Different parts of the brain control different thought processes. It is thought that the left hemisphere of the brain dominates in language processing while the right hemisphere dominates in spatial and mathematics processing. In general men are thought to have dominant right hemispheres while women have dominant left hemispheres. It is thought that these differences are due to sex hormones in the womb although it is difficult to measure these without painful, intrusive and potentially dangerous procedures. However the same hormones affect the relative length of people's 2nd and 4th fingers with male hormones producing relatively longer 4th fingers and female hormones producing relatively longer 2nd fingers. A study of 75 children between 6 and 7 in the UK compared the length of their fingers with their scores in their SATs. A significant correlation was found between digital ratios (the relative lengths of 2nd and 4th fingers) and SAT scores. The boys with longer 4th fingers scored relatively highly in their numeracy SATs while the girls with longer 4th fingers scored relatively highly in their literacy SATs.
Brosnan, Mark J. - Digit ratio as an indicator of numeracy relative to literacy in 7-year-old British schoolchildren British Journal of Psychology February 2008, 99(1), 75-85