The main idea of Jack London's novel 'The Call of the Wild' is the journey of transformation undertaken by Buck, a domesticated dog who is forcibly taken to the harsh and unforgiving wilderness of the Yukon during the Klondike Gold Rush. Central themes explored include the conflict between societal restrictions and primal instincts, the survival instinct, the influence of nature on the individual, and the exploration of the duality between civilization and the untamed wild.