Plans For Topics

Unit 3

- Aggression

- Eating Behaviour 

- Biological Rhythms and Sleep 

Neural Mechanisms in Eating Behaviour - Plan

Discuss neural mechanisms involves in the control of eating behaviour (8+16) - plan

• AO1 Homeostasis and the internal working environment - the time gap between eating and satiety.
• AO1 Reduction of glucose causes the message to lateral hypothalamus. 
• AO1 Seen as ‘eating centre’ and creates feeling of hunger.
• AO2 Anand and Brobeck 1951 - A lesion in the lateral hypothalamus led to a loss of feeding behaviour in rats known as aphagia. Electrical stimulation produced feeding 
• AO3 Use of rats and lab setting - high internal validity but struggling to generalise due to differences in rats and humans, despite similar brain structures. 

• AO1 Ghrelin released by lateral hypothalamus and human feels hungry and then seeks out and consumes food. 
• AO1 triggers response from ventromedial hypothalamus which sends message to stop eating 
• AO2 Hetherington and Ranson 1942 - Lesions in the VMH caused rats to overeat and become obese. 
• AO2 Damage to VMH has caused hyperphagia and obesity in many species, including humans. (although usually damage much be present in the paraventricular nucleus)
• AO3 much much applicable to humans sue to some studies being tested on them. Unecthical treatment of rats. 
• AO1 the feeling of satiety prevents overeating.

• AO1 Neuropeptide Y is sometimes seen as the neurotransmitter which could be responsible to overeating. 
• AO2 This could be seen as the (real-world-application) reason why people become obese - due to an overproduction of neuropeptide Y. 
• AO2 When rats were injected with neuropeptide Y, they became obese due to overeating. 
• AO2 however, Marie et al 2005 genetically modified rats without NPY and eating behaviour didn't change. 
• AO3 conflicting studies make results low in validity and hard to generalise. 

• AO1 also looked at is the role of the stomach and its contractions when hungry. 
• AO2 Canon and Washburn put balloon in stomach and witnessed more contractions of balloon when hungry. 

• AO3 IDAs - Use of animals - rats - similar brain structure, god control, not directly relatable with behaviour/biology, doesn't have implications like social pressures, immoral due to unethical treatment, speciesism, more ethical than using humans, cost-benefit analysis
• AO3 IDAs - Biological Approach - biology dictates choices, genes are the main contributing factor, no explanation of social pressures, doesn't explain association, links to ….
• AO3 IDAs - Determinism vs free will - biological impact of genes leaves no control, things like NPY can’t be altered, role of stomach is central to human biology and can’t be changed though this is debatable - gastric bands (real life applications?) 

Evolutionary Eating Behaviour - Plan

Evolutionary Theory of Eating Behaviour 

Factor 1: high calorie and meat 

AO1: Ancestors had to consume high calorie foods in the EEA for energy and store this for when food supply is low. This trait makes them survive and then passes on to offspring. 

AO2: Gibson and Wardle (2001) - presented 4-5 year olds with lots of vegetables and they chose the highest calorific ones - potatoes and bananas - showing no taste preference, just calories. 

AO3 Evaluation: Children are difficult to rely on - could have been texture, taste or familiarity that caused these children to choose the specific fruit and veg. 

AO1: Preference for meat comes from decline in quality of plants. Hunter-gatherer societies makes meat a faster option to feed everyone. The amino acids are essential in intelligence development - more intelligent survive and pass on trait. 

AO2: Milton (2008) - without animals, people could not have evolved into an intelligent species and meat allowed humans to gather all of the necessary nutrients they needed to survive. 

AO3 Evaluation: Cordain et al (2006) argued that early humans consumed most of their calories from plant materials and were vegetarians. 

IDAs: Psychology as a science - difficult to falsify. Evolutionary approach doesn't acknowledge cultural influences and why some cultures don't look at high calorie foods - makes it culture biased. 

Factor 2: Taste preference

AO1: Sweet foods - Sweet foods are often high calorie. Also associated with ripe fruit which was rare and therefore a treat. Sweet foods are usually not poisonous. 

