Twin studies typically compare identical and fraternal twins to eliminate such environmental factors (Obviously there are still errors, but they generally wind

Twin studies typically compare identical and fraternal twins to eliminate such environmental factors (Obviously there are still errors, but they generally wind up as counting towards environmental). And of course polygenetic factors probably have a sort of necessary-but-not-sufficient type of relationship with the traits they contribute too, but that doesn't mean that anything that isn't pegged to a single gene can be thought of as environmental.