Digit Ratio (2D:4D): A Biomarker for Prenatal Sex Steroids and Adult Sex Steroids in Challenge Situations

Abstract

Digit ratio (2D:4D) denotes the relative length of the second and fourth digits. This ratio is considered to be a biomarker of the balance between fetal testosterone (T) and estrogen (E) in a narrow window of early ontogeny. Evidence for this assertion is derived from direct and indirect measures of prenatal hormonal exposure (in experimental animals, via amniotic fluid samples and in the study of sex-typical traits) in relation to 2D:4D. In contrast, the relationships between 2D:4D and levels of sex steroids in adults are less clear, as many correlational studies of 2D:4D and adult sex steroids have concluded that this association is statistically non-significant. Here, we suggest that in order to understand the link between 2D:4D and sex hormones, one must consider both fetal organizing and adult activating effects of T and E. In particular, we hypothesize that 2D:4D correlates with organizing effects on the endocrine system that moderate activating effects in adulthood. We argue that this is particularly evident in “challenging” conditions such as aggressive and sexual encounters, in which individuals show increased levels of T. We discuss this refinement of the 2D:4D paradigm in relation to the links between 2D:4D and sports performance, and aggression.

Females Have Larger Ratio of Second‐to‐Fourth Digits Than Males in Four Species of Salamandridae, Caudata

“…Amphibians are good bioindicators of environmental pollution (Blaustein and Johnson, 2003); thus, digit ratio may vary among populations due to different hormonal conditions (Manning et al, 2014;Orton et al, 2014). Therefore, in future studies on digit ratio in amphibians, samples of a single species from different populations should be taken into account.…”

Digit Ratio (2D:4D) and Attachment Styles in Middle Childhood: Indirect Evidence for an Organizational Effect of Sex Hormones

“…In our study, we strived to maximize the reliability of 2D:4D by employing computer-assisted measurement, which has been shown to be superior to other indirect methods (Allaway et al 2009;Kemper and Schwerdtfeger 2009). However, it is important to note that a number of other associations between digit ratios and behavioral traits have failed to replicate, especially when the original studies had been conducted in small samples (reviewed in Manning et al 2014). The reasonable size of our sample and the fact that we found the same pattern of effects in both sexes reduce the likelihood that the present findings are spurious; still, our results should be treated as tentative until replicated or corroborated by other methods.…”

“…The fourth digit tends to be shorter in females; as a result, females have higher digit ratios than males. Digit ratios develop prenatally, and are partly determined by the balance of androgen and estrogen signaling during the time window for digit development in the fetus (see Berenbaum et al 2009;Manning et al 2014;Zheng and Cohn 2011). While the prenatal origin of digit ratios has been established conclusively, there is suggestive evidence that-at least in humans-sex hormones levels in early infancy may further contribute to individual and sex differences in relative finger length (Galis et al 2010;Knickmeyer et al 2011).…”

Bases hormonals de la conducta prosocial: una revisió de la literatura

“…Aquesta afirmació queda perfectament il·lustrada pels resultats d'un estudi basat en una mesura indirecta del grau d'exposició intrauterina a andrògens (Breedlow, 2010), com és la ràtio entre els dits índex (2D) i anular (4D). En general, el dit índex dels homes sol ser més curt, en relació amb l'anular, que el de les dones, i s'assumeix que aquesta ràtio més baixa és conseqüència de l'exposició in utero a concentracions de T més elevades (Manning, Kilduff, Cook, Crewther i Fink, 2014;Teatero i Netley, 2013).…”