As you can see in the linked Wikipedia article, in developed countries, adult IQ is more heritable than child IQ. This is not consistent with IQ differences being primarily environmental. If they were, we would expect IQ to become less heritable as environmental factors such as “two decades of very expensive private schooling” accumulate over time.
In poor countries, IQ is on average lower than in developed countries, and idividual IQ differences are less heritable, and they tend to be correlated with observable environmental factors such as malnutrition and infectious diseases.
These observations are consistent with a model where genetic factors largely determine a maximum potential IQ and environmental factors determine how much of this potential people actually reach and how fast they reach it. In developed countries, most people eventually reach a level close to their genetic potential, but people from a more advantaged background reach it faster. In undeveloped countries, environmental factors have a much larger impact and only few people reach their genetic potential. This is probably complicated by epigenetic factors that make the environmental influences carry over, to some degree, to one or two generations.
Human stature follows similar patterns of heritability.
As you can see in the linked Wikipedia article, in developed countries, adult IQ is more heritable than child IQ.
This is not consistent with IQ differences being primarily environmental. If they were, we would expect IQ to become less heritable as environmental factors such as “two decades of very expensive private schooling” accumulate over time.
In poor countries, IQ is on average lower than in developed countries, and idividual IQ differences are less heritable, and they tend to be correlated with observable environmental factors such as malnutrition and infectious diseases.
These observations are consistent with a model where genetic factors largely determine a maximum potential IQ and environmental factors determine how much of this potential people actually reach and how fast they reach it.
In developed countries, most people eventually reach a level close to their genetic potential, but people from a more advantaged background reach it faster. In undeveloped countries, environmental factors have a much larger impact and only few people reach their genetic potential.
This is probably complicated by epigenetic factors that make the environmental influences carry over, to some degree, to one or two generations.
Human stature follows similar patterns of heritability.