The boat as a symbol for work
The cast of this novel is primarily two runaway workers who abandon their crew to do even more work on their way home, because they feel the captain is tyrannical and abusive. That's probably the case, if they feel that way, but they do abandon a hard job in the process, so when they get to the island, they are ready to relax and recuperate. That means they are not leaving the hard work of a boat to go do new work—they are falling into sloth.
The symbols of nature
Nature is ultimately the central idea of the novel, as anyone who has traveled to an island paradise well knows. The bliss one feels on a remote beach is unimaginable, and to be greeted like a god back into natural bliss and paradise, where the people are not bound by European law or custom, surrounded by beautiful women and fed delicious food by servants—that's a pretty sweet spot. It's also a symbol of human dominion, because we are animals, but we enjoy immense luxury. However, nature has a twist, symbolized by the carnivorous underworld. The same sexy women who do their thing for Tommo are also at those war parties, eating the flesh of their human victims. The fact that nature includes death, and the horror of animal death coming primarily from predators, is truly horrifying, but it is natural.
The balance of nature
There is a Daoist kind of balance in the novel, where information is being withheld and provided evenly. For instance, either the tribe is a friendly tribe with a history of kindness toward Europeans, or they are the savage tribe who cannibalizes those who come close to them. We're in one of those two stories, but we can't tell which one. Then, when one of the two adventurers disappears, suddenly we have half a story. We see one half of the story, but the other half is concealed in mystery, leaving Tommo and the reader both in a state of suspense.
The balance of government
The guys in this story aren't allergic to work. They're just tired of getting abused by their bosses. On the other hand, they can lean toward indulgence. They can satisfy every lust, enjoying island life to the max, ignoring the fact that, as time passes, the odds of them getting eaten are going up and up. Why else would these natives be so inclines to fatten them? So, this is a spectrum of government. Where there is no government, there are cannibals, and where there is too much government, there are tyrant captains.
The act of cannibalism
The signal of cannibalism is the snake eating its own tail, which is symbolized in this book by the human cannibals who eat humans to sustain their human lives. One interesting comment here would be that mentioning cannibalism is universally disgusting, which means that we are revolted by the idea in our bodies. Another association would be to mention that cannibalism shouldn't really be that much more disturbing than regular old death, but for some reason it does sting. The idea of nature being an endless cycle of self-consuming life force is utterly unfathomable, but that is exactly the quality of Tommo's sublime experience. Imagine stumbling upon the half-eaten flesh of another human—Tommo did.
