The significance of Ahab's leg being made from whale bone aligns with the idea that "Ahab has pitted himself against nature in an effort to dominate it." This represents not only Ahab's personal struggle with the whale, which serves as a symbol of the natural world, but also his broader conflict against nature itself.
Ahab's choice to replace his lost leg with an artifact of the very creature he hunts underscores the paradox of his relationship with nature. He is both a part of that natural world and an adversary to it. This duality reflects the themes of obsession, vengeance, and the human desire to conquer nature, central to the narrative of "Moby-Dick." Ahab's quest to hunt the whale becomes a manifestation of humanity's broader struggle against the forces of nature, emphasizing the peril of such hubris. Thus, Ahab's ivory leg signifies his combative stance against the natural world.