what recurrent dream did buck have? what did the dream symbolize and why was buck having the dream so often at this point in the story?

"The vision of the short-legged hairy man came to him more frequently, now that there was little work to be done; and often, blinking by the fire, Buck wandered with him in that other world which he remembered.

The salient thing of this other world seemed fear. When he watched the hairy man sleeping by the fire, head between his knees and hands clasped above, Buck saw that he slept restlessly, with many starts and awakenings, at which times he would peer fearfully into the darkness and fling more wood upon the fire. Did they walk by the beach of a sea, where the hairy man gathered shell- fish and ate them as he gathered, it was with eyes that roved everywhere for hidden danger and with legs prepared to run like the wind at its first appearance. Through the forest they crept noiselessly, Buck at the hairy man's heels; and they were alert and vigilant, the pair of them, ears twitching and moving and nostrils quivering, for the man heard and smelled as keenly as Buck."

This section and Buck's dream symbolizes the equality between the animal and the man in ancient times.

"Buck's mind is taken over once again by the hairy, primitive man of the ancient world. Buck's desires become clearer along with his memories. he recalls that "the salient thing seemed fear." When Buck's ancestor wandered the forests with his human-companion, their needs and desires were always one. The human was as wild as the animal, seeking food, shelter, companionship, and safety. Buck craves and needs danger and insecurity in his life. Without it, he does not really feel alive."

http://www.gradesaver.com/call-of-the-wild/study-guide/section7/