Islam is the fastest-growing religion in the world and, if current trends continue, will pass Christianity somewhere in the middle of this century, before going on to become the world’s dominant religion by 2070.
On April 2, the Pew Research Center released its report on “The Future of World Religions: Population Growth Projections, 2010-2050,” which explores not only demographic trends, but also the underlying causes behind them. The study projects the number of Christians as a percentage of the global population remaining stable for the next several decades, while the number of Muslims—both in absolute figures and as a percentage of the population—increases steadily.
Muslims, in fact, are the only major religious group projected to outpace the growth of the world’s population as a whole.
In 2010, Christians significantly outnumbered Muslims, with the former totaling 2.17 billion worldwide and Muslims 1.6 billion. Data suggest that this relationship will shift in coming years, with Islam reaching numeric parity with Christianity around 2050.
If current demographic trends continue, Pew projects that by mid-century, the Muslim population will have increased by 73 percent and make up 30 percent of the world’s population, totaling 2.8 billion.
According to Alan Cooperman, Pew’s director of religion research, location is a major factor in determining the growth of a given religious population. “The main reason Muslims are growing not only in number but in share worldwide is because of where they live,” said Cooperman. “Muslim populations are concentrated in some of the fastest-growing parts of the world.”
The most important factor in this demographic shift is a matter of breeding. Muslims have the highest fertility rate in the world, with an average of 3.1 children per woman, which is well above the replacement level of 2.1, considered the minimum needed to maintain a stable population. Christians, though well above replacement level, have a fertility rate significantly lower than Muslims, at 2.7 children per woman, which helps explain the trend toward parity and eventually Muslim numeric dominance.
Both Hindus and Jews have fertility rates above replacement level (2.4 and 2.3, respectively), though slightly lower than the global average of 2.5, meaning their populations as a percentage of global totals are declining.
As a group, Buddhists have the lowest fertility levels, and at only 1.6 children per woman, they are well below replacement level and destined to drop, both in absolute numbers and as a percentage of the world population, if current trends hold.
Besides fertility, a second important determinant of population change is the age distribution of each religious group. When members are predominantly young, with their prime childbearing years still ahead, they will experience much greater growth than if their populations are older and largely past their childbearing years.
The age factor, too, helps explain Islam’s projected growth spurt. As of 2010, 27% of the world’s total population was under the age of 15, whereas an even higher percentage of Muslims (34%) were younger than 15. Christians, on the other hand, matched the global average (27%) in their under-15 population. Islam’s notable youth helps account for projections that the Muslim population will grow faster than the world’s overall population, while Christians are projected to roughly keep pace with it.
Conversion into or out of a particular religious group plays a lesser and more complex role than fertility. According to the report, Christians are expected to experience the largest net losses from conversion in coming decades. On the world scale, 40 million people are projected to switch to Christianity, while 106 million are expected to leave, most of these joining the ranks of the religiously unaffiliated.
Jews are projected to experience a net loss of about 300,000 people due to conversion, while Buddhists are expected to lose nearly 3 million.
Muslims, on the other hand, are projected to experience modest net gains through conversions (3 million), as are adherents of folk religions (3 million), and members of other religions (2 million).
Much has been made recently of the increase of the religiously unaffiliated—“nones”—in the United States. Though this trend is expected to continue, atheists, agnostics and other people who do not affiliate with any religion will make up a decreasing share of the world’s total population. This is due in part to the low fertility rate of the unaffiliated, which at just 1.7 children per woman, is well below replacement level.
One lacuna in the Pew report was data on China, absent due to unavailability. China’s 1.3 billion population is currently five percent Christian, with significant conversions to the faith each year, which could have an effect on the growth of Christians worldwide.
Follow Thomas D. Williams on Twitter @tdwilliamsrome.
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