The nature and dynamics of world religions by Nicolas Baumard & Coralie Chevallier (2015, also as PDF) examines archaic religions, current world religions, and the ongoing decline of religiosity in rich countries by the light of life history theory, here applied to the varying circumstances of human societies rather than the evolution of different species. The results are quite enlightening and strike me as a plausible explanation of at least part of the historical changes in the nature and intensity of religion.
Tribal & Archaic Religions
The original human environment is one of few resources and high uncertainty regarding the future. Correspondingly, early religions chiefly attempt to alleviate this dangerous situation:
In hunter–gatherer societies, in agro-pastoralist tribes and in archaic chiefdoms, religious behaviour was mostly about exchanging goods and services with supernatural powers: performing rituals, sacrificing resources and respecting particular taboos in order to get harvests, healing, offspring or protection from enemies.
This much is well-known, but there is a correlate in the “life history” of the members of such societies. Since they live with few reserves and high uncertainty, future-orientated (low time preference) behavior such as trusting others and delaying gratification is quite risky. Anyone might face any sort of calamity at any time that prevents the expected future payoff, so it is indeed more rational to take what one can, right now. Of course, this habit itself would then further lower trust and cooperation.
Remarkably, this “fast life strategy” also comprises biological effects: earlier onset of puberty and faster aging, as well as earlier and more sexual partners and lower investment in the resulting offspring. Baumard & Chevallier cite studies that can identify the fast strategy even in subgroups of the same society, such as poorer city districts.
This basic result has been replicated a number of times. Participants growing up or currently living in harsh environments tend to defect more, to forgive less, to display more anti-social behaviours and to punish cheaters less. They also describe themselves as less prosocial and they score lower on agreeableness questionnaires. Finally, experiments conducted with children suggest that some of these differences can already be observed at a relatively young age.
Modern World Religions
One striking feature of modern religions is their moralizing aspect: God gives ethical commands which are to be obeyed because they define goodness, not because they improve the next harvest. The general nature of these commands is highly instructive: “extended cooperation, restricted sociosexuality, and delayed gratification.” These form a “slow life strategy” that is the opposite of that practiced in archaic or otherwise harsh and unpredictable environments.
To succeed, this strategy correspondingly needs a wealthy and predictable environment that rewards a low time preference. This was provided by the great Eurasian empires during the first millennium BC when these religions first arose, and continues to be provided until the present day in the industrialized nations, with some disruptions and exceptions.
World religions appeared quite late in history—well after the emergence of agriculture, large-scale societies and early states—and in very specific places (i.e. the Yellow and Yangzi valleys, the Ganga valley and the eastern part of the Mediterranean region). Quantitative studies reveal a sharp increase in energy capture (a reliable proxy for affluence) occurring at the same time in these three regions of Eurasia. At the end of the first millennium BCE, these regions reached an economic level (greater than 20 000 kcal capita-1 d-1) that greatly surpassed the economic level of previous societies, from 4000 kcal for hunter–gatherer societies to 15 000 kcal for archaic large-scale civilizations like Egypt or Sumer.
There is one other notable feature of moralizing religions: they do not just encourage a slow life strategy for their believers, but strongly condemn anyone still following a fast life strategy. Greed, lust, violence are all typical “fast” behaviors defined as sins. This, Baumard & Chevallier argue, solves the puzzle why ever increasing wealth and security has recently resulted in a decline of religion.
Condemnation of a “fast” strategy is necessary as long as followers of that strategy, or harsh circumstances that encourage it, are still around. A low time preference is beneficial to everyone in a predictable environment, but only if everyone shares it. High time preference “defectors” can easily prey on the trust of others, and must be deterred from doing so. Consequently, it is no accident that religion still flourishes in seemingly unlikely places:
[In the USA,] between-state comparisons confirm that higher levels of religiosity correlate with greater frequency of fast behaviours, such as teen pregnancy, teen abortion, alcohol consumption, school drop-out rates or homicide, as well as with higher levels of poverty and inequality—two well-known triggers of a fast strategy. By contrast, in richer and more equal states, where the environment is less harsh and the frequency of fast behaviours is lower, religiosity is in decline in the same way as in other affluent nations.
Once a society has become so affluent and stable that fast life strategy shrinks from a general rule to a rare exception, moralizing religions that preach slow life strategy cease to serve their original purpose and gradually vanish. The open question (which the authors do not address) is what other benefits aside from resource optimization the vanishing religion might have provided, or what psychological needs it satisfied. Completely areligious societies have not existed probably since humans learned speech, and have not existed long enough in modernity to prove their viability. That experiment is still ongoing.