One of the problems of not separating identical twins in the myopia study is the inability to distinguish between the effect of pathological gene and behavioral gene, i.e., love-to-read gene. (Credit to hunhun for eliciting this point.)

I think our debate on heredity vs. environment, as well as the research cited in Fang’s article, is all about the pathological gene vs. environment. The myopia-causing gene we talked about is the pathological gene DIRCTLY linked to myopia, i.e., gene --> myopia, NOT the behavioral gene, which causes love-to-read behavior first, then the behavior causes myopia, i.e., gene --> behavior --> myopia.