AO2: Bell et al - sweet food given to Eskimos who don't usually have it and it was not rejected - sweet food preferred universally. Also found sweet receptors in tongue. 

AO3 Evaluation - Only tested on Eskimos - lacks population validity and doesn't necessarily mean that all cultures worldwide would accept sugar due to their different upbringing and adaptions, e.g. Thailand prefer spicy foods. 

AO1: Taste Aversion - bait shyness, avoiding foods that have become associated with being ill. 

AO2: Garcia (1955) - rats who were made ill by radiation avoided foods they’d been fed directly before becoming ill. 

AO3 Evaluation: The use of rats isn't generalisable to humans despite similar brain structure - they do not have the same social pressures, behaviour or intelligence that humans have. 

IDAs: Deterministic - people have no free will, everything is decided by adaptive traits developed by early ancestors. Also doesn't take into account the social impacts of eating behaviour, although does touch on the behavioural approach with the bait shyness due an association being made. Food preferences, however, can also be influenced by other people. 

Success/Failure of Dieting - Plan

Discuss factors into the success and failure of dieting (8+16 marks)

Factor 1: Failure

AO1: Restraint theory - restraint synonymous with dieting. 89% female population in UK restrain food intake at some point.

AO2: Herman and Mack (1975) - 15 participants, 3 conditions. Low-restraint eat less in condition 2 and 3 than zero. High-restraint eat more in conditions 2 and 3. Positive correlation between score on eating restraint questionnaire. High restraint = more eaten. (women)

AO3 Evaluation: Only 15 participants - low population validity and an inability to generalise results to a wider population. Also correlations do not prove cause and effect and mean reliability is affected. 

AO1: Boundary model - the dietary boundary between hunger and satiety leading to the ‘what-the-hell’ effect. Role of denial - denying food makes an individual crave them more. 

AO2: Wegner et al (1987) - Asked participants to not think about a white bear and ring bell if they did. Condition where told not to think about bear rang bell more. 

AO3 Evaluation: Instructions were very vague and inconclusive - lacks validity and reliability. 

IDAs: Gender bias: Most research conducted on women - different hormones and biology to men, as well as social pressures. 

Factor 2: Success

AO1: Motivation - important in success of dieting, usually more successful with more motivation, links to social support also. 

AO2: Lowe et al (2004) - Weight losses achieved through WeightWatchers were maintained over a five-year period and an average of 71.6% of people maintained a loss of 5% of body weight. 

AO3 Evaluation: Other contributing factors aren't considered - the type of diet could biologically work rather than it being due to social support. 

AO1: Detail - When people get into a routine, food becomes boring and same-ish. People need to focus on details of specific foods. 

AO2: Jelly Bean Experiment Redden -  135 people 22 jelly beans, one at a time, information given, 2 conditions. More specific detailed condition enjoyed experiment more. 

AO3 Evaluation: Doesn't necessarily explain eating behaviours, preferences etc. 

IDAs: Free Will - people voluntarily diet but are often expected to by society - does this affect the success/failure?

Attitudes to Food - Plan

Discuss factors influencing attitudes to food.

factor one - health

AO1 outline - Pressure to have a healthy balanced diet - link to Crohn’s and coeliac disease - limited on food choice which also links to convenience and the issues with the availability of food and links to cost also 

AO2/3 Research evidence linked to factors - Turila & Pangborn (1998) - questionnaire data - women’s consumption of dairy - actual consumption was based more on liking than on health concerns. 

Evaluation of research - Questionnaires - social desirability bias making results low in validity. Only focuses on women making it difficult to generalise to men. 

AO2/3 Research evidence - Rapoport (2003) - growing interests in healthy foods, but more people are eating out and the population is becoming heavier 

Evaluation of research - Doesn't really have any empirical data that can be analysed and results are very conflicting - reduces validity. 

IDA - Biological approach - focuses mainly on illnesses that can’t necessarily be prevented (excluding diabetes) which limits food choices. Arguable when it comes to available, cost, e.t.c. 

Links to determinism - health forces some people to make considered food choices. 

