DS: Genetics create the *individual* dog. How does environment influence the temperament?

I've spent the lat 20 years volunteering in rescues and I KNOW environment is not everything. I have seen dog that have gone through hell but are sweet and only want to be loved and I have seen dogs who are suffering from nothing more than mild lack of training be so completely unmanageable and aggressive they need to be put down. There are genetically unstable dogs that no amount of "love" can fix. Sure, nuture has some effect and you can shape what you have to some degree. Nearly all dog can do better with training and manners and a secure place. But I have worked at rehabilitating foster dogs and I find many make progress up to a certain point and that is all you are going to get. They remain feaful no matter how secure they are or they remain aggressive under some circumstances. You can teach obedience but the underlying personality is stil there. Nurture is not always able to make up for bad breeding.