new study from Spain provides a glimpse of one possible future for the United States: a society in which people marry those who are similar to them, and where children's chances in life are increasingly determined by their last names.

Recent research on the United States has found that poor American children are just as likely to get ahead today as they were in the past, a contrast with the portrait of Catalonia, the province of Spain, drawn in the study. At the same time, many economists think that the United States is becoming more similar to Catalonia in that people are becoming more likely to marry someone with a similar economic background to them. If so, this trend could mean that future generations of U.S. children will be more likely to imitate their parents in life, said José Rodriguez Mora, an economist at the University of Edinburgh and one of the authors.

The tendency of people to marry someone similar, which economists call "assortative mating," is one of the most important factors in determining how wealth is distributed throughout a society and whether children are born with genuinely equal opportunities to succeed. "This is a first-order issue," Rodriguez Mora said. Still, economists don't know just how parents transmit their advantages or disadvantages to their children -- whether through congenital ability, skills learned early in childhood or a bias on the part of society in favor of those from well-off families.

The authors of the study took advantage of the unusual structure of Spanish surnames to trace hundreds of thousands of Catalonian families over several generations. In Spanish society, the first surname is inherited from the father, and the second from the mother, which gave the researchers a clear view of who was marrying whom. When they found two people with two rare surnames, for example, the researchers could be almost certain that the pair were siblings.

The authors found that Catalonians were becoming more likely to marry people from families similar to their own, both in terms of education and in terms of ethnicity and language. Catalonia is divided between those who speak Catalan, who tend to be better educated and wealthier, and those who do not.

Before, a child with an educated father was more likely to have had a mother whose family was less educated. Today, both parents are more likely to be either relatively educated or uneducated.

The intuitive result, one generation later, is that their children are more likely to be similar to both of them. The researchers found that while the Catalonian population as a whole is becoming more educated, parents' educational achievement is also becoming more important in determining how much schooling their children eventually complete.

Yet Rodriguez Mora cautioned that the exact reasons why educational achievement is inherited are still unclear.

It could be that parents pass on a set of intellectual gifts to their children, through their genes or, say, by reading to them from a young age. As a result, some would argue that it's only natural that they spend more time in school and are likely paid better afterward. "This meritocratic thing is, in general, something that people like," Rodriguez Mora said. "The more talented should be paid better."

On the other hand, it could be that the children of educated Catalan speakers simply have more opportunities for education because they have access to their parents' social network, who can help them navigate secondary school and university, or because they don't have to work to support their families, which gives them more time to focus on their studies.

In any case, the data suggest that economic mobility between generations could become more limited in the United States with time.

Mobility is already constrained here, compared to similar countries in Northern Europe. Rodriguez Mora suggested this could be because the United States is also a very meritocratic place, in which the economic system generously rewards skills and talents. But how those abilities are acquired, and whether all have an equal chance to acquire them, is an open question.