Perhaps the single best piece of evidence is support of racially genetic differences in IQ is the Minnesota Transracial Adoption study which was interpreted by Richard Lynn (in his 2006 book Race Differences in Intelligence: An Evolutionary Analysis) as showing that the U.S. black-white 15 point IQ gap is 100% genetic, because in this study, even when whites and blacks are both adopted into white upper class homes, more than the full IQ gap remained.

However as commenter Race Realist reminds me, recently the study has been undermined by British physicist Drew Thomas who argued that one reason adopted whites scored so much higher than adopted blacks is that the white sample suffered from attrition.  Thomas writes:

 A total of 25 White adoptees were in the study when it began, nine of whom were lost at follow-up. The lost adoptees had relatively low IQs, so the remaining White adoptees were unrepresentatively high in IQ, as Mackintosh observed [25]. One can prove this by comparing the original IQs of the full sample and the subgroup who were measured at both ages 7 and 17; the latter subgroup had an initial mean IQ of 117.6 (with a minimum IQ of 92) but the full sample had an initial mean of 111.5 (minimum 62). Because initial and final IQs had a correlation of 0.63 among the White group, the elite subgroup would likely have had their final mean IQ inflated by about 0.63 × (117.6 − 111.5) = 3.8 points. Meanwhile, the BW and Black–Black adoptees lost to follow-up hardly differed in IQ from the remaining adoptees, so attrition inflated those groups’ mean IQs by about only 0.2 and −0.7 points respectively.  Adjusting the final mean IQs accordingly (Table 2) implies smaller racial differences of 3.5 points (White vs. BW adoptees) and 11.7 points (White vs. Black–Black adoptees) in the study’s final wave.

The figure that most interests me in this study is not the black-white IQ gap, but the IQ gap between whites and half-blacks.  The reason is the black kids, despite being adopted into an upper middle class white home, still had a black prenatal environment, and were adopted at older ages on average, but the half-black kids not only were raised in a white upper middle class white home, but had white prenatal environments (white biological mothers), so I interpret the estimated 3.5 IQ gap between them and adopted whites (also raised in upper middle class white homes) to be 100% genetic.
Since African Americans average about 74% black ancestry, African Americans with white biological mothers might average about 37% black ancestry.  So if 37% black ancestry causes them to score 3.5 points lower than whites when both prenatal and home environment are fairly controlled.  it suggests that 74% black ancestry (a typical African American) would cause them to score 7 points lower.
Thus contrary to proving the U.S. black-white 15 point IQ gap is 100% genetic as some thought,  I now think the Minnesota study shows it’s only around 50% genetic, and that if the average  African American had the exact same prenatal and home environment as the average white, their IQs would rise from 85 (white norms) to 93, compared to the white American mean set at 100.
As I reported back in May 2016, a 7 point IQ gap is about what you’d expect from the racial differences in brain size observed in the United States.
If races as genetically distant as blacks and whites differ so little in genetic IQ, it suggests that all racial IQ gaps are a lot less genetic than most HBDers think.
Advertisements