Through the '60s and '70s, albums like Fragile, Close to the Edge and Tales from Topographic Oceans, and tracks "Starship Trooper," "I've Seen All Good People," "Roundabout," and "Long Distance Runaround" became classic-rock staples.

And after making a surprising comeback in the early '80s with two songs whose videos were constantly in rotation on the then-fledgling MTV ("Owner of a Lonely Heart," "Leave It"), the band found new life. They've continued to make new music and tour with changing (and returning) members on and off ever since.

Bassist Chris Squire is the only Yes man present from the beginning and through every lineup, including the upcoming "In the Present" tour. Houston is the first U.S. stop for the second-leg jaunt, which celebrates the band's 40th anniversary.

Forty years? Hell, even Ringo Starr famously noted in early Beatlemania interviews that, after a couple of years on the pop-star train, when it all fizzled out he hoped to open a hair salon.

"It's funny you mention the Beatles!" an energetic Squire says via cell phone from a restaurant. "We formed in 1968 just before they broke up. Their visible career started in 1963. So I remember at the time how great it would be for me to have a five- or six-year run like the Beatles had!"

He's also learned that prog and art-rock fans are a bit of a different breed, less prone to flash-in-the-pan pop music.

"Our music needs a little more attention, more for a head-type person," he laughs. "But pot smokers like it too! We're big with them!"

Yes's current string of shows, however, has not been without controversy. Because singer Jon Anderson is suffering from a series of health issues including respiratory attacks, last year's tour was canceled.

But classic lineup core members Chris Squire (bass), Steve Howe (guitar) and Alan White (drums) decided later to forge ahead anyway, with young vocalist Benoît David taking over the mike. Classic Yes keyboardist Rick Wakeman's son, Oliver, is also on board.

That decision provoked a sharp rebuke from Anderson on his Web site (since taken down). And perhaps to soothe feathers, David is listed as a "stand-in" vocalist (with Anderson "on hiatus"), and this tour has the unwieldy title of "In the Present: An Evening with Steve Howe, Chris Squire and Alan White of Yes."

"We had to balance the fact that we'd been looking to tour in 2006, then 2007, and Jon's health was not good," Squire notes.

"But there was a huge demand for live audiences to get a "Yes fix," if you will, so we decided to go out with someone and really create an understudy for Jon, not knowing if Jon would improve or not," the bassist adds. "He's having a lot of procedures for various ailments, but we hope that he makes a full recovery."

And while Squire says that Anderson has given his tacit approval now, it's not like he's calling up after shows asking, "So, how did the kid do?"

"Jon will be welcome to come do some things on [record] and maybe feature shows," he adds, "but I'm afraid he won't be able to do large-scale tours."

Squire goes on to call vocalist David a "godsend," and is looking forward to making new music with him and Wakeman in the near future.

Yes's musical career has lasted so long that fans can even be divided into groups. The "Troopers" are those who latched onto the band in the '70s, while "Generators" picked up on the band in the '80s.

"It was amazing to have had this whole new age group listening to us in 1983," he says. "In a way, we were lucky to be able to transition into that decade because [a lot of other] bands didn't."

Trevor Horn, who had previously done a stint as the band's singer, stepped into the producer's chair for 1983's 90125 record, pushing the band into a more compact sound. Also, guitarist Trevor Rabin came in, playing with what Squire terms "a bit more rock style than a muso-style."

So, must any lineup of Yes have at last one guy named "Trevor" in it?

"Ha!," Squire laughs. "Well, it did work out that way."

Ask bass-playing enthusiasts, and many will rank Squire at the top of the heap, an honor also accorded to Squire's own muse, Who bassist John Entwistle. Both men (along with Cream's Jack Bruce) approach playing bass as a lead, rather than just a rhythm instrument.

"John was one of my biggest influences," Squire explains. "But expanding the bass part is usually one of the last things I do. I tend to write on piano and acoustic guitar first."

Squire also contributes his secondary vocals to the band, creating the familiar harmony sound many believe is Anderson's voice double-tracked.

Finally, asked about any particular memories of Houston, Squire blurts out that he almost got arrested here back in the '70s at the downtown Hyatt. It all started when the bassist, nursing a brandy at the bar, got bored with the scene and started to take his drink back to his room.

Squire can take it from here...

"I was at the elevator and this Asian guy who must have been the manager came running and screaming at me and yelling for security!

"Then these guys came and took me to a little room. And I was saying, 'What is the problem?' And they told me, 'Oh, you can't take that glass out of the restaurant to your room!' And they interrogated me for like a half an hour!"