'Family Tree' comes to HBO

* FAMILY TREE. 10:30 p.m. Sunday, HBO.

ANCESTOR worship's all the rage these days.

So HBO's newest comedy, "Family Tree," about a man tracing his roots, should have built-in appeal for those not already sold by the name of co-creator Christopher Guest ("Best in Show," "Waiting for Guffman").

A writer, composer, director and actor known for improvisational comedies structured like documentaries (and for being married to Jamie Lee Curtis), Guest, who says the show was inspired by his own ventures into genealogy, boasts an ancestry that's probably more hoity-toity than that of most people scrolling Ancestry.com.

Son of a British diplomat, he's the fifth Baron Haden-Guest, which is not the kind of title usually associated with someone who grew up in Greenwich Village.

Since it's also not associated with becoming one of the funnier people on the planet, it may be time we all began taking heredity less seriously. And the gently charming "Family Tree" is as good a place to start as any.

Created by Guest and actor Jim Piddock, the show stars Chris O'Dowd ("Girls") as Tom Chadwick, who starts exploring his heritage after being left a trunk full of poorly labeled mementos.

Tom's not exactly a winner, having recently been separated from both girlfriend and job. But, as befits a character we're meant to stick with for longer than a two-hour film, he's self-aware enough not to be a complete loser.

"Women would just get in the way of my wallowing," Tom tells his sister, Bea (Nina Conti), when she wonders if he's seeing anyone. "I've got like another six months of wallowing in me."

Bea, meanwhile, has been wallowing for years, thanks to a childhood trauma I won't spoil for you that's resulted in a more than slightly obsessive attachment to a monkey puppet.

Their father (Michael McKean), a retired "yeoman warder" - think the guy on the label of Beefeater Gin - fancies himself an inventor, but spends his days watching '70s-style sitcoms (each of them created for the show, along with a historical drama, "The Plantagenets," that Tom sometimes watches).

The shows-within-a-show speak to the attention to detail lavished on "Family Tree." Improvising, it's clear, doesn't translate into loss of control.

"In England, a journalist said, 'It must be the cushiest job in the world, writing an improvised show,' " Piddock told reporters in January. "And, in fact, it took longer than almost anything else I've ever worked on in about 25 years of writing. . . . Our job is to lay out the characters in such specificity and detail that we do back stories for all of them so that people know literally what school they went to."

Piddock, like McKean and others, is a veteran of Guest's films. Here he plays Glenn Pfister, owner of Mr. Pfister's Bits & Bobs, and Tom's first guide into what quickly becomes an exploration of British eccentricity. (Presumably Americans won't be spared, as Episode 5 takes Tom to America to meet family members who'll include characters played by Ed Begley Jr. and Guest.)

Along the way, Tom becomes briefly attached to potential ancestors who don't pan out or aren't quite what they first seem - a not unfamiliar experience is frequently rendered funny by just a small dollop of strangeness.

Sometimes it's more than a dollop, but "Family Tree" doesn't dwell so long on any single absurdity to make anyone uncomfortable. Laugh, or not, it seems to say, at the woman who believes in the Loch Ness monster or the sister whose childhood trauma doesn't sound all that traumatic.

There'll be another opportunity along at any moment.

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