and guessing a combination of genes and environment is weird when there’s only actual evidence of one and not the other.
In response to the Bell Curve controversy, a large number of intelligence researchers, the best in their field, authored a letter to the New York Times on the state of the scientific consensus about intelligence, genes and environment. The conclusion of over 100 top experts in the field was that intelligence was caused by a combination of genes and environment. So that was the consensus of the top experts in the field ~15-20 years ago. So my conclusion is not weird at all. In fact, it is consensus in the field and in the 18 years since, the consensus has only gotten stronger.
And I believe the twin studies are excellent evidence for a genetic role in IQ. Identical twins raised apart were very close in IQ.
Monozygotic twins correlate very highly on IQ. I believe it is .7
Dizygotic twins correlate quite a bit lower and siblings have an even lower correlation.
In families where you have one or more of the types – MZ twins, DZ twins and siblings, they are obviously all being raised in the same environment.
There are other things too. Black kids adopted away into upper middle class White homes crash back down to 89 IQ by adulthood.
Korean kids adopted into White homes end up with 109 IQ’s, higher than their adopted family and much closer to their birth families. The IQ’s of the Korean adoptees were also higher than for their siblings in the adopted family. The children of the adoptee family had IQ’s that looked like their parents. The Korean kids had IQ’s that looked like their birth parents and the Korean kids were smarter than the White nonadoptee siblings even though they were all raised together.
Kids adopted away have IQ’s that are a lot closer to their birth parents than to the adopted family in which they were raised.
Black people’s IQ scores go up as they get lighter. The more White they have in them, the higher the IQ.
African immigrants to the US have IQ’s of 108. However, their children born in the US have IQ’s of only 89. What is going on here is that the children’s IQ’s are regressing down towards the African genetic mean.
All of that looks excellent evidence for genetic effects on IQ to me.
