At first glance, it looks as though the Sea of Faith has well and truly evaporated. At the start of Lent this year, the BBC expressed puzzlement when Glasgow MP Carol Monaghan turned up to a parliamentary meeting wearing ash on her forehead, and asked whether this was “appropriate”. As the general election was called, Liberal Democrat leader Tim Farron came under fire because of his Evangelical Christianity, a belief system historically central to liberalism but now incompatible with secular (but seemingly no less sacred) ideas about sexuality. The message: that religion is not just outdated but also absurd.

Western Christianity has been under sustained pressure for at least three centuries, a process that began with the Dutch philosopher Spinoza but accelerated in the 19th century with Darwin and the German Higher Criticism. In the Middle East Islamists may bomb churches and behead “Nazarenes”, but ridicule has been a highly effective way of driving Christianity out of public life in Europe.

This has really begun to tell in the past three decades, an acceleration dictated by demography, as older churchgoers are succeeded by young atheists. Christians are dying and not being replaced, and the balance has even tipped in the United States, long seen as the exceptional highly religious Western country. There the decline of the mainline Protestant churches is finally starting to show, while the Catholic Church is also ailing: not even mass migration from Latin America can save it, with Hispanics leaving the faith in droves.

The number of Americans identifying as atheists doubled between 2007 and 2014, according to the Pew Research Centre, while Catholicism loses six times as many followers as it gains, becoming part of the worldwide Church Despondent. Even the most religious countries in Western Europe – Catholic Ireland, Portugal and Malta – are catching up with France and Britain.

It seems we’re doomed, as the Calvinists might say. Secularisation theory holds that as countries develop economically, so religious belief declines. This has certainly been the case in Europe, where it has reached the stage where faith is regarded as an eccentricity, incomprehensible to a religiously illiterate media, as Mr Farron learned. Yet believers have for some time held out hope of a miracle to give them final victory: the battle of the cradle. They may now have found it.

As religious belief declines, birth rates fall dramatically. France was the first country to undergo secularisation, and by the late 19th century it had a fertility rate half that of the more churchgoing Britain. But the paradox is that as overall fertility decreases the gap between the religious and secular starts to grow, so that the next generation comes disproportionately from religious families.

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