Factor two - learning 

AO1 outline - Operant conditioning from parents - eat vegetables to get dessert. Parental attitudes and preferences. Association and also social learning through media and image. 

AO2/3 - Birch and Malin (1982) - 2 year olds to new food over 6 weeks. 1 food presented 20 times, 1 five times and 1 was novel. Direct relationship between exposure and food preference. 8-10 exposures necessary to shift preference. supports neophobia. 

Evaluation - study on children make result limited to a certain age group and lower population validity. 

AO2/3 - Meyer and Gast (2008) - 10-12 year old boys and girls - found a positive correlation between peer influence and disordered eating. 

Evaluation - correlations do not establish cause and effect - lack in reliability and make results difficult to generalise. 

IDA - Nature vs nurture - doesn't take into consideration the nature/biological side of the approach (illnesses or genetic make up) focuses on upbringing and social influences. Also deterministic because of the social influences’ inability to be changed. 

Neural Mechanisms of Eating Behaviour

Homeostasis

This involves mechanisms which detect the state of the internal environment. There is a time lag between restoring equilibrium and measuring effect. 

For a hunger mechanism to be adaptive, it must anticipate and prevent energy deficits.

Dual-Process Model

Decline in glucose
              |
Activates lateral hypothalamus
              |
         Hunger
              |
Search and consume food
              |
     Glucose rises
              |
Activates ventromedial hypothalamus
              |
  Feeling of satiation
              |
  Stops further eating       

Lateral Hypothalamus
- Functions as the feeding centre, stimulating feeding in response to signals from the body.
- Damage to LH can cause aphagia. Stimulation elicits feeding behaviour.
- The view that LH serves as an 'on switch' for eating has problems - damage to LH had other behaviour deficits (thirst and sex).

Research: Sakuri (1998)

Ventromedial Hypothalamus 
- Part of the hypothalamus that functions as a satiety centre to inhibit feeding.
- Damage to the VMH caused rats to overeat - hyperphagia.
- Usually overeating only occurred when there was also damage to the paraventricular nucleus.

Research: Gold (1973)

Neuropeptide Y
- Important in turning on eating. When injected into hypothalamus of rats, it caused them to begin eating despite having eaten before.
- Obese people may have an over-production of NPY.

Research: Marie et al (2005)

Neural Control of Cognitive Factors
- The Amygdala - Thought to be primarily in the selection of foods on the basis of previous experience.
- Rolls and Rolls (1973) 

- Inferior Frontal Cortex - Thought to be linked with odours and food response. Diminished odour response decreased eating.

Research: Zald and Pardo (1997)
    

Neural Mechanisms - Studies

Sakuri (1998) 

Eating behaviour is controlled by neural circuits that run through the brain. The lateral hypothalamus may not be the brain's 'eating centre'. This research involved using rats. 

Gold (1973) 

- Lesions to the VMH alone did not result in hyperphagia in rats and only had effect when PVN was also damaged.
- Subsequent research failed to replicate Gold's findings.

Marie et al (2005) 

Genetically modified rats (without NPY) had no change in eating behaviour. 

Rolls and Rolls (1973) 

Surgically removing the amygdala in rats would cause them to consume familiar and unfamiliar foods. 

Zald and Pardo (1997) 

The amygdala participates in the emotional processing of olfactory stimuli. 

Dieting

Restraint Theory 

Restraint has become synonymous with dieting. Research suggests 89% of the female population in the UK consciously restrain their food intake at some point in their lives. 
Research: Herman and Mack (1975)

Support for the claim that dietary restraint can lead to overeating comes from Wardle and Beales (1988). 


Boundary Model

Introduced by Herman and Polivy - explains why restrained eaters eat more after preloads. 

The Boundary Model - Hunger keeps intake of food above a certain minimum, and satiety works to keep intake below some maximum level. Between these two levels, psychological factors have the greatest impact on consumption. Dieters tend to have a larger range between hunger and satiety. Restrained eaters have a self-imposed desired intake and once they have gone over this boundary, they continue to eat until they reach satiety. This leads to the 'what-the-hell' effect. 

