No individuals, except other pack members, guarded them from injury and there was no large pharmaceutical industry to protect them from disease. Through natural selection a canine model was formed that had the physical and mental abilities to continue their species. Their behavior patterns guided them through their day to day and year to year existence helping them to make the right choices to protect themselves and their offspring. If this wouldn't have been accomplished they would be classified with the dinosaurs. Their daily life was guided by behavior and interactions that occurred between them and other members of their group.
Wild dogs choose to live in packs.
This is a better way of guaranteeing a near constant supply of food if they work together. Being carnivores or at least high level omnivores , wild dogs are usually predators. To kill an adequate amount of food at one time typically means bringing down a large animal. This is much easier for a pack of dogs to accomplish than it is for a single animal. Not only is it easier to find food if many different sets of eyes are looking but they can then cooperate in the chase and kill.