Hi Jay, Is your argument on the flaw of twin studies based on the EEA? I am under the assumption that twin researchers assess environment not just as shared but as non-shared environment. In actuality, non-shared environment has been well-established even within previously assumed ‘shared’ environmental factors such as parental negativity. The EEA surely suggests that the effect of twinning (which may elicit similar environments such as an evocative genotype-environment correlation) does not account for variance between MZ and DZ twins? So differences between MZ twins are equated to non-shared effects, within the family and without, and similarities are genetic and shared environmental factors. Twins reared separately shows us that the importance of genetics and the lack of importance of shared environment in that it matters little. Or is the EEA here still infringed? Thanks, Fred.