White Fang by Jack London

By the time his mother began leaving the cave on hunting expeditions, the cub had learned well the law that forbade his approaching the entrance. Not only had this law been forcibly and many times impressed on him by his mother's nose and paw, but in him the instinct of fear was developing. Never, in his brief cave-life, had he encountered anything of which to be afraid. Yet fear was in him. It had come down to him from a remote ancestry through a thousand thousand lives. It was a heritage he had received directly from One Eye and the she-wolf; but to them, in turn, it had been passed down through all the generations of wolves that had gone before. Fear! -that legacy of the Wild which no animal may escape nor exchange for pottage.

So the grey cub knew fear, though he knew not the stuff of which fear was made. Possibly he accepted it as one of the restrictions of life. For he had already learned that there were such restrictions. Hunger he had known; and when he could not appease his hunger he had felt restriction. The hard obstruction of the cave-wall, the sharp nudge of his mother's nose, the smashing stroke of her paw, the hunger unappeased of several famines, had borne in upon him that all was not freedom in the world, that to life there was limitations and restraints. These limitations and restraints were laws. To be obedient to them was to escape hurt and make for happiness.