The largest environmental suppressor of IQ is violence. Instead of grouping the studies by race why not group them by use of corporal punishment. My hypothesis is that you will see an even greater delineation.,(reply>), This would also explain IQ drift. As society becomes less violent, IQ drifts upwards.,(reply>), I would also argue that even the decision to group people by race and not any one of the innumerable other potential variables, if not racist, is at least indicative of a racially delineated view of humanity.