It’s also not clear what selection effects adoption has;
Also, probably the effects of nurture contribute to keeping their average IQ that low; it seems unlikely to me that the fact that the average IQ of African Americans is 22 points higher is entirely due to the European genetic admixture in the latter. (EDIT: And I hadn’t even noticed you mentioned Ethiopians have lots of Caucasoid ancestry too!)
Also, probably the effects of nurture contribute to keeping their average IQ that low; it seems unlikely to me that the fact that the average IQ of African Americans is 22 points higher is entirely due to the European genetic admixture in the latter. (EDIT: And I hadn’t even noticed you mentioned Ethiopians have lots of Caucasoid ancestry too!)