Genetics of Personality and Intelligence Causes of Personality · Watson (1924/1931, p. 104) "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 ... " · Pinker "Of course genes can't pull the levers of our behavior 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." Which perspective is correct? Twin and family study designs - relationship between genes and personality has been made by looking at similarities and differences between populations of individuals to assess the influence of shared genes in personality · Family studies - on their own tell us little because all children share an estimated average of 50% of their genes with each of their parents and brothers and sisters. Also, using observation, interviews and questionnaire measures are problematic because similarities between personalities might be because of environmental influence e.g. extraverted son might be like his extraverted father because he copies his father's behaviour. This is solved when we consider occasions where families don't typically share genes in this way ... · Classical Twin Design - uses identical ttor monozygotic - share all their genes) and non-identical ttor dizygotic - share half their genes) twin pairs. - If genes are all important, MZs would be 100% similar and DZs would be 50% similar. If shared-environments are all important, both MZs and DZs would be 100% similar. If unique-environments are all important, both MZs and DZs would be 0% similar. What does literature tell us? · Bouchard (2004) shared environment more important in younger till around age 10 then genes have a bigger influence in intelligence, found in Dutch cross-
sectional twin data. Heritability found for personality traits but no effect of shared environment. · Loechlin & Martin (2001) compared Eysenck's personality scales given to 5,400 pairs of twins from the Australian Twin Registry. Heritability ranged from 0.47 to 0.28 for extraversion, neuroticism and psychoticism respectively. Similar sized heritability statistics have been computed from twin studies using the FFM of personality in the US and Canada with a range from 0.33 to 0.58. This suggests that personality is influenced by genetic factors. . Plomin & Deary (2015) a meta-analysis of 11,000 pairs of twins shows that the heritability of intelligence increases significantly from childhood ttage 9) to adolescence ttage 12) and to young adulthood ttage 17). · Deary et al. (2012) compared results of 1940 PPs in childhood (11 yrs) and in old age (65, 70 0r 79) and found the stability of cognitive ability from childhood to old age has a genetic contribution estimated at 38% of the