Is testosterone linked to human aggression? A meta-analytic examination of the relationship between baseline, dynamic, and manipulated testosterone on human aggression

Man is inclined to affirm his personality by trying to be distinguished and gain influence and power in his career, in sports and in everyday life, by competing with others. His intension was to review the research in the features and effects of these fundamental research findings with the physiology and psychology of man. In more sensitive laboratory paradigms, it has been observed that participant’s testosterone rises in the winners of; competitions, dominance trials or in confrontations with factitious opponents.
Subsequent studies in the 1970s and 1980s further explored this relationship, using a range of methodologies, including hormone administration and measurement of hormone levels in relation to aggressive behavior. Developing targeted interventions that address the biological and psychosocial aspects of aggression can contribute to more effective treatment strategies and improved outcomes for individuals experiencing challenges related to aggressive behavior. The integration of findings from diverse sources has contributed to a holistic understanding of how testosterone influences aggressive behaviors. By elucidating the intricate cellular and molecular mechanisms, this section contributes to a more nuanced understanding of how testosterone exerts its influence on neurotransmitter systems, ultimately shaping aggressive behaviors. This subsection reviews research that examines the relationship between naturally occurring variations in testosterone and observed aggressive behaviors. Correlational studies play a pivotal role in understanding the association between testosterone levels and aggressive behavior in real-world contexts.
Careful examination of the nature of the questions being asked is critical, as growing evidence suggests that relationships may not be conserved across different levels of analysis (Goymann et al. 2007; Nussey et al. 2007; Breuner and Berk 2019). Some are tested at different timescales, ranging from minute-to-minute changes in hormones or behavior to those changes that are visible over the course of weeks, reproductive cycles, or seasons. These questions and predictions can be framed at the level of the individual, or they may apply to comparisons among individuals. Across this line of research , studies vary in how T and aggression are examined in relation to one another. In the lab, castration can lead to a reduction in aggression, while treatment with exogenous T can restore the behavior (e.g., Beeman 1947; Barkley and Goldman 1977; Moore 1988).
The effects of early exposure to gonadal steroids have been described for a variety of vertebrate species. Aggression in males is facilitated by implants of AVT in the limbic system and inhibited by implants of AVP. Men with fewer CAG repeats have more active androgen receptors and enhanced testosterone action. All the above studies have methodological limitations because of the small number of subjects and samples. In more sensitive laboratory paradigms it was observed that a participant’s testosterone rises in the winners of competitions and dominance trials, or in confrontations with factitious opponents. Most of the studies, however, were conducted by self reported questionnaires, the accuracy of which is questionable.
Studies with a limited number of subjects have shown a positive relationship of testosterone with aggressive phases of the game in judo contests and hockey players (4, 6, 24). It is of interest, however, that supraphysiological doses of testosterone in the order of 200 mg weekly (20), or even 600 mg weekly (21), which were administered to normal men had no effect on their aggression or anger levels. In a single sample measurement of free testosterone in the saliva of 89 prison inmates, it was found that at the extremes of the testosterone distribution, the relationship between testosterone shop to aggression was more striking (14). The omission of a vast body of experimental work in animals regarding the relationship of testosterone with aggression, by no means indicates a reduction of interest and esteem in the importance of these publications by the author. Violent and aggressive behavior is a natural and physiological element that rules animal life, driven as it is by the instincts of survival and the preservation of species through reproduction. The degree of impulsivity is regulated by serotonin inhibiting receptors, and with the intervention of this neurotransmitter the major agents of the neuroendocrine influence on the brain process of aggression forms a triad.
In our tree swallow case study, we hypothesize that the most aggressive individuals experience the greatest change in T post-challenge. However, we found that females had lower T levels after real or simulated social challenges, relative to controls (George et al. 2022), echoing several other studies in songbirds (summarized above). In line with Prediction 1, there is some evidence that baseline T levels and aggression are positively correlated among individuals, at least during territorial establishment. At the same time, individuals with the greatest potential to increase aggression may be the ones with the smallest potential to elevate T, resulting in little visible effect of endogenous T elevations (say, elicited with GnRH injections) on behavior. However, such repeated sampling also introduces handling-induced stress effects that may influence subsequent reactivity along the hypothalamo-pituitary-gonadal (HPG) axis (Deviche et al. 2012; Abolins-Abols et al. 2018), or influence an individual’s aggressive response (Summers and Winberg 2006).
It was our a priori impression that Predictions 1–3 have been tested most frequently, largely via among-individual comparisons. For each question, we present a prediction that is based on the positive link between exogenous T and aggression seen in experimental manipulations. Pharmacological treatments with drugs that prevent the binding or metabolism of androgens can also diminish aggression (e.g., Schlinger and Callard 1990; Sperry et al. 2010; but see Apfelbeck et al. 2013).
In a large scale study in India reported by Rajender et al., 241 men convicted for rape, 107 for murder and 26 for murder and rape had significantly shorter CAG repeats than the 271 male controls (40). Blood serotonin (5-HT) and its metabolites found in the cerebrospinal fluid are negatively related with aggression and selective 5-HT reuptake inhibitors have been shown to exhibit aggression lowering effects (37). Clinical studies have shown that the serotoninergic system regulates impulses and aggressiveness, as it has activating and inhibitory receptors in the prefrontal and the subcortical areas. The degree of impulsivity present also plays a significant role in the activity of the emotional subcortical brain and this adds a third factor to the buy testosterone booster-cortisol balance, codimd.communecter.org serotonin (35, 36). The degree, however, of local testosterone’s contribution to its action on the brain is not known at present, but the promptness of its production and the variety of stimuli it can receive from neighboring neurons may render it more important than the testosterone arriving to the neurons through the circulation. The neurons of the prefrontal area, the hypothalamus and amygdala which are concerned with aggression, express significant quantities of androgen and estradiol receptors, along with the enzymes necessary for the steroidogenesis of these hormones.
Moving forward, we advocate for greater attention to two additional layers of complexity, regarding (1) short- vs. long-timescales, and (2) within- vs. among-individual levels of analysis. We view apparent inconsistencies as opportunities to embrace and empirically explore greater complexity in behavioral endocrinology. For instance, at baseline, individual differences in T production and aggression are not necessarily correlated.