Twin studies have not shown that. Please cite it and state the definition of "heritable" used in the study you cite (in general, they do not use the definition one might expect).
Also, going from "genetic" to "immutable" is a non sequitur, and is not supported in any way by twin studies. It sometimes turns out that genetic features (such as hair color) are not so hard to change after all (e.g. with dye).
Your implication that it's disingenuous that the layman's definition differs from the scientist's definition... is dumb.
And again, I didn't say that personality was immutable. I said that part of it was. Longitudinal studies show that a correlations of personality across an individual's lifetime is about .83, which is pretty damn high. http://arjournals.annualreviews.org/doi/abs/10.1146/annurev....
Whether a person does change their personality is a different issue than whether it could be changed (possibly requiring some new knowledge, or possibly simply requiring a change in preferences). So that correlation study doesn't provide evidence of immutability.
I know there are a lot of studies on heritability. Now, if you are interested in an open discussion, cite one study that you stand behind, and state the definition of heritability it uses, in your own words or quoting from the study itself.
I didn't call you dumb. I said that your implication was dumb. And it still is.
I'm not really sure what you wanted me to get out of that blog post. I did cite a study- I linked to it. And the definition of heritability is still the same.
Also, going from "genetic" to "immutable" is a non sequitur, and is not supported in any way by twin studies. It sometimes turns out that genetic features (such as hair color) are not so hard to change after all (e.g. with dye).