The digit ratio (2D:4D) was set at the end of the first trimester especially between week 8 and 12. Some researchers look at multiple methods of digit ratio. Right hand, left hand, right hand and left hand disparity, and mean digit ratio. My question is as the digit ratio in the womb of mothers responsible for both hands of the fetus. Why do we not only use a mean digit ratio to infer the behavior of fetus (before birth) prenatal hormones?
In my opinion, there are two answers to this question:
1. Sex differences as indicators of quality of markers of organizing hormone effects: There is meta-analytical evidence (Hönekopp & Watson, 2010), that the sex difference is larger on the right hand. Only forming a mean score may obscure a possibly "stronger signal" of one hand.
2. Important information about prenatal hormones may reside in body asymmetry: When it comes to the right-left-difference of 2D:4D (Dr-l), one has to consider the Geschwind-Galaburda-hypothesis of brain lateralization. Roughly speaking, prenatal testosterone may be more of a developmental disadvantage for the left than for the right brain hemisphere (Geschwind & Galaburda, 1987). Thus, Dr-l may be an additional marker of prenatal testosterone vs estrogen ratio (Manning et al., 2014).
Hope this helps!
Dear Martin G. Köllner,
Thank you very much for your informative and with reference answer. Now i am specific about the multiple methods of digit ratio especially Dr-I.