There is so much love, dread, tenderness and brutality in “The Humans” that it is hard to believe just 90 minutes pass through Stephen Karam’s deeply-felt family tragicomedy thriller.

“Humans,” nurtured by the Roundabout Theatre’s Off-Broadway program, has transferred to Broadway with director Joe Mantello’s wonderful six-actor company intact. The move to a larger showcase feels right, enlarging the impact without losing the nuances of light and dark.

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And things are both light and very dark in what seems at first like just another three-generation Thanksgiving play. Mom (Jayne Houdyshell), Dad (Reed Birney) and the mentally-disappearing granny (Lauren Klein) drive from Rust Belt Pennsylvania in a snowstorm to join the troubled lawyer-daughter (Cassie Beck) for holiday dinner. The setting is the dilapidated new Chinatown basement-and-ground-floor apartment of the struggling composer-daughter (Sarah Steele) and her privileged but depressed boyfriend (Arian Moayed). David Zinn’s two-story set is a genuinely disorienting character all its own.

But the familiar family bickering has more than the usual rough edges. The father has been waking up in a sweat. The lesbian lawyer has a broken heart and devastating stomach trouble. Banging noises are coming from the old Chinese woman upstairs, the trash compactor growls and, not irrelevantly, the father worries that the apartment is in the shadow of the collapsed World Trade Center and in a flood zone.

Karam, raised in working-class Pennsylvania with a Lebanese-American father and an Irish-American mother, burrowed into his father’s side in his more wildly creative “Sons of the Prophet,” a 2012 Pulitzer finalist. Here he dives into less exotic Irish roots for a sense of vanishing tradition without cliche.

On second viewing, the retelling of bad dreams now seems woven into a richer psychological carpet and the few plot threads that seemed undeveloped now feel beautifully wrought. We understand better when a character jokes that monsters gather around and tell human stories. Clearly, our most monstrous horrors are all too human.

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Last season, there was talk about initiating a new Tony category that would honor an acting ensemble instead of singling out individuals. If ever a cast deserved an award for sublime ensemble interdependence, this is it.