Gerrold, David. The Man who Folded Himself.. 1973.

This time travel novel's strength is its almost-systematic exploration of the idea of time travel paradoxes, and in so doing it not only almost manages a coherent theory of time travel, and the possibilities and limitations of changing the past and, by extension, the future, but even manages to create touching relationships between a character and himself, or, in one case, herself.

The novel's weakness is the long list of famous people, places, and events the narrator claims to have visited. Any one of those events would have been worthy of a long description, if not the entire plot of the novel, and to do everything the character boasts of would have been impossibly difficult, dangerous, awkward, and time-consuming. How could a person from the 1970s find Christ? I honestly think that would take years and you'd never be sure you picked the right carpenter. You'd probably be killed by an ancient disease or beaten to death by superstitious grunts.

I read this is one sitting. I suspect that there are more insurmountable plausibility issues, than I noticed and the story shows its cultural hand in a way that can be jarring. This man's guilt at being his own lover is reconciled when he meets a female variation of himself. The female version of himself apologizes because she is not a virgin. The male version offers no such apology. The intriguing homoautoerotic (?) subplots are undermined by this attempt to demonstrate that heterosexual monogamy is a superior type of love, even though a coupling (and conception) between a man and the version of himself born female is beyond incest and inbreeding and into something deeply creepy.

This book is not a classic, but I recommend it to anyone interested in time travel paradox stories. Despite the seemingly penultimate weirdnesses described above, a somewhat better and much shorter example of a freaky sexual time travel paradox story is Heinlein's "All you Zombies."