PW: Is the problem of our existence the other? Is that what Soro comes to find in the cave?
I think that for most of us isolation affords a special opportunity to establish meaning. In the quiet of the beach, with all his shipwrecked fellow survivors deep in winey sleep farther inland, the story’s narrator can not just carry the skull but can commune with it, slip out of his regular mind and understand himself and his place in the world in an entirely alien yet eminently comforting way. The skull is the new central focus of meaning for him. He’s obviously threatened by the idea someone might take the thing, but I think he is just as threatened when the other survivors merely watch him, or don’t watch him, or question him, or don’t. Other people don’t have to directly challenge our private beliefs to drain them of power. When others are skeptical of or indifferent to our understanding of the world, that understanding is no longer flawlessly attractive, unquestionable. And in the opposite case, when others share our very personal understanding of the world and our place in it, that understanding ceases to be personal. There seems to be no way to share the deepest, most primal sort of mystical experience without sapping it of some strength.
So the answer to the first part of the question is yes. As for what waits in the cave: that’s harder to say.