Good podcast," but Richard Haier gives a misleading account of the early adoption studies (around <a href=""https://www.youtube.com/watch?v=hppbxV9C63g&amp;t=2h05m58s"">2:05:58</a>). Adoption from a highly problematic background (low-IQ dysfunctional natural parents) into highly functional middle class families had a huge effect on the group IQ of the adopted children", who scored much higher than their natural siblings who had stayed with the mother and also much higher than their mothers, even though they correlated with their mothers with regard to the individual differences between the adopted kids. This correlation with their mothers does not at all mean that adoption had no effect, only that the IQ-raising effect of adoption from a low to a high IQ household did not obliterate preexisting genetic differences between the kids. As it is always both nature and nurture, this can hardly be surprising.  As a group, the adopted children, all from low <del>IQ</del> natural families,  scored intermediate between their natural families and their adoptive parents and siblings. This was probably as high as their potential from genes and uterine environment and immediate post natal environment allowed, i e they had lower potential than their adoptive siblings. Adoption from a problematic environment to a good environment was the treatment given to all of the children in the study, and the effect of the treatment is properly tested with a t-test between the adopted kids and their natural mothers or the siblings who had stayed home, not with correlation coefficients. The effect was on the high side for psychological interventions, but will have been attenuated over time when the children grew older and their environment became more self-selected (gene-environment interaction).