determines development, nature or nurture.

Both, but nurture would play a much greater role as it affects so many different parts, nurture affects your preference and approaches to learning, your interactions with people even your diet which in turn can reflect your mental/social/physical capabilities. Nature can however yield certain qualities, as say a mutant gene in a species proves to be helpful and beneficial then no amount of nurture could encourage future generations do mutate. ut all in all it is your environment that develops you and how you are nurtured in that environment.