I’m pushing through Gibbon and related works (like Robin Lane Fox’s “Pagans and Christians”.) I know you’ve studied this time period, DH. Do you think religiously its analogical to our own time period, where we saw one belief system, polytheism, replaced with monotheism? I know the demographics argue otherwise, but as you point out, they’re not everything.

It makes perfect sense to me that the religious will inherit the Earth. Secularism seems to do best in places like Europe, where there is significant public assistance. If the correlation is not just accidental, the mechanism may have to do with individual psychological imperatives. The harder life is, the more people need religion. If something like that is true–and I’d be interested to know whether the data sets in Kaufmann can shed light on the idea–then it would follow that at some point austerity will set the conditions for a religious revival apart from heredity.

In the 1970s-1980s, I remember the one hope in a world of inevitable overpopulation (think Paul Ehrlich) was the emancipation of women in the Third World. That could still be the main impetus of fertility decline, if the data show a correlation between the fertility of a religious group and the amount of choice faithful women have in the number of children they bear. But either way, whether it’s because of public assistance or because of women’s empowerment, the logic of a rebound among believers has an almost Darwinian logic. If something in religion uniquely contributes to fertility, then the faithful will outbreed the skeptical.

Since religious faith is not strictly heritable, the rate of apostasy is relevant to the ultimate religious profile of a nation. But if apostates do not match the fertility of their faithful kin, then again religion will surge by demography.

On the transition from paganism to Christianity, that change had obviously fully happened by the time of the Islamic invasions. Still, maybe it’s relevant that the Muslims considered Christians polytheists.

“The Europe being over run by Sharia law?”

It’s not being overrun. Laicite in France, for example, is still vital (e.g., burka ban).

Sharia exists in insular, immigrant populations that brought it with them. Accommodations from weak local councils in the UK, for example, are evidence of weakness brought on by multicultural orthodoxy. They’re not evidence of conversions among previously secular Europeans.

But you raise the interesting point of what religion will the (native) Europeans return to, if they return to religion. Whether because of a diminished welfare state after economic reality demands austerity, or for whatever other reason, it would be fascinating if the next generation in Europe embraced Islam instead of Christianity.