Christian Cultural Drift
Re civ decline, my basic story is that a key contribution to the fall of civilizations is plausibly that as a civ gets big, rich, and peaceful, its local cultural evolution process parameters get worse, at least at the culture level. There is typically lower variety, weaker selection pressures, and faster environmental change. So the process goes bad, its cultures drift into maladaption, and the civ falls. Our current civ will plausibly suffer this fate, with the added problem that due to modern cultural activism we also have higher rates of internal cultural drift.
What does this say about Christianity? Early on it was a small sect competing with many others, and the fact that it won against them suggests that it was unusually adaptive then, at least in that context. Then it took over the Roman Empire and most of Europe, and became securely in pace for millennia. And while securely in place, Christianity substantially changed its character many times. So doesn’t my theory suggest that those changes would on average have been maladaptive?
Well first notice that most Europeans didn’t know much about Christian doctrine re how to live ordinary peasant lives until about 1600 or so. Before then Christianity mainly influenced elites, cities, and larger institutions. Also, there was often lots of competition within Christianity; the cultural evolution problem would only be re cultural features that were imposed on everyone in Christianity, allowing little local deviation.
Okay, but Christianity influenced marriage much earlier, from about 1200, promoting monogamy and banning cousins marriage, and that suppressed family clans. Christianity also pushed individualism early on, via consent in marriage and the freedom to write wills, especially donations to the Church. And those wills funded many big monasteries, which slowly took over lots of European land. Also, conflicts between the church and crowns started early and weakly contributed to the lack of a single power taking over all of Europe. (Though note: most of these things didn’t actually change much over the history of Christianity.)
The protestant revolution created more competition among forms of Christianity, but it also induced record high level of religious hostility and destruction. But then the strangest thing happened: after the thirty years war (1648+), Europe suddenly agreed to great religious tolerance, at least among variations on Christianity, inducing world record low levels of religious destruction.
It turns out that religious tolerance, individualism, suppressing family clans, and preventing a single empire, were important enablers of modern capitalism, which enabled the Industrial Revolution. Which seems to have been quite adaptive in many ways, and least on the timescale of a few centuries. So does this show that some pro-adaption process was driving changes in Christianity over millennia? Or did it just get lucky?
I think Europe just got lucky. The accumulation of land by the church, and the increase in religious hostility, seem maladaptive, and suppressing family clans was also probably maladaptive at first. Then Europe got lucky in that religious hostility dramatically (and puzzlingly) reversed, crowns grabbed back most of that church land, and then individualism, suppressed family clans, and no central empire together turned out to be very good for capitalism and industry.
But maybe to get this lucky, Europe needed to make some big changes from prior cultures, and an out-of-control drifting Christian culture is part of what gave Europe the ability to make such big changes. Usually big random changes go badly, but they sometimes allow evolution to make big jumps to new peaks, in ways that wouldn’t be possible without them. Yes, this means maybe we today will also get lucky in a similar way. But don’t count on it.
I am going to say something that is inherently sexist, but there is probably at least a kernel of truth in it. Women tend to be worriers - but evolution heavily selected on the ability of women to successfully raise their children - and worrying about risk to their children was - and is adaptive. But without young children to focus their worries, young women can and do focus their worries on other issues where such worries are less adaptive. With the drop in child rearing, particularly child rearing while relatively young, societies around the world are being greatly impacted by worrying women.
John Michener (in comments) raised the question of displaced worry: Is the vigilance regarding harm to loved ones—which was adaptive for ancestral women occupied by childcare—now being redirected by contemporary women toward social activism?
This is worth discussing because evolutionary mismatch is important. The mismatch Michener identified is: Ancestral women typically started having children at age 19 (with 22 being peak fertility) and continued into their late 30s, birthing an average of five children over a 20-year span. This involved natural birth spacing due to caloric restriction and high physical activity. In contrast, contemporary urban women may have only one to three children, mostly in their 30s.
So, I did a quick literature search. Childless women in their 20s are indeed more involved in social activism than same-aged women with children. Does this support the displaced worry thesis? Scholars note that this displacement can be a straightforward consequence of the time and energy demands of parenting, but it may also be related to education and financial resources. Young women who have postponed childbearing often possess resources and personality traits that differ from those of women rearing children in their 20s; these include higher education, financial autonomy, and greater political interest.
Ok, continuing on with 'displaced worry.'
Young women's social activism is often centered on safety, equity, and harm reduction—including long-term harm reduction such as environmentalism. This emphasis on creating a social environment where children can thrive characterizes some of the most famous activist movements in the West. Historic examples include social movements against child labor during the Industrial Revolution, the Temperance movement (1840s–1920s), and contemporary movements such as Mothers Against Drunk Driving (MADD). Women have also been heavily involved in social justice movements where men were the primary leaders, such as the abolition of slavery and the Civil Rights Movement (1960s).