1. BIOLOGICAL EXPLANATIONS OF AGGRESSION BIOCHEMICAL FACTORS IN AGGRESSION

2. Objectives  Understand the effect of hormones on aggressive behaviour  Understand how hormones and selected neurotransmitters can influence aggressive behaviour  Evaluate the contribution of research into neural and hormonal influences on aggressive behaviour.

3. Hormonal insanity !  In the Uk  Since the 1980s  A series of high profile cases where hormonal fluctuations surrounding pre-menstrual tension have been used as grounds for claims of temporary insanity.  A murder charge was reduced to manslaughter on account of PMT.

4. Lawyers’ argument  Their clients were ‘automatons’ of their body.  The aggressive act was caused by uncontrollable hormonal changes associated with the monthly cycle.

5. Hormonal influences  Androgens = male hormones  There is a positive correlation between the level of androgens and aggressive behaviour in female and male prisoners.

6. Testosterone  An androgen produced by Leydig cells in the male testes and adrenal cortex.  The release of testosterone follows a natural circadian rhythm.

7.  During puberty aggression increases when androgen levels are higher (especially in males)  Testosterone has masculinising effects.

8. Castration  This technique has been used for making domestic and farm animals more manageable for many years.  Lab studies established the involvement of testosterone in increased aggression at puberty.

9. Wagner et al. 1979  A castrated mouse showed less aggression.  After testosterone treatment, aggression increases again.

10. Changing levels of testosterone in mice pre-castration and post-castration Blue = pre- castration Pink = post- castration Green = 150 microgm testosterone per day. BEEMAN (1974)

11. Commentary  Aggression did not disappear after castration  It cannot be stated that testosterone causes aggression.  Subsequent studies found that aggressiveness in mice is only reduced if castration occurs before puberty.  Therefore, testosterone contributes to the development of aggression and once it has accomplished this, its effects become relatively permanent and largely unaffected by the subsequent loss of testosterone.

12. Testosterone in humans  The role of testosterone is clear in lower animals, but androgens can’t be given to humans to see if changes in aggression occur.  Dabbs et al (1995) investigated the relationship between testosterone, crime and prison behaviour.  They measured testosterone in saliva of 692 adult male prisoners.

13. Findings  Those who had committed crimes involving sex and violence had higher testosterone levels and violated more prison rules than those who had committed burglary and theft.

14. Fraternity behaviour  Dabbs et al (1996)  Relationship between testosterone and fraternity behaviour.

15. Fraternity testosterone  They measured testosterone of 240 members of 12 fraternities in 2 universities.  Compared to descriptions of behaviour.  Found less smiling and generosity and lower academic achievement in high testosterone fraternities.

16. Further findings  High testosterone - boisterous and macho  Low testosterone – attentive and helpful

17. Problems with research  Do not establish cause.  There may be other factors causing aggression apart from testosterone.  Behaviour is open to interpretation e.g. Lack of smiling may not be related to testosterone at all. Correlations Unreliable measurements

18. Women and testosterone  84 female prison inmates  Testosterone highest in cases of unprovoked violence  Lowest in defensive aggression (abused wives who retaliated) Dabbs et al 1988 Testosterone high

19. Problem!  Testosterone was highest in defensive aggression  Olweus referred to ‘provoked’ aggression when participants were frustrated or restricted in some way. Contradictory to Olweus 1983 Operationalisation of aggression

21. Pillay 2006  Testosterone levels varied according to which sport different athletes played.  Males and females in aggressive sports had the highest levels of testosterone.

22. Kimura 1999  Female spatial ability tends to improve with high levels of testosterone. ttp://www.youtube.com/watch?v=rn0e6xA5G

23. Two models of testosterone  Reciprocal model  Aggression causes raised testosterone  Basal model  Testosterone is the cause of aggression

24. The reciprocal model of testosterone  The reverse of the basal model. It suggests that testosterone levels are influenced by changes in the level of dominance.

25. The basal model of testosterone  The level of testosterone influences dominance. The more testosterone, the more competitive and hence more dominant they become. Dominance is the effect of testosterone.  The more testosterone a person has, the more competitive and dominant they become.  It follows that..

26. The more testosterone  The greater the likelihood of anti- social behaviour, fighting, expressions of dominance etc.

27. Mazur and Booth 1998  Men with higher levels of testosterone were  More likely to  Divorce,  Remain single,  Be arrested for offences other than traffic violations  Buy and sell stolen property  Incur bad debts  Use weapons in fights.

28. Mazur and Booth 1998 cont.  The reciprocal model of testosterone  Levels vary with the person’s dominance  2,100 air force veterans studied  Over 10 years given 4 medical examinations  Testosterone levels varied  Reduced when married  Increased when divorced.

29. The role of serotonin  Serotonin is a neurotransmitter  Davidson, Putnam and Larson (2000)  Serotonin may have inhibitory function  i.e. Helps individuals to fight their aggressive urges.

30. Research evidence  Serotonin levels lower in violent criminals.  Reducing serotonin levels in Vervet monkeys resulted in increased aggressive behaviour.

31. Effects of low serotonin  Also known as 5- hydroxytryptamine -5HT  Affects whole body:  Impulsive behaviour  aggression  Overeating  Depression  Alcohol abuse  Violent suicide

32. Studies of domestic pets  Bred for reduced aggression  They seem to have higher levels of serotonin.

33. Russian silver foxes  Tamed for more than 30 years  Higher levels of serotonin and lower levels of monoamine oxidase.

34. Research evidence  Various research suggests that low levels of serotonin are linked with aggression.  While high levels of serotonin are linked with more peace-loving behaviours.

35. Evidence for link with serotonin  Tryptophan = a precursor of serotonin (found in starchy foods)  Tryptophan and other serotonergic drugs have been given to patients with unpredictable behaviour.  The effectiveness of this treatment indicates a link with aggression and levels of serotonin.

36. But  While serotonergic drugs modify aggressive behaviour, this cannot be the only cause of activity in these regions of the brain.