You ain’t never seen the tango as smooth, sexy and varied as in Forever Tango … unless you saw it first time around a decade ago. Born out of African and Latin rhythms in Buenos Aires waterfront dives, the tango swept the world in the 1920s, influencing everyone from Kurt Weill and Shostakovich to Gershwin and Aaron Copeland. At its best it’s a power dance and mating ritual, and so it is in Forever Tango, performed by 14 dancers and 11 musicians including four bandoleon (Argentine accordian) players, through Oct. 31 at the Athenaeum; (312) 902-1500 (Ticketmaster); $29.50-$55.