Though it sounds like a one-off prank, Mr. Bader’s burritos exemplify today’s most thrilling sculpture, which at the moment can be seen all over town, standing in stark contrast to the muscular, macho, hard-won objects of a John Chamberlain (whose Guggenheim retrospective is up through May 13). The new sculpture is deliriously playful, unstable (it changes over time: living, decomposing, collapsing, or threatening to) and frequently renewable. The readymade has returned in 21st-century rococo clothes, Duchamp’s legacy used for sinister, hallucinogenic and comical ends.

Mr. Bader, 34, has presented as sculpture live goats, a lawnmower, buttered rolls, and cat litter and olive oil. When first viewed, the pieces often shock—either for their seeming banality, or because the work (or its operation) may be hidden in plain sight, legible only with some assistance. Last December, at Art Basel Miami Beach, Mr. Bader drove his aunt’s minivan to Miami and parked it on the grass in front of the Bass Museum. The piece was called my aunt’s car.

This work privileges live experience, and it is often sculpture in only the most expansive definition of the term. Mr. Bader once proposed an art fair booth that included a Foo Fighters song, a Sarah Morris painting and a tarantula in a terrarium. “The artworks would all be sculptures,” the proposal read.

But Mr. Bader is only a single, prototypical example of many artists toying with sculpture and the readymade. Last year, Anicka Yi placed powdered milk, antidepressants, palm tree essence and other materials in a large pot on an electric burner, sending a faint, sweet odor into the air at the gallery Bortolami and the alternative space White Columns. For her debut solo show at 47 Canal in September, she fried flowers in tempura and built an installation that slowly leaked olive oil. Three years ago, at the New Museum, Adriana Lara had a museum guard eat a banana every day and drop a fresh peel on the floor. In January, Klara Lidén crammed old, but still fragrant, Christmas trees into Reena Spaulings Fine Art so tightly that the mere touch of people moving through the space was enough to make the desiccated needles crack and scatter. Also at 47 Canal, Josh Kline offered deformed plastic water bottles—he boiled them in their own water then refilled them, making new work without effectively adding anything but heat.

In 2008, in a dramatic expansion on Rauschenberg’s Erased De Kooning Drawing Mr. Bader wrote to a few dozen artists asking for a work in their “signature style,” explaining that he would present their works as his own, and sell them at his prices at that year’s Art Basel Miami Beach—$2,000 to $10,000. The well-established British painter Gary Hume wrote back, in a letter published in one of Mr. Bader’s artist books, “For me to gift to a total stranger hundreds of thousands of dollars is fucking crazy.” At MoMA PS1, Mr. Bader has three cats in a gallery that are available for adoption. (When one is adopted, the SaveKitty Foundation supplies a replacement.) These, too, he says in an artist statement, are sculptures. Next door, an iguana is available, and still another gallery is filled with pedestals bearing vegetables that, twice a week, a museum staffer uses to make a salad for visitors.

In a recent issue of New York magazine, critic Jerry Saltz described Mr. Bader’s work as “late-late-late post–Conceptual Relational Aesthetics,” referring to the feel-good, still-born movement that had 1990s artists engineering miniature events, serving up Thai food and hosting parties as artworks.

Mr. Saltz’s description seems almost willfully mystifying. It is certainly unsatisfying. For many of these other artists, a critical literature is just beginning to develop. So, what is going on here? To be clear, these artists are not a cohesive school. Many are friends or acquaintances. They show at a handful of mostly young New York galleries. Their tactics overlap, but they’re playing many different games, pursuing diverse ends.

They also share a few clear forebears. Swiss sculptor Urs Fischer, one of today’s most successful artists, is one. (Mr. Bader was his longtime assistant.) Mr. Fischer has made sculptures involving apples and bananas, sugar and egg whites, a croissant and a dead butterfly, and candles that look like people, which can be ordered fresh each time they are burned down. When he makes an actual, stable sculpture, it often looks like it is on the verge of collapsing—a piano or bed made of aluminum that is imploding or turning into a puddle on the ground. But Mr. Fischer can often be grandiose—he looks, admittedly or not, to the polished decadence of Jeff Koons. Perhaps responding to that weightiness, these (mostly) younger artists are determinedly light-hearted: out of the Baroque came the Rococo. Instead of huge steel Koons Easter eggs, we get a pair of burritos.

The Italian arte povera artists of the 1960s and ’70s also provide more distant precedents. Think of Giovanni Anselmo placing a head of green lettuce between blocks of granite—continually refreshed when it wilted—or Mario Merz filling a long spiral table with fruits, vegetables and beeswax, a feast of ephemeral sculpture. And then there was Joseph Beuys, with his fixation on fat, felt and animals, though he advanced a sort of mythology that today's artists sidestep.

