IQ is the last taboo. We don't want it to matter for socioeconomic success in life. We don't want it to be inherited to such a high degree that environmental factors like parenting and education hardly matters. Its all too depressing. People are born unequal, and there is little that can be done about it.
IQ correlation studies:
Same person (tested twice) .95
Identical twins—Reared together .86
Unrelated children—Reared together—Adults .04
https://en.wikipedia.org/wiki/Heritability_of_IQ#Correlation...