And I think it also has a lot to do with training from day one.....Being quite strict with them and setting the standard form day one.
I grant it there are some different lines, but I have also seen how sometimes puppies are allowed to do a lot of things, which people would never want a mature dog to do. So you need to set the limits from day one. Not just the "it's only a puppy".
Some dogs are more mellow in every breed and some are more over the top.
Also a puppy from a single pup litter need heavy-duty socialization ASAP......They did not have their own littermates to teach them certain things
We socialize our dogs a lot from the day we bring them home. And that is at eight-ten weeks, often well before all the vaccinations and all that stuff is finished. I feel it is more important to have good socialization then anything else. I believe puppies should meet as many breeds, size and age dogs as possible. And also as many people of different ages, size and ethnicity. This makes for good all-rounders of whatever Breed.
The other important thing is to never let them get a fright at this young an age. Because that also can have an everlasting effect.
I was blasted for brining my puppies out and about very early.now I get asked why they are so confident and happy. I also socialize a lot of other people's puppies from all different breeds and I compare litter-mates who were not socialized and taken out and about.
The best example is some of the newfie litters i have been involved with and whom I do follow ups with. Katy has on sister and brother who went to a loving home, but did not get socialzed until much later as per their vet (16 weeks) Even though they are quite nice happy newf's they are not as social and do not behave as well in other dog/people company. They are over exited and quite rude in some ways....Whilst her other brother went to a home, where he was out and about very early and is also very social and calm.
Even Breeders have some effect as to how the puppies end up...Look at how much effort some of the Breeders on NN put in on socializing and giving their puppies lots of experiences. That will make for great dogs, even if the owners are not as good at following through.
So a lot of it is from the genetic make-up, but a very large amount is from how dogs are raised and trained...The environmental factor
So think a lot of the behavior (not all) comes from how dogs are raised......
I will get off my soapbox now