Role of Denial 

Attempting to suppress or deny a thought frequently has the opposite effect, e.g. Wegner et al (1987). 
As dieters begin to restrain themselves and make certain foods 'forbidden', they begin to think about the foods more. 

Motivation

Motivation from the individual and others has shown important in the success/failure of dieting. If someone is motivated, they are usually more successful in their diet. 
Research: Thomas and Stern (1995)

Detail

When people get into a routine, food becomes boring and same-ish. To avoid this, people should concentrate on details of their food to be more successful with their dieting. 
Research: Jelly Beans Experiment

Social Support

Support groups like WeightWatchers have a huge success rate mainly attributed to their support systems and the support people get from other members. 
Research: Lowe et al (2004)

Goal Setting

When people set goals, they generally feel more motivated to continue until they reach the goals they've set. 
Research: Bartlett (2003) 

Dieting - Studies

Herman and Mack (1975)

Procedure
- 15 participants in three conditions.
- No preload; one milkshake; two milkshakes.
- Groups 2 and 3 asked to rate the taste qualities of milkshake.
- All participants given 3 tubs of ice cream and 10 minutes to rate the tastes of them.
- Told they could eat as much as they'd like.
- All given a questionnaire on their degree of dietary restraint.

Findings
- Low-restraint participants ate less ice cream in the two milkshake condition than the one or zero (considered to be 'fuller')
- High restraint participants ate more ice cream in the one and two conditions than the zero condition.
- Significant positive correlation across all participants between score on eating restraint questionnaire and amount eaten after two preloads - higher restraint = more eaten.

Wegner et al (1987)

- Asked some participants not to think about a white bear.
- Ring a bell when thinking of bear.
- Told others to think about bear.
- Participants told not to think about bear rang bell more.

Thomas and Stern (1995) 

- Modest payments as a reward for weight loss do not enhance initial weight loss.
- Strategies to improve social networks have focused on teaching spouses to provide support during weight loss has had modest success rates.

Jelly Beans Experiment - Redden

Procedure
- Gave 135 people 22 jelly beans each, one at a time.
- As each bean dispensed, information on bean was given.
- One group saw general information, another group saw specific flavour details.

Findings
- Participants got more bored with eating beans if they saw the general information.
- Detailed group enjoyed the experiment.

Lowe et al (2004) 

- Weight losses achieved through WeightWatchers were reasonably maintained over a five-year period and that an average of 71.6% of people maintained a loss of 5% of body weight or more.

Bartlett (2003) 

- Dieting is most successful when goals are realistic and objectively defined.
- Optimal target levels centre around reducing calorific intake by 500-1000 calories per day for a six month period.

Attitudes to food

Health

Different dietary conditions impact the types of foods people can consume.

Crohn's - 
- Inflammatory bowel syndrome
- 115,000 in the UK
- Avoid gluten, dairy, raw fruit & veg, dairy, fatty and fried foods, alcohol, caffeine

Coeliac- 
- 1 in 100 worldwide
- Small intestine
- No gluten because it can't be digested

Diabetes 
- 3.3 million diagnosed in the UK
- 590,000 have it and don't know
- Struggle with glucose and try not to consume high sugar foods

- Another factor that influences people's eating behaviour is the desire to eat foods that are regarded as nutritious and to avoid ones that have been labelled unhealthy.
- Education campaigns advise us to eat a diet that is low in fat and salt, high in carbohydrates and includes 5 portions of fruit and veg.
- Convenience and effort
- Availability
- Cost
- Health information & media

Research 
- Rapopori (2003) 
- Tuorila & Pangborn (1988) 
- Steptoe et al (1995) 

Learning 

Neophobia is a basic survival mechanism which tends to decrease with age. Experience and familiarity increase food preference. 

Operant Conditioning 

- Direct reinforcement from parents is used, commonly by reward e.g. 'eat your greens and you can have pudding'.
- This doesn't usually work because it increases desire for reward foods and decreases liking of non-preffered foods.

Parental Attitudes and food preference (parental modelling) 

- Mother provides food for child, therefore, the mother's attitude will affect the child's preference.
- If the mother is concerned by nutrition, she will work harder to give her child a balanced diet.
- Parents are key role models for children.
- When children reach school, peers become important.

