If Cal’s tale is not exactly mystical or supernatural, it is indisputably marvelous. He himself does not appear (as a she, of course) until almost halfway through the book, and narrates much of his family’s pre-Cal history from a position that might be called limited omniscience: He knows and sees all, from Turkey to Greece to New York to Detroit — but occasionally admits he’s filling in details, extrapolating from the available evidence, making things up.

So we travel back to the tiny village of Bithynios, on the slopes of Olympus, where Cal/Calliope’s grandfather Lefty, unseduced by the charms of either of the village’s two marriageable women, is driven by history (and, frankly, by powerful lust) to marry his sister Desdemona. And to Detroit in the years around World War II, when Lefty and Desdemona’s son Milton, the future hot-dog king of Michigan, Ohio and Florida, seduces his cousin Tessie by playing his clarinet against her bare skin in a variety of compromising positions.

Milton and Tessie know that they’re cousins; they don’t know that Milton’s parents are brother and sister, or understand the comic-genealogical tangle their union will create, let alone that it will produce a child with a rare genetic anomaly called 5-alpha-reductase deficiency syndrome. Cal attempts to summarize: “Sourmelina Zizmo (née Pappasdiamondopoulis) wasn’t only my first cousin twice removed. She was also my grandmother. My father was his own mother’s (and father’s) nephew. In addition to being my grandparents, Desdemona and Lefty were my great-aunt and -uncle. My parents were my second cousins and Chapter Eleven was my third cousin as well as my brother.” (We never learn, by the way, why Cal calls his brother Chapter Eleven, although an explanation of sorts may be inferred.)

“Middlesex” isn’t really about Calliope/Cal’s shifting sexual identity, as important a role as it plays in the story. The transfiguration of a child from girl to boy, after all, is only one of the marvelous things that happens in the Stephanides family history, possibly not as strange as the psychotic breakdown experienced by the Greek commander in Asia Minor (he believes his legs are made of glass) that precipitates Lefty and Desdemona’s flight from Smyrna, or Desdemona’s preposterous involvement with the Nation of Islam and its founder, the mysterious “mulatto” Wallace D. Fard.

Eugenides’ novel — his first was the memorable suburban miniature “The Virgin Suicides” — has little to do with sexual-chic politics, although they surface briefly when 14-year-old Cal/Calliope, on the verge of being surgically “feminized” by a leading New York sexologist, runs away to the gender-bender paradise of San Francisco in 1974 (a not wholly convincing rendering of that place and time). An explanation for Calliope’s lack of breasts, hips or menstrual periods has at last emerged, in part because of a not-quite-lesbian romance with a fellow student, which is rendered, for all its unlikeliness, in exquisite and utterly convincing detail.

“Middlesex” begins as a generous, tragicomic family chronicle of immigration and assimilation, becomes along the way a social novel about Detroit, perhaps the most symbolic of American cities, and incorporates a heartbreaking tale of growing up awkward and lonely in ’70s suburbia. It’s a big, affectionate and often hilarious book, whose point seems to be that every human being, not just Cal/Calliope, is the culmination of an infinitely unlikely journey through genetic and social history, the product of coincidence and passion, fate and free will, “what love bequeaths to us before we’re born” and what we do with it.

This book will inevitably be compared to Jonathan Franzen’s “The Corrections,” not least because both authors are American men in early middle age who seem to have leapt to the head of their class with ambitious family/social novels that suggest George Eliot, Thomas Mann and Sinclair Lewis at least as much as they suggest Thomas Pynchon or Don DeLillo. (Yes, industry-watchers, both were published by Jonathan Galassi at Farrar, Straus and Giroux.) Indeed, both books are stirring reclamations of the full-scale realistic novel as both a popular and literary form, as well as ruminations on fate and mortality and critical examinations of 20th-century America.

Beyond those broad contours, the two works aren’t all that similar. For better or worse, Franzen’s world in “The Corrections” is the prison-house of the postwar Anglo-American family. Presumably his Lambert family had ancestors who arrived in the fictional Midwestern metropolis of St. Jude from somewhere else, but if so they’ve been obliterated in the general whitewash of American history. Franzen’s often scabrous satire is focused on the mendacity and denial that he sees pervading our national life, whereas Eugenides isn’t a satirist at all, regarding America, his much-maligned hometown of Detroit and even the most ridiculous members of the Stephanides family with unreserved and compassionate sympathy. (Just try to read the death scene of Cal’s racist and disagreeable father Milton, the hot-dog tycoon, without crying.)

If Franzen’s strength is the almost merciless clarity of his vision, Eugenides’ is his prodigious grasp of history and ancestry as limitless fields that surround us and through which we travel, both forward and backward, toward our unknown destination. “Living sends a person not out into the future but back into the past,” Cal reflects, “to childhood and before birth, finally, to commune with the dead.” This novel’s capaciousness and sense of deep time partly reflect the Greek immigrant experience — certainly “Middlesex” is a great Greek-American novel, and for all I know it may be the great Greek-American novel — but it was the WASP William Faulkner, after all, who told us that the past isn’t dead and isn’t even past.

At one point in his narrative, Cal bemoans the tendency of language to oversimplify emotion. “I don’t believe in ‘sadness,’ ‘joy,’ or ‘regret,’” he writes. English has no words to connote “complicated hybrid emotions” such as “the disappointment of sleeping with one’s fantasy” or “the sadness inspired by failing restaurants.” (Or, in a more positive direction, “the excitement of getting a room with a minibar.”) Cal himself, once a pretty, dark-eyed girl and now a “severe, aquiline-nosed, Roman-coinish person” is a complicated hybrid, an inexpressible concept whom facts and language can never capture. But then, aren’t we all?

Our next pick: From the author of “White Teeth,” the story of a dealer in celebrity signatures who has serious girl trouble