Biological explanations: Genetic factors Flashcards
(33 cards)
Genetics
When looking at how genes affect aggression; this is effectively asking the question of Nature vs Nurture.
The main ways the role of genes in aggression has been examined is through the use of Twin Studies, Adoption Studies and looking at Individual Genes that may play a role.
Twin studies
In twin studies; identical twins are compared between non- identical twins for levels of aggression between them. This is be- cause identical twins share the exact genetic makeup as each other while non-identical share only up to 50%.
If identical twins have more similar levels of aggression then it is thought to be due to genetics.
Adoption studies
Adoption Studies have looked at examining levels of aggres- sion between adopted children and that of their biological parents. If a positive correlation is found between adopted children and their biological parents then a genetic effect is implied. If a positive correlation is found between the adopted children and their rearing family; a environmental effect is implied suggesting aggression may be due to learning.
McGuffin et al (1985)
- In humans aggressive behaviour is more highly correlated with identical twins than in fraternal twins.
- McGuffin found a concordance rate of 87% for ASB for MZ’s compared to 72% for DZ twins.
Evaluation of McGuffin et al.
At first glance they support genetics in ASB and aggression.However, these findings indicate that the children are bought up in equal family environments (but it’s diff for MZ’s generally)
Mason & Frick (1994)
-Meta-analysis of 12 twin studies (and 3 adoption) involving 3795 twin pairs. They found that 50% of difference between ASB and non-ASB could be due to genetics. (larger estimates of genetic influence)
Evaluation of Mason & Frick.
- Meta-analysis means much larger sample than singular study, so potentially cancels out methodological weaknesses in some studies.
- But again twin studies are criticised for assuming equal shared environments.
Coccaro et al. (1997)
- Investigates specifically aggressive behaviour rather than ASB or criminal convictions.
- Assessed the degree of genetic and environmental influences on aggression in males.
- Data from 182 MZ’s and 118 DZ’s
- Found that genes accounted for 40% of agg
- Environmental influences on physical agg= 50%
- Environmental influence of verbal agg= 70%
Evaluation of Coccaro et al.
- Accounts for both genetic and environmental factors
- Again assumes brought up in equal environments
- Also accounts for different types of aggression.
Hutchings & Mednick (1973)
- Reviewed 14000 adoptions in denmark.
- Found a sig positive correlation between the number of convictions for criminal violence among the biological parents and that of their children who had been adopted.
Evaluation of Hutchings & Mednick.
- Very large sample so good external validity
- Adoption study so accounts for how genetics are related to environment.
- However the environment could be a factor here with adopted children having a more difficult time adjusting to their environment, learnt behaviour from biological parents previously or even the stigma that is attached with being adopted affecting how they are treated by friends, family and even how they view themselves.
Rhee & Waldman (2002)
- Meta-analysis of 51 twin and adoption studies comprising of over 87000 individuals.
- ASB operationalised (behavioural aggression, delinquency, psychiatric diagnoses)
- Genetic influence = 40%
- Environmental influence = 60%
- Little evidence of gender differences.
Evaluation of Rhee & Waldman.
- Issues with reporting; these studies included self-reports or reports of pps of similar aggression levels.
- For instance sig differences were found between methods. 39% showed aggression with self reports, and 53% where assessment was done by another person. Shows that method of assessment plays a role in estimates of genetic influence.
- Large sample = good external validity.
Overall conclusions of research on twins and adopted children.
- Genetics alone don’t cause aggression, but they may predispose people to aggression.
- Rhee & Waldman suggest that environment is slightly more telling in whether someone will become aggressive.
- Genes perhaps play more of a roles where violence is more serious (Mason & Frick)
Why there may an issue with self reports:
- Rhee and Waldman’s study showed that self-reports compared to others assessing the child’s aggression has a significant difference.
- This could be due to the fact when one twin is assessing the other, they use their aggressive twin as a baseline comparison for themselves and so mark themselves low in comparison.
Evaluation points: Equal environments.
-One major issue with twin studies is that many researchers assume that MZ and DZ twins raised in the same homes will experience equal living environments. However research has shown that adults (such as teachers, carers, parents) would be more like to treat MZ’s more similarly than DZ’s. This is because they look so much alike, society tends to treat them as the same person.
Evaluation: The imperfect nature of twin studies.
-Finding large numbers of MZ twins who are reared apart is extremely rare, therefore researchers must compare MZ’s to DZ’s. However Mz’s are generally treated more similarly than DZ’s. Consequently twin studies are not the perfect genetics versus environment experiment that we would like to imagine.
Evaluation: Problems with interpretations of adoption studies.
-One methodological problem is that same countries, such as new zealand +the us, have a higher rate of ASB at the time of adoption than the general pop (sharma et al). Tremblay (2003) maintains that parents who give their child up for adop have higher trends of ASB themselves. Therefore correlations could be due to either genetics, or growing up with ASB parents (environment) prior to adoption and also the feelings of abandonment.
Individual genes (MAOA)
Individual genes have also been examined and some candi- date genes have been identified that may play a role. MAOA is a gene that regulates the metabolism of Serotonin which low levels of such have been associated with aggressive impulsive behaviour. A faulty variant of the gene however could result in low levels of serotonin and thus lead to such aggressive behaviour.
MAOA Description
- MAOA is an enzyme that breaks down neurotransmitters; noradrenaline, serotonin, and dopamine.
- If the gene responsible for producing MAOA is defected, then these neurotransmitters are not broken down, leaving excess amounts in the bod.
- Each are thought to increase aggression, for instance serotonin and dopamine imbalance are common in aggressive patients.
Brunner et al. (1993)
- Conducted a study examining a dutch family who had a history of many of its male members involved with serious violent crimes (rape, Arson). Studying them low levels of MAOA were found and later a defective gene was identified in the male members.
- The defect of MAOA was found in all violent men but none was found in the nonviolent members.
- Brunner et al. believe that excess neurotransmitters may predispose the men to violence under stress.
Evaluation of Brunner et al.
Limited influence of gene- It’s unlikely that there is a causal relationship between a single gene and specific behaviour. Genetic deficiencies may exert some influence but not the sole cause.
-Environmental factors-
similar behaviour could also be explained due to similar exposure and learning from role models within the family influencing behaviour through SLT
-Only male members were tested and found to generally have aggressive traits however none of the female members were checked nor were they commonly found to have aggressive tendencies despite having a 50% chance of carrying the gene.
Caspi et al. (2002)
-Looked at role of environment in predicting aggressive, antisocial behaviour, specifically at severe childhood maltreatment.
-Those with low levels were associated with higher levels of aggression however only if they were maltreated previously.
Those with high levels of MAOA and were mistreated and those with low levels of MAOA and were not mistreated did not exhibit any anti-social behaviour.
-Tested only 442 individuals
Conclusion of Caspi et al.
- Low MAOA on its own did not lead to aggression, maltreatment during childhood was weakly associated with later aggression.
- If a child has a defect of MAOA and the child is subjected to maltreatment, then they will likely show and conduct ASB and have a predisposition towards violence.