Associative learning: classical conditioning 

- There may be aspects of the environment, specific behaviours or even food that impacts on what we eat.
- We can associate foods with physiological consequences like being ill.

Social Learning theory

- Learning through observation and vicarious reinforcement.
- Peers and parents model behaviour.
- Media models behaviour.

Media

- Magazines and TV influence.
- Makes foods look more appealing through advertising.


Research:
- Birch & Malin (1982) 
- Meyer and Gast (2008)

Attitudes to food - Studies

Rapopori (2003) 

People are motivated by health in contradictory ways. Existence of healthy foods so health must be a motivation for some. At the same time, people are becoming heavier. More people are eating out and consuming processed foods.

Tuorila & Pangborn (1988)

Obtained questionnaire data about women's intended and actual consumption of milk, cheese, ice cream and high fat and found that actual was based more on liking than on health concerns. 

Steptoe et al (1995) 

Put into rank order the factors taken into account by participants when choosing food to eat at, top - sensory appeal, health then convenience and price. 

Birch & Malin (1982) 

- Introduced 2 year olds to new foods over 6 weeks.
- 1 food presented 20 times; 1 ten times; 1 five times; 1 was novel.
- There was a direct relationship between exposure and food preference.
- 8-10 exposures were necessary for a shift in preference.

Brown & Ogden (2004) 

- Reported consistent correlations between parents and their children in terms of snack food intake, eating motivations and body dissatisfaction.

Mood and Eating Behaviour

Hunger is associated with increased arousal, vigilance and irritability. Studies have shown that people who are stressed or depressed increase the carbohydrate and fat content of their meals. This is associated with better mood and more energy. 

The Serotonin hypothesis: Carbohydrates such as chocolate contain the amino acid tryptophan. This is used by the brain in the manufacture of the neurotransmitter serotonin. Low levels of serotonin are associated with depression and it has been proposed that people with stress or depression take in more carbohydrates because this increases serotonin. 

However, the presence of a small amount of protein prevents the tryptophan from entering the brain and so serotonin will not increase. This means the serotonin hypothesis is unlikely to explain the effects of high carbohydrate diets.

The Opiate hypothesis: Examples are enkephalin and beta-endorphin. They are released from neurons and act at synapses with opiate receptors. Opiates are similar to the opiate drug heroin. This is highly addictive which can also produce pleasurable feelings, therefore it seems likely that the brain's opiate pathways are part of our reward system, a network of pathways that control out feelings of pleasure and reward. Opiate drugs increase food intake and the perceived tastiness of food. 

Binge Eating

- Research has shown that individuals with bulimia nervosa complain of anxiety prior to binge.
- Studies show that before a binge, bulimic individuals have more negative mood states than one hour before a normal snack or meal.
- In studies, binge days were associated with low moods.
- Low moods may make binge-eating more likely.
- Many people tend to comfort eat - supported by Garg et al (2007)

Reinforcement

- Although binge-eating can offer gratification, reinforcement is feeling and studies report a drop in mood immediately after the binge.
- Chocolate has been seen as the ultimate comfort food. Attitudes towards chocolate are influenced by  claims that it can lift our mood - supported by Parker et al (2006)

Binge-Eating Disorder - Supported by Wolff et al (2000)  

Mood and Eating Behaviour - Studies

Garg et al (2007) 

Procedure

- Observed the food choices of 38 participants who watched either a funny movie or sad one.
- Participants were offered buttered popcorn and seedless grapes.

Findings

- Those watching the sad film consumed 36% more popcorn than those watching the funny film.
- People watching the funny film ate far more grapes than the other group.
- People who feel sad want to 'jolt themselves out of the dumps' and are more likely to want a anck that will give them a sudden rush of euphoria.
- Happy people choose healthy foods.

When people were presented with the nutritional value beforehand, consumption of unhealthy foods dropped dramatically. 

Parker et al (2006)

Found that, although chocolate has a slight antidepressant effect, when consumed as an emotional eating strategy, it is more likely to prolong rather than alleviate the negative mood. 

