I believe that both nature and nurture plays a part, with a greater role being played by nurture
Nature - Ensuring that the human has perfect body parts, brain, no mental/physical disease from birth.
Nurture - Make sure that the child comes up with a positive mindset, desire to succeed and other characteristics necessary for success.
Without 'nature', 'nurture' is useless. Whereas, without 'nurture', 'nature' is wasted.