Digit ratio (length of index finger divided by length of ring finger) is an index of exposure to prenatal testosterone. Prenatal testosterone slows the growth rate of the left side of the brain while enhancing growth of the right side. Right hemisphere processing is associated with better visual-spatial and mathematical abilities, as is digit ratio. Thus, traditional sex differences in visual-spatial and mathematical abilities can be attributed to differences in exposure to prenatal testosterone, indexed by a sex dimorphic pattern in digit ratio (female = 1.00, male = 0.98 for UK samples). Additionally, the digit ratio is a marker for within-sex variance in visual-spatial ability. This study examines the digit ratio of an academic sample. No sex differences are found and there is a significant difference between the Science Faculty and Social Science Faculty. Social Scientists of both sexes have a ratio consistent with the male norm (0.98) whilst Scientists have a digit ratio consistent with the female norm (1.00). These results are discussed in terms of the lower normal range of male testosterone being associated with highest visual spatial abilities. Relationships with fertility and Dyslexia are also identified.