We tend to think of causation as a phenomenon that occurs in one direction. "A" causes "B". The cueball strikes the eightball at a certain angle and velocity, and we can precisely map the eightball's subsequent motion using mathematical formulas. The universe is rational and deterministic: laws govern reality as it plays out in an orderly and predictable cascade of events.
That's why the concept of "nature via nurture" is so memorable, and so striking. It forces us to alter certain cherished paradigms, to shift our "natural" views of cause and effect. "Nature via nurture" describes the mechanism by which genes shape the development of the self. It refers to the principle that our natural inclinations and talents tend to influence our environment, which in turn influences our inclinations and talents. It also describes a system within which causation is bi-directional: "A" causes "B" while "B" simultaneously causes "A".
I used to worry that there was a person inside of us, defined by our genes, that we were meant to become. I worried that personal development could be hijacked by environmental circumstances, generating a false, misshapen self--that is, a self tragically at odds with our genetic destiny. Of course these views were naively teleological, and a touch grotesque. Still, I couldn't help but harbor a certain anxiety that I had been betrayed by my upbringing, which operated as a kind of alien imposition on the self. The principle of "nature via nurture" functions as a nice corrective for these fears. It states, in short, that we shape the environment that shapes us; that whatever circumstances contribute to our development already bear the mark of the self's influence.