Buck succeeded when others did not because of atavism. His breed what more aggressive and he wanted to survive. Buck’s dad Elmo who was a St. Bernard, and St. Bernard’s are working dogs. They can do more work and not get tired, they are also very strong. Buck’s mom Shep, the Scotch Sheppard, is a dog that came be formed in most types of dogs including working dogs or sport/performance dogs. These specific traits helped Buck dominate and stand out from all the other dogs and succeed more than them. Buck’s breed obviously isn’t the only thing that made him succeed. Certain personality and skill is crucial. Just like how Curly died, he died because he tried to be friendly but like the Law of Fang states, Strong with survive, weak will die.