Last night, as the dust settled on the news that Stephen Colbert would be taking over ‘Late Show’ from David Letterman at some point in 2015, I was engaged in a conversation that drifted toward just how someone qualifies to be a viable candidate for a network late night talk show in the first place. More specifically, how is it that 28 years ago, a woman actually did host a network late night network talk show and, now, in 2014, that would seem almost revolutionary.

In October of 1986, ‘The Late Show’ debuted on the then-fledging Fox network, hosted by Joan Rivers. (The network was so young at the time that ‘The Late Show’ was Fox’s first original programming; its second, ‘Married… With Children,’ wouldn’t debut until April.) Without, at that point, a true network to push the show, affiliates balked at airing ‘The Late Show’ and Rivers was out as host by May of 1987. Making matter worse for Rivers, she never told Carson about her plans to compete directly against him. Carson, feeling betrayed, never spoke to Rivers again.

What’s interesting here is that Rivers was tapped as host of ‘The Late Show’ after rising to prominence over the prior three years as Johnny Carson’s permanent guest host of ‘The Tonight Show.’ Today, if you want your own 11:30 p.m. network talk show, you at least have to start out in the 12:30 a.m. (or equivalent) slot first. Jimmy Fallon, Conan O’Brien, David Letterman, Jimmy Kimmel and now Colbert all hosted the follow-up show before they were given the keys to their network, or another network’s, flagship late night show. (Kimmel never switched shows, unless we are counting ‘The Man Show,’ but ‘Jimmy Kimmel Live!’ used to air after ‘Nightline.’)

Johnny Carson’s first appearance as host of ‘The Tonight Show’ was filling in for then-host Jack Paar, before Carson eventually became the permanent host in October of 1962. The tradition of guest hosts continued and flourished under Carson’s 30-year tenure as the host of ‘Tonight.’ Letterman, Rivers and Jay Leno were all mainstays of Carson’s guest host stable and all three went on to host their own shows (with Leno, controversially, succeeding Carson on ‘The Tonight Show’).

Kermit the freaking Frog even once guest hosted ‘The Tonight Show.' He interviewed Vincent Price.

What was once a breeding ground for young comedians like Letterman and Leno disappeared once Letterman and Leno became the 11:30 p.m. hosts of their respective shows.

Perhaps it was the two men’s drive to beat the other after their very public feud that killed the guest host. Carson’s ‘Tonight Show’ was the only game in town for pretty much his entire 30-year run. Perhaps this is why Carson felt so comfortable taking so many frequent vacations. And, by the early 1980s, even when Carson wasn’t on vacation, he was only hosting three new shows a week. A guest host was pretty much mandatory.

In comparison, both Letterman and Leno were absolute workhorses over their runs as host. Both men hosted five shows a week (Letterman would, and still does, tape two shows in a row once a week so that he has Fridays off) and, in comparison, their vacation time was negligible.

During Letterman’s run, he never used a guest host on NBC’s ‘Late Night with David Letterman.’ After having quintuple bypass surgery, a series of guest hosts appeared on CBS’s ‘Late Show,’ including Paul Shaffer, Regis Philbin and Bill Cosby. In early 2003, after contracting shingles, Letterman once again employed guest hosts that included Will Ferrell and, once again, Bill Cosby. Letterman then flirted with the idea of non-medical emergency guest hosts in 2003 – Jimmy Fallon even hosted! – but, after a few weeks, the idea was dropped. In 2007, Adam Sandler, who was scheduled to be a guest that night, filled in for Letterman, who had stomach flu. This was the last time anyone other than Letterman hosted ‘Late Show.’

Jay Leno employed a guest host only one time, which was a publicity stunt when he and then-‘Today’ host Katie Couric switched jobs for one day.

The exception to all of this is the case of John Oliver. While Jon Stewart took a long hiatus over the summer of 2013 to direct ‘Rosewater,’ John Oliver, in a rare move today, became the guest host of ‘The Daily Show.’ What’s remarkable is that, even though the tradition of a guest host is now a thing of the past, the end result is still the same: John Oliver now has his own show on HBO.

I reached out to a late night insider to ask about why this tradition ended. First and foremost, it’s not just the host who needs some time off, it’s the entire staff.

I think it's a pretty simple answer. The rest of the staff. You can't just give the host a week off. The entire staff and crew would burn out.

But then how did Carson pull that off? Our insider explains:

It was a different era. Apples and oranges to the periods the state of late night was in. If you worked at Carson, you were thrilled to have a job. Where else were you going?... It's also much cheaper to run a repeat. It's always about the money.

This makes sense, but the death of the late night guest host has made the field of viable candidates a far narrower field than it once was, even with the plethora of hosting opportunities available today. Even with the abundance of shows, it was still easier (and less of a commitment for everyone involved) to fill in for one night than it is to fully commit to one person has a host of any show, no matter how small the audience.

Today, a committee and focus groups decide the fate of a prospective host. Back in Johnny Carson’s era, Joan Rivers got a shot because Carson thought she was funny. That’s all it took. And John Oliver proved that this process can still work today. Perhaps someday we will see the return of the guest host. And, perhaps, the next Joan Rivers will get her network shot someday, too.

Mike Ryan is the senior editor of ScreenCrush. You can contact him directly on Twitter.

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