Sex hormone-related variations of cognitive performance in !Kung San hunter-gatherers of Namibia.

The relation of circulating sex hormones and cognitive abilities was investigated in 114 healthy !Kung San men ('bushmen') of Namibia/Southern Africa who lived mainly as traditional hunter-gatherers. Blood and saliva samples were analysed by use of radioimmunoassays in order to determine the serum concentrations of total testosterone (Tser), 5 alpha-dihydrotestosterone (DHT), and estradiol (E2), as well as the level of bioavailable, non-SHBG-bound 'free' testosterone in the saliva. The cognitive ability was assessed with two verbal (verbal fluency) and three nonverbal tests (tactual-spatial functioning, field independence/field dependence). As to be expected from previous research on Western samples, all three androgens but not E2 are of significance to the !Kung San men's cognitive performance. Tser exhibits a positive relation to tactual-spatial abilities and to the degree of lateralization of this task; on the other hand, Tser is negatively correlated with verbal fluency. Testosterone in the saliva is also significantly positively correlated to tactual-spatial test scores and, in addition, to field independence. DHT and the ratio DHT/Tser are positively related to verbal fluency and negatively to the degree of lateralization of tactual-spatial performance.