What's the overall theme because like so many of them are roaming in my mind?

As Buck metamorphoses into a wild creature, he discovers within himself instincts that have been dormant for generations. In The Call of the Wild, London glorifies the almost metaphysical element of Buck's nature that allows him to survive in conditions that are completely foreign to him. He does more than learn to adapt, London argues, he draws on his ancestral memory to show him how to behave.