Dogs are pack animals; they require socialization with people, other dogs and even other types of animals, but they are descendants of wolves. Dogs do not necessarily need other canines in their packs, as a pack can be achieved within any family setting, whether there is one dog or multiple dogs in the home.
Dr. Stanley Coren -- a noted dog expert -- has stated that as dogs have become domesticated, they may have bonded more with humans than with other dogs. So whether or not your dog needs a canine companion will depend on your dog's personality. Dogs need companionship, but your dog may not need the companionship of another dog. It is his individual preference that determines whether or not your dog prefers or needs the company of another dog, another animal, such as a cat, or a human. Some dogs thrive with canine companionship, whereas others merely tolerate it. Some never coexist peacefully with other dogs.