Wolff et al (2000)

Procedure

- Investigated differences between 20 female bing eaters and 20 female normal eaters.
- Daily measures of mood, coping and eating behaviour were self-recorded for three weeks.

Findings

- Binge group reported more stress and negative moods but stress levels were similar on their binge and non-binge days.
- Negative mood states are related to abnormal eating practices such as binge eating.

Evolutionary Theory

The evolutionary theory suggests that the behaviours and thinking that we currently have, have adapted an advantage in our evolutionary past. It focuses on: 

- Jealousy and infidelity.
- Aggression as an evolutionary advantage.
- Cuckoldry
- Mate retention tactics - violence and vigilance
- Individual survival
- Procreation potential
- Competition for limited resources
- Competing to increase own fitness
- Natural selection
- Adaptive trait
- Group display
- Warfare

Jealousy and infidelity 

Early human males lived in fear of losing their mate to another male - something that would have devastating consequences for them in terms of passing on genes. This may have led to sexual jealousy. Male sexual jealousy was caused by the female's suspected infidelity.

Research:
- Buss et al (1992) 
- Pipat

Group Display

There is a widespread belief that people behave differently when in groups compared to how they behave as individuals. Some behaviours only occur when like-minded people come together for the same purpose. This is often seen in: 

Hooliganism and Xenophobia

Research: 
- Marsh (1978) 
- Cialdini (1976)

Territoriality

- Threat displays - Protective response to an invasion of one's territory. Aggressive displays would have been adaptive for our distant ancestors because they allowed groups to defend valuable resources associated with their territory.

Research: 
- Neave and Wolfson (2003) 
- Pollard and Pollard (2005) 

Warfare

War is an extreme course of action contradictory to survival so it must be assumed that the benefits will outweigh the cost. Male warriors have been found to be more sexually attractive to females, making them more likely to get a mate and pass on their genes. Even in modern day, men fight to secure access to women. More than 20,000 Muslim women were raped in Bosnia by the Serbs in order for them to increase the number of Serbian babies born. 

Research: 
- Lehmann and Feldman (2008) 
- Kelly and Dunbar (2001) 
- Farthing (2005) 

Warfare - Studies

Lehmann and Feldman (2008) 

Men who are stronger and more aggressive will win wars and survive to pass on genes, leading to an increasingly aggressive species. Two traits that have evolved in humans that determine the likelihood of conflict: 
- Belligerence
- Bravery 
Men with both traits have a higher chance of winning. 

Kelly and Dunbar (2001) 

Claim that bravery or heroic acts my have evolved owing to a female preference for brave, risk prone men. It is more likely that males that are willing to commit such 'brave' acts will also protect them in times of danger. 

Farthing (2005) 

Surveyed whether men and women desired physical risk tears as partners. The result was that only when the risks were considered 'brave' there was a significant advantage in mate selection. Physical risks that were not considered 'brave' were not an advantageous mate quality. 

Group display - studies

Marsh (1978) 

Football hooliganism is the human equivalent of 'ceremonial conflict' in animals and involves trials of strength over territory. 

Cialdini et al (1976) 

After a university football team had performed well, students were more likely to wear university scarves and sweaters - 'basking in reflected glory'. 

Neave and Wolfson (2003) 

Found that football teams playing at home were far more likely to win than the visiting team partly because players have the benefit of a huge surge in testosterone before the match. They believed this could be due to an evolved drive to defend home territory. 

Pollard and Pollard (2005) 

The relationship with crowd sir is unclear as the advantage had been shown to operate even with very small crowds. 

Jealousy and Infidelity - studies

Buss et al (1992) 

Procedure
- Asked male and female students the question 'what would distress you more?'
'(a) imagining your mate having sexual intercourse with someone else'
or
'(b) imagining your mate forming a deep emotional attachment to someone else'

(a) represents a threat to paternity security
(b) represents a threat to domestic paternity

Findings

- 60% of men said A
- 80% of women said B
- 40 % of males who didn't choose A - most had never experienced a committed sexual relationship and therefore unlikely to experience sexual jealousy.
- Suggests even if there is an underlying evolutionary mechanism behind male sexual aggression, it is modified by experience.

