7th Heaven (costarring Beverley Mitchell and Barry Watson, left) has marked a rare achievement for a family drama, and I don’t mean Jessica Biel getting named ”sexiest woman alive” by Esquire magazine last week. Rather, the show has entered its 10th season and has quietly logged its 200th episode, making it, by some measures, the longest-running family drama in primetime TV history. (Actually, the milestone comes with a couple of asterisks: The Waltons lasted only nine seasons, from 1972-81, but it produced 221 episodes. Little House ran nine full seasons from 1974-83, then had a brief 10th season of just three episodes in 1984, for a lifetime total of 207, a number that 7th Heaven will surpass in a few weeks. And that’s all for this momentary lapse into geeky numbers-crunching; we now return to your regularly scheduled PopWatch.)

Anyway, 200 episodes is pretty impressive, especially considering all the kids who’ve matured into little grownups during the show’s decade on the air. Anyone want to offer a theory as to what’s behind the show’s longevity — the acting, the writing (which addresses delicate topics in a surprisingly non-preachy way), the lack of similar fare on the WB or anywhere else?