Recent adoption studies of IQ.

At least a half-dozen adoption studies of intelligence or related traits (such as socioeconomic status) have been reported in the past three or four years. They have yielded somewhat divergent findings, but the majority of the studies continue to provide evidence of a substantial genetic contribution to family resemblance in IQ. The recent studies have generally reported lower overall correlations among family members than were obtained in the classical adoption studies. The restricted IQ range in the samples of the recent studies may be responsible for this difference.