In fact, the idea of universal grammar contradicts evidence showing that children learn language through social interaction and gain practice using sentence constructions that have been created by linguistic communities over time. In some cases, we have good data on exactly how such learning happens.

For example, relative clauses are quite common in the world’s languages and often derive from a meshing of separate sentences. Thus, we might say, “My brother … He lives over in Arkansas … He likes to play piano.” Because of various cognitive-processing mechanisms — with names such as schematization, habituation, decontextualization and automatization — these phrases evolve over long periods into a more complex construction: “My brother, who lives over in Arkansas, likes to play the piano.” Or they might turn sentences such as “I pulled the door, and it shut” gradually into “I pulled the door shut.”