Likewise, in Klinefelter’s syndrome, higher or feminine digit ratios, attributable to a low testosterone exposure have been reported. Likewise, the females have lesser testosterone exposure and therefore, higher (feminine) ratios.Įvidence in support of this view comes from the presence of masculine or lower digit ratios in children with Congenital Adrenal Hyperplasia (CAH) who have higher androgen exposure and females suffering from CAH. Usually, the male foetuses have a higher testosterone exposure and hence, the males always have lesser digit ratios when compared to females. In other words, a foetus with more exposure to testosterone is expected to have lower (masculine) digit ratio. Analysis of amniocentesis samples have shown that the digit ratio is negatively correlated to prenatal tes-tosterone, but positively to oestrogen exposure. ĭigit ratio is reported to be influenced by the prenatal androgen exposure to the foetus. Studies in South Indian Population have also identified the sexual dimorphism in 2D:4D ratios. Another study on children showed higher ratios among the Caucasians when compared to the Blacks and the Hans ethnicity of China. Measures of 2D:4D from various ethnic groups were done by Manning et al., and it was shown that in addition to the significant sexual dimorphism in 2D:4D, the mean ratios varied between the English, Scottish, Uygur, Han and Jamaican children. The ratios vary among different ethnic groups which is far larger than different between the sexes. Variations have been reported in different ethnic and geographic groups. Digit ratio is a sexually dimorphic trait found in a variety of species ranging from humans and mice to zebra finches and is constant since birth. However, most commonly, digit ratios indicate only 2D (index finger):4D (ring finger) ratios. Also, the authors have discussed the relevant molecular basics and the methods of measurement of digit ratios.ĭigit ratio is the ratio of length of different digits or fingers typically measured from the mid-point of bottom crease where the fingers join the hands to the tip of the fingers. The authors have attempted to write a brief account on the digit ratios and the dimorphism observed in various physiological, psychological and behavioural traits. Prenatal androgen exposure and therefore, digit ratios have been reported to be associated with numerical competencies, spatial skills, handedness, cognitive abilities, academic performance, sperm counts, personalities and prevalence of obesity, migraine, eating disorders, depression, myopia, autism etc. Usually, males have lower ratios when compared to females. Interestingly, it is constant since birth and not influenced by the adult hormone levels. Ratio of 2D:4D is found to correlate negatively to testosterone and positively to oestrogen in the foetus. Existing literature and recent research show accumulating evidence on 2D:4D ratio showing correlations with various phenotypic traits in humans. Digit ratios, especially 2D:4D ratio, a potential proxy marker for prenatal androgen exposure shows sexual dimorphism.
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