Spolaore, Enrico, and Romain Wacziarg. 2019. “Fertility and Modernity.” Working Paper Series. National Bureau of Economic Research. https://doi.org/10.3386/w25957.

We investigate the determinants of the fertility decline in Europe from 1830 to 1970 using a newly constructed dataset of linguistic distances between European regions. We find that the fertility decline resulted from a gradual diffusion of new fertility behavior from French-speaking regions to the rest of Europe. We observe that societies with higher education, lower infant mortality, higher urbanization, and higher population density had lower levels of fertility during the 19th and early 20th century. However, the fertility decline took place earlier and was initially larger in communities that were culturally closer to the French, while the fertility transition spread only later to societies that were more distant from the cultural frontier. This is consistent with a process of social influence, whereby societies that were linguistically and culturally closer to the French faced lower barriers to the adoption of new social norms and attitudes towards fertility control.

As hbd*chick points out, this suggests that the fertility transition in Europe was substantially independent of the Industrial Revolution, and was a process of cultural diffusion that emanated from France (where it began before 1830).

Incidentally, that sea change in turn began with the French nobility, amongst whom fertility rates plummeted during the 18th century. This is mentioned in the article:

For example, Jean-Baptiste Moheau, in his R echerches et considérations sur la population de la France (1778), noticed that the French were having less children than in the past because people had become more focused on their own selfish material interests and were reluctant to bear the high cost of having children, while they no longer felt a moral obligation to reproduce out of religious and civic duty.

hbd*chick also points out that even within France, the speed of the fertility transition was correlated to the level of cousin marriage regionally. Though I suspect this is just a function of those areas being more backwards and less secular, and this less open to cultural transfusion from core France.

He also finds that subscriptions to Diderot’s Encyclopédie is negatively correlated with fertility across French départements in 1831, even when controlling for industrial output per capita, urbanization, literacy and pre-industrial development. The Encyclopédie was a fundamental source of secular philosophy and scientific knowledge that had persistent e¤ects on French long-term development (Squicciarini and Voigtländer, 2015). The findings strongly point to a cultural mechanism to explain the onset of the fertility decline in France, operating through the weakening of traditional religious values and the emergence of secular attitudes.

So dysgenic fertility has also been operating for a long time.

Incidentally, France was the first European country where atheism developed to a point where it was embraced by a significant proportion of its revolutionary elites, e.g. see the Temple of Reason: “For instance, at the Notre-Dame Cathedral in Paris, on November 10, 1793, a special ritual was held for the “Feast of Reason”: the nave had an improvised mountain on which stood a Greek temple dedicated to Philosophy and decorated with busts of philosophers. At the base of the mountain was located an altar dedicated to Reason, in front of which was located a torch of Truth. The ceremony included the crowd paying homage to an opera singer dressed in blue, white, red (the colours of the Republic), personifying the Goddess of Liberty.”

For most of European history up until the Napoleonic Wars, the French accounted for around 20%-25% of Europe’s population. But a century hence, having increased from just 28 million to 40 million at the eve of the Great War, they were outnumbered by the British (47 million), the Germans (65 million), and the Great Russians (~90 million). However, as I pointed out in Breeding Breeders, past dissolution may well lead to future restoration. France essentially has a 50-100 year head start on the rest of Europe so far as selection for “breeder” characteristics go.