One reason these studies might all turn up the same result is that they all are looking at the same correlation. I’m not sure they do give the same result, either.

You cite an article from 2000, which contains the memorable passage regarding the Human Genome Project: “What should we expect from this endeavor? Behavior geneticists anticipate vindication: At long last, statistical variance components will be rooted in the actual causal consequences of actual genes. Critics of behavior genetics expect the opposite, pointing to the repeated failures to replicate associations between genes and behavior as evidence of the shaky theoretical underpinnings of which they have so long complained.” As far as I know, none of that came true. In place of “actual genes” was substituted this GREML stuff, which is the sort of high-R-squared-means-good-model methods economics threw out in the 1970s. At least the referees at PNAS made them write it up as a correlation that “possibly corroborates” these other theories. You might consider citing it accordingly.

Wouldn’t misidentified identical twins still look very much alike? If one was tall, the other would be tall, and plenty of research has shown that height correlates with how people treat you. They would have the same eye and hair color, similar skin tones, similar features- unfortunately, these all predict how people treat you, too. …

What exactly does it mean to find “misclassified” identical twins- wouldn’t they likely have some idea they were identical? Might these shared characteristics lead them to identify with one another more than fraternal twins?

The similarity between misidentified identical twins is one of the features the researchers are after. They want fraternal twins that are treated like identical twins, meaning that they have equally similar environments. If the misidentified identical twins identify with each other as identical twins do, that’s also good for the test.

Don’t identical twins have different in utero experiences than fraternal twins, whether it is that they develop in the same amniotic sac, or just the fact that they developed from the same egg?

Mono-amniotic twins are a small percentage of identical twins, so that is a minor confound at best. I’m not aware of any research that points to the in-utero environment being more similar for identical twins than for fraternal twins, and that in turn affecting the traits that we’re examining to any noticeable degree.

Who are the parents who misclassify their twin children- isn’t that an implicit omitted variable that you can never get rid of here? If there are gene-environment interaction terms missing from the equation (and include a bunch of interactions with the unobservables I’ve listed here, and those I haven’t) wouldn’t you run into all the same problems with the “heritability” estimates?

Heritability of behavioural traits has been examined from many directions – twin studies, adoption studies, family studies, GREML, etc and they all turn up the same result. There’s a reason why the first law of behavioural genetics is that all human behavioural traits are heritable.

Lastly, there are also confounds that may lead us to be underestimating heritability.

Perhaps I misunderstand the claims being made (I’m certainly not a geneticist), but it sounds a lot like causality, when all I see is a correlation with many confounders.