Pipat

Pipat given a decrease sentence for killing his wife dye to his young children and a 'fit of jealousy'.

Adoption - studies

Mednick et al (1975) 

From 14,000 adoptions in Denmark, it was found that a significant number of adopted boys with criminal convictions had biological parents with criminal convictions. 

Miles and Carey (1997) 

Procedure
- Meta-analysis of 24 twin adoption studies.
- Concerned with genetic basis of aggression.

Findings
- A strong genetic influence accounted for as much as 50% variance in aggression.
- Both genes and family environment were influential.
- At later ages, influence of rearing environment decreased and influence of genes increased.

Brennan and Mednick (1993) 

A series of adoption studies in which the criminal history of an adopted male was compared with criminal history of both biological and adoptive fathers, found that genetic influences were significant in cases of property crime but not in violent crime. 


Adoption studies have shown the highest rates of criminal violence in adopted children occur when both biological and adoptive parents have a history of violent crime - clear evidence of a gene-environment interaction. 

Twin - Studies

Berkowitz (1993) 

Studies from the 1930s found an average concordance rate of 75% for MZ twins and 24% for DZ. Support that genetics do influence levels of aggression. 


McGuffin and Gottesman (1985) 

Found a concordance rate of 87% for aggressive and antisocial behaviour for MZ twin pairs, compared with DZ twin pairs (72%). 
Findings also indicate that family environment, shared across siblings, exerts an important influence. 
Studies support the importance of genetic factors in aggression - but also environments that siblings share. 

Meta analysis by Mason and Frick (1994)

Procedure
- Analysed 12 twin studies involving 3795 twin pairs.

Findings 
- Approximately 50% of the difference between antisocial and non-antisocial behaviours could be attributed to genetic factors.

Coccaro et al (1997) 

In one of the twin studies, Coccaro assessed the degree of genetic and environmental influences on aggression in male participants. Data from 182 MZ twin pairs and 188 DZ twin pairs were analysed. 
Genes accounted for more than 40% of individual differences in aggression. 
Environment accounted for 50% of individual differences in physical aggression and 70% in verbal aggression. 

Genetic Causes of Aggression

XYY Karyotype

Sandberg (1961): First identified what is scientifically known as the 47 XYY Karyotype. Most individuals have 46 chromosomes (23 from each parent). Female have XX and male XY. It is possible for males to have an extra Y chromosome (making XYY).

The link between XYY males and increased aggressiveness was an early assumption that Court-Brown made prior to the examination of the patients. This point was later retracted, although it was too late because many scientists had already incorporated this incorrect view into their thinking. While the gene has actually only been proved to have effects on height and acne, but the stigma is still there and men with the XYY chromosome are assumed to be more aggressive despite research opposing this.

Research in this  area is conflicting so it is not possible to conclude that the XYY gene causes aggression. Using projective tests, Theilgaard showed that XYY men tend to give more aggressive interpretations of the images compared to XY males.

Research: 
- Court-Brown (1965-1967)
- Theilgaard (1984) 


Twin Studies

Monozygotic twins share all of their genes.
Dizygotic twins share 50% of their genes.

If a researcher compares the similarity between sets of MZ twins to the similarity between DZ twins for  a trait like aggression and finds that  MZ twins are more alike, then this likeness should be due to genetics rather than environmental factors. Most twin studies have focused on criminal behaviour.

Research: 
- Berkowitz (1993) 
- McGuffin and Gottesman (1985) 
- Meta analysis by Mason and Frick (1997) 
- Coccaro et al (1997) 


Adoption Studies

A way of studying genetic factors in aggressive behaviour is by studying children who have been brought up by adults who aren't their biological parents. Adoption studies can help to untangle the relative contributions of environment and heredity in aggression. If a positive correlation is found between aggressive behaviour in adopted children and aggressive behaviour in their biological parents, a genetic effect is implied.

Research
- Mednick et al (1975) 
- Miles and Carey (1997) 
- Brennan and Mednick (1993)