Digit ratio (2D:4D) and handedness: A meta-analysis of the available literature

The Geschwind-Behan-Galaburda and sexual differentiation models predict an association between elevated foetal androgen exposure left-handedness whereas the callosal hypothesis predicts opposite. We present a meta-analysis of correlations handedness digit ratio (2D:4D), putative marker prenatal testosterone. Left-handedness predicted low (male-typical) right-hand (R2D:4D), high (female-typical) left-hand (L2D:4D), R2D:4D-L2D:4D directional asymmetry (D[R−L]). Effect sizes were extremely small not moderated by sex or method measuring 2D:4D. same general pattern was observed after excluding very large study (110,329 males, 90,412 females) Manning Peters ([2009]. Digit (2D:4D) hand preference for writing in BBC Internet Study. Laterality: Asymmetries Body, Brain Cognition, 14(5), 528–540. doi:10.1080/13576500802637872); however, no significant effects R2D:4D once these samples removed. results do confirm any theory linking androgens with handedness, so we speculate they instead reflect mechanical action causing subtle changes musculature and/or fat pads fingers. Gripping pen/pencil might cause increase 2D relative to 4D (and/or decrease 2D) resulting higher ratios on writing-hand; furthermore, this could differ left- right-handers due left-to-right direction (as English) having asymmetrical depending which is used.