Their Results Demonstrated That Serotonin Levels Are Negatively Correlated

Their results demonstrated that serotonin levels are negatively correlated with aggression. Virkkunen and Linnoila (1993) supported these findings with their own study. They showed that individuals who consume alcohol excessively have comparatively lower serotonin metabolites concentrations (e.g. HIAA concentrations) in their cerebrospinal fluid. These applied also to animal torturing children (Kruesi, 1979) and due to aggressive behaviour expelled American Marines (Brown et al., 1979). As a matter of fact, serotonin levels are affected by environmental context and stimuli. Dominant and high ranking primates for example who stand on the top of the hierarchical social status ladder display greater serotonin levels than primates who rank lower in the pecking order. If however the higher ranked primates loses his social status he analogously experiences a decrease in serotonin levels.
Testosterone and Aggressive Behaviour
Schaal and colleagues (1996) investigated more recently the association between physical violence and social dominance of pubescent male youths and their respective testosterone levels. It was shown that less socially dominant youths had lower levels of testosterone in comparison to socially more dominant peers who possess concurrently bigger amounts of testosterone amounts. Nevertheless, this finding could not be repeated with aggression levels as those pubescent youths who were perceived as more aggressively behaving had significantly lower testosterone concentrations than those males who had a low history of being physically aggressive and violent. Thus it was concluded that testosterone was related not so much to antisocial characteristics than to experienced social status. In other words, those who successfully achieve higher social dominance statuses experience an increase in testosterone while those who fail to gain high social status face a reduction in their testosterone production.
Experiments with younger children (e.g. 5-year-olds) it was found that boys with higher testosterone concentrations were more playfully aggressive in social interactions. However, this relationship could neither be established with girls nor in play contexts (Ahedo et al., 2002). This again implies that testosterone levels are not solely a modulator of aggressive behaviour but rather a mediator of any kind of social behaviour. Additionally, Ahedo and collaborators study demonstrated that sex differences in behaviour establish themselves already very early on in life.
In another study (van Goozen et al., 1998) the androstenedione, testosterone, dehdroepiandrostenedione (DHEA) levels in prepubescent boys exhibiting antisocial conduct disorders was examined. Van Goozen and colleagues results revealed that antisocial conduct disordered infants' aggressiveness was not significantly relatable to testosterone.