> difficulty of defining an objective measure for intelligence IQ is not a perfect metric, but it is a decent predictor of many outcomes. > the confounding fa

> difficulty of defining an objective measure for intelligence 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-effects-of-shared-environment-on-adult-intelligence-a-critical-review-of-adoption-twin-and-mza-studies.pdf 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.