Yeah but some comparisons suck. If you measure the IQ for the same ethnicity you will notice that the IQ changes over time. Having proper levels of iodine is

Yeah but some comparisons suck. If you measure the IQ for the same ethnicity you will notice that the IQ changes over time. Having proper levels of iodine is responsible for about 15 points of IQ. Removing lead from fuel, some extra increase. Pollution, nutrition, water purity, all the accrued knowledge about fetal and child development that is applied in modern economies, etc. plays a role. Also, there are negative factors like exposure to violence and trauma, substance abuse, which is correlated with poverty and inequality... which is a legacy of slavery, racial segregation, etc.