Humans have a long tradition of holding genes responsible for individual differences in behavior (of course, we called it "blood", then, or "family"). In the 20th century, a counter-belief arose: that it was all down to environment, to upbringing. In more recent decades, we have become increasingly aware of how tightly and complexly genes and environment are entwined.
It's not enough to say merely that environment tempers genes, or that genes affect how the environment works on an individual — genes and environment work on each other in an ongoing interaction, that continues throughout our lifetimes. This ongoing change even affects attributes most people deeply believe are, if not hard-wired in the womb, at least set in childhood: attributes such as intelligence, 'natural' talent, and gender differences.