The 2D:4D Ratio: Discovering the relationship between brain lateralization and cognitive
Geschwind and Galaburda (1987) had a theory that brain growth is changed by the prenatal sex hormones
that control the ratio of the second to fourth digit ratio (2D:4D), with testosterone most likely arousing right
sided development of the brain over the left.
Therefore 2D:4D ratio is seen to be a marker for pre-natal sex hormones, being negatively correlated with
prenatal testosterone while positively associated with prenatal estrogen (J. T. Manning, Scutt, D., Wilson, J.,
Lewis-Jones, D. I. , 1998). Manning (2002) deduced a sex difference in 2D:4D ratio, with males usually
showing a lower ratio, and thus thought to be exposed to more testosterone.
Sex differences in brain lateralization are thought to correlate to differences in cognitive ability between fe-
males and males. Geschwind and Galaburda (1987) and Kimura (1996) said that the brain shows a “function-
al pattern of cerebral lateralization characterized by left hemisphere dominance for verbal processing and
right hemisphere dominance for non verbal/emotional processing” (Fink, 2006). Prenatal sex hormones af-
fect lateralization of the brain and have organizing effects on the brain in utero (Trivers, 2006).
Numeracy skills can be affected by prenatal hormones and it has been reported that males, or adults with
masculined 2D:4D ratio, excel on right sided dependent tasks (spatial and numerical tasks) (Luxen, 2005).
There have been a number of previous studies concerning 2D:4D, with differing results. Geary (1996) repor-
ted no differences between girls and boys in numeracy and mathematics, while Fink et al. (2006) deduced
there were only some significant correlations between digit ratio and numeracy tasks but only for males.
Austin (2002) found no ties between cognitive abilities and 2D:4D ratio. However, positive relations have
been found by Luxen and Buunk (2005) who deduced there was a relationship between 2D:4D ratio on the
right hand and verbal and numerical cognitive skills, and Kimura (1999) who reported that females per-
formed better in verbal and literacy field.
Prior study has not been conclusive about the tie between prenatal sex hormones (represented by 2D:4D ra-
tio) and verbal and numerical intelligence, and the aim of this study was to determine this relationship.
It was hypothesized that males would have a lower mean 2D:4D ratio, similar to previous findings, and that