An individual’s body odour is a characteristic that is used to obtain information about conspecifics. However, to our knowledge the role of body odour and the degree of facial symmetry on testosterone changes among men as indicators of possible rivals has not been investigated yet. A group of 113 men were photographed to obtain their degree of facial symmetry, i.e., the small random deviations in facial bilateral traits. They smelled and assessed the odour of men with different grades of facial symmetry, and donated two saliva samples (pre- and post-stimulus sample) to measure the change in their testosterone levels. We found that testosterone levels decreased in symmetrical men who perceived the odour of asymmetrical men. Our results suggest that men could perceive characteristics in other men that are highly valued by women through odour to identify possible rivals, and that the observed decrease in testosterone levels could be related to an inhibition of competitive behaviours.
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.