If you're looking for signs that the world is changing (or possibly ending), consider this: Joe Segal, the notoriously territorial proprietor of Jazz Showcase, has opened his doors to a series of benefit performances for a rival club. Of course, Fred Anderson's Velvet Lounge--an integral part of Chicago's new-jazz resurgence in the past decade--doesn't exactly compete with Segal's club, a longtime bastion of mainstream jazz. And besides, these two old lions, both now in their mid-70s, have something in common: Anderson's astonishing longevity as a vital tenor saxophonist (strong on the scene since the early 60s) rivals Segal's hardscrabble persistence as a promoter (booking jazz at various venues since the late 40s). Few listeners have ever regarded Anderson with ambivalence--nor should they. Like Von Freeman, he's carved out a uniquely Chicagoan style of improvising that's rough around the edges, voluptuous at its center, and physically demanding in its reliance on massive volume and busy technique; also like Freeman, he's maintained this approach for decades and even improved upon it, offering epic pantonal improvisations with ever-increasing polish and lyricism. Anderson will perform "with friends"--in other words, a shifting cast of supporting players--every Monday this month. The Showcase bills it as a "relocation fund-raiser" to defray the expenses of building out the new space the Velvet Lounge will move to at an as-yet-unannounced date. Mon 1/16, 8 PM, Jazz Showcase, 59 W. Grand, 312-670-2473, $15, $10 students.