Testosterone

• Supporting evidence +

  Wagner et al (1979)-  castrated mice to reduce testosterone levels & found this led to a decrease in aggression.
• Contradictory evidence -

  McBurnett et al (2000)- found that boys with low levels of cortisol (stress hormone) began antisocial acts at a younger age and exhibited 3x the number of aggressive symptoms compared to boys with higher levels of cortisol.