Catholics will decide the future of the West.

That’s the conclusion we reach after reading Mark Steyn’s much e-mailed Wall Street Journal online column, “It’s the Demography, Stupid. ”

In it, Steyn made a simple argument: Birthrates demonstrate that European societies are dying out and will become Muslim in our lifetime. “When it comes to forecasting the future, the birthrate is the nearest thing to hard numbers,” he wrote. “And the hard data on babies around the Western world is that they’re running out a lot faster than the oil is.”

The “replacement fertility rate” today is 2.1 babies per woman — that’s the number of babies a society needs to have in order to keep from decreasing in size.

Steyn points out that some countries are well above that. But they are, for the most part, countries known for their strict application of Sharia (Islamic law) and for human-rights abuses, particularly against women. Somalia’s average is 6.91 births per woman, Niger’s is 6.83, Afghanistan’s is 6.78, Yemen’s is 6.75.

Western, democratic nations have far lower birthrates. The United States is about at the replacement rate, with 2.07 births per woman (thanks to immigrants from Mexico with larger families). Ireland averages 1.87 births per woman, New Zealand 1.79, Australia 1.76. Steyn, a Canadian, notes that in Canada women have 1.5 children on average — “well below replacement rate.” Germany and Austria are at 1.3, “the brink of the death spiral.” Spain is at 1.1 — “Spain’s population is halving every generation.”

Steyn’s conclusion: “To avoid collapse, European nations will need to take in immigrants at a rate no stable society has ever attempted.”

Today, the West is known for exporting consumer products. Islamic countries are known for exporting people and ideas. Mosques throughout Europe are reaching disaffected immigrant Muslim youths and inspiring them with religious fervor. Looking just at birthrates, Steyn sees a worst-case scenario of Sharia becoming the law of the land in Europe in 2040 and “semi-Sharia a lot sooner.”

So, what do Catholics have to do with all of this?

The Catholic Church still holds — and vigorously teaches at the highest levels — doctrines that would transform this demographic scenario virtually overnight, if Catholics actually followed them.

“Human life must be respected and protected absolutely from the moment of conception,” teaches the Catechism of the Catholic Church (No. 2270). And yet the rate of abortion among Catholics is almost indistinguishable from that of the larger population.

In reiterating the Church’s teaching against using artificial contraception, the Catechism (No. 2373) reminds us that “Sacred Scripture and the Church’s traditional practice see in large families a sign of God’s blessing and the parents’ generosity.” And yet the birthrate among Catholics in a given society isn’t much higher than the average.

It could even be said that the West faces a demographic crisis precisely because Catholics have rejected — or have been taught to ignore — the Church’s teaching.

It ought to be that Catholics are the “little flock” that builds the Kingdom of God, to echo Christ’s words. But in our day, the dynamic seems to have gone the other way around — Catholics are too often the ones who are being transformed by the spirit of our age.

What can we do about it?

This was precisely the question that Pope John Paul II attempted to answer throughout his pontificate. He made the Church’s teachings on human life, marriage and family a cornerstone of his pontificate, and called tirelessly for Catholics to re-evangelize the West.

If this new evangelization seems like an impossibly difficult task, it needn’t. It will certainly be difficult, but the same God who blessed the first evangelization is every bit as interested in the follow-through.

The first small signs that show a change in the tide may already be occurring. Bishops are starting to teach in a dynamic way what the Church does about marriage and family life. Where there is a leader willing to tell the truth, there are Catholics willing to follow it, and many are doing so.

Catholic universities have been very slow to embrace and apply the Church’s teaching on marriage and families, too often spending more energy rejecting the Church’s teaching than they do unpacking and applying them. Some universities are beginning to teach what the Church does. Catholic theology departments that embrace the magisterium are marked by energy and enthusiasm. Dissenting ones are marked by decline and doldrums.

These might be the first signs of the new springtime.