The novel is more clear. Dave has evolved, literally. The monoliths are mile markers set out by ethereal aliens; the first teaching apes how to use tools, the other monitoring our progress to becoming space-faring.
Aliens ushering us into a next plane of evolution is a recurring them with Clark. Childhood’s End has the extraterrestrials taking a much more deliberate role in our species transition.




After a certain amount of time I think rights to spoiler warnings are forfeit. It’s been decades.