intelligence I

why are ppl different?

  • behavioral genetics

    • field of scientific research that uses genetic methods to investigate individual differences in behavior

    • how related genetically you are to someone linked to how similar you are in behavior?

twin study design

twins reared apart

adoption study design

  • adopted children are more similar to biological parents

  • doesn’t mean adopted parents do not have an impact on development

nature effects

  • occur at all levels of analysis & stronger than we think

    • eye-tracking methodology

  • laws

    • all human behavioral traits are heritable 

    • effect of being raised in the same family is smaller than the effect of genes

  • heritability

    • measure of the variability of behavioral traits among individuals that can be accounted for by genetic factors

    • IQ - heritability coefficient of .5 - .7 → 50-70% of differences
      in intelligence is due to genetic factors

    • doesn’t mean 50-70% of one’s intelligence is genetic

environmental effects

  • parenting

  • law

    • substantial portion of the variation in complex human behavioral traits is not accounted for by the effects of genes or families

  • adoption studies

    • study of children adopted into high socio-economic status (SES) families

      • compared to new adopted siblings

      • compared to biological siblings who were not adopted

    • adoption & SES has positive effects on IQ, school performance

  • just bc a trait (intelligence) is heritable, does not mean environment doesn’t matter

    • ex) human height

      • height is highly heritable

      • but environment can still have a big effect

  • flynn effect

    • trend of rising IQ scores over past 120 years

    • what accounts for it

      • unlikely a genetic effect

      • differences in nutrition, health, schooling, environmental quality

      • increase reliance on analytical thinking

    • birth order effects on IQ

      • older siblings reliably score higher on IQ tests bc of:

        • unlikely a genetic effect

        • differences in parenting, stimulation, resources

        • role of teaching the younger siblings 

IQ tests

  • predictive validity

    • extent to which a score on a scale / test predicts some
      outcome measure of interest

  • IQ predicts

    • academic achievement

    • job success

    • salary & wealth

    • happiness

    • health & longevity - higher = alive longer

2 factor theory of intelligence - spearman

  • diff IQ subtests were positively correlated

    • correlation driven by general intelligence (g)

  • g is supplemented by specific intelligence (s), specific to the subtests

crystallized & fluid intelligence

  • crystallized intelligence (gC)

    • ability to apply knowledge that was acquired through experience (vocabulary, facts)

    • ex) to be choleric is to be___ (MCQ)

  • fluid intelligence

    • ability to solve & reason abt novel problems

evidence crystallized & fluid intelligences are distinct

  • exhibit diff developmental trajectories

    • fluid decreases w age

    • crystallized increases w age

  • have diff neural correlates

    • fluid

      • dorsolateral prefrontal cortex

      • damage to this impairs fluid intelligence, not crystallized

      • connection between frontal & parietal areas → parieto-frontal integration theory)

    • crystallized

      • less obvious neural correlate (more distributed across neocortex)

      • alzheimer’s disease likely to impact crystallized, not fluid