For a century or two now, people have been predicting the eventual disappearance of religion. As education spreads and scientific knowledge increases, people were supposed to cast off their old superstitions and come into the light of reason. While that has happened in many places—basically, the developed countries of the West, with the exception of the United States—for the most part religion has stubbornly persisted. An interesting survey of religious belief in 30 countries just out from the University of Chicago shows overall religious belief is declining, but at a very slow rate. And even in countries with high rates of atheism, as people get older, they are more likely to become religious. There is evidence from the survey that this is both a cohort effect (older generations being more religious than younger generations), and an aging effect, that individuals may actually be changing their beliefs as they age, particularly as they hit senior citizenship. Why? Death, of course. Which helps explain why religion has such staying power.
As in so many other areas, we are more likely to believe that the thing we would like to be true is in fact true. As you age you see more and more of your family and friends die, and the thought that they are living in paradise and you'll see them again one day is enormously comforting (although I have to admit, as an atheist I've always found it odd that even deeply religious people who claim not a shred of doubt about the existence of heaven nonetheless feel profound sadness and grief when their loved ones die, despite the fact that those loved ones are supposedly not only not dead, but are experiencing a joy beyond imagining). Even more powerful is the thought of your own mortality, which becomes harder and harder to ignore with each passing year. And immortality is, after all, religion's killer app. The need to confront and overcome the horrible finality of death—grim, merciless, terrifying, bleak death— is one of the principal reasons religion came into being in the first place, and the reason it persists no matter how much its ground of explanation is encroached on by science. It's no accident that every religion that ever existed promises some form of immortality. People will tolerate an awful lot of cognitive dissonance to hold on to that promise.
But if that kind of elemental force was what made all the difference in whether people believe or don't, we'd see only small variations between countries. Yet as the Chicago study shows (here's the full write-up), the variations are enormous. In the Philippines, 83.6 percent of people say, "I know God exists and I have no doubts about it." In Great Britain it's only 16.8 percent. Even among some similarly developed countries there can be a wide variation; 38.4 percent of Spanish people have no doubts about God, but only 15.5 percent of French people feel the same. One fascinating result comes from Japan, where only 4.3 percent have no doubts about the existence of God, but only 8.7 percent say they don't believe in God at all. So almost nine out of ten Japanese are in the believing-ish category.
Then there's us. According to this survey, 60.6 percent of Americans say they have no doubt about the existence of God, and 80.8 percent agree with the statement, "I believe in God now and I always have." The United States is the most religious of the highly developed nations, and most scholars attribute this to our tradition of separation between church and state. Countries in Europe with state churches found that as they developed and education increased, people had a declining interest in the hidebound church that couldn't speak to the realities of modern life. In America, in contrast, the constant competition for adherents made religious institutions more varied and dynamic. It's the difference between going into a store that has only one old, tasteless brand of cereal, and going into a store with 1,000 different kinds. In the former case, many more people say, "Eh, maybe I'll have a muffin for breakfast." In the latter case, most people can find something they're happy to eat.