* Identical twins have a much higher correlation coefficient of intelligence than fraternal twins (table 5).
* Identical twins raised apart have a correlation coefficient for intelligence of around .73 (MZA studies).
* Correlation coefficients of IQs of biologically unrelated siblings raised in the same adoptive environment are approximately 0.
There are obvious confounds the paper mentions:
* Fraternal twins may not have identical environments.
* Adoptive environments may not represent typical parenting environments.
* Some of these studies have had poor controls and practices.
* Distribution of results from studies looks bimodal which indicates something weird is going on.
Still, even if you take the most critical view I think you have to accept that there is still substantial heritability of intelligence. These results cannot be convincingly explained any other way.
IQ is not a perfect metric, but it is a decent predictor of many outcomes.
> the confounding factors of upbringing
This is why you do twin studies and studies using adoption as a control. We have quite a wealth of them. A good critical review of the evidence on both sides is here: https://humanvarietiesdotorg.files.wordpress.com/2013/05/the...
* Identical twins have a much higher correlation coefficient of intelligence than fraternal twins (table 5).
* Identical twins raised apart have a correlation coefficient for intelligence of around .73 (MZA studies).
* Correlation coefficients of IQs of biologically unrelated siblings raised in the same adoptive environment are approximately 0.
There are obvious confounds the paper mentions:
* Fraternal twins may not have identical environments.
* Adoptive environments may not represent typical parenting environments.
* Some of these studies have had poor controls and practices.
* Distribution of results from studies looks bimodal which indicates something weird is going on.
Still, even if you take the most critical view I think you have to accept that there is still substantial heritability of intelligence. These results cannot be convincingly explained any other way.