intelligence 2

intelligence 2

1. heredity

   • intelligence is determined by genetic factors and the environment has no effect McGurk (1975)
   • heritability estimates
     • proportion of trait variability in a population due to variations in genetic inheritance
     • group statistic says nothing about individuals
     • heritability is aout variables not averages
     • can be changed
   • evidence
     • Twin Studies: show identical twins more similar in intelligence than fraternal (intelligence therefore at least partly inherited)
     • • McCartney et al (1990) meta analysis studies, found mean correlation for identical twins +.81 and +.59 for fraternal twins

2. enviroment

   • flynn effect
     • IQ has risen all over the world in late 20th century in all ages
   • Adoption studies show some similarity in IQ to foster parents/adopted siblings (Scarr & Weinberg (1976
   • IQ scores correlate with house environments
   • Environmental deprivation and environmental enrichment shown to influence intelligence
     • depriation
       • Lack of stimulation (Gottfried, 1984- meta analysis) Skeels (1938,1966)
       • poverty, malnutrition, illness may all lower IQ (Sternberg et al 2000)
       • lack of resources, difficulty acquiring skills, concentration affected, different reward system
     • enrichment
       • special educational programmes e.g. Operation Headstart (Lazar & Darlington (1982)
       • birth order (Confluence Theory - Zajonc & Markus 1975)
       • other environmental factors
         • length of time in school
         • familly background
         • quality of education
         • factors in the home
         • Child’s IQ score not predictive of adult IQ until 4 years (Bloom 1964)

3. the role of heredity and environment

   • widely controvercial
   • argued thee is a reaction range, Reaction range - upper and lower limits to intelligence set by genetic makeup (Scarr 1991)
     • range estimated to be 20-25 points (Weinberg (1989)

4. group differences

   • Jensen (1969) - ethnic differences in IQ due to heredity
     • Herrnstein & Murray (1994) Bell Curve - basically same view
     • African-Americans score average 15 points less than Caucasians
     • •however, differences reduce over time so must be environmental causes (Williams & Ceci 1997)