[Scriptor]

The article goes on to mention that it likely developed gradually over several generations. The first kids with the mutation would have never been taught recursive language by adults. Instead, they probably developed some semblance of it from speaking with siblings/cousins their age. While this would be pretty weak, it probably gave them enough of an advantage over others.

Once they themselves had kids they would be able to teach them their imperfect version of recursive language. This probably continued and amplified over generations.

It's a pretty interesting case of nature and nurture combining. The mutation is a prerequisite, but largely useless unless there's enough "nurture" happening during the critical period.