Is Testosterone Really Linked to Aggression? What Does the Science Say
Testosterone is often associated with aggression, but how strong is that link? Let’s explore what the research says, focusing on findings from ‘The relationship between testosterone and aggression: A Meta-Analysis.’ [1].
The Organisation/Activation Model explains how, during development, exposure to male sex hormones, such as testosterone, plays a key role in shaping aggressive behaviour [1]. As men enter early adulthood, they are re-exposed to hormones responsible for male traits like testosterone, which leads to increased aggression [1].
Animal studies strongly support the relationship between testosterone and aggression; however, human studies show mixed results [1].
Factors that Influence Testosterone and Aggression
Several factors influence how testosterone affects aggression:
- Hormonal Fluctuations: Testosterone levels vary throughout the day and seasonally, peaking in the morning and declining by the afternoon [1]. The most significant decline occurs between 7:00 am and 10:00 am [1]. This suggests that men also experience a hormonal cycle, though it follows a different timeline from women’s.
- Age: Testosterone levels are highest in late teens and early twenties, then gradually decline [1].
- Sex: Men generally have higher testosterone and display more physical aggression [1]. However, both men and women can experience a relationship between testosterone and aggression [1]. This means that women with higher testosterone may also display more aggression.
- Social Status: Testosterone levels rise in response to competition and changes in dominance or social status [1].
Reasons Why This Relationship Exists
Testosterone's link to aggression is evident in several behaviours:
- Competition: Testosterone rises before competitive events, enhancing risk-taking, focus, and performance [1]. Winners maintain higher levels, while losers experience a decline [1]. This phenomenon has been observed in both physical sports and non-physical competitions, such as chess [1]. Researchers have also observed this pattern among fans of winning teams compared to those of losing teams [1]. Medical students also show increased testosterone after graduation, likely due to the rise in social status [1]. The use of Aggression and Dominance to secure mates against competing males is often seen in Animals, thus suggesting that this is an evolutionary reason for the link between testosterone and aggression.
- Mating: Testosterone levels drop when men marry and rise again after divorce, suggesting that testosterone plays a role in mate competition [1].
- Cross-species and cultural evidence: In multiple animal species, higher testosterone levels are linked to increased aggression [1]. Additionally, human studies show that this relationship between testosterone and aggression is relevant regardless of ethnicity or culture [1].
- Young Male Syndrome: refers to the fact that males aged 12-25 are the primary perpetrators and victims of violence [1]. Testosterone peaks during this period, potentially driving aggression and competition for social status as young men reach sexual maturity [1]. This indicates that the relationship may be linked to mating strategy.
What has Been Studied?
The study analysed 45 studies with 9,760 participants, combining data to identify trends [1].
Aggression was defined broadly, including competition, self-reported aggression, criminal records, and ratings of aggressive behaviour from close ones [1]. However, the paper does not clarify what specific aggressive behaviours were measured, leaving room for interpretation for what is considered an aggressive trait [1].
The analysis only included studies that reported effect sizes or p-values.
- A p-value indicates whether results are likely to have occurred by chance, with values below 0.05 showing a statistically significant relationship.
- Effect size measures how strong a relationship is.
To reduce bias, unpublished studies were excluded, and only peer-reviewed (quality-checked) studies were included [1]. Duplicate participants were removed to avoid overrepresentation [1].
What Do the Results Show?
The meta-analysis supports a weak but positive link between testosterone and aggression in 83% of the results, regardless of the time of day [1]. This means that even though there is a correlation between testosterone and aggression, it does not mean that everyone with high testosterone is aggressive. Not all aggressive behaviour is caused by testosterone.
This relationship was exhibited in men across all age groups: 13-20, 21-25, and 35+ [1]. The relationship was strongest in males aged 13-20, likely due to the natural rise in testosterone during this period due to sexual maturity [1].
The connection weakened as men aged, potentially because older males prioritise parenting over competitive behaviours as they no longer need to compete with other males for mates. [1].
Sex, offender status, testosterone measurement method, and aggression measurement type did not significantly affect the relationship between testosterone and aggression, indicating consistency across different groups and methods [1].
Testosterone Actually Causes Dominance
Some researchers suggest testosterone may primarily influence dominance, not aggression. Furthermore, the relationship might also be bidirectional, meaning aggressive behaviour could lead to higher testosterone levels, as seen in animal studies [1].
Future Research
Future research should examine competitive aggression in social settings, especially when potential mates are involved, to understand the evolutionary role of testosterone and aggression [1].
Papers Limitations
This analysis averages the results from all these studies to identify trends. However, this averaging could mask meaningful variations and the true correlation between the two, thus limiting the analysis.
A key issue in the public version of the study is referencing the wrong figure for a key finding, raising concerns about its accuracy. This error may indicate other misinterpretations, affecting the reliability of the conclusions.
Many Questions Remain
While this analysis supports the idea that testosterone influences aggression, many questions remain, offering opportunities for future research to explore this complex relationship.
References
Reference paper "The relationship between testosterone and aggression: A meta-analysis. Aggression and violent behaviour"