Hormonal Mechanisms

• Observations indicate that males are generally more aggressive than females.
• This means researchers have focused their attention on the male sex hormone testosterone.
• Testosterone is an androgen responsible for the development of masculine features.
• It also has a role in regulating social behaviour via its influence on certain areas of the brain related to aggression.

• Animal studies, such as those conducted by Giammanco et al. (2005), have demonstrated that increases in testosterone are related to greater aggression in several species.
• Decreases in testosterone has also been shown to lead to reductions in aggressive behaviour in castration studies.

• Studies of prison populations and violent offenders have provided evidence of a similar association in humans.
• Dolan et al. (2001) studied a sample of 60 male offenders in UK maximum-security hospitals.

• They found a positive correlation between testosterone levels and aggressive behaviours.
• Many of these men suffered from personality disorders, such as psychopathy, and had histories of impulsively violent behaviour.

• Mazur (1985) formulated the biosocial model of status (BMoS) to explain the link between testosterone and aggression in humans.
• Testosterone levels change rapidly during the course of the day, especially in response to social interactions related to status - in other words, competition.
• A change in testosterone levels following the loss of status, for example, should affect post-competition aggression.

• Mehta and Josephs (2006) measured changes in their male participants’ testosterone levels before and after a competitive game, which they lost.
• Once the second sample was taken, the participants were given a choice:
  • They could either challenge their victorious opponent to another competition (aggression);
  • Or complete an unrelated task (non-aggression).

• Out of the losers whose testosterone levels rose after their loss, 73% re-challenged.
• Out of the losers whose testosterone dropped, only 22% re-challenged.
• So after a loss of status, individuals behaved aggressively by choosing to re-challenge but only after an increase in testosterone levels.

• These findings confirm Mazur’s BMoS.
• This increases its validity as an explanation of how testosterone may exert its effect on aggression.

• Carre and Mehta (2011) developed the dual-hormone hypothesis.
• This claims that high levels of testosterone leads to aggressive behaviour only if levels of cortisol are low.
• When cortisol is high, testosterone’s influence on aggression is blocked.
• (Cortisol is a glucocorticoid hormone that plays a central role in the stress response).

Popma et al. (2007) confirm this in a study of adolescent males.

• They found that the combined activity of testosterone and cortisol may be a better predictor of human aggression than either hormone on its own.