More than ten years after writing my bachelor's thesis on the European demographic transition, I have come to a different conclusion. The Princeton European Fertility Project convincingly demonstrated that fertility decline could not be explained by industrialization or economic development alone. However, it never fully explained why low fertility spread across societies.
Today I interpret the demographic transition through the lens of Dual Inheritance Theory. Human behaviour evolves through two inheritance systems: genes and culture. Like biological evolution, culture is subject to selection, but cultural traits spread through vertical, horizontal and oblique transmission rather than genetic reproduction.
This distinction is crucial. Biological evolution favours reproductive success, whereas cultural evolution favours ideas and behaviours that are more easily transmitted, imitated and rewarded. The two processes can therefore diverge.
From this perspective, the demographic transition reflects the spread of a culture that no longer promotes fertility. Education, career, autonomy, consumerism and individual achievement became culturally successful because they were prestigious and widely imitated—not because they increased reproductive fitness.
This makes modern low fertility one of the clearest examples of maladaptive cultural evolution: a cultural system can successfully spread behaviours that reduce the biological reproduction of the very individuals who adopt them.
Darwinian evolution alone cannot explain this phenomenon because natural and sexual selection should favour higher reproductive success. Dual Inheritance Theory resolves this apparent paradox by recognizing that cultural selection follows its own evolutionary dynamics, which may conflict with genetic evolution.