In a previous post, I discussed the paradox that while certain cultural traits tend to be associated with the north and others with the south, when you cross from the northern part of a warm country to the southern part of its neighbor to the north, the pattern reverses. Thus, despite being further north, southern France has southern cultural features whereas northern Italy has northern cultural features. The same is true of Vietnam and China.  I provided a couple possible explanations:

One hypothesis is that cultural change is gradual and continuous, and that those in northern Spain and Italy are not really like the dour and business-like northern Europeans, they only seem that way relative to their compatriots in the south. Another hypothesis is that people sort within each country, and that those who feel more comfortable with the culture of Milan or Barcelona migrate up there from the south.

Tyler Cowen recently linked to a new study by Hoang-Anh Ho, Peter Martinsson and Ola Olsson that suggests my second explanation may be part of the story.  Here is the abstract (and note the final sentence):

Cultural norms diverge substantially across societies, often within the same country. We propose and investigate a self-domestication/selective migration hypothesis, proposing that cultural differences along the individualism–collectivism dimension are driven by the out-migration of individualistic people from collectivist core regions of states to peripheral frontier areas, and that such patterns of historical migration are reflected even in the current distribution of cultural norms. Gaining independence in 939 CE after about a thousand years of Chinese colonization, historical Vietnam emerged in the region that is now north Vietnam with a collectivist social organization. From the eleventh to the eighteenth centuries, historical Vietnam gradually expanded its territory southward to the Mekong River Delta through repeated waves of conquest and migration. Using a nationwide household survey, a population census, and a lab-in-the-field experiment, we demonstrate that areas annexed earlier to historical Vietnam are currently more prone to collectivist norms, and that these cultural norms are embodied in individual beliefs. Relying on many historical accounts, together with various robustness checks, we argue that the southward out-migration of individualistic people during the eight centuries of the territorial expansion is an important driver, among many others, of these cultural differences.

In the US, we may have sorted into “New York type people” and “California type people” in the post-WWII decades.  Indeed a new sorting may be occurring, with liberal New York types in NYC and conservative New York types in Miami.  Or liberal California types in California and conservative California types in Texas.