Second to fourth digit ratio in relation to age, BMI and life history in a population of young adults: a set of unexpected results
There is a wealth of studies supporting a link between 2D:4D ratios and prenatal exposure to testosterone and oestrogen. Furthermore, 2D:4D ratios appear to relate to several aspects of human sexual behaviour, which suggests that these characteristics are determined in early embryological stages and not largely affected by factors later in life. However, not all studies have found associations as predicted, and we know relatively little about postnatal changes in 2D:4D ratios. This preliminary study in 100 young males and females explores associations between 2D:4D ratios on the one hand and age, life history and BMI on the other hand. In women, I found a decrease in 2D:4D ratios from typically feminine to typical masculine in the right hand of women; in men, I found a negative association between 2D:4D ratio and BMI. Both results were contrary to expectations. In spite of the relatively small sample size, these results might question the general validity of 2D:4D ratios as a predictor of human sexual behaviour that in turn could relate to prenatal exposure to sex hormones. It calls for further research focussing on factors that may disrupt expected associations between 2D:4D and aspects of human behaviour related to hormone levels.