This is a very broad question that is not too specific. The dogs you refer to are major characters in the novel as a whole, and so you need to specify which dog and which action you are refering to in Chapter Four to help us answer this question.
For example, one of the interesting aspects of Buck in this chapter is the way that he is presented as being something of a mystical dog who is able to see the ancient past and man's relationship with dogs back then. Note the description of what Buck sees:
He was all but naked, a ragged and firescorched skin hanging partway down his back, but on his body there was much hair... He did not stand erect, but with trunk inclined forward from the hips, on legs that bent at the knees. About this body there was a peculiar springiness, or resiliency, almost catlike, and a quick alertness as of one who lived in perpetual fear of things seen and unseen.
Note the way in which this vision is richly symbolic of the long relationship between man and dog, that stretches back even unto the period in history when man was a caveman and depended on his relationship with his canine friend to help protect him from the fears of the night.