The Nature-Nurture Debate
Both nature and nurture seem to be important, they may even act together.
For example if a fear of dogs runs in the family it could be either the idea of preparedness because dogs could have been predators for early humans so it was good thing to fear because it helped keep us alive and so this could have been passed down through the family gentically. So we have learned to fear dogs more easily than other things which supports the nature side of the debate.
However it could also be Social Learning Theory and because the parents are scared of dogs whenever they see dogs they act scared and their children see this behaviour and think it is normal so they copy and imitate this behaviour also whenever they see a dog and fear of dogs hads been learned. This supports the nurture side of the debate.