I'm often asked, "What is the world's fastest growing religion?"
Questioners are stirred both by hope -- that "our" religion is so evidently the best that it is sweeping the world -- but also by the fear that "they" (usually Muslims) are going to overwhelm us.
Actually, that growth question crosses faith boundaries. Wikipedia's entry on "Claims to be the Fastest-Growing Religion" collects many such boasts, which variously claim the prize for Islam, Christianity, Buddhism, Wicca, Deism, the Falun Gong, Scientology, and other competitors. Obviously, even compiling such a list has the tongue-in-cheek implication that most such claims are bogus or misinformed. Accurate quantitative information about any faith is hard to come by, and any plausible comparisons are difficult. Having said this, the growth question does tell us a lot about how and why faiths change over time.
At first sight, the contest should be a shut-out, leaving Christianity the clear winner. During the twentieth century, Christian numbers expanded mightily around the world, but especially in the Global South. According to the respected World Christian Database, since 1900 the number of African Christians has grown by an incredible 4,930 percent, and the growth in Latin America was 877 percent. The increase for particular denominations was even more startling. During the twentieth century, Africa's Catholic population grew from 1.9 million to 130 million -- an increase of 6,700 percent.
The total number of African believers of all shades soared, from just 10 million in 1900 to almost 500 million today, and (if projections are correct) to an astonishing billion by 2050. Put another way, the number of African Christians in 2050 will be almost twice as large as the total figure for all Christians alive anywhere in the globe back in 1900.
But before we open the envelope and hand over the statuette, it's sobering to compare Islamic growth in the same period.
Both religions have acquired vastly more adherents in the past century, but in some ways, Muslims have significantly outpaced Christians. However staggering their growth rate might seem, Christian numbers have actually proved strikingly stable as a share of global population. In 1900, about one-third of the world's people were Christians, and that proportion remains more or less unchanged today. Moreover, if we project our estimate forward to the year 2050, that proportion should still be about one third.
Seen in those terms, Islam's surge has been still more impressive. In 1900, the 200-220 million Muslims then living comprised some twelve or thirteen percent of humanity, compared to 22.5 percent today, and a projected figure of 27 percent by 2050. Christians in 1900 outnumbered Muslims by 2.8 to 1. Today the figure is 1.5 to 1, and by 2050 it should be 1.3 to 1. In historical terms, the gap is closing fast.
If Christians point to Africa as the ultimate success story, then Muslims can boast their growing numbers across their historic heartlands. In 1900, for instance, Egypt had perhaps nine million Muslims, compared to 75 million today. In the same period, the number of Iranian Muslims grew from ten million to perhaps 65 million. In 1900, the lands that would become Indonesia had perhaps 34 million Muslims, compared to 190 million today.
Put another way, four times as many Christians are alive today as there were in 1900; but over the same period, Muslims have grown at least seven-fold.
How can this be? If Christian numbers are exploding, how can they be left so far behind Muslims in the rate of expansion? The answer lies in differential demographics, namely that some parts of the world are growing much faster than others. Islam grew so mightily because Muslims were so heavily concentrated in those regions that maintained very high fertility rates throughout the twentieth century, chiefly in Africa and Asia. A rising tide lifts all faiths.
In contrast, overall Christian numbers lagged because that faith was traditionally concentrated in Europe, and Europe's demographic growth has been very slow in comparison with other parts of the globe. Back in 1900, Europeans made up around a quarter of the world's population, but by 2050, that number will probably be closer to eight percent. In 1900, there were three Europeans for every African. By 2050, there should be three Africans for every European. If we take Europe out of the picture, then, Islam and Christianity have been running a very close race worldwide, but Christians find it hard to overcome that demographic handicap.
When I am asked about the world's fastest growing religion, then, I answer unequivocally: Islam. Or, Christianity outside Europe.