All traits have been shown to be somewhat hereditary, but the nature of these studies is very difficult. Looking outside MBTI, every trait is, to some degree, hereditary. E, neuroticism and openness, I believe are the most (if anyone is really curious, I can look it up again.)E/I is indeed heriditary, but not in the way MBTI operates with E/I. Instead take a look at eigther Eyseck's or Jerome Kagans books.