Behavioural-Genetic Studies Have Shown That

Behavioural-genetic studies have shown that:

A) for children and adolescents, heritability estimates average around 0.75; that is, about three-quarters of the variance in IQ scores is explainable by genetic differences.
B) for adults, heritability estimates average around 0.45 to 0.50; that is, about half of the variance in IQ scores is explainable by genetic differences.
C) the scores of fraternal twins reared together are more highly correlated than the scores of identical twins reared apart.
D) as adopted children grow into adulthood, the correlation between their IQ scores and those of their biologically unrelated family members diminishes to zero.