The writers and the Hand of God!

[LOCIfan]

Well, not all of the writers listed have worked on the series at the same time. And some have written only one or two episodes. There has always been writer turnover on the show, and when one or more leave, they've always been replaced. If you look at the interview Stephanie SenGupta did for this site (in Articles & Interviews), she talks about how quick the turnaround time is from script to production, so I would think there's probably a minimum number of writers Balcer needs to have in order to keep up with that pace.

[Metella]

absolutely - a writer needs some time to formulate and be creative and all that jazz; too few would put too much pressure on the writers to churn out something just to meet a deadline.

[Lilee]

I'm betting there's a rigerous interview process when hiring new writers, too.

[myneinturn]

the writers are amazing, and yes they probably do have a high standard for writers.