Gerhard Meisenberg (2012)
Using a sample of up to 62 countries, this study finds that differential fertility influences trend lines in the prevalence of theistic religious belief at the country level. High religiosity of females relative to males is an additional, though less consistent, predictor. These effects are demonstrated on the background of two other causal influences: Recovery from communist rule predicts a rising trend, and indicators of economic, social and cognitive development predict a declining trend. Several alternative hypotheses about the determinants of religious trends receive no support.
The most important conclusion of the present study is that differential fertility is a significant influence on trends in the strength of religious belief at the country level. This adds to earlier results suggesting that differential fertility is important for the growth of Christian denominations in the United States (Hout et al, 2001), and for future religiosity in most religious traditions worldwide (Kaufmann, 2008, 2010). The belief that differential fertility can affect trends in psychological and behavioral traits in human societies has been brought forward since the late 19th century as an implication of Darwinian evolutionary theory, and is still held by many researchers today (Lynn, 2011; Rowthorn, 2011). However, empiric evidence linking differential fertility for any behavioral trait to country-level trends in the trait has never been presented in comparative studies. The results presented here for religion provide the first empiric evidence that this theoretically postulated link exists for religion on a worldwide scale. The reason why the effect is detectable even over rather short time periods of 5 to 26 years is that in the case of religion, genetic transmission is amplified greatly by cultural transmission in the family.
The results of this study indicate that the future of religion is determined by two factors. First, rising cognitive and economic development are predicted to undermine religion in the “threshold countries” of Asia, North Africa and Latin America in the near future. Second, differential fertility favoring religious individuals and groups within countries is likely to assure the survival of religion in many of the advanced post-industrial societies, most likely through the formation of highly religious and highly fertile subpopulations as postulated by Rowthorn (2011).
One development that is not addressed in the present study is the positive relationship between the country-level total fertility rate (TFR) and religiosity. The TFR (1990-2005 average) correlates with religious belief at r = .618 (N = 94 countries). The 5.73 billion people in countries covered in the World Values Survey had an average religiosity rating of 7.32 in 2005. Based on data about population size and annual population growth rates from the CIA’s World Fact Book, the 7.93 billion expected to live in these countries in 2035 will have an average religiosity score of 7.61 because of differential fertility between countries, assuming no change of religiosity within countries.