What physical disadvantage does Buck possess compared to other sled dogs?

Buck's primary physical disadvantage compared to other sled dogs is his unhardened feet. When Buck is first introduced to the harsh conditions of the Yukon, he is not accustomed to the rigorous lifestyle of a sled dog, which includes running over icy terrain for extended periods. His feet have not yet adapted to the rough conditions, making him more susceptible to injuries and discomfort.

In contrast, the other sled dogs typically have toughened feet that have developed through experience in the wilderness, allowing them to endure the harsh elements and terrain without injury. Buck's journey throughout the novel involves not just physical adaptation but also a transformation that will eventually enable him to cope with the challenges of his environment, including toughening up his feet over time. This early disadvantage highlights his initial vulnerability in a cruel and unforgiving world.