Answer:
"Buck had killed man, the noblest game of all, and he had killed in the face of the law of club and fang." Buck realises that he had done something wrong he had broken the law of club and fang. He learns that he only has to follow the law if he has a reason to (arrows and spears and clubs). "They had died so easily. It was harder to kill a husky dog than them. They were no match at all, were it not for their arrows and spears and clubs. Thenceforward he would be unafraid of them except when they bore in their hands their arrows, spears, and clubs." this conferms that Buck is now unafraid of man and only follows the law of club and fang if he has a reason to.