The most segregated hour of the American week is 11am on a Sunday morning, when black and white Americans all get dressed up and go to separate churches to worship the same God.
The next most segregated hour is 8pm on any weekday, when the clock strikes prime time and the nation observes its second favourite religion - watching television.
And now Friends is preparing for the arrival of the first major non-white character to its cast in its nine-year history. This is truly symbolic of developments both on screen and in front of it, as it signifies how little has changed and how long that little has taken to come about
For if you're looking for evidence of how deep-rooted segregation remains in America, you need reach no further than the TV remote. Before their behinds have hit the couch, black and white Americans have retreated into separate worlds.
There is only one programme - CSI: Crime Scene Investigation - which features in the top 10 for both black and white viewers. "White" hits like Seinfeld or Will & Grace have scarcely featured on African-Americans' radar. Meanwhile, most white people have never even heard of the most popular black shows like Girlfriends and Bernie Mac.
Friends is the sixth most watched show among white US viewers. But among black viewers, it came only 65th. White characters have long been forced on "black" shows to "broaden their appeal". But, up until now, "white" shows have been regarded as sufficiently mainstream to justify their exclusivity.
So when Aisha Tyler ap pears on Friends next week as a fossil expert torn between Ross and Joey, she will face the familiar dilemma of black professionals in an all-white environment.
In the course of doing her job, she will be expected to single-handedly integrate an all-white institution, satisfy the frustrated expectations of black people who have been unrepresented and fend off criticisms from whites that she only got the job because she's black (as though the fact that everyone else is white is merely a coincidence). All of this will fall on her slender shoulders - for regardless of your race, all women's shoulders must be slender on prime time.
On one level, the segregated viewing habits and segregated casts do reflect reality. America is a deeply racially segregated country. And while a power differential remains between whites, blacks and Hispanics, the truth is also that much of that segregation is voluntary.
"I like it that there are no black friends on Friends," writes Michael Moore in Stupid White Men. "Because, in real life, friends like that don't have black friends. It's an honest, believable show."
The fact that these racial differences are most pronounced in comedy is a depressing reflection just how little commonality there is between racial groups. "Humour," wrote the Martiniquan poet, Aime Cesaire, "alone assures me that the most prodigious reversals are legitimate. Humour alone alerts me to the other side of things."
But if laughter is a universal language, black, white and Hispanic Americans still need translators.
"Comedies don't cross over," says Doug Alligood, vice-president at the advertising agency BBDO. "You can't tell the same joke ... It shows we come from different places."
This cleavage is tempered by age. I watched Ali G's American show with 30 students from New York University of all races. They all found it as funny and problematic as any British students would. But, in discussion, it transpired that central to their understanding of the humour was the fact that Ali G is English.
"Could an American comedian do this and get away with it?" I asked. They looked at me as as I was insane.
"We'd picket the studio until they took it off the air," said one student, to general assent.
So long as Will and Grace, Chandler and Monica, stay in their houses, their lives were a reflection of this dislocated, fragile, segregated reality. But as soon as they walk down the street, or go to a coffee shop, the surreal takes over. Racial segregation in New York, as in most other American cities, is defined more by culture than by geography. Blacks, Asians, Latinos and whites occupy the same physical space in most of Manhattan for most of the day, whether they are couriers, cab drivers, businessmen or bellboys. Different races congregate even if they rarely coalesce - each individual having a segregated experience within an integrated space.
With white people comprising just over half of Manhattan, and less than a third of New York as a whole, it is difficult to imagine the city without a sizeable non-white population. And yet in all the major sitcoms, they have ethnically cleansed the city of any visible minority presence in streets, bars and cafes.
Their selective myopia is contagious. A recent Panorama, shot with the avowed intention of showing what New Yorkers thought of the war, had a panel of 10, of whom one was non-white.
When challenged, one of the producers said: "We do not cast by quota."
Casting by intelligence or sensitivity had clearly not occurred to him, either.
And, with that phrase, he split my sides, showing that the best examples of racial humour are not always intentional.
