Biological explanations of aggression.

L/objectives

• ALL: Will be able to Describe how biological and physiological processes affect aggressive behaviour

Grade/Level: E/D

• MOST: Will be able to Understand how biological explanations are split into genetic, biochemical and neuro-anatomical explanations

Grade/Level: C/D

• SOME: Will be able to elaborate & evaluate these explanations (inc research for and against)

Grade/Level: B+

Types of Aggression

• Aggression • Evo explanations• Instrumental• Person orientated• Reactive Aggression• Proactive Aggression

• Initiated by an individual to achieve a desired outcome.

• Response to someone else's aggression.

• Obtaining personal reward

• Attempt to harm another person.

• Adaptive/hunter gatherer • Behaviour with intent to

harm.

‘Aggression is in our nature’

• Aggression in animals and humans is an inherited, spontaneous tendency much the same as the motivation to eat, drink and make love.

According to who? • Inheritance of behavioural

capacity for aggression. Behavioural genetics

James Watson

• Control of aggression by brain, blood and hormones. Physiological psychology Frank beach

• Interaction between genetic and physiological factors. Ethology - animal behaviour Konrad lorenz

NATURE

What do these two have in common?

How can biology have a role in aggression?

• The resulting aggressive behaviour can be the result of imbalance of the four main theories:

• Neurotransmitters. • Genes.• Hormones.• Neuroanatomy

Genetics

• Biology has a role in aggression. Genetic influences play a major part in some aggression, as evidenced in animals specifically bred to exhibit such behaviour. Studies of identical twins have frequently shown that if one twin exhibits aggressive behaviour, the other often does so as well.

Neuroanatomy

• Aggression may also have a neural basis; aggressive behaviour has been produced in animals through electrical stimulation of parts of the brain.

Biological Aggression

• Konrad Lorenz, an ethologist, proposed that aggression arises from instincts and that such instincts help members of a species maximize the use of food, space, and other resources. Other biologists have studied the aggression produced by exposing the nervous system to chemicals (drugs, such as alcohol) or hormones (such as testosterone).

Biological Aggression

• It is a common myth that testosterone causes aggression but is there biological reason to back up this assertion?

• Some say there is, while others are armed with refuting information with which to contest this argument.

• The bottom line is that we do not know for sure whether or not testosterone causes aggression .

• So what do we know…well lets examine the evidence.

Aggression in the brain.• The hypothalamus and

periaqueductal gray of the midbrain are the most critical areas controlling aggression in mammals, as shown in studies on cats, rats, and monkeys.

• (Can we extrapolate from these findings?)

• They have direct connections with both the brainstem nuclei controlling these functions and areas such as the amygdala and prefrontal cortex.

Biology cont…

• According to the evolutionary biology theory aggression serves an important function in terms of both individual survival as well as reproduction potential.

• Competition arises when resources are limited and therefore animals/species must actively compete in order to increase their own fitness.

• Inferring that aggression is advantageous at both the individual and genetic levels

Biology cont..• In terms of aggression, there exists evidence that there is a

definite connection between the hormonal effects of testosterone and the outward expression of aggressive behaviour.

Empirical evidence #1• Castration leads to a marked decrease in aggression as

shown by castration experimentation on various species. Furthermore, when testosterone is replaced through hormone therapy in these castrated animals, the amount of aggression increases and is restored to its original pre-castration level.

• Taken together, this seems to present a strong argument for the role of testosterone in aggression.

• However, the story does not end here: if we are to suppose that testosterone does in fact lead to aggressive behaviour we must then necessarily ask how and why it does.

Empirical Evidence #2

• Moffitt et al (1998) studied the blood serotonin levels of 781 21-year-old men and women.

• The researchers report that "in this study, elevated whole blood serotonin was characteristic of violent men." (Low brain levels of serotonin, but high levels of blood serotonin, are associated with behaviour disorders-apparently because of serotonin's different origin and function in blood and brain.)

• The violent men's mean serotonin level was .48 standard deviations (SD) above the norm for males as a group, and .56 SD above the mean for non-violent men. Among female subjects, no relationship between serotonin levels and aggression was seen.

Biology cont…

• Maxon (1998), a leading theorist proposed a theory that one's genes affect one or more types of aggression in mice, which may be applied to humans as a genetic explanation of aggression.

• Childhood experiences appear to be especially powerful, because a child's brain is more malleable than that of an adult. A young brain is extra vulnerable to hurt in the first years of life. A child who suffers repeated abuse, neglect as well as terror experiences physical changes in his brain

Cont biological evidence..1. The amygdala is also critically involved in aggression. Stimulation of the

amygdala results in augmented aggressive behaviour in hamsters (Decoster et al 2006)

2. Lesions of an evolutionarily homologous area in the lizard greatly reduce competitive drive and aggression (Bauman et al. 2006).

3. In adulthood, several studies of the concentration of blood testosterone of convicted male criminals who committed violent crimes compared to males without a criminal record or who committed non-aggressive crimes revealed in most cases that men who were judged aggressive/dominant had higher blood concentrations of testosterone than controls.

4. Studies of testosterone levels of male athletes before and after a competition revealed that testosterone levels rise shortly before their matches, and are dependent on the outcome of the event: testosterone levels of winners are high relative to those of losers.

5. Testosterone levels in female criminals versus females without a criminal record mirror those of males: testosterone levels are higher in women who commit aggressive crimes or are deemed aggressive by their peers than non-aggressive females. However, no specific response of testosterone levels to competition was observed in female athletes, although a mood difference was noted (Mazer et al 1998)

So what are we saying?

• Genetic and biological theories of aggression both have strong points as well as weak points.

• Causation is not well established in genetic theories. If it is found that one gene exists in aggressive individuals and not in non-aggressive individuals it is not determined if the genetic information causes aggression or if aggression causes a change in genetic information. Biological theories are strong in that the choice of treatment is obvious and it has been shown to be effective.

• Genetic theories' weakness is that it does not explain every case of aggression. These theories also put the responsibility within the individual.

Real Life examples of how aggression can be affected by biology!

• In women, premenstrual tension syndrome is associated with a number of aggressive behaviours, such as violent crime.

• (That hormonal time of the month!!)

• People with a serious physiological illness, such as cancer, may be affected by negative mood states.

• These mood states may indirectly affect the aggressive behaviour of individuals.

• Temperament may be indirectly related to aggressive behaviour. People who are impulsive are more likely to be aggressive than people who have a deliberate temperament.

The mind of a killer!!

• Read the located on the URL below and be prepared to make a contribution to the discussion of aggression being largely a biological by product.

• http://archive.salon.com/books/int/2001/07/27/killers/print.html

Aggression in real life.

• Columbine High school/The Littleton killers• University of Texas massacre: Charles

Whitman.• Hungerford massacre• Dunblane massacre• Virginia Tech massacre

• Could you use any of these real life cases to illustrate the effects of biology on aggression?