“These are the new superheroes for kids,” he said of the mixed martial arts fighters. “It’s just given them a whole new set of idols. People don’t wake up today and want to be Sugar Ray Leonard. They want to be Georges St-Pierre.” Mr. St-Pierre is the currently sidelined U.F.C. welterweight champion.

Birthday parties with M.M.A. themes are now popular with the under-10 set. “We cut the cake with a sword, which is always a big hit,” said Chad Weiss, an owner of Westchester MMA-Fit a school in Mount Kisco, N.Y., which also runs an M.M.A. summer camp.

The fascination with the sport has even seeped into the walls of academia. Robert Thompson, a professor of popular culture at Syracuse University, said that many of his male students wanted to write papers about mixed martial arts. And they are not always the students you would expect.

“People who don’t know these sports very well think their fans must be these kind of crazed, people-on-the-verge-of-a-breakdown, violent kind of thing,” he said. But the students he sees who are most interested in the sport “tend to have really good grade-point averages and be really fine students,” he said. “This is not something that smart young people look down their noses at.”

He agreed that the impact of “Fight Club” could not be discounted; it became a manifesto for a generation of boys who felt estranged from their masculinity. “It became this kind of magnum opus, and it described a certain culture of this kind of sport,” Professor Thompson said. “This was their thing, and they defined themselves accordingly.”

Evidence that cage fighting has replaced boxing as the combat sport of choice, at least to some men of a certain age, has been quietly mounting for years. The annual pay-per-view audience for Ultimate Fighting Championship matches first surpassed boxing and professional wrestling in 2006, and has continued to rise almost every year since. And among men ages 18 to 34, the sport is fourth in popularity only to baseball, basketball and football, according to research by Scarborough Sports Marketing in New York.