Nature vs. Nurture, Intelligence and Education

Modules 21 and 27

Learning Objectives

l To what extent is human behavior determined by genetics and the environment?

l Is it possible to measure the effects of nature and nurture?

l What do we learn from studying family members, twins, and adoptees?

l Is intelligence inherited? Is it influenced by the environment?

Methods for quantifying genetic influence

l Family studies

– Compare blood relatives who vary in the amount of genetic material that they share

– Identical twins (share 100%)

– Parent/child, siblings (share 50%)

– Grandparent/grandchild (share 25%)

l Twin studies

– Identical versus fraternal twins

Methods for quantifying environmental influence

l Adoption studies

– Compare identical twins raised together to those raised apart

– Provide information about genetics and environment

– Siblings reared together are more similar than those reared apart

l Shared vs. non-shared environment

– Even for identical twins, genetics usually accounts for less than 50% of the variability in personality, somewhat more for intelligence

Heritability of IQ

l Identical twins (100%)/together .86

l Identical twins (100%)/apart .72

l Fraternal twins (50%)/together .60

l Siblings (50%)/together .48

l Siblings (50%)/apart .24

l Adoptive siblings (0%)/together .31

Environmental influence

l Better home environments are related to higher IQ

l School attendance is related to IQ

l The Flynn effect

– Average intelligence appears to be rising

– Can’t be genetic--change is too rapid

l Reaction range

– Genetically determined limits on IQ

Are intelligence tests biased?

l Racial differences in IQ scores

– Genetic?

– Socioeconomic disadvantage?

l African-American children adopted by White families (and raised in more affluent homes) score above average

– Stereotype threat?

l When told a test is nondiagnostic, no differences

l When told the test is diagnostic, differences

– Cultural bias in the test?