Conservative commentator Mark Steyn declares that Europe will soon be dominated by Muslims. The polemicist Sam Harris observes that half of Swedes are atheists, portending a godless future. They can't both be right, but they are both making the same mistake.
While Harris' fellow travellers exult over the fact that the number of Americans affirming that they have "no religion" has doubled in less than a generation, others point out that individual fertility in the west is directly proportional to personal religiosity. American women with a religious affiliation bear nearly a third more children than those without, and this, as much as changing beliefs, will influence the religious makeup of future generations.
It is an old trope that one can lie with statistics, but it might be more accurate to admit that selective use of numbers can easily mislead. Introductory biology students often learn that one bacterium in a petri dish will clone itself so that if it kept going at the same rate it would in short order fill up the universe. But common sense soon tells them this won't happen. Projecting from the first generations is folly.
Human societies are infinitely more complex in their structure than bacterial colonies, so one should be exceedingly cautious about games of prediction. Across the west the 1960s was a period of cultural change as church affiliation dropped precipitously. If one extends that decline out from the interval 1960-1970 Christianity should be extinct, and yet it is not. The decline in religiosity slowed by around 1980. Why? The will of God? A more plausible explanation is that social pressures which enforced religiosity before 1960 no longer operate, so those who were never particularly devout are more honest with themselves and society.
Labels matter a great deal here. It is not true that modern societies are divided between atheism and institutional religion. Sam Harris implicitly assumes this model when he says that half of Swedes are atheists, and it allows him to rig the game. In reality a February 2005 Eurobarometer survey (pdf) reported that 23% of Swedes did not believe in God, 20% did, and 53% believed in a spirit. A quick survey of European nations shows that the decline of traditional institutional religion has benefited both atheism and unaffiliated spirituality, but the latter has grown more robustly than the former!
The universe of statistics is vast, so polemicists can choose congenial data to "prove" their trends. Labels often hide more information than they reveal. Prophecies of the extinction of religion, or its total ascendancy, inevitability fall prey to the weaknesses of linear extrapolation. The most important thing that science can tell us about most trends is that they will some day reverse.
