The terms "nervy" and "weak-nerves" are not well-defined. I think people rate dogs differently depending on what they are producing or what they have. I do not have dogs that are fearful at the vet. I may consider a dog that is fearful to the point of aggressing at the vet to be unstable or nervy. And yet a lot of people with k9s have to handle their own dogs at the vet because they (the dogs) will not allow some treatment. Certainly all of these dogs do not have weak-nerves.
I guess the point is that some of us consider a lot of things weak, and would not want to breed it. Like a dog who is fearful of storms. But really, a lot of what we see most often, fear-reactivity to dogs or people may be attributed to poor handling, weak-nerved, shy people transmitting their uneasyness and lack of confidence to their dogs from early on.
And yes, litters can have a range of temperaments. Think about dog packs that are often formed when a dog and bitch have a litter of puppies and raise them. Not all of those pups are going to be alpha-leader pups. Many more will be middle of the road follower pups. And there may be a few softer puppies, which are not necessarily defective, they probably have their place in the pack and provide something that causes the pack to work better.
Some dogs recover to a change or whatever might frighten a young dog quickly, and some take longer to recover. Some react strongly, some do not react at all, and some react badly, and some react very badly.
I am not sure about all the answers. I know they raised a litter of pups from a nervy bitch, using a solid bitch and the pups had the nervy temperament. Do we know where those pups went and who raised them? Do we know the surrogate dam truly was a solid bitch. Is a sample of on sufficient?
Personally I think each pup has a continuum of potential in the area of temperament. This is what nature deals him. 50% of the genes come from the dam and 50% from the sire. If the bad genes are coming from the dam it is a double whammy because she imprints her temperament on the puppy, some say before birth and throughout the time they are with her. So if she goes ballistic every time someone comes to the door, the puppies will most likely develop that problem. I am not sure what I believe on that. I tend toward the pups being imprinted after their eyes and ears open at around about 2 weeks through 8 weeks, unless the bitch is moved to another household when the pups are weaned.
I think the dog is who it is, by its genes and how it was imprinted. That gives us that continuum. At that point, excellent handling will give the dog the best possible chance at reaching the positive end of that continuum. If it is written in the genes that the puppy will be gun shy, the puppy will be gun shy or afraid of storms or what have you. It is possible that with one handler the dog will pace and tremble a little when hearing thunder, and another handler if they raised that same dog, might have the dog cowering under a desk or chewing on itself. I don't know, because EVERY dog is different and you cannot go back and erase the raising process and try again with different leadership.
But you can take a pup or dog out of one situation and with another handler, have bad habits cease, be trained out, what have you. A dog might be reactive with a wife, and not reactive with husband. A dog might be fearful at the vet with the owner, and not be fearful at all at the vet when the daughter takes him.
So yes, I believe a dog has a range of potential and handling does play a part. Good handling does not produce better than what the dog naturally can be. And bad handling does not produce a dog worse that what his nature is. But better handling produces a dog with fewer issues.
Bear Cub, Hepsi-Pepsi
Cujo2, Karma Chameleon
Ramona the Pest, Kojak -- who loves you baby?
Tiny Tinnie, Susie's Uzzi, Kaiah -- The Baby Monster.