Is Jean-Jacques Rousseau to blame for France's missing millions?

famille nombreuse

Here is a game of consequences.

France was the first country in the world widely to practise birth control, starting in the second half of the 18th century.

As a consequence, at least 60 million French people have gone missing and I can travel for half price on the Paris Metro.

Come again?

France, a fertile and temperate place, has the lowest population density of any large industrialised country in western Europe (save Spain which is not so fertile or industrialised). If France was populated as thickly as Britain - and there is no reason why it should not be - there would be 120 million French people instead of almost 60 million. If it was as crowded as England, it would have a population approaching 180 million. France would be overwhelmingly the dominant country in Europe; it would rival the United States as a power on the planet.

To its chagrin, it isn't (populous) and it doesn't (dominate). France is a remarkably empty place.

As a consequence, it has an obsessive policy of encouraging large families. For more than 100 years - and intensively in the last 50 years - creating babies has been a preoccupation of successive governments in Paris.

To be the father or mother of three children or more in France is to be a privileged person: an official hero of the state; the parent of a "famille nombreuse" (numerous family).

We had two children when we moved to France a year ago: we acquired our third child, Grace, a month ago. We have thus become, overnight, a famille nombreuse. As a consequence, we qualify for all kinds of goodies.

I can now travel for half price on the Paris metro (23 pence for any journey within the city). The privilege, entirely funded by the state, applies even when I am travelling alone. I can get 30 per cent off second- class rail fares and internal air travel. I pay substantially less tax and qualify for increased family allowances (although these are under threat). Once I have lived in Paris a little longer, I will qualify for a Paris-Famille card: this will give me pounds 200 a year towards metro travel, car tax, school meals or child care. It will also give us free admission to museums, swimming pools and play-grounds.

I am, of course happy to claim the benefits, grace a baby Grace, but they also made me curious.

Does any of this largesse do any good? Does it really encourage French people to have babies? Why is France so empty in the first place?

The low population density, by European standards, is sometimes attributed to the slaughter of young French males during the First World War. But Laurent Touleman, a demographic expert at the French statistic institute, explained that the phenomenon is, in fact, much older. Every other European country had a population explosion in the late 18th and early 19th centuries. Advances in medicine and diet stopped people dying young but, for several decades, the birth rate remained as high as ever: as a consequence, the European population leaped.

But not in France. French people also stopped dying young (if they avoided the guillotine) but they also stopped having so many children. Long before other countries, the French began to practise birth control, mostly though coitus interruptus, according to Mr Touleman, since condoms were not yet widely available. Why they did this remains a mystery: some historians put forward economic explanations; others suggest that it was something to do with Jean-Jacques Rousseau and the cult of the child. Families, even poor families, wanted to cherish a small number of children rather than neglect them in large numbers.

For whatever reason, the French birth-rate collapsed long before it did elsewhere. France, which had for centuries been the most populous, and one of the most thickly populated, European countries, saw other nations catch up and even go ahead. At the beginning of the 19th century, there were 27,600,000 people in France and about 10,500,000 in Britain. Both countries now have about 58,000,000. In other words, if France had grown as fast as Britain it would have a population of 150,000,000 today.

By the middle of the 19th century, the French were worried by their shortage of children; there was a "preoccupation du desert", an obsession with emptiness, according to another French demographic expert, Quang-che Dinh. This was reinforced by the slaughter in the trenches in the First World War; but, in fact, those losses were more than made up by Spanish and Italian immigration in the 1920s and 1930s.

The defeat in 1940 - when Germany mobilised 40 divisions to France's 10 - led to something like "demographic panic", according to Mr Quang.

The Vichy government enormously increased subsidies to families, partly for ideological reasons. But the policy was pursued vigorously post-war. The definition of a famille nombreuse was reduced to three children, and the benefits increased, as recently as 1982.

Mr Quang has studied the effects of family subsidies on French fertility rates and population growth: his conclusion, backed by other studies, is that they have no discernible impact. The French fertility rate - now 1.72 children for every woman of child-bearing age - is marginally above the European average, but little different from the rate in Britain.

Last month the new Socialist-led government in France did something brave and sensible, without quite admitting it. It broke with more than a century of procreation policy in France by imposing a means test on family allowances. In other words, it abandoned the principle that the state should reward its citizens for having large families, however wealthy the citizens might be. Similar restrictions on the other perks of multiple parenthood can only be a matter of time.

The truth is that France missed the demographic bus 200 years ago. It could now replace the missing legions of French people only by immigration on a vast scale (any takers, Mr Le Pen?).

My wife and I have done our best to fill the gap: Grace can become a French citizen, if she wishes, when she is 13 (she is already Irish and British). Three children, we agree, is quite enough. However, if we were to have a fourth child, we would get 40 per cent off rail travel; a fifth child would give us 50 per cent off ...