BIOLOGICAL EXPLANATIONS OF AGGRESSION BIOCHEMICAL FACTORS IN AGGRESSION

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.

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.

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

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

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

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

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.

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

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)

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.

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.

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.

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

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.

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

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

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

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

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

Kimura 1999  Female spatial ability tends to improve with high levels of testosterone. ttp://

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

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.

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..

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

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.

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.

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.

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

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

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

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

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.

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.

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