Genetic factors of aggression

Bio approach to agg- belief that agg beh is determined by genetic makeup- researchers test this by seeing if related indi's are similar in their agg tendencies more than non-related indi's. G explanations suggest - genetic abnormalities =aggression , by causing a change n one's brain development ie change in NT levels and the function/structure of brain OR change in development of endocrine system - hormone levs. 

XYY Karyotype: men w exra Y chromosome- more agg, as extra Y is male + agg is widely considered a masculine trait. 

-Sandberg 1961- identified the 47 XYY karyotype - research from court brown found that those that were XYY = mroe agg - but these chromosomal abnormalities have only shown weak correlation w agg. 

lots of supportive emperical evidence- testable + a STRENGTH

-Lagerspetz (1979) - bred 25 generations of mice - in each gen, mated most aggressive+least agg mice. This led to super agg mice on one hand, and docile mice on the other. In order to get over the issue that mice may have been agg by being raised by agg parents, rather than thru genes, some agg mice raised by docile parents+they remained agg! 

-supportive-> findings eliminate the potential exp of the social learning theory in explaining agg beh. Findings suggest even w environmental influence  of docile parents, the agg beh does not  change-- there is a genetic factor! - strengthens credibility of the theory genetic factors influence agg beh
- MICE- cannot extrapulate findings onto humans 

IDA: reductionist; does allow for genetic basis of agg to be explored- but limits limits ur understanding of agg beh to a sole influence of genetic makeup - fails to consider there may be exceptions - we may have other influences! Caspi et al (2002) suggested gene-environment interaction - genes influencing which environmental factors influence behaviour. Therefore- genetics on its own is inadequate- explanatory power reduced.

Court brown study 1967- 300 hosp patients . 
Patients w XYY karyotype found to display more agg beh than those without XYY. supports the theory, that this defect can cause agg beh and is supportive as a genetic explanation.

Lacks historical validity! Modern studies show an inconsistent link between genetics and aggression- therefore results could be down to experimenter effects- bias of previous knowledge between testosterone+ agg. Coincides w old-fashioned considerations of the era that agg is a more masculine trait! weakens its credibility!
- large sample- good pop validity of patients 

No individual gene for aggression- gene responisble in producing protein called monoamine oxidase A (MAOA) has been associated w aggressive behaviour - MAOA regulates the metabolism of serotonin in the brain+ low levs of serotonin are associated w impulsive+agg beh. 

AO2:
Brunner et al- dutch family - male members especially aggressive, being charged w offences like ****+ arson- later found that they actually had low levs of MAOA- supports theory (signpost). Shows inheritance of the gene within a family of related indi's however, case study- idiographic, hard to extrapulate- low ext val. 

Caspi et al- 500 male children - found that children who had defect only expressed agg bhe if they were maletreated at home! Suggests that presence of agg is an interaction of gene + environment- example of nature vs nurture debate in the diathesis stress model. Big sample size= good pop val, but all male - beta bias- how would females behave as a result of this defect? how different would the expressions of aggresison be? 

-difficult to determine the role of genetic factors- agg is a polygenic characteristic + therefore not dependant to one gene - defect in one gene may not inevitably cause aggression! 

SSR- major reprocussions- abortions of those w genes? this could be considered ethically catastrophic- should we impriosn those w gene if they are more likely to commit crime- this notion would ignore the idea that we have the free will to exert control over our behaviour and we are not solely driven by our egens- determinisitc. eg a boy who has gene and watched mother beaten may choose to NOT engage in such behaviour- exerts free will. this deterministic view IRL could lead to those w gene to be cleared by legal system bc of genetic dispostion - the explanatory powers of genetic exp reduced- bc we have FREE WILL.

Gender bias- research mainly male p's, high levs of beta bias. females do act aggressively and research should test to see if gene defects such as extra Y and MAOA gene have the same effects as they do on men on women.