The most surprising thing about the breathy announcement last week that Marcel Duchamp’s Fountain was named the most influential artwork of our times by a panel of 500 art world worthies is not that the prize should have gone to a signed urinal. That was obvious. Of course Duchamp’s Fountain, created in 1917, is the most influential art work of the modern age.

What is surprising is that it took the worthies so long to reach their conclusion. This announcement could have been made at any time in the past 50 years or so, and would have been just as true then as it is now.

I am not thinking here about self-evident stuff. Sure, without the urinal there would be no Tate Modern, Nick Serota, Charles Saatchi, Turner prize and conceptual art. Some of you will be cheering this news — and shouting for the return of a pre-urinal age. But chew on this, Philistine. Half the earlier isms of the 20th century were also given succour by the great pissoir, or appeared as a result of it. Surrealism could not have been what it was without the urinal. Nor Dada, minimalism and most certainly not pop art.

If that doesn’t impress you then let’s look beyond art, at life as we know it today. Had the urinal not introduced the concept of radical conversion and therefore found a way to make the useless priceless, I’m sure there would be no loft-living today.

Warehouses would have stayed warehouses. The less-is-more aesthetic would not have triumphed either, so there would be no Scandinavian shelving, Hugo Boss nor even Ikea. Anything fashionable that involves taking stuff away rather than adding can trace its family tree back to that pure outline from the gents’.

In the field of attitude, the urinal’s impact was nuclear. I seriously doubt that the 1960s could have turned out how they did — sassy, irreverent, youthful, up for it — if the urinal hadn’t shown the way.

And when you switch on the television and catch the ads, and someone tries to sell you something by talking about something else, where do you think the technique originated? Put in the crudest terms, before the urinal things looked backward. After it they looked forward. It’s that simple.

Lots of people don’t like any of this. Lots of people would rather the whole caboodle — Serota, the Tate, the pissoir, Tracey Emin — all of it would go away. But it won’t. If you cannot deal with the extraordinary legacy of Duchamp’s Fountain then I suggest you enter a monastery or move to Wales. Because you will never be able to hack it in the modern world.

The story about how Duchamp came to make Fountain and exhibit it, or rather not exhibit it, is worth repeating for the light it casts on the history of contemporary art.

Duchamp was a Frenchman born in 1887 who managed to skip the first world war by feigning invalidity and resettled himself in New York in 1915. He left behind what we might call the old art world: Matisse, Picasso, Braque.

Some people fondly imagine this rejected generation to represent the proper spirit of modern art. But while Braque was fighting in the trenches, Duchamp was amusing Americans at art openings and becoming the unelected leader of the Manhattan avant-garde. The war that was decimating his generation back in France might as well not have been happening for him. It was just another conceptual unreality.

We can frown at this unserious behaviour or we can recognise it as Duchamp’s exasperated protest at the sheer silliness of the old ways. While the Germans, the French and the English were slugging it out to the death in the mud — in order to achieve what? — Duchamp was learning how to bed the first generation of ladies who lunch and cocking a snook at the whole appalling mindset that had brought the great European cocks to war. Who was getting this right? Braque or him? What is clear is that Duchamp’s decampment to New York is the single most symbolic act in the transfer of cultural power from old world to new. America was the place to be. Everything going on there — the skyscrapers, cars, movies, lippiness and jazz — added up to nothing less than the invention of today.

As a Frenchman, Duchamp was looked up to for all the old reasons. Snobbery made him the toast of the Manhattan art world. But what is wonderful about him — what saves him, glorifies him and makes him special — is the imperishable cultural truth that you can take a Frenchman out of France but you cannot take France out of a Frenchman.