prenatal cortisol deficiency, as well as early postnatal administration of glucocorticoids and mineralocorticoids shortly after birth in cases of CAH treatments 11. sex differences in the deposition of adipose tissue in the fingers 13, 14 and 3. reduced concentrations of glucocorticoids and mineralocorticoids, both of which affect bone growth 2. suggested that, at least in the case of CAH, there may be a number of other possible explanations of lower 2D:4D ratios: 1. This seems to provide some evidence in favour of the initial hypothesis that higher prenatal testosterone leads to the development of lower digit ratios 12. more ‘male typical’) in CAH populations than in sex-matched controls 11. A recently conducted meta-analysis on the 2D:4D ratio and congenital adrenal hyperplasia (CAH) showed that the digit ratios were typically lower (i.e. Both indirect and direct data deserve mention in this respect. One of the most important questions is the extent to which the digit ratio may serve as a proxy for prenatal androgenisation, and whether 2D:4D actually indexes prenatal sex steroid exposure. In the majority of studies, researchers deal with 2D:4D in postnatal samples, with a wide range of age groups 8, 9, 10. Hence, the popularity of the use of indirect measures as a biomarker of prenatal androgenisation, namely, 2D:4D, is growing 4, 5, 6, 7. Due to ethical reasons, accurate measurements of prenatal testosterone exposure in humans are difficult, and a limited number of studies have been conducted in this area to date. The ‘Organisational hypothesis’ suggests that prenatal sex steroids, particularly testosterone, modify growth and development in a sexually dimorphic way 3. Hence, the 2D:4D ratio in adults may partly reflect neonatal testosterone exposure, along with prenatal exposure 1, 2. It is hypothesised that sexual dimorphism in the 2D:4D ratio is a product of the cumulative effects of both prenatal and postnatal developmental processes 1. recently strengthened opposition against the use of the 2D:4D ratio, partly based on the idea that the 2D:4D ratio is a mere artifact of the allometric effects of digit growth. the high popularity of the 2D:4D ratio used for testing different traits related to androgenisation and estragenisation during critical periods of prenatal development and 2. The idea for this study stemmed from two facts: 1. We conclude that sex differences in 2D:4D are not an artifact of allometry. No allometric effect was observed in this case. Height was applied as another measure of allometric effect on the limited sample (≤ 30 years) from the European population, along with sex and age. Both sex and population origin were permanent reliable predictors of 2D:4D, whereas average digit length was not. To test for an allometric effect on 2D:4D, the average digit lengths were calculated. However, the 2D:4D magnitude and its sexual dimorphism remained stable throughout the ontogeny. The second and fourth digits showed strong positive linear relationships on both hands, and demonstrated an increase with age digit length in women from the youngest age cohort was longer or equal to that of men, and shorter than men in older age cohorts. Additionally, we separately tested four age cohorts (≤ 13, 14–18, 19–30, and 31 ≥ years) to test the effect of developmental allometry. Analyses were conducted separately for each hand for the whole sample and in succession for the three large populations. Digit ratios were computed according to standard procedures. The lengths of the second and fourth digits on both hands were measured. The study sample comprised 7,582 individuals (3,802 men and 3,780 women) from three large world populations: Europeans (n = 3043), East Africans (n = 2844), and Central Asians (n = 1695). The goal of our study is to verify the validity of these assumptions. Recently, a number of authors have claimed that sexual dimorphism in the second-to-fourth digit ratio (2D:4D) is simply dependent on digit length and is an artifact of allometry.
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