Low intrasexual competitiveness and decreasing testosterone in human males (Homo sapiens): the adaptive meaning

The development of indirect mechanisms of intrasexual competition (e.g., visual identification of possible rivals) could be related to personality traits such as aggressiveness and self-esteem. However, the study of endocrine changes associated to indirect mechanisms of intrasexual competition is scarce. The aim of this study was to investigate the changes in testosterone levels after a rival choice test in men and how intrasexual competitiveness, aggressiveness, and self-esteem modulate these changes. A group of 160 healthy men answered four personality questionnaires, participated in a rival choice test, and donated saliva samples to measure the changes in their testosterone levels. We found a significant decrease in testosterone levels of men with lower intrasexual competitiveness, but testosterone levels remained stables in competitive men. Non-significant results were found for aggressiveness and self-esteem. These decreases in testosterone levels could be interpreted as an adaptation aimed to reduce costs in male-male contests in Western modern societies.