenatal androgens on some physical, psychological, and medical conditions, such as body shape, fertility, cognitive abilities, aggression, athletic performance, autism, many cancers and heart diseases, by using the 2D : 4D ratio . However, although the prenatal androgen peak time period (between 13 and 15 weeks of gestation) coincides with both the development of the sebaceous gland and digits, the relationship between acne and the 2D : 4D ratio has not yet been investigated.…”

“…8,12 A number of studies have evaluated the putative impact of prenatal androgens on some physical, psychological, and medical conditions, such as body shape, fertility, cognitive abilities, aggression, athletic performance, autism, many cancers and heart diseases, by using the 2D : 4D ratio. 8,12,18 However, although the prenatal androgen peak time period (between 13 and 15 weeks of gestation 8,19 ) coincides with both the development of the sebaceous gland and digits, the relationship between acne and the 2D : 4D ratio has not yet been investigated. In this study, we investigated the relationship between digit ratio and AV to determine if the 2D : 4D ratio could be a predictor of acne, acne severity, and/or duration.…”

Feminist activist women are masculinized in terms of digit-ratio and social dominance: a possible explanation for the feminist paradox

“…We are aware of only three studies that have measured 2D:4D in Swedish women, with 24 (Sanders et al, 2005), 48 (Troche et al, 2007), and 185 participants (von Horn et al, 2010). All of these measured finger lengths directly with calipers, which has been found to yield 2D:4Ds slightly higher for men (0.03) and lower for women (Dressler and Voracek, 2011: 0.03, n.s.) as compared to scans.…”