[Maximo]

I believe it is mostly individual disposition of the dogs, with environmental factors mixed in.

The only way to guarantee what kind of personality you are getting is to adopt an adult. However, if you choose your breeder carefully, you likely will not end up with an uncontrollable, loud pup.

My boys learn behaviors from each other. Most of the mutual influence is good, but they do have their moments when they egg each other on in undesirable behavior, namely the car barking game that they have developed.