Another precedent here is Haim Steinbach, whose shelves of readymade objects welcome vast constellations of interpretation, and prefigure the rogue readymades of Mr. Bader, and even Damien Hirst. Even as critics piled on Mr. Hirst’s 11-Gagosian spot painting show earlier this year, many fondly recalled his adventurous early work, like the masterful A Thousand Years (1991), a glass cube in which maggots fed on a cow’s head, turned into flies and then died by crashing into an Insect-O-Cutor. It was a sculpture in motion—readymade materials marching to gruesome ends.

The current crop of sculptors delight in such transformations and materials, like Mr. Hirst (sans his Baroque proclivities) or Dieter Roth (who made a number of artworks out of chocolate) or even Sigmar Polke (who once exhibited paintings in Venice that changed based on the city’s notorious humidity). Mutating, traveling and melting away (and sometimes even regenerating), their work takes place over time.

Last summer, at the Cleopatra’s gallery, Sam Falls filled two vitrines with apples and worms to eat them away. He has also coated sculptures with different amounts of protective paint, ensuring that various parts degrade in sunlight differently. At the current Whitney Biennial, Sam Lewitt pours black ferromagnetic liquid over plastic and magnetic materials. Small orbs of the magical material, typically used inside electronic equipment, quiver in the air currents from two nearby fans. The piece evaporates, and new liquid is poured on once a week to refresh it. Thomas Kovachevich affixed materials to walls at two recent gallery shows (tape at Callicoon Fine Arts, in October; tape and grosgrain ribbon at Show Room, on view through Sunday) that change shape as humidity rises and falls. The changes sometimes take place at the institutional level: when the Grand Openings collective was in residence at the Museum of Modern Art last summer, German artist Jutta Koether splashed liquid glass on black wood planks that became paintings (her preferred term) when leaned against the walls, props for visitors to use during events or, at other times, sculptures on the ground of the museum’s atrium, not to be touched.

Even seemingly solid objects—sculptures in the most traditional sense—are coming unfixed. They are in motion, or could be at any moment. For a pop-up show at abandoned offices in the Lipstick Building in Midtown, David Muenzer molded Eero Saarinen tables out of hundreds of pounds of tempered varieties of chocolate. Visitors could break off a chunk and take a bite, and the tables eventually started breaking apart. David Adamo’s show at Untitled last May had sculptures emerging out of blocks of wood, a floor strewn with woodchips, as if the artist were still working. For her current show at the Kitchen, through May 6, Virginia Overton has scavenged various castoff items from its basement, wedging those (readymade) objects between walls. Gravity threatens to undo them at any moment. At her just-closed show at Alex Zachary Peter Currie, Lutz Bacher covered one floor of the gallery with sand, which shifted and spread throughout the show as visitors trampled it. And at Simone Subal Gallery, ostensibly straightforward Minimalist sculptures are, in fact, only half there: their maker, Frank Heath, has sawed them in half and mailed one section to nonexistent addresses, using the Lower East Side gallery as his return address. Will they return before his show closes on April 26?

So, we have delirious readymades, like Mr. Bader’s sculptures, which can be glib and smug (taking other artists’ work) but also ingratiating (those cats!) and goofy (burritos), as well as artists like Mr. Falls and Ms. Yi, who are interested more in transformation and degradation: their rotting fruit and dripping, cooking sculptures, respectively, seem to invite Proustian madeleine moments, webs of references, whether elegiac or blissful, sociopolitical or personal. The news release for Ms. Yi’s show cited WikiLeaks hero Bradley Manning, while Mr. Falls’s memento mori may call to mind abject moments—the bug in your salad, the worm in your Big Mac, the body wasting away under the ground. And then there are more traditional practitioners, like Ms. Overton and Mr. Adamo, who offer sculpture seemingly in the process of changing—frozen before a collapse or ready for a bit more labor. Often, these fields overlap, as in Ms. Lidén’s room of evergreens—readymades that gradually wasted away, and will be reborn soon by the collector that bought the right to make the piece again and again.

These artists have diverse interests—they are individual cases—but what their work shares is a clear demand for physical presence. It appreciates, even requires, repeat visits—a bit of your time—and it changes each time you go back. It tacitly acknowledges that, in an age when capital and information—to say nothing of art—are transferred effortlessly through virtual networks, there may be nothing more radical, more intoxicating and refreshing, as art, than tangible, physical objects for viewers to make sense of. Doing so may mean adopting a cat, eating a salad or taking a whiff of antidepressants.

It is going to be thrilling to see what comes next. What comes after—how do you improve on—two burritos in the sun, or a room full of Christmas trees? We’ll soon find out.

arusseth@observer.com