>which is why, I think, atheist culture over time devolves to childlessness

I don't think the data supports this, yet. Religiously affiliated completed TFR is 2.2 while unaffiliated is 1.8. However, completed TFR means this is looking at those older than 60, so expect those numbers to drop in the future.

https://www.pewresearch.org/religion/2025/02/26/religion-fer...

From my observations, TFR is not much different between most people who describe themselves as religious and most people who describe themselves as non religious. However, the TFR is different for those who I would describe as the most religious, compared to the "casually" religious/non religious.

For example:

https://danielgordis.substack.com/p/israel-has-high-birth-ra...

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xyzelement 4 days ago | parent [-]

Totally agree, even without reading your links. What matters is the actual faith in Gd. I see this myself. We're members of two temples - one more orthodox and one more what you'd call casual.

The people that show up to the casual one once a year or even a few times a year aren't really "different" than someone who doesn't bother to show up. It's good they are there but the religion isn't influencing how they think and act - which is why the TFR is similar between casually religious and casually non-religious.

Where things differentiate is on the extremes. Someone explicitly atheistic (vs just non-religious) has a TFR around 1 from what I remember, while orthodox and ultra-orthodox have 3.3 and 6.6 respectively. What makes the difference is the degree to which they allow the religion to permeate their mundane existence, which is a factor of faith.

	▲	tsimionescu 4 days ago \| parent [-]
		This doesn't seem to track with broader sociological trends. For example, let's compare the USA, one of the most religious Western countries, with the USSR, where 60%+ of the population was atheistic, and where the state promoted atheism. Between 1960 and 1980, the US population grew from 179M to 226M (a 26% increase). The USSR population grew from 208M to 262M (a 25% increase). So, despite massive differences in religiosity, the population rate was pretty similar. China, another largely atheistic state, grew from 582M to 1B in roughly the same period - a 73% increase. So while it may be true that certain small deeply religious populations are more incentivized to have children, this doesn't seem like a significant effect at population levels overall. You'll also find small non-religious groups with similar behaviors.