When it comes to learning a new language, grasping unfamiliar words is not the hardest part. Practice with flash cards, or keep your ears open, and you’ll pick things up fairly quickly. But for most people, grammar takes a longer time. “We know from studies of second-language learning that if you have to learn a language with complex morphology, that is really hard for ... learners to pick up,” says Morten Christiansen, a cognitive scientist at Cornell University who is an author of the paper. If your first language doesn’t flag tables as feminine, or group nouns into clusters according to shape, it is going to take a little while for you to learn to do it in your second. Even in first languages, learning grammar takes a while.

In the model, the researchers represented this with some hard-to-learn linguistic changes, standing in for grammar. Words were represented by easy-to-learn ones. With an “easy” innovation, others only had to hear it once before they too would start using it. With a “hard” one, an individual had to hear it twice before adopting it. Then the researchers ran their model again and again, watching to see how things played out in social networks ranging from 30 to 500 hypothetical people.

As these innovations spread, it became clear that indeed, in large groups, new words spread quickly. There were more individuals to coin them, too, generating a lot of new vocabulary. In contrast, innovations in grammar spread slowly, as people might not have a second meeting for quite a while.

Meanwhile, in small groups, because the individuals were more likely to reencounter each other frequently, grammar innovations took root much more easily. “If somebody has come up with a hard-to-learn convention, you’re more likely to come across it more frequently in your lifetime and learn it,” Christiansen says. New words were fewer than in large groups, stemming simply from the fact that there were not so many people.

This suggests that the number of people who speak a language may shape it in ways they don’t realize. Furthermore, the model could apply to other aspects of culture that are easy or hard to transmit to other people, like dance, or music, or rituals, Christiansen notes. Small groups might generate very complex, perhaps self-referential or internally consistent, styles that become more standardized when larger numbers of people adopt them. “Gradually, as it becomes more popular ... it becomes easier for more people to pick it up,” Christiansen says. “But it also becomes simpler in nature.”

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