Emily A.Willough and James J.Lee:

Highlights
Genetic and environmental sources of variance in IQ were estimated from 486 adoptive and biological families

Families include 419 mothers, 201 fathers, 415 adopted and 347 biological fully-adult offspring (M age = 31.8 years; SD = 2.7)

Proportion of variance in IQ attributable to environmentally mediated effects of parental IQs was estimated at .01 [95% CI 0.00, 0.02]

Heritability was estimated to be 0.42 [95% CI 0.21, 0.64]

Parent-offspring correlations for educational attainment polygenic scores show no evidence of adoption placement effect