Genetic Explanations

• the assumption of biological approaches is that behaviours, including aggression, are down to our genetic makeup
• Coccaro et al (1997) found that 50% of the variance in aggression could be attributed to genetics
• adoption studies allow us to separate environment from genetics. if adopted children and their biological parents demonstrate similar behaviours a genetic link is implied. if adopted children and their adoptive parents demonstrate similar behaviours an environmental link is implied
• Hutchings and Mendick (1975) studied 14,000 adoptions in Denmark. they found that a significant number of adopted boys with criminal convictions also had biological parents with conviction for violent crime. this is evidence of a genetic basis for aggression
• Rhee and Waldman (2002) conducted 51 twin and adoption studies. they found that anti-social behaviour is largely related to genetics. they also found that there is a variance with age and assessment method
• Miles and Carey (1997) conducted 24 twin and adoption studies and found that genetics accounts for as much as 50% of the variance but there's more likely to be an influence on behaviour as the individual gets older
• monoamine oxidase A (MAOA) is an enzyme that regulates the metabolism of serotonin in the brain. a family in holland that had high number of male members with serious violent criminal record was found to have abnormally low levels of MAOA
• Caspi et al (2002) studied 500 male children and identified two variants of the MAOA gene, MAOA-L low levels and MAOA-H high levels. those with MAOA-L variant were more likely to grow up and exhibit anti-social behaviours. but, only if they had been maltreated as children
• MAOA-L is much more prevalent in population with a history of warfare. for this reason, it has become known as the warrior gene
• Tilhonen et al (2015) studied Finnish prisoners and found that those that had both MAOA-L and CDH13 were more likely to have committed serious violent crimes. there was no evidence of this combination in non-violent criminals
• the MAOA gene is related to the X chromosome. men have one X chromosome while women have two which means that men are more vulnerable to the effects of an abnormality
• research on genetic explanations for aggression sample individuals with criminal convictions for violent crime. the problem with this is that a lot of violent crimes go unreported, so lots of aggressive people haven't been studied
• genes very rarely work alone so singling them out is not easy.​ usually, a great number of different genes contribute to any given behaviour or trait.​