based on the last two paragraphs of chapter 4, to what degree is buck "hearing" the call of the wild?

The last two paragraphs of chapter 4 deal with the death of Dave. It isn't so much the call of the wild rather than Buck understanding the law of the wild. Buck's dreams of ancient times suggest that a dog's passion for work may be related to it's desire for an existence similar to that ancient existence. Dave "pleads" with his eyes to remain with the team. Dave seems to understand that when his ability to work ends, his life ends, for a life without labor is no real life. Once again the reader must be reminded of Buck's earlier existence. No matter how coddled he was, London appears to be suggesting that Buck must be happier in his present life.