In the autumn of 1787, gallery-going Parisians didn't know where to look. On the walls of the Louvre hung a self-portrait by the eminent artist Elisabeth-Louise Vigée Le Brun. In some ways the painting was deeply conventional. Mme Vigée Le Brun was dandling her infant daughter on her knee in a gesture that managed to invoke both the Virgin Mary and the new bourgeois ideal of "natural" motherhood. The problem was her mouth. It was smiling. Not just an enigmatic Mona Lisa smirk, but a proper one which showed her teeth. Was Vigée Le Brun mad, a slut or some kind of wild revolutionary? The only thing to do was rush past, and pretend you hadn't seen.

In this compelling Cheshire cat of a book, Colin Jones charts the moment in the mid-18th century when Paris learned to smile. Until that point, the court, tucked away at Versailles, had insisted that everyone kept a straight face. This was partly because France's most privileged mouths had been spoiled by too much sugar, and no one wanted their black stumps flashed to infinity in the Hall of Mirrors. But it was also because smiling in general risked making you look either plebeian or insane.

To understand why you have to go to the roots. Sourire, a smile, comes from sous-rire, a little laugh, and laughing was something that definitely belonged to the lower orders. Just like a yawn or a fart, a side-splitting guffaw breached the boundary between the body and the rest of the world. This inside-outsideness was fine if you were of a Rabelaisian turn of mind, but disturbing if you weren't. For in the bellylaugh's uninhibited rumble, it was possible to hear the stirrings of serious social and political dissent. No wonder the toffs at Versailles kept their mouths clamped shut, refusing to mobilise their features beyond the occasional sneer.

But in the 1760s, Jones argues, all this changed. The court was beginning to cede its prestige to the city, and the city felt like smiling. Bourgeois men had started doing it at work, and also in the coffee houses that were springing up around the bourse. A smile was infectious, closed the gap between friends and strangers, allowed deals to be struck and views exchanged. And whereas women had once been forbidden from showing their teeth in public, now salonnieres such as Suzanne Necker and Marie Thérèse Geoffrin made a point of greeting their guests with an upturned mouth.

Driving all this was a new culture of sensibility that valued the expression of emotion as a marker of an individual's essential humanity. Indeed, to smile the right kind of smile – truthful, unforced – was to announce yourself as a person of taste, discernment and, above all, feeling. You couldn't fake it, though. When a few adventurous nobles escaped to the city for the evening and tried pasting on a grin, they were quickly spotted as impersonators and sent back to Versailles where they were made to re-apply a poker face.

This is a difficult kind of history to pull off. Ancient bones can be dug up from car parks, DNA can be tested centuries later, but expressions are fleeting and leave little trace. Eight years ago, Vic Gatrell published his magnificent City of Laughter, which mapped the satire boom of late Georgian London. But Gatrell had hundreds of Rowlandson and Gillray prints on which to peg his argument about the political power of a dirty chuckle. Jones is obliged to work from thinner material. Still, he does well with the paintings of Jean-Baptiste Greuze, in whose descriptions of bourgeois family life you can spot plenty of jeunes filles and bonnes mamans facing down triumph and tragedy with a stoical smile pinned to their features.

He also pays great attention to literary texts, pointing out how the Parisian reading public became fixated on Samuel Richardson's Clarissa (1748) not so much because of the overwrought plot but because of the heroine's lovely smile. Later, Rousseau's Nouvelle Héloïse (1761) became a bible for thousands of city women who hoped that their own leathered features might be made to move with the same exquisite lability as those of Julie, the smiling-through-tears ingenue who managed to keep everyone cheerful even as she lay dying.

Proving that all these textual and painted smiles migrated to the real world is, of course, another matter. To make his case, Jones points to the rise of a new kind of dentistry. Under the old regime of teeth, anyone suffering from a pesky molar went to the Pont Neuf and put themselves in the hands of a fairground buffoon with a pair of pliers. But from the 1720s, you had the option of visiting the gentlemanly Pierre Fauchard in his well-appointed surgery in the sixth arrondissement, where each tooth was treated like an honoured family friend whose loss was the occasion for deep sorrow. By the middle of the century, Parisian dentists were recognised not simply as master technicians but as midwives to the new sociability. Thanks to their insistence on good oral hygiene, a spray of spittle or blast of halitosis no longer need come between a man and his coffee house confreres.

When the revolution finally arrived in 1789, two years after Vigée Le Brun's twinkling appearance in the Louvre, there seemed every reason to greet it with a smile. For what enlightened man or woman could quarrel with the promise of universal happiness? But by 1793, the mild and moderate bonheur of the early reformist phase had been replaced with the spiteful cackle of the Terror. To keep on smiling at such a time was to risk looking like a false friend to the people, a secret reactionary who was desperate to keep in with absolutely everyone. All you could do now was make sure that, as you were led away to your death, your features were arranged as they had been in happier times. To smile on the scaffold had become the ultimate act of political resistance.

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• This article was amended on 17 October 2014. The French word "souris" means "mouse", not "smile" as an earlier version of this article suggested. This has been corrected