The French thriller “The Animal Kingdom” is set in an alternate reality where humans are starting to transition into animals of various species — snakes and lizards to walruses and birds. The authorities treat this as a contagion that must be isolated and attacked.

But to those whose loved ones are infected, like François and his son Émile, that woman was his wife and his mother. She is “still there,” just in a less recognizable form.

So the latest film from Thomas Cailley (“Love at First Fight”). co-written by Pauline Munier, touches on themes that films from the various X-Men installments to the zombie infection tragedy “Maggie,” on back to “Teen Wolf” wrestled with.

Someone you love has changed. Does that mean the end of your love for them? Yes, that’s an allegory for our “transition” headlined age, handled here with sensitivity if not a lot of emotion.

Romain Duris of the recent “The Three Musketeers” remakes and “Waiting for Bojangles” plays François, whom we meet trapped in traffic with his 16 year-old (Paul Kircher) and the family dog.

A violent racket emerges from an ambulance stuck in the same traffic jam, and damned if a human in “critter” form doesn’t bust out. People take cell phone videos. Some even get out of their cars. But nobody’s freaked-out. This has been going on awhile.

“Strange days” a stranger mutters (in French with subtitles) to François, who shrugs “Strange days, yeah” back at him.

What rattles father and son is the news that their plans to move, with wife/mother Lana in care (containtment) to a treatment facility outside the city has gone awry. The vehicle carrying her and others like her crashed and most inside escaped.

Father and son have to break the law to drive into the forest looking for her. But the cop on the case (Adèle Exarchopoulos of “Blue is the Warmest Color” and “Mandibles”) seems sympathetic. Father and son and their dog Albert hunt for Lana when they can, and adjust as they must.

Starting a new school in a new town, Émile should be a lot more bothered than he seems. He’s just lost his mother, and in the most bizarre way imaginable. His coping mechanism is to tell his new classmates she’s “dead.”

Maybe on-the-spectrum curious Nina (Billie Blain) will get it out of him. Maybe he’ll tell after he’s the one who secretly makes contact with a couple of “the creatures/critters” in the forest. Maybe “contact” means he himself will sprout feathers and try to fly.

This world is divided into people who fear and attack the formerly human animals which they don’t understand, people who lost family that way and want to understand, and people like Nina and some of her classmates, who leave food out for them for their own reasons — compassion chief among them.

Cailley never really reaches for the heartstrings in this story, which seems odd. The emotional heart of the picture is the father seeing his philosophy and moral center tested, and the son’s underreaction to what he’s finding out about “them” and himself.

And while the effects are terrific, the action beats are effective but limited in number. One chilling chase features locals wearing drywall stilts to wade through a cornfield on the hunt for “critters.”

“The Animal Kingdom” does what it does fairly well. But what it does isn’t all that original, and lacks the pathos you’d think such a situation might generate in those who live through it.

Rating: unrated, violence, disturbing content, smoking, profanity

Cast: Romain Duris, Paul Kircher, Adèle Exarchopoulos, Tom Mercier and Billie Blain

Credits: Directed by Thomas Cailley, scripted by Thomas Cailley and Pauline Munier. A Magnet release.

Running time: 2:08