First: it affects whether you marry someone from home or abroad. According to a Spanish study on marriages between locals and foreigners, heterosexual Spaniards with lower levels of education tend to marry a non-Spanish person more often than those with higher educational levels do. This is true especially for lower-educated men.

In contrast, almost two thirds of Spanish men who attended university married a foreign woman with their same educational level.

Of the university-educated Spanish women that married a foreigner, however, over half married a man with a medium or low level of education.

“It is a question of who is available on the partnering market,” Anna Naszodi, founding director of the International Demographic Inequality Lab, explained to us.

In that market, supply and demand may help explain why highly-educated Spanish women increasingly marry foreigners with less education. The proportion of women attending university is growing beyond the proportion of men, leaving the pool of college-educated men smaller.

Generally, we prefer pairing up with people from our own social group and class, Albert Esteve, director of the Demographic Studies Centre at the Universidad Autònoma de Barcelona, told us. And yet: “if you go to the grocery market looking for tomatoes and only find zucchini, you’ll go home with zucchini, right?”

However, even if they cannot find the kind of partner they're looking for, women with higher education still “marry men with the higher income among those with a lower degree,” Esteve said.

The trend of “like marries like” holds across Europe. According to a report from the European Commission that analysed four European countries (France, Hungary, Portugal, and Romania) and the US, the preference for marrying someone with a similar educational level increased in all studied countries in the 2010s compared to a decade earlier.

“The sharp decline since the turn of the millennium in the proportion of individuals cohabiting with or married to a partner with a different level of educational attainment may be a sign of the weakening of the ‘social glue’,” the report explains. This, in turn, may represent a “challenge to the European Union objective of building a more egalitarian and resilient society”.