Genetic and Environmental Influence on Intelligence

Is it in the Genes?

• Heritability – extent to which intelligence test score variation can be attributed to genetic variation (Is it inherited?)

• Intelligence runs in families…Does that mean intelligence is inherited or fostered by our environment?

• The big question…AGAIN…• What do you think would be the best way to

test this?

Is it in the Genes?

Twin & Adoption Studies• Intelligence test scores of identical twins raised

together are as similar as the same person taking the test twice

• Brain scans show identical twin brains are built and function similarly

• Some genes have been identified, but intelligence involves many genes and the combinations

Twin & Adoption StudiesDoes this chart support nature or nurture?

Or is it the environment?

Twin & Adoption Studies• Adoption enhances IQ scores of neglected

children• When environment is varied, environment is

more predictive of scores (often occurs with less-educated parents)

What do you think?

Twin & Adoption Studies• Studies have compared biological/adoptive/

twins/not twins…• Do you think kids become mentally more like

their biological parents or their adoptive parents?

• Genetic influences, not environmental become more apparent with age

Environmental Influences• Genes make a difference, but life experiences do

too• Early Environment– Studies of impoverished orphanages showed extreme

deprivation destroys native intelligence– Low-economic schools often have less qualified

teachers – leading to lower achievement scores– Malnutrition also contributes to the decline– No studies support any way to “fast forward” intellect

• Study compared Baby Einstein users to control group = no difference in word-learning

Environmental Influences

Schooling and Intelligence• Schooling does enhance later income• College – study motivation and skills are as

good as previous grades to determine academic achievement

• Motivation – when promised money for doing well, adolescents score higher on tests

• The brain is like any other muscle – it grows stronger as neuron connections grow