Studies have shown boys with lower testosterone have greater intelligence

Studies have shown that intelligence is a heritable trait with heritablility between 60% and 80%.  Intelligence is also slightly biased in favor of the boys.  In the top 3% of intellectually gifted children there are 12-times more boys than girls.  The main endocrine difference between sexes is the different concentration of sex hormones with especially high testosterone levels in men.  Testosterone and its effects on cognitive ability have been studied, but the association has not been clear.  In this study, over 280 boy between the ages 6 and 9 provided saliva samples that were tested for testosterone with 107 of the boys being intelligently gifted, 77 being mentally challenged, and the rest of average intelligence.  The results have shown that mentally challenged and intelligently gifted boys had lower levels of testosterone when compared to the boys of average intelligence.  A later study shows that three polymorphisms of genes related to testosterone metabolism in association with intellectual giftedness in boys. Polymorphisms of interests were chosen in genes including androgen and estrogen receptors, 5-alpha reductase, aromatase and sex hormone binding globulin. Significant differences between control and gifted boys in genotype.  The higher trans-activational activity of the androgen receptor in gifted boys might explain the finding of lower testosterone levels in these children in a previous study.