FWIW, there is actually a pretty great technique for sussing out the degree to which environment and heredity impact various traits: twin studies. Twin studies

FWIW, there is actually a pretty great technique for sussing out the degree to which environment and heredity impact various traits: twin studies. Twin studies have repeatedly shown that genetics contribute from 30%-80% of the variance in most psychological traits. Interestingly, they have also shown that the shared environment (family, parents, socioeconomic status, etc.) has zero contribution to variation in psychological traits. All of the environmental variation is due to what is called the non-shared environment. I highly recommend a book by Judith Rich Harris called The Nurture Assumption if this kind of stuff is interesting to you.