This is an excellent and succinct article on the history of ideas in the realm of how humans acquire language, with a special focus on the emergence of Relational Frame Theory (RFT). The article rightly starts with the vexed question, whether language is learned or innate. RFT is biased towards the learned end of the spectrum. Language, in the sense described, is uniquely human (until, that is, machines are coded to replicate the ability to produce and understand it too).
Link to article: https://www.newscientist.com/article/mg23431280-200-spoken-rules/
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