Judaism is a useful ethno-religion for modeling mitochondrial/viral meme interactions because it is relatively small.

Depending on which study you read, the US has between 4 and 6 million Jews, neatly split into four main groups:

A bit confusingly, Orthodox are the most conservative and Conservatives are more moderate. Reforms are liberal, and “No denomination” is mostly atheists who are, of course, the most liberal.

Orthodox have a TFR (total fertility rate, or children per woman,) of 4.1.

Conservatives have a TFR of 1.8.

Reform have a TFR of 1.7.

Atheist Jews have a TFR of 1.5. (source)

(Here I have to stop and point out an error in the source, which claims that “TFR”=total number of children per adult, when TFR is defined as childen per woman. The US TFR of 2.2 means the average woman has 2.2 kids, not that the average woman has 4.4 kids.)

Back to our data. We can see immediately that only Orthodox Jews have a TFR above replacement (approximately 2.) Let’s run through the numbers, just for fun (using a compromise starting number of 5 million total Jews):

Generation 1: 500,000 Orthodox Jews; 900,000 Conservative Jews; 1.75 million Reform Jews; and 1.5 million atheist Jews.

Generation 2: 1,010,000 Orthodox; 810,000 Conservative; 1.488 million Reform; and 1.125 million atheist Jews.

If this trend continued, by Generation 5 we’d have: 8.8 million Orthodox; 530,000 Conservative; 776,000 Reform; and 356,000 atheist. From 10% Orthodox to 84% in just a century; from 30% to 3% atheist.

In reality, though, this doesn’t happen, because many of the children of Orthodox Jews don’t stay Orthodox: “Fewer than half of Jews raised in Orthodox homes have remained Orthodox, with more than 20 percent leaving the religion altogether.”

But this finding requires a caveat, the authors are quick to add: those who left Orthodoxy in droves came of age in the 1950s, 1960s, and 1970s. The 1980s and 1990s have been a lot kinder to the Orthodox denomination; fully 83 percent of respondents between the ages of 18 and 29 who were raised Orthodox are still Orthodox.

!! If that doesn’t look like the less-devout boiling off, leaving a more genetically-inclined-to-Orthodoxy core, I don’t know what does.

Among Jews who were raised Conservative, the number who have left Jewish observance rises to 30 percent; among Jews raised Reform, 35 percent.

Notice that no one talks about Reform Jews becoming Orthodox, because very few do. Orthodox Jews may know how to have children, but their beliefs are simply unattractive to anyone who isn’t raised Orthodox. By contrast, Reform Jews can’t replenish themselves, but their ideas are attractive to non-Reform Jews.

In other words, Orthodoxy is mitochondrial; Reform and atheist Judaism are viral.

Here’s a graph for you:

I love a good graph.

Okay. So let’s recalculate Generation 2:

1,010,000 Orthodox => 48% O, 15%C, 11% R, and 26% A (as a practical matter, “no denomination” is pretty darn close to atheist,) or 485,000 O; 152,ooo C; 111,000 R; and 263,000 A +

810,000 Conservative => 4% O, 36% C, 30% R, 30% A, or 32,000 O; 292,000 C; 243,000 R; 243,000 A.

1.488 million Reform => 1% O, 6% C, 55% R, 37% A, or 15,000 O; 89,000 C; 818,000 R; 551,000 A.

and 1.125 million atheist Jews => mostly atheists.

For a total of 532,000 O; 533,000 C; 1,172,000 R; 2,182,000 A. In case you’ve forgotten, Gen 1 had:

500,000 O; 900,000 C; 1,750,000 R; and 1,500,000 A.

The numbers aren’t extreme (which makes sense, since the average TFR is close to 2,) but notably, even though 52% of Orthodox children elected to go be something else, Orthodox is the only Jewish denomination that actually managed to grow. Conservative and Reform numbers, despite influxes from Orthodox Judaism, (and, for Reform, from Conservatives,) fell. Atheist Jews, of course, had a significant rise.

Carry on this pattern for several generations, and you get a Judaism that is increasingly split between Orthodox on one hand and atheism on the other.

Now suppose that the more recently observed trend of younger people staying Orthodox at higher rates than previous generations holds true, and the future looks even grimmer for the Conservatives. I’m not going to work out the math, because you can probably estimate for yourself what an 83% retention rate combined with a 4.1 TFR looks like–a very Orthodox Judaism. And very atheist.

I suspect that Christianity (at least white, American Christianity; Ugandan Christianity is totally beyond my knowledge zone,) is following a similar pattern, with a large increase in atheists on the one hand, massive losses from the moderate center, and the most conservative elements almost hanging on:

I suspect that the “unaffiliateds” include both atheists and people who believe in god or spirituality in some sort of vague way, but not enough to actually attend a real church.

These drops are just over the past 7 years; looking further back, in 1948, nearly 70% of Christians described themselves as “Protestants” (including both mainline and Evangelicals;) today, that’s dropped to 38%. (I think Black Protestant churches and the Mormons are doing fine, however.)

I don’t want to get into the details of the changing Christian landscape, because that’s way too much to cover in the tail end of a post, but the pattern looks very similar, especially the precipitous drop in the Catholics and Mainline Protestants (the Christian moderates and liberals.) Evangelical Protestants don’t have the birth rates of Orthodox Jews, otherwise they’d probably be doing a little better.

Moldbug proposed that Reform Judaism is Judaism infected with the Progressive virus, where Progressivism itself is a viral form of Mainline Protestant (ie Puritan) Christianity that has shed its specifically theistic aspects in order to compete in our officially a-religious political sphere.

But how much could just be convergent memetic evolution, given an identical meme-vironment?