Genetics of Personality and Intelligence Causes of Personality: Environmental Factors · "Give me a dozen healthy infants, well-formed, and my own specified world to bring them up in and I'll guarantee to take anyone at random and train him to become any type of specialist I might select ... " (Watson 1924/1931, p. 104) · Environment mattered for generating outcome of peoples lives . Based on the environments you can dictate the outcome of an individual . Criticizes the innate view on personality, not unaware of their view Causes of Personality: Biological Factors . "Of course, genes can't pull the levers of our behaviour directly. But they affect the wiring and workings of the brain, and the brain is the seat of our drives, temperaments and patterns of thought. Each of us is dealt a unique hand of tastes and aptitudes, like curiosity, ambition, empathy, a thirst for novelty or for security, a comfort level with the social or the mechanical or the abstract." - (Steven Pinker) · Behaviour has a biological basis · Genes don't entirely give rise to personality, but differences in genes give different brain which results in different personalities Classical Twin Design · Uses identical (or monozygotic) and nonidentical (or dizygotic) twin pairs · Monozygotic - Identical twins, single egg fertilized by single sperm then splits into two · Dizygotic - Fraternal twins, separate eggs fertilized by separate sperm Prediction 1: If genes are all important . If differences were entirely based on genetics, the similarities between MZ would be 100% where as DZ would be 50% . MZ share all their genes so based on genetic theory they should be almost identical in personality · DZ share half of their genes therefore based on genetic theory they should be approximately 0.5 correlated Prediction 2: If shared environment are all important · The environment individuals are exposed to drives the personality, both MZ & DZ twins should correlate to almost 100% · Personality should be essentially identical, genetic make up is irrelevant. Prediction 3: If unique-environments are all important · Unique Environment = environmental situations which occur to one individual (fatal injuries) · If 'unique' events cause personality the correlation between twins (MZ & DZ) should be non- existent, no correlation
Bouchard 2004 · Eminent behavioural psychologist · Tables in slides · Reviewed different personality traits against heritability (how large genetic effects are to explain the differences in a given sample) . Heritability rated from 0-1: at 1 all of the differences were explained by genetic similarities, 0 no genetic underpinning · Shared Environmental Effect (SEE): the environment stimulus which are important to shaping personality . SEE is 'No' across all traits, twin design displays very little evidence that environment heavily underpins similarity in personality · Also reviewed intelligence, stratified by age . Heritability of intelligence is more heavily affected by genetics as individuals grow older, H. rate gets higher over the years . SEE effected initially in first 10 years